Bio

Bio


Dr. Vasanawala received his bachelor's degree in mathematics from Caltech, and then completed his medical training and PhD at Stanford. His research efforts are focused on developing fast and quantitative MRI methods. He serves as the Director of MRI at Stanford Hospital and Clinics and at Stanford Children's. He also serves as the division chief of Body MRI.

Clinical Focus


  • Diagnostic Radiology
  • Pediatric and Abdominal MRI
  • Cardiovascular Diagnostic Techniques

Administrative Appointments


  • Director of MRI, Stanford Childrens (2017 - Present)
  • Chief, Body MRI, Stanford (2011 - Present)
  • Co-Director of MRI, Stanford (2011 - Present)

Honors & Awards


  • Tashia and John Morgridge Faculty Endowed Scholar in Pediatric Translational Medicine, Child Health Research Institute

Boards, Advisory Committees, Professional Organizations


  • Member, ISMRM (1997 - Present)

Professional Education


  • Fellowship:Stanford University - Fellowship (2007) CA
  • Residency:Stanford University - Fellowship (2006) CA
  • Fellowship:Children's Hospital Medical Center (2006) OH
  • Internship:Stanford University - Dept of Surgery (2002) CA
  • Medical Education:Stanford University School of Medicine (2001) CA
  • Board Certification: Diagnostic Radiology, American Board of Radiology (2006)
  • Board Certification: Pediatric Radiology, American Board of Radiology (2008)
  • Fellowship:Hospital for Sick Children (2007) Canada

Research & Scholarship

Current Research and Scholarly Interests


Our group is focused on developing new MRI techniques, and in particular, developing novel applications for children. We take a comprehensive approach, exploring novel hardware, data acquisition, image reconstruction, and image analysis techniques. These approaches are then evaluated for cardiovascular, abdominal, and musculoskeletal pediatric MRI exams. Additionally, we seek to develop quantitative MRI methods, including those for cardiovascular function, renal function, and tumor perfusion.

Clinical Trials


  • A Study to Evaluate Sildenafil for the Treatment of Lymphatic Malformations Not Recruiting

    There is an unsatisfied medical need for a first-line treatment of lymphatic malformations with a good benefit/risk profile. Based on a patient experience in the institution, the investigators plan to verify whether or not the medication sildenafil has a beneficial effect on lymphatic malformations. The investigators plan to do this by treating patients with lymphatic malformations with the medication sildenafil for a 20 week period. This is an investigator initiated study funded by an Innovations in Patient Care grant and a SPARK grant.

    Stanford is currently not accepting patients for this trial. For more information, please contact Andrea Tichy, Ph.D., 650-724-1982.

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  • Confounder-Corrected Quantitative MRI Biomarker of Hepatic Iron Content Recruiting

    The purpose of this multi-site research is to validate a rapid magnetic resonance based confounder-corrected R-2 mapping method as a quantitative imaging biomarker of liver iron concentrations.

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  • Combined 18F NaF/18F FDG PET/MRI for Detection of Skeletal Metastases Not Recruiting

    This clinical trial studies sodium fluorine-18 (18F NaF)/fluorine-18 (18F) fluorodeoxyglucose (FDG) positron emission tomography (PET)/magnetic resonance imaging (MRI) in detecting skeletal metastases in patients with stage III-IV breast cancer or stage II-IV prostate cancer. 18F NaF and 18F FDG are radioactive substances that are absorbed by cancerous cells and allow for the cancer to be found using diagnostic procedures such as PET/MRI. PET/MRI is a procedure that combines detailed pictures of areas inside the body from PET and MRI scans and may help find and diagnose skeletal metastases in patients with breast or prostate cancer. It is not yet known whether 18F NaF/18F FDG PET/MRI is better than standard imaging methods in detecting skeletal metastases.

    Stanford is currently not accepting patients for this trial. For more information, please contact Risa Jiron, 650-736-1598.

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  • Feasibility of Using Real-time Cine-MRI for Treating Moving & Deforming Tumors Not Recruiting

    This study aims to investigate and optimize imaging sequences and parameters of rapid real-time MRI in order to obtain adequate guidance for accurately and precisely delivering radiation to moving abdominal and thoracic tumors.

    Stanford is currently not accepting patients for this trial. For more information, please contact Melody Chung, (650) 736 - 0798.

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Teaching

2018-19 Courses


Stanford Advisees


Graduate and Fellowship Programs


Publications

All Publications


  • View-Sharing Artifact Reduction With Retrospective Compressed Sensing Reconstruction in the Context of Contrast-Enhanced Liver MRI for Hepatocellular Carcinoma (HCC) Screening. Journal of magnetic resonance imaging : JMRI Shaikh, J., Stoddard, P. B., Levine, E. G., Roh, A. T., Saranathan, M., Chang, S. T., Muelly, M. C., Hargreaves, B. A., Vasanawala, S. S., Loening, A. M. 2018

    Abstract

    BACKGROUND: View-sharing (VS) increases spatiotemporal resolution in dynamic contrast-enhanced (DCE) MRI by sharing high-frequency k-space data across temporal phases. This temporal sharing results in respiratory motion within any phase to propagate artifacts across all shared phases. Compressed sensing (CS) eliminates the need for VS by recovering missing k-space data from pseudorandom undersampling, reducing temporal blurring while maintaining spatial resolution.PURPOSE: To evaluate a CS reconstruction algorithm on undersampled DCE-MRI data for image quality and hepatocellular carcinoma (HCC) detection.STUDY TYPE: Retrospective.SUBJECTS: Fifty consecutive patients undergoing MRI for HCC screening (29 males, 21 females, 52-72 years).FIELD STRENGTH/SEQUENCE: 3.0T MRI. Multiphase 3D-SPGR T1 -weighted sequence undersampled in arterial phases with a complementary Poisson disc sampling pattern reconstructed with VS and CS algorithms.ASSESSMENT: VS and CS reconstructions evaluated by blinded assessments of image quality and anatomic delineation on Likert scales (1-4 and 1-5, respectively), and HCC detection by OPTN/UNOS criteria including a diagnostic confidence score (1-5). Blinded side-by-side reconstruction comparisons for lesion depiction and overall series preference (-3-3).STATISTICAL ANALYSIS: Two-tailed Wilcoxon signed rank tests for paired nonparametric analyses with Bonferroni-Holm multiple-comparison corrections. McNemar's test for differences in lesion detection frequency and transplantation eligibility.RESULTS: CS compared with VS demonstrated significantly improved contrast (mean 3.6 vs. 2.9, P<0.0001) and less motion artifact (mean 3.6 vs. 3.2, P=0.006). CS compared with VS demonstrated significantly improved delineations of liver margin (mean 4.5 vs. 3.8, P=0.0002), portal veins (mean 4.5 vs. 3.7, P<0.0001), and hepatic veins (mean 4.6 vs. 3.5, P<0.0001), but significantly decreased delineation of hepatic arteries (mean 3.2 vs. 3.7, P=0.004). No significant differences were seen in the other assessments.DATA CONCLUSION: Applying a CS reconstruction to data acquired for a VS reconstruction significantly reduces motion artifacts in a clinical DCE protocol for HCC screening.LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

    View details for DOI 10.1002/jmri.26276

    View details for PubMedID 30390358

  • Motion-robust reconstruction of multishot diffusion-weighted images without phase estimation through locally low-rank regularization. Magnetic resonance in medicine Hu, Y., Levine, E. G., Tian, Q., Moran, C. J., Wang, X., Taviani, V., Vasanawala, S. S., McNab, J. A., Daniel, B. A., Hargreaves, B. L. 2018

    Abstract

    PURPOSE: The goal of this work is to propose a motion robust reconstruction method for diffusion-weighted MRI that resolves shot-to-shot phase mismatches without using phase estimation.METHODS: Assuming that shot-to-shot phase variations are slowly varying, spatial-shot matrices can be formed using a local group of pixels to form columns, in which each column is from a different shot (excitation). A convex model with a locally low-rank constraint on the spatial-shot matrices is proposed. In vivo brain and breast experiments were performed to evaluate the performance of the proposed method.RESULTS: The proposed method shows significant benefits when the motion is severe, such as for breast imaging. Furthermore, the resulting images can be used for reliable phase estimation in the context of phase-estimation-based methods to achieve even higher image quality.CONCLUSION: We introduced the shot-locally low-rank method, a reconstruction technique for multishot diffusion-weighted MRI without explicit phase estimation. In addition, its motion robustness can be beneficial to neuroimaging and body imaging.

    View details for DOI 10.1002/mrm.27488

    View details for PubMedID 30346058

  • 4D Flow MRI Quantification of Mitral and Tricuspid Regurgitation: Reproducibility and Consistency Relative to Conventional MRI JOURNAL OF MAGNETIC RESONANCE IMAGING Feneis, J. F., Kyubwa, E., Atianzar, K., Cheng, J. Y., Alley, M. T., Vasanawala, S. S., Demaria, A. N., Hsiao, A. 2018; 48 (4): 1147–58

    Abstract

    In patients with mitral or tricuspid valve regurgitation, evaluation of regurgitant severity is essential for determining the need for surgery. While transthoracic echocardiography is widely accessible, it has limited reproducibility for grading inlet valve regurgitation. Multiplanar cardiac MRI is the quantitative standard but requires specialized local expertise, and is thus not widely available. Volumetric 4D flow MRI has potential for quantitatively grading the severity of inlet valve regurgitation in adult patients.To evaluate the accuracy and reproducibility of volumetric 4D flow MRI for quantification of inlet valvular regurgitation compared to conventional multiplanar MRI, which may simplify and improve accessibility of cardiac MRI.This retrospective, HIPAA-compliant imaging-based comparison study was conducted at a single institution.Twenty-one patients who underwent concurrent multiplanar and 4D flow cardiac MRI between April 2015 and January 2017.3T; steady-state free-precession (SSFP), 2D phase contrast (2D-PC), and postcontrast 4D flow.We evaluated the intertechnique (4D flow vs. 2D-PC), intermethod (direct vs. indirect measurement), interobserver and intraobserver reproducibility of measurements of regurgitant flow volume (RFV), fraction (RF), and volume (RVol).Statistical analysis included Pearson correlation, Bland-Altman statistics, and intraclass correlation coefficients.There was high concordance between 4D flow and multiplanar MRI, whether using direct or indirect methods of quantifying regurgitation (r = 0.813-0.985). Direct interrogation of the regurgitant jet with 4D flow showed high intraobserver consistency (r = 0.976-0.999) and interobserver consistency (r = 0.861-0.992), and correlated well with traditional indirect measurements obtained as the difference between stroke volume and forward outlet valve flow.4D flow MRI provides highly reproducible measurements of mitral and tricuspid regurgitant volume, and may be used in place of conventional multiplanar MRI.4 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1147-1158.

    View details for DOI 10.1002/jmri.26040

    View details for Web of Science ID 000446539100027

    View details for PubMedID 29638024

  • Volumetric segmentation-free method for rapid visualization of vascular wall shear stress using 4D flow MRI MAGNETIC RESONANCE IN MEDICINE Masutani, E. M., Contijoch, F., Kyubwa, E., Cheng, J., Alley, M. T., Vasanawala, S., Hsiao, A. 2018; 80 (2): 748–55

    Abstract

    To develop a rapid segmentation-free method to visualize and compute wall shear stress (WSS) throughout the aorta using 4D Flow MRI data. WSS is the drag force-per-area the vessel endothelium exerts on luminal blood; abnormal levels of WSS are associated with cardiovascular pathologies. Previous methods for computing WSS are bottlenecked by labor-intensive manual segmentation of vessel boundaries. A rapid automated segmentation-free method for computing WSS is presented.Shear stress is the dot-product of the viscous stress tensor and the inward normal vector. The inward normal vectors are approximated as the gradient of fluid speed at every voxel. Subsequently, a 4D map of shear stress is computed as the partial derivatives of velocity with respect to the inward normal vectors. We highlight the shear stress near the wall by fusing visualization with edge-emphasized anatomical data.As a proof-of-concept, four cases with aortic pathologies are presented. Visualization allows for rapid localization of pathologic WSS. Subsequent analysis of these pathological regions enables quantification of WSS. Average WSS during peak systole measures approximately 50-60 cPa in nonpathological regions of the aorta and is elevated in regions of stenosis, coarctation, and dissection. WSS is reduced in regions of aneurysm.A volumetric technique for calculation and visualization of WSS from 4D Flow MRI data is presented. Traditional labor-intensive methods for WSS rely on explicit manual segmentation of vessel boundaries before visualization. This automated volumetric strategy for visualization and quantification of WSS may facilitate its clinical translation.

    View details for DOI 10.1002/mrm.27159

    View details for Web of Science ID 000430469300033

    View details for PubMedID 29516632

    View details for PubMedCentralID PMC5910222

  • Conical ultrashort echo time (UTE) MRI in the evaluation of pediatric acute appendicitis. Abdominal radiology (New York) Roh, A. T., Xiao, Z., Cheng, J. Y., Vasanawala, S. S., Loening, A. M. 2018

    Abstract

    PURPOSE: Magnetic resonance imaging (MRI) sequences with conical k-space trajectories are able to decrease motion artifacts while achieving ultrashort echo times (UTE). We assessed the performance of free-breathing conical UTE MRI in the evaluation of the pediatric pelvis for suspected appendicitis.METHODS: Our retrospective review of 84 pediatric patients who underwent MRI for suspected appendicitis compared three contrast-enhanced sequences: free-breathing conical UTE, breath-hold three-dimensional (3D) spoiled gradient echo (BH-SPGR), and free-breathing high-resolution 3D SPGR (FB-SPGR). Two radiologists performed blinded and independent evaluations of each sequence for image quality (four point scale), anatomic delineation (four point scale), and diagnostic confidence (five point scale). Subsequently, the three sequences were directly compared for overall image quality (-3 to +3 scale). Scores were compared using Kruskal-Wallis and Wilcoxon signed-rank tests.RESULTS: UTE demonstrated significantly better perceived signal-to-noise ratio (SNR) and fewer artifacts than BH-SPGR and FB-SPGR (means of 3.6 and 3.4, 3.4 and 3.2, 3.1 and 2.7, respectively; p<0.0006). BH-SPGR and FB-SPGR demonstrated significantly better contrast than UTE (means of 3.6, 3.4, and 3.2, respectively; p<0.03). In the remaining categories, UTE performed significantly better than FB-SPGR (p<0.00001), while there was no statistical difference between UTE and BH-SPGR. Direct paired comparisons of overall image quality demonstrated the readers significantly preferred UTE over both BH-SPGR (mean +0.5, p<0.00001) and FB-SPGR (mean +1.2, p<0.00001).CONCLUSIONS: In the evaluation of suspected appendicitis, free-breathing conical UTE MRI performed better in the assessed metrics than FB-SPGR. When compared to BH-SPGR, UTE demonstrated superior perceived SNR and fewer artifacts.

    View details for DOI 10.1007/s00261-018-1705-y

    View details for PubMedID 30066168

  • 18F-florbetaben whole-body PET/MRI for evaluation of systemic amyloid deposition. EJNMMI research Baratto, L., Park, S. Y., Hatami, N., Gulaka, P., Vasanawala, S., Yohannan, T. K., Herfkens, R., Witteles, R., Iagaru, A. 2018; 8 (1): 66

    Abstract

    BACKGROUND: Florbetaben, a 18F-labeled stilbene derivative (Neuraceq, formerly known as BAY-949172), is a diagnostic radiopharmaceutical developed to visualize beta-amyloid plaques in the brain. Here, we report a pilot study evaluating patients with suspected cardiac amyloidosis for systemic extent of disease.METHODS: We prospectively enrolled nine patients, 61-86year old (mean±SD 69.4±8.6), referred from the cardiac amyloid clinic. First, dynamic imaging of the heart was acquired immediately after injection of 222-318.2MBq (mean±SD 270.1±33.3) of 18F-florbetaben using the GE SIGNA PET/MRI. This was followed by a whole-body PET/MRI scan 60-146.4min (mean±SD 98±33.4) after injection. Cardiac MRI sequences included ECG-triggered cine SSFP, T2-weighted, and late gadolinium-enhanced imaging. Whole-body MRI sequences included MRAC and axial T1-weighted imaging.RESULTS: High early uptake and delayed high uptake in the left ventricle correlated with amyloid deposition in five patients, while low uptake on early and delayed cardiac imaging was noted in four patients. Cardiac function measurements were successfully obtained in all participants. Areas of increased abnormal 18F-florbetaben accumulation were noted on delayed whole-body imaging in the bone marrow (seven patients), stomach (diffuse in five patients and focal in one patient), brain (five patients), salivary glands (three patients), tongue (three patients), spleen (three patients), skeletal muscles (three patients), ocular muscles (two patients), thyroid (two patients), pleura (two patients), kidneys (two patients), and lungs (two patients).CONCLUSIONS: Whole-body 18F-florbetaben PET/MRI is promising for localization of systemic amyloid deposition. This technique may provide important structural and functional information regarding the organs involved by disease, with potential to guide biopsy and evaluate response to treatment.TRIAL REGISTRATION: Clinicaltrials.gov registration: NCT03119558 .

    View details for DOI 10.1186/s13550-018-0425-1

    View details for PubMedID 30043115

  • Variable-Density Single-Shot Fast Spin-Echo MRI with Deep Learning Reconstruction by Using Variational Networks. Radiology Chen, F., Taviani, V., Malkiel, I., Cheng, J. Y., Tamir, J. I., Shaikh, J., Chang, S. T., Hardy, C. J., Pauly, J. M., Vasanawala, S. S. 2018: 180445

    Abstract

    Purpose To develop a deep learning reconstruction approach to improve the reconstruction speed and quality of highly undersampled variable-density single-shot fast spin-echo imaging by using a variational network (VN), and to clinically evaluate the feasibility of this approach. Materials and Methods Imaging was performed with a 3.0-T imager with a coronal variable-density single-shot fast spin-echo sequence at 3.25 times acceleration in 157 patients referred for abdominal imaging (mean age, 11 years; range, 1-34 years; 72 males [mean age, 10 years; range, 1-26 years] and 85 females [mean age, 12 years; range, 1-34 years]) between March 2016 and April 2017. A VN was trained based on the parallel imaging and compressed sensing (PICS) reconstruction of 130 patients. The remaining 27 patients were used for evaluation. Image quality was evaluated in an independent blinded fashion by three radiologists in terms of overall image quality, perceived signal-to-noise ratio, image contrast, sharpness, and residual artifacts with scores ranging from 1 (nondiagnostic) to 5 (excellent). Wilcoxon tests were performed to test the hypothesis that there was no significant difference between VN and PICS. Results VN achieved improved perceived signal-to-noise ratio (P = .01) and improved sharpness (P < .001), with no difference in image contrast (P = .24) and residual artifacts (P = .07). In terms of overall image quality, VN performed better than did PICS (P = .02). Average reconstruction time ± standard deviation was 5.60 seconds ± 1.30 per section for PICS and 0.19 second ± 0.04 per section for VN. Conclusion Compared with the conventional parallel imaging and compressed sensing reconstruction (PICS), the variational network (VN) approach accelerates the reconstruction of variable-density single-shot fast spin-echo sequences and achieves improved overall image quality with higher perceived signal-to-noise ratio and sharpness.

    View details for DOI 10.1148/radiol.2018180445

    View details for PubMedID 30040039

  • Safety of ferumoxytol in children undergoing cardiac MRI under general anaesthesia. Cardiology in the young Wise-Faberowski, L., Velasquez, N., Chan, F., Vasanawala, S., McElhinney, D. B., Ramamoorthy, C. 2018; 28 (7): 916–21

    Abstract

    BACKGROUND: Ferumoxytol, an "off-label" contrast agent, allows for better cardiac MRI quality as compared with gadolinium-based contrast agents. However, hypotension has been reported with the use of ferumoxytol for indications other than cardiac MRI. The purpose of our investigation was to evaluate the safety of ferumoxytol in children undergoing general anaesthesia for cardiac MRI.METHODS: Medical records of children undergoing general anaesthesia for cardiac MRI were reviewed. Baseline demographic and medical characteristics, as well as imaging and anaesthetic duration and technique, were collected. The incidence of hypotension or other adverse events', need for vasoactive support, or airway intervention throughout the anaesthetic, was recorded.RESULTS: A total of 95 patients were identified, 61 received ferumoxytol and 34 received gadolinium. There were no significant differences between groups with respect to age, weight, or baseline blood pressure. The incidence of low blood pressure - systolic or mean - after contrast administration did not differ between groups, and there was no difference in sustained hypotension or use of vasopressors between groups. One patient who received ferumoxytol had possible anaphylaxis. The image acquisition time (45 versus 68 min, p=0.002) and anaesthesia duration (100 versus 132 min, p=0.02) were shorter in the ferumoxytol group.CONCLUSION: Transient low blood pressure was common in children undergoing cardiac MRI with anaesthesia, but the incidence of hypotension did not differ between ferumoxytol and gadolinium groups. The use of ferumoxytol was associated with significantly shorter scan time and anaesthesia duration, as well as a decreased need for airway intervention.

    View details for DOI 10.1017/S1047951118000306

    View details for PubMedID 29848399

  • Body diffusion-weighted imaging using magnetization prepared single-shot fast spin echo and extended parallel imaging signal averaging MAGNETIC RESONANCE IN MEDICINE Gibbons, E. K., Vasanawala, S. S., Pauly, J. M., Kerr, A. B. 2018; 79 (6): 3032–44

    Abstract

    This work demonstrates a magnetization prepared diffusion-weighted single-shot fast spin echo (SS-FSE) pulse sequence for the application of body imaging to improve robustness to geometric distortion. This work also proposes a scan averaging technique that is superior to magnitude averaging and is not subject to artifacts due to object phase.This single-shot sequence is robust against violation of the Carr-Purcell-Meiboom-Gill (CPMG) condition. This is achieved by dephasing the signal after diffusion weighting and tipping the MG component of the signal onto the longitudinal axis while the non-MG component is spoiled. The MG signal component is then excited and captured using a traditional SS-FSE sequence, although the echo needs to be recalled prior to each echo. Extended Parallel Imaging (ExtPI) averaging is used where coil sensitivities from the multiple acquisitions are concatenated into one large parallel imaging (PI) problem. The size of the PI problem is reduced by SVD-based coil compression which also provides background noise suppression. This sequence and reconstruction are evaluated in simulation, phantom scans, and in vivo abdominal clinical cases.Simulations show that the sequence generates a stable signal throughout the echo train which leads to good image quality. This sequence is inherently low-SNR, but much of the SNR can be regained through scan averaging and the proposed ExtPI reconstruction. In vivo results show that the proposed method is able to provide diffusion encoded images while mitigating geometric distortion artifacts compared to EPI.This work presents a diffusion-prepared SS-FSE sequence that is robust against the violation of the CPMG condition while providing diffusion contrast in clinical cases. Magn Reson Med 79:3032-3044, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

    View details for DOI 10.1002/mrm.26971

    View details for Web of Science ID 000426866400017

    View details for PubMedID 29044721

  • High-resolution 3D volumetric contrast-enhanced MR angiography with a blood pool agent (ferumoxytol) for diagnostic evaluation of pediatric brain arteriovenous malformations. Journal of neurosurgery. Pediatrics Iv, M., Choudhri, O., Dodd, R. L., Vasanawala, S. S., Alley, M. T., Moseley, M., Holdsworth, S. J., Grant, G., Cheshier, S., Yeom, K. W. 2018: 1–10

    Abstract

    OBJECTIVE Patients with brain arteriovenous malformations (AVMs) often require repeat imaging with MRI or MR angiography (MRA), CT angiography (CTA), and digital subtraction angiography (DSA). The ideal imaging modality provides excellent vascular visualization without incurring added risks, such as radiation exposure. The purpose of this study is to evaluate the performance of ferumoxytol-enhanced MRA using a high-resolution 3D volumetric sequence (fe-SPGR) for visualizing and grading pediatric brain AVMs in comparison with CTA and DSA, which is the current imaging gold standard. METHODS In this retrospective cohort study, 21 patients with AVMs evaluated by fe-SPGR, CTA, and DSA between April 2014 and August 2017 were included. Two experienced raters graded AVMs using Spetzler-Martin criteria on all imaging studies. Lesion conspicuity (LC) and diagnostic confidence (DC) were assessed using a 5-point Likert scale, and interrater agreement was determined. The Kruskal-Wallis test was performed to assess the raters' grades and scores of LC and DC, with subsequent post hoc pairwise comparisons to assess for statistically significant differences between pairs of groups at p < 0.05. RESULTS Assigned Spetzler-Martin grades for AVMs on DSA, fe-SPGR, and CTA were not significantly different (p = 0.991). LC and DC scores were higher with fe-SPGR than with CTA (p < 0.05). A significant difference in LC scores was found between CTA and fe-SPGR (p < 0.001) and CTA and DSA (p < 0.001) but not between fe-SPGR and DSA (p = 0.146). A significant difference in DC scores was found among DSA, fe-SPGR, and CTA (p < 0.001) and between all pairs of the groups (p < 0.05). Interrater agreement was good to very good for all image groups (κ = 0.77-1.0, p < 0.001). CONCLUSIONS Fe-SPGR performed robustly in the diagnostic evaluation of brain AVMs, with improved visual depiction of AVMs compared with CTA and comparable Spetzler-Martin grading relative to CTA and DSA.

    View details for DOI 10.3171/2018.3.PEDS17723

    View details for PubMedID 29882734

  • K-Means Clustering for High-Resolution, Realistic Acoustic Maps Looby, K., Sandino, C., Zhang, T., Vasanawala, S., Dahl, J., Duric, N., Byram, B. C. SPIE-INT SOC OPTICAL ENGINEERING. 2018

    View details for DOI 10.1117/12.2293990

    View details for Web of Science ID 000450861900027

  • Pelvic Blood Flow Predicts Fibroid Volume and Embolic Required for Uterine Fibroid Embolization: A Pilot Study With 4D Flow MR Angiography AMERICAN JOURNAL OF ROENTGENOLOGY Malone, C. D., Banerjee, A., Alley, M. T., Vasanawala, S. S., Roberts, A. C., Hsiao, A. 2018; 210 (1): 189–200

    Abstract

    We report here an initial experience using 4D flow MRI in pelvic imaging-specifically, in imaging uterine fibroids. We hypothesized that blood flow might correlate with fibroid volume and that quantifying blood flow might help to predict the amount of embolic required to achieve stasis at subsequent uterine fibroid embolization (UFE).Thirty-three patients with uterine fibroids and seven control subjects underwent pelvic MRI with 4D flow imaging. Of the patients with fibroids, 10 underwent 4D flow imaging before UFE and seven after UFE; in the remaining 16 patients with fibroids, UFE had yet to be performed. Four-dimensional flow measurements were performed using Arterys CV Flow. The flow fraction of the internal iliac artery was expressed as the ratio of internal iliac artery flow to external iliac artery flow and was compared between groups. The flow ratios between the internal iliac arteries on each side were calculated. Fibroid volume versus internal iliac flow fraction, embolic volume versus internal iliac flow fraction, and embolic volume ratio between sides versus the ratio of internal iliac artery flows between sides were compared.The mean internal iliac flow fraction was significantly higher in the 26 patients who underwent imaging before UFE (mean ± standard error, 0.78 ± 0.06) than in the seven patients who underwent imaging after UFE (0.48 ± 0.07, p < 0.01) and in the seven control patients without fibroids (0.48 ± 0.08, p < 0.0001). The internal iliac flow fraction correlated well with fibroid volumes before UFE (r = 0.7754, p < 0.0001) and did not correlate with fibroid volumes after UFE (r = -0.3051, p = 0.51). The ratio of embolic required to achieve stasis between sides showed a modest correlation with the ratio of internal iliac flow (r = 0.6776, p = 0.03).Internal iliac flow measured by 4D flow MRI correlates with fibroid volume and is predictive of the ratio of embolic required to achieve stasis on each side at subsequent UFE and may be useful for preprocedural evaluation of patients with uterine fibroids.

    View details for DOI 10.2214/AJR.17.18127

    View details for Web of Science ID 000418427200039

    View details for PubMedID 29090998

  • Robust Self-Carlibrating nCPMG Acquisition: Application to Body Diffusion-Weighted Imaging IEEE TRANSACTIONS ON MEDICAL IMAGING Gibbons, E. K., Le Roux, P., Vasanawala, S. S., Pauly, J. M., Kerr, A. B. 2018; 37 (1): 200–209

    Abstract

    This paper demonstrates a robust diffusion-weighted single-shot fast spin echo (SS-FSE) sequence in the presence of significant off-resonance, which includes a variable-density acquisition and a self-calibrated reconstruction as improvements. A non-Carr-Purcell-Meiboom-Gill (nCPMG) SS-FSE acquisition stabilizes both the main and parasitic echo families for each echo. This preserves both the in-phase and quadrature components of the magnetization throughout the echo train. However, nCPMG SS-FSE also promotes aliasing of the quadrature component, which complicates reconstruction. A new acquisition and reconstruction approach is presented here, where the field-of-view is effectively doubled, but a partial k-space and variable density sampling is used to improve scan efficiency. The technique is presented in phantom scans to validate SNR and robustness against rapidly varying object phase. In vivo healthy volunteer examples and the clinical cases are demonstrated in abdominal imaging. This new approach provides comparable SNR to previous nCPMG acquisition techniques as well as providing more uniform apparent diffusion coefficient maps in phantom scans. In vivo scans suggest that this method is more robust against motion than previous approaches. The proposed reconstruction is an improvement to the nCPMG sequence as it is auto-calibrating and is justified to accurately treat the signal model for the nCPMG SS-FSE sequence.

    View details for DOI 10.1109/TMI.2017.2741421

    View details for Web of Science ID 000419346900018

    View details for PubMedID 28829307

    View details for PubMedCentralID PMC5784776

  • The impact of computed high b-value images on the diagnostic accuracy of DWI for prostate cancer: A receiver operating characteristics analysis. Scientific reports Ning, P., Shi, D., Sonn, G. A., Vasanawala, S. S., Loening, A. M., Ghanouni, P., Obara, P., Shin, L. K., Fan, R. E., Hargreaves, B. A., Daniel, B. L. 2018; 8 (1): 3409

    Abstract

    To evaluate the performance of computed high b value diffusion-weighted images (DWI) in prostate cancer detection. 97 consecutive patients who had undergone multiparametric MRI of the prostate followed by biopsy were reviewed. Five radiologists independently scored 138 lesions on native high b-value images (b = 1200 s/mm2), apparent diffusion coefficient (ADC) maps, and computed high b-value images (contrast equivalent to b = 2000 s/mm2) to compare their diagnostic accuracy. Receiver operating characteristic (ROC) analysis and McNemar's test were performed to assess the relative performance of computed high b value DWI, native high b-value DWI and ADC maps. No significant difference existed in the area under the curve (AUC) for ROCs comparing B1200 (b = 1200 s/mm2) to computed B2000 (c-B2000) in 5 readers. In 4 of 5 readers c-B2000 had significantly increased sensitivity and/or decreased specificity compared to B1200 (McNemar's p < 0.05), at selected thresholds of interpretation. ADC maps were less accurate than B1200 or c-B2000 for 2 of 5 readers (P < 0.05). This study detected no consistent improvement in overall diagnostic accuracy using c-B2000, compared with B1200 images. Readers detected more cancer with c-B2000 images (increased sensitivity) but also more false positive findings (decreased specificity).

    View details for DOI 10.1038/s41598-018-21523-6

    View details for PubMedID 29467370

    View details for PubMedCentralID PMC5821845

  • Self-Calibrating Wave-Encoded Variable-Density Single-Shot Fast Spin Echo Imaging. Journal of magnetic resonance imaging : JMRI Chen, F., Taviani, V., Tamir, J. I., Cheng, J. Y., Zhang, T., Song, Q., Hargreaves, B. A., Pauly, J. M., Vasanawala, S. S. 2018; 47 (4): 954–66

    Abstract

    It is highly desirable in clinical abdominal MR scans to accelerate single-shot fast spin echo (SSFSE) imaging and reduce blurring due to T2 decay and partial-Fourier acquisition.To develop and investigate the clinical feasibility of wave-encoded variable-density SSFSE imaging for improved image quality and scan time reduction.Prospective controlled clinical trial.With Institutional Review Board approval and informed consent, the proposed method was assessed on 20 consecutive adult patients (10 male, 10 female, range, 24-84 years).A wave-encoded variable-density SSFSE sequence was developed for clinical 3.0T abdominal scans to enable high acceleration (3.5×) with full-Fourier acquisitions by: 1) introducing wave encoding with self-refocusing gradient waveforms to improve acquisition efficiency; 2) developing self-calibrated estimation of wave-encoding point-spread function and coil sensitivity to improve motion robustness; and 3) incorporating a parallel imaging and compressed sensing reconstruction to reconstruct highly accelerated datasets.Image quality was compared pairwise with standard Cartesian acquisition independently and blindly by two radiologists on a scale from -2 to 2 for noise, contrast, confidence, sharpness, and artifacts. The average ratio of scan time between these two approaches was also compared.A Wilcoxon signed-rank tests with a P value under 0.05 considered statistically significant.Wave-encoded variable-density SSFSE significantly reduced the perceived noise level and improved the sharpness of the abdominal wall and the kidneys compared with standard acquisition (mean scores 0.8, 1.2, and 0.8, respectively, P < 0.003). No significant difference was observed in relation to other features (P = 0.11). An average of 21% decrease in scan time was achieved using the proposed method.Wave-encoded variable-density sampling SSFSE achieves improved image quality with clinically relevant echo time and reduced scan time, thus providing a fast and robust approach for clinical SSFSE imaging.1 Technical Efficacy: Stage 6 J. Magn. Reson. Imaging 2018;47:954-966.

    View details for DOI 10.1002/jmri.25853

    View details for PubMedID 28906567

  • A Novel High-Resolution Magnetic Resonance Imaging Protocol Detects Aldosterone-Producing Adenomas in Patients with Negative Computed Tomography. American journal of hypertension Raber, I., Isom, R. T., Louie, J. D., Vasanawala, S., Bhalla, V. 2018

    View details for DOI 10.1093/ajh/hpy054

    View details for PubMedID 29648568

  • An RF-gated wireless power transfer system for wireless MRI receive arrays CONCEPTS IN MAGNETIC RESONANCE PART B-MAGNETIC RESONANCE ENGINEERING Byron, K., Robb, F., Stang, P., Vasanawala, S., Pauly, J., Scott, G. 2017; 47B (4)
  • Free-breathing pediatric chest MRI: Performance of self-navigated golden-angle ordered conical ultrashort echo time acquisition. Journal of magnetic resonance imaging : JMRI Zucker, E. J., Cheng, J. Y., Haldipur, A., Carl, M., Vasanawala, S. S. 2017

    Abstract

    To assess the feasibility and performance of conical k-space trajectory free-breathing ultrashort echo time (UTE) chest magnetic resonance imaging (MRI) versus four-dimensional (4D) flow and effects of 50% data subsampling and soft-gated motion correction.Thirty-two consecutive children who underwent both 4D flow and UTE ferumoxytol-enhanced chest MR (mean age: 5.4 years, range: 6 days to 15.7 years) in one 3T exam were recruited. From UTE k-space data, three image sets were reconstructed: 1) one with all data, 2) one using the first 50% of data, and 3) a final set with soft-gating motion correction, leveraging the signal magnitude immediately after each excitation. Two radiologists in blinded fashion independently scored image quality of anatomical landmarks on a 5-point scale. Ratings were compared using Wilcoxon rank-sum, Wilcoxon signed-ranks, and Kruskal-Wallis tests. Interobserver agreement was assessed with the intraclass correlation coefficient (ICC).For fully sampled UTE, mean scores for all structures were ≥4 (good-excellent). Full UTE surpassed 4D flow for lungs and airways (P < 0.001), with similar pulmonary artery (PA) quality (P = 0.62). 50% subsampling only slightly degraded all landmarks (P < 0.001), as did motion correction. Subsegmental PA visualization was possible in >93% scans for all techniques (P = 0.27). Interobserver agreement was excellent for combined scores (ICC = 0.83).High-quality free-breathing conical UTE chest MR is feasible, surpassing 4D flow for lungs and airways, with equivalent PA visualization. Data subsampling only mildly degraded images, favoring lesser scan times. Soft-gating motion correction overall did not improve image quality.2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017.

    View details for DOI 10.1002/jmri.25776

    View details for PubMedID 28570032

  • Free-breathing pediatric chest MRI: Performance of self-navigated golden-angle ordered conical ultrashort echo time acquisition. Journal of magnetic resonance imaging : JMRI Zucker, E. J., Cheng, J. Y., Haldipur, A., Carl, M., Vasanawala, S. S. 2017

    Abstract

    To assess the feasibility and performance of conical k-space trajectory free-breathing ultrashort echo time (UTE) chest magnetic resonance imaging (MRI) versus four-dimensional (4D) flow and effects of 50% data subsampling and soft-gated motion correction.Thirty-two consecutive children who underwent both 4D flow and UTE ferumoxytol-enhanced chest MR (mean age: 5.4 years, range: 6 days to 15.7 years) in one 3T exam were recruited. From UTE k-space data, three image sets were reconstructed: 1) one with all data, 2) one using the first 50% of data, and 3) a final set with soft-gating motion correction, leveraging the signal magnitude immediately after each excitation. Two radiologists in blinded fashion independently scored image quality of anatomical landmarks on a 5-point scale. Ratings were compared using Wilcoxon rank-sum, Wilcoxon signed-ranks, and Kruskal-Wallis tests. Interobserver agreement was assessed with the intraclass correlation coefficient (ICC).For fully sampled UTE, mean scores for all structures were ≥4 (good-excellent). Full UTE surpassed 4D flow for lungs and airways (P < 0.001), with similar pulmonary artery (PA) quality (P = 0.62). 50% subsampling only slightly degraded all landmarks (P < 0.001), as did motion correction. Subsegmental PA visualization was possible in >93% scans for all techniques (P = 0.27). Interobserver agreement was excellent for combined scores (ICC = 0.83).High-quality free-breathing conical UTE chest MR is feasible, surpassing 4D flow for lungs and airways, with equivalent PA visualization. Data subsampling only mildly degraded images, favoring lesser scan times. Soft-gating motion correction overall did not improve image quality.2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017.

    View details for DOI 10.1002/jmri.25776

    View details for PubMedID 28570032

  • Fast Comprehensive Single-Sequence Four-Dimensional Pediatric Knee MRI With T-2 Shuffling JOURNAL OF MAGNETIC RESONANCE IMAGING Bao, S., Tamir, J. I., Young, J. L., Tariq, U., Uecker, M., Lai, P., Chen, W., Lustig, M., Vasanawala, S. S. 2017; 45 (6): 1700-1711

    View details for DOI 10.1002/jmri.25508

    View details for Web of Science ID 000401259900015

  • Feasibility of Ferumoxytol-Enhanced Neonatal and Young Infant Cardiac MRI Without General Anesthesia JOURNAL OF MAGNETIC RESONANCE IMAGING Lai, L. M., Cheng, J. Y., Alley, M. T., Zhang, T., Lustig, M., Vasanawala, S. S. 2017; 45 (5): 1407-1418

    Abstract

    To assess the feasibility of ferumoxytol-enhanced anesthesia-free cardiac MRI in neonates and young infants for complex congenital heart disease (CHD).With Institutional Review Board approval, 21 consecutive neonates and young infants (1 day to 11 weeks old; median age of 3 days) who underwent a rapid two-sequence (MR angiography [MRA] and four-dimensional [4D] flow) MRI protocol with intravenous ferumoxytol without sedation (n = 17) or light sedation (n = 4) at 3 Tesla (T) (except one case at 1.5T) between June 2014 and February 2016 were retrospectively identified. Medical records were reviewed for indication, any complications, if further diagnostic imaging was performed after MRI, and surgical findings. Two radiologists scored the images in two sessions on a 5-point scale for overall image quality and delineation of various anatomical structures. Confidence interval of proportions for likelihood of requiring additional diagnostic imaging after MRI was determined. For the possibility of reducing the protocol to a single rapid sequence, Wilcoxon-rank sum test was used to assess whether 4D flow and MRA significantly differed in anatomical delineation.One of 21 patients (4.8%, 80% confidence interval 0-11%) required additional imaging, a computed tomography angiography to assess lung parenchyma and peripheral pulmonary arteries. Only 1 of 13 patients (7.7%) with operative confirmation had a minor discrepancy between radiology and operative reports (80% confidence interval 0-17%). 4D flow was significantly superior to MRA (P < 0.05) for the evaluation of systemic arteries, valves, ventricular trabeculae, and overall quality. Using Cohen's kappa coefficient, there was good interobserver agreement for the evaluation of systemic arteries by 4D flow (κ = 0.782), and systemic veins and pulmonary arteries by MRA (κ > 0.6). Overall 4D flow measurements (mean κ = 0.64-0.74) had better internal agreement compared with MRA (mean κ = 0.30-0.64).Ferumoxytol-enhanced cardiac MRI, without anesthesia, is feasible for the evaluation of complex CHD in neonates and young infants, with a low likelihood of need for additional diagnostic studies. The decreased risk by avoiding anesthesia must be balanced against the potential for adverse reactions with ferumoxytol.2 J. Magn. Reson. Imaging 2016.

    View details for Web of Science ID 000399657300015

  • Resolving phase ambiguity in dual-echo dixon imaging using a projected power method MAGNETIC RESONANCE IN MEDICINE Zhang, T., Chen, Y., Bao, S., Alley, M. T., Pauly, J. M., Hargreaves, B. A., Vasanawala, S. S. 2017; 77 (5): 2066-2076

    Abstract

    To develop a fast and robust method to resolve phase ambiguity in dual-echo Dixon imaging.A major challenge in dual-echo Dixon imaging is to estimate the phase error resulting from field inhomogeneity. In this work, a binary quadratic optimization program was formulated to resolve the phase ambiguity. A projected power method was developed to efficiently solve the optimization problem. Both the 1-peak fat model and 6-peak fat model were applied to three-dimensional (3D) datasets. Additionally, the proposed method was extended to dynamic magnetic resonance imaging (MRI) applications using the 6-peak fat model. With institutional review board (IRB) approval and patient consent/assent, the proposed method was evaluated and compared with region growing on 29 consecutive 3D high-resolution patient datasets.Fast and robust water/fat separation was achieved by the proposed method in different representative 3D datasets and dynamic 3D datasets. Superior water/fat separation was achieved using the 6-peak fat model compared with the 1-peak fat model. Compared to region growing, the proposed method reduced water/fat swaps from 76 to 7% of the patient cohort.The proposed method can achieve fast and robust phase error estimation in dual-echo Dixon imaging. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26287

    View details for Web of Science ID 000399666400034

    View details for PubMedCentralID PMC5123983

  • 3D Cartesian MRI with compressed sensing and variable view sharing using complementary poisson-disc sampling MAGNETIC RESONANCE IN MEDICINE Levine, E., Daniel, B., Vasanawala, S., Hargreaves, B., Saranathan, M. 2017; 77 (5): 1774-1785

    Abstract

    To enable robust, high spatio-temporal-resolution three-dimensional Cartesian MRI using a scheme incorporating a novel variable density random k-space sampling trajectory allowing flexible and retrospective selection of the temporal footprint with compressed sensing (CS).A complementary Poisson-disc k-space sampling trajectory was designed to allow view sharing and varying combinations of reduced view sharing with CS from the same prospective acquisition. These schemes were used for two-point Dixon-based dynamic contrast-enhanced MRI (DCE-MRI) of the breast and abdomen. Results were validated in vivo with a novel approach using variable-flip-angle data, which was retrospectively accelerated using the same methods but offered a ground truth.In breast DCE-MRI, the temporal footprint could be reduced 2.3-fold retrospectively without introducing noticeable artifacts, improving depiction of rapidly enhancing lesions. Further, experiments with variable-flip-angle data showed that reducing view sharing improved accuracy in reconstruction and T1 mapping. In abdominal MRI, 2.3-fold and 3.6-fold reductions in temporal footprint allowed reduced motion artifacts.The complementary-Poisson-disc k-space sampling trajectory allowed a retrospective spatiotemporal resolution tradeoff using CS and view sharing, imparting robustness to motion and contrast enhancement. The technique was also validated using a novel approach of fully acquired variable-flip-angle acquisition. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26254

    View details for Web of Science ID 000399666400005

    View details for PubMedCentralID PMC5074926

  • Current and potential imaging applications of ferumoxytol for magnetic resonance imaging. Kidney international Toth, G. B., Varallyay, C. G., Horvath, A., Bashir, M. R., Choyke, P. L., Daldrup-Link, H. E., Dosa, E., Finn, J. P., Gahramanov, S., Harisinghani, M., Macdougall, I., Neuwelt, A., Vasanawala, S. S., Ambady, P., Barajas, R., Cetas, J. S., Ciporen, J., DeLoughery, T. J., Doolittle, N. D., Fu, R., Grinstead, J., Guimaraes, A. R., Hamilton, B. E., Li, X., McConnell, H. L., Muldoon, L. L., Nesbit, G., Netto, J. P., Petterson, D., Rooney, W. D., Schwartz, D., Szidonya, L., Neuwelt, E. A. 2017

    Abstract

    Contrast-enhanced magnetic resonance imaging is a commonly used diagnostic tool. Compared with standard gadolinium-based contrast agents, ferumoxytol (Feraheme, AMAG Pharmaceuticals, Waltham, MA), used as an alternative contrast medium, is feasible in patients with impaired renal function. Other attractive imaging features of i.v. ferumoxytol include a prolonged blood pool phase and delayed intracellular uptake. With its unique pharmacologic, metabolic, and imaging properties, ferumoxytol may play a crucial role in future magnetic resonance imaging of the central nervous system, various organs outside the central nervous system, and the cardiovascular system. Preclinical and clinical studies have demonstrated the overall safety and effectiveness of this novel contrast agent, with rarely occurring anaphylactoid reactions. The purpose of this review is to describe the general and organ-specific properties of ferumoxytol, as well as the advantages and potential pitfalls associated with its use in magnetic resonance imaging. To more fully demonstrate the applications of ferumoxytol throughout the body, an imaging atlas was created and is available online as supplementary material.

    View details for DOI 10.1016/j.kint.2016.12.037

    View details for PubMedID 28434822

  • Increased Speed and Image Quality for Pelvic Single-Shot Fast Spin-Echo Imaging with Variable Refocusing Flip Angles and Full-Fourier Acquisition. Radiology Loening, A. M., Litwiller, D. V., Saranathan, M., Vasanawala, S. S. 2017; 282 (2): 561-568

    Abstract

    Purpose To assess image quality and speed improvements for single-shot fast spin-echo (SSFSE) with variable refocusing flip angles and full-Fourier acquisition (vrfSSFSE) pelvic imaging via a prospective trial performed in the context of uterine leiomyoma evaluation. Materials and Methods Institutional review board approval and informed consent were obtained. vrfSSFSE and conventional SSFSE sagittal and coronal oblique acquisitions were performed in 54 consecutive female patients referred for 3-T magnetic resonance (MR) evaluation of known or suspected uterine leiomyomas. Two radiologists who were blinded to the image acquisition technique semiquantitatively scored images on a scale from -2 to 2 for noise, image contrast, sharpness, artifacts, and perceived ability to evaluate uterine, ovarian, and musculoskeletal structures. The null hypothesis of no significant difference between pulse sequences was assessed with a Wilcoxon signed rank test by using a Holm-Bonferroni correction for multiple comparisons. Results Because of reductions in specific absorption rate, vrfSSFSE imaging demonstrated significantly increased speed (more than twofold, P < .0001), with mean repetition times compared with conventional SSFSE imaging decreasing from 1358 to 613 msec for sagittal acquisitions and from 1494 to 621 msec for coronal oblique acquisitions. Almost all assessed image quality and perceived diagnostic capability parameters were significantly improved with vrfSSFSE imaging. These improvements included noise, sharpness, and ability to evaluate the junctional zone, myometrium, and musculoskeletal structures for both sagittal acquisitions (mean values of 0.56, 0.63, 0.42, 0.56, and 0.80, respectively; all P values < .0001) and coronal oblique acquisitions (mean values of 0.81, 1.09, 0.65, 0.93, and 1.12, respectively; all P values < .0001). For evaluation of artifacts, there was an insufficient number of cases with differences to allow statistical testing. Conclusion Compared with conventional SSFSE acquisition, vrfSSFSE acquisition increases 3-T imaging speed via reduced specific absorption rate and leads to significant improvements in perceived image quality and perceived diagnostic capability when evaluating pelvic structures. (©) RSNA, 2016 Online supplemental material is available for this article.

    View details for DOI 10.1148/radiol.2016151574

    View details for PubMedID 27564132

    View details for PubMedCentralID PMC5283873

  • Body Diffusion Weighted Imaging Using Non-CPMG Fast Spin Echo IEEE TRANSACTIONS ON MEDICAL IMAGING Gibbons, E. K., Le Roux, P., Vasanawala, S. S., Pauly, J. M., Kerr, A. B. 2017; 36 (2): 549-559

    Abstract

    SS-FSE is a fast technique that does not suffer from off-resonance distortions to the degree that EPI does. Unlike EPI, SS-FSE is ill-suited to diffusion weighted imaging (DWI) due to the Carr-Purcell-Meiboom-Geill (CPMG) condition. Non- CPMG phase cycling does accommodate SS-FSE and DWI but places constraints on reconstruction, which are resolved here through parallel imaging. Additionally, improved echo stability can be achieved by using short duration and highly selective DIVERSE radiofrequency pulses. Here, signal-to-noise ratio (SNR) comparisons between EPI and nCPMG SS-FSE acquisitions and reconstruction techniques give similar values. Diffusion imaging with nCPMG SS-FSE gives similar SNR to an EPI acquisition, though apparent diffusion coefficient values are higher than seen with EPI. In vivo images have good image quality with little distortion. This method has the ability to capture distortionfree DWI images near areas of significant off-resonance as well as preserve adequate SNR. Parallel imaging and DIVERSE refocusing RF pulses allow shorter ETL compared to previous implementations and thus reduces phase encode direction blur and SAR accumulation.

    View details for DOI 10.1109/TMI.2016.2622238

    View details for Web of Science ID 000396115800019

  • Conspicuity of Malignant Lesions on PET/CT and Simultaneous Time-Of-Flight PET/MRI PLOS ONE Minamimoto, R., Iagaru, A., Jamali, M., Holley, D., Barkhodari, A., Vasanawala, S., Zaharchuk, G. 2017; 12 (1)

    Abstract

    To compare the conspicuity of malignant lesions between FDG PET/CT and a new simultaneous, time-of-flight (TOF) enabled PET/MRI scanner.All patients underwent a single-injection of FDG, followed by a dual imaging protocol consisting of PET/CT followed by TOF PET/MRI. PET/CT and PET/MRI images were evaluated by two readers independently for areas of FDG uptake compatible with malignancy, and then categorized into 5 groups (1: PET/MRI and PET/CT positive; 2: PET/MRI positive, PET/CT positive in retrospect; 3: PET/CT positive, PET/MRI positive in retrospect; 4: PET/MRI positive, PET/CT negative; 5: PET/MRI negative, PET/CT positive) by consensus. Patients with no lesions on either study or greater than 10 lesions based on either modality were excluded from the study.Fifty-two patients (mean±SD age: 58±14 years) underwent the dual imaging protocol; of these, 29 patients with a total of 93 FDG-avid lesions met the inclusion criteria. The majority of lesions (56%) were recorded prospectively in the same location on PET/CT and PET/MRI. About an equal small fraction of lesions were seen on PET/CT but only retrospectively on PET/MRI (9%) and vice versa (12%). More lesions were identified only on PET/MRI but not on PET/CT, even in retrospect (96% vs. 81%, respectively; p = 0.003). Discrepant lesions had lower maximum standardized uptake value (SUVmax) than concordant lesions on both modalities (p<0.001).While most lesions were identified prospectively on both modalities, significantly more lesions were identified with PET/MRI than with PET/CT.

    View details for DOI 10.1371/journal.pone.0167262

    View details for Web of Science ID 000392381100001

    View details for PubMedID 28103230

    View details for PubMedCentralID PMC5245859

  • T-2 shuffling: Sharp, multicontrast, volumetric fast spin-echo imaging MAGNETIC RESONANCE IN MEDICINE Tamir, J. I., Uecker, M., Chen, W., Lai, P., Alley, M. T., Vasanawala, S. S., Lustig, M. 2017; 77 (1): 180-195

    View details for DOI 10.1002/mrm.26102

    View details for Web of Science ID 000391038800020

  • Prospective Evaluation of 68Ga-RM2 PET/MRI in Patients with Biochemical Recurrence of Prostate Cancer and Negative Conventional Imaging. Journal of nuclear medicine : official publication, Society of Nuclear Medicine Minamimoto, R., Sonni, I., Hancock, S., Vasanawala, S., Loening, A., Gambhir, S. S., Iagaru, A. 2017

    Abstract

    Purpose:68Ga-labeled DOTA-4-amino-1-carboxymethyl-piperidine-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 (68Ga-RM2) is a synthetic bombesin receptor antagonist that targets gastrin-releasing peptide receptors (GRPr). GRPr proteins are highly overexpressed in several human tumors, including prostate cancer. We present data from the use of 68Ga-RM2 in patients with biochemical recurrence (BCR) of prostate cancer (PC) and negative conventional imaging (CI). Methods: We enrolled 32 men with BCR PC, 59-83 year-old (mean±standard deviation (SD): 68.7±6.4). Imaging started at 40-69 minutes (mean±SD: 50.5±6.8) after injection of 133.2-151.7 MBq (mean±SD: 140.6±7.4) of 68Ga-RM2 using a time-of-flight (TOF)-enabled simultaneous positron emission tomography (PET) / magnetic resonance imaging (MRI) scanner. T1-weighted (T1w), T2-weighted (T2w) and diffusion-weighted images (DWI) were acquired. Results: All patients had rising prostate specific antigen (PSA) (range: 0.3-119.0 ng/mL; mean±SD: 10.1 ± 21.3) and negative CI (CT or MRI, and 99mTc MDP bone scan) prior to enrollment. The observed 68Ga-RM2 PET detection rate was 71.8%. 68Ga-RM2 PET identified recurrent prostate cancer in 23 of the 32 participants, while the simultaneous MRI scan identified findings compatible with recurrent prostate cancer in 11 of the 32 patients. PSA velocity (PSAv) values were 0.32±0.59 ng/ml/year (range: 0.04-1.9) in patients with negative PET scans and 2.51±2.16 ng/ml/year (range: 0.13-8.68) in patients with positive PET scans (P: 0.006). Conclusion:68Ga-RM2 PET can be used for assessment of GRPr expression in patients with BCR PC. High uptake in multiple areas compatible with cancer lesions suggests that 68Ga-RM2 is a promising PET radiopharmaceutical for localization of disease in participants with BCR PC and negative CI.

    View details for DOI 10.2967/jnumed.117.197624

    View details for PubMedID 29084827

  • Relative value of three whole-body MR approaches for PET-MR, including gadofosveset-enhanced MR, in comparison to PET-CT. Clinical imaging Obara, P., Loening, A., Taviani, V., Iagaru, A., Hargreaves, B. A., Vasanawala, S. 2017; 48: 62–68

    Abstract

    Evaluate MR protocol for PET-MR including coronal DWI (cDWI), fat-suppressed T2 (T2w), and gadofosveset-enhanced T1 (CE).18 patients underwent same-day PET-CT and PET-MR. Image quality and performance of each sequence, and combination of all three sequences, was evaluated with respect to PET-CT.Lesion conspicuity was best on cDWI, while delineation was best on CE. Considering all three sequences combined, both readers showed good sensitivity and specificity (>80%). Relative sensitivity was highest on CE and lowest on T2w.Whole-body MR performed well in detecting malignant lesions compared to PET-CT. CE showed overall highest performance.

    View details for DOI 10.1016/j.clinimag.2017.09.016

    View details for PubMedID 29031209

  • High-resolution diffusion-weighted imaging of the breast with multiband 2D radiofrequency pulses and a generalized parallel imaging reconstruction MAGNETIC RESONANCE IN MEDICINE Taviani, V., Alley, M. T., Banerjee, S., Nishimura, D. G., Daniel, B. L., Vasanawala, S. S., Hargreaves, B. A. 2017; 77 (1): 209-220

    Abstract

    To develop a technique for high-resolution diffusion-weighted imaging (DWI) and to compare it with standard DWI methods.Multiple in-plane bands of magnetization were simultaneously excited by identically phase modulating each subpulse of a two-dimensional (2D) RF pulse. Several excitations with the same multiband pattern progressively shifted in the phase-encode direction were used to cover the prescribed field of view (FOV). The phase-encoded FOV was limited to the width of a single band to reduce off-resonance-induced distortion and blurring. Parallel imaging (PI) techniques were used to resolve aliasing from the other bands and to combine the different excitations. Following validation in phantoms and healthy volunteers, a preliminary study in breast cancer patients (N=14) was performed to compare the proposed method to conventional DWI with PI and to reduced-FOV DWI.The proposed method gave high-resolution diffusion-weighted images with minimal artifacts at the band intersections. Compared to PI alone, higher phase-encoded FOV-reduction factors and reduced noise amplification were obtained, which translated to higher resolution images than conventional (non-multiband) DWI. The same resolution and image quality achievable over targeted regions using existing reduced-FOV methods was obtained, but the proposed method also enables complete bilateral coverage.We developed an in-plane multiband technique for high-resolution DWI and compared its performance with other standard DWI methods. Magn Reson Med 77:209-220, 2017. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26110

    View details for Web of Science ID 000391038800022

  • Autocalibrating motion-corrected wave-encoding for highly accelerated free-breathing abdominal MRI. Magnetic resonance in medicine Chen, F., Zhang, T., Cheng, J. Y., Shi, X., Pauly, J. M., Vasanawala, S. S. 2016

    Abstract

    To develop a motion-robust wave-encoding technique for highly accelerated free-breathing abdominal MRI.A comprehensive 3D wave-encoding-based method was developed to enable fast free-breathing abdominal imaging: (a) auto-calibration for wave-encoding was designed to avoid extra scan for coil sensitivity measurement; (b) intrinsic butterfly navigators were used to track respiratory motion; (c) variable-density sampling was included to enable compressed sensing; (d) golden-angle radial-Cartesian hybrid view-ordering was incorporated to improve motion robustness; and (e) localized rigid motion correction was combined with parallel imaging compressed sensing reconstruction to reconstruct the highly accelerated wave-encoded datasets. The proposed method was tested on six subjects and image quality was compared with standard accelerated Cartesian acquisition both with and without respiratory triggering. Inverse gradient entropy and normalized gradient squared metrics were calculated, testing whether image quality was improved using paired t-tests.For respiratory-triggered scans, wave-encoding significantly reduced residual aliasing and blurring compared with standard Cartesian acquisition (metrics suggesting P < 0.05). For non-respiratory-triggered scans, the proposed method yielded significantly better motion correction compared with standard motion-corrected Cartesian acquisition (metrics suggesting P < 0.01).The proposed methods can reduce motion artifacts and improve overall image quality of highly accelerated free-breathing abdominal MRI. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

    View details for DOI 10.1002/mrm.26567

    View details for PubMedID 27943402

  • Depletion-Mode GaN HEMT Q-Spoil Switches for MRI Coils IEEE TRANSACTIONS ON MEDICAL IMAGING Lu, J. Y., Grafendorfer, T., Zhang, T., Vasanawala, S., Robb, F., Pauly, J. M., Scott, G. C. 2016; 35 (12): 2558-2567

    Abstract

    Q-spoiling is the process of decoupling an MRI receive coil to protect the equipment and patient. Conventionally, Q-spoiling is performed using a PIN diode switch that draws significant current. In this work, a Q-spoiling technique using a depletion-mode Gallium Nitride HEMT device was developed for coil detuning at both 1.5 T and 3 T MRI. The circuits with conventional PIN diode Q-spoiling and the GaN HEMT device were implemented on surface coils. SNR was measured and compared for all surfaces coils. At both 1.5 T and 3 T, comparable SNR was achieved for all coils with the proposed technique and conventional Q-spoiling. The GaN HEMT device has significantly reduced the required power for Q-spoiling. The GaN HEMT device also provides useful safety features by detuning the coil when unpowered.

    View details for DOI 10.1109/TMI.2016.2586053

    View details for Web of Science ID 000391547700005

    View details for PubMedID 27362895

  • Body diffusion weighted imaging using non-CPMG fast spin echo. IEEE transactions on medical imaging Gibbons, E., Le Roux, P., Vasanawala, S., Pauly, J., Kerr, A. 2016: -?

    Abstract

    SS-FSE is a fast technique that does not suffer from off-resonance distortions to the degree that EPI does. Unlike EPI, SS-FSE is ill-suited to diffusion weighted imaging (DWI) due to the Carr-Purcell-Meiboom-Geill (CPMG) condition. Non- CPMG phase cycling does accommodate SS-FSE and DWI but places constraints on reconstruction, which are resolved here through parallel imaging. Additionally, improved echo stability can be achieved by using short duration and highly selective DIVERSE radiofrequency pulses. Here, signal-to-noise ratio (SNR) comparisons between EPI and nCPMG SS-FSE acquisitions and reconstruction techniques give similar values. Diffusion imaging with nCPMG SS-FSE gives similar SNR to an EPI acquisition, though apparent diffusion coefficient values are higher than seen with EPI. In vivo images have good image quality with little distortion. This method has the ability to capture distortionfree DWI images near areas of significant off-resonance as well as preserve adequate SNR. Parallel imaging and DIVERSE refocusing RF pulses allow shorter ETL compared to previous implementations and thus reduces phase encode direction blur and SAR accumulation.

    View details for PubMedID 27810802

  • Fast comprehensive single-sequence four-dimensional pediatric knee MRI with T2 shuffling. Journal of magnetic resonance imaging : JMRI Bao, S., Tamir, J. I., Young, J. L., Tariq, U., Uecker, M., Lai, P., Chen, W., Lustig, M., Vasanawala, S. S. 2016

    Abstract

    To develop and clinically evaluate a pediatric knee magnetic resonance imaging (MRI) technique based on volumetric fast spin-echo (3DFSE) and compare its diagnostic performance, image quality, and imaging time to that of a conventional 2D protocol.A 3DFSE sequence was modified and combined with a compressed sensing-based reconstruction resolving multiple image contrasts, a technique termed T2 Shuffling (T2 Sh). With Institutional Review Board (IRB) approval, 28 consecutive children referred for 3T knee MRI prospectively underwent a standard clinical knee protocol followed by T2 Sh. T2 Sh performance was assessed by two readers blinded to diagnostic reports. Interpretive discrepancies were resolved by medical record chart review and consensus between the readers and an orthopedic surgeon. Image quality was evaluated by rating anatomic delineation, with 95% confidence interval. A Wilcoxon rank-sum test assessed the null hypothesis that T2 Sh structure delineation compared to conventional 2D is unchanged. Intraclass correlation coefficients were calculated for interobserver agreement. Imaging time of the conventional protocol and T2 Sh was compared.There was 81% and 87% concordance between T2 Sh reports and diagnostic reports, respectively, for each reader. Upon consensus review, T2 Sh had 93% sensitivity and 100% specificity compared to clinical reports for detection of clinically relevant findings. The 95% confidence interval of diagnostic or better rating was 95-100%, with 34-80% interobserver agreement. There was no significant difference in structure delineation between T2 Sh and 2D, except for the retinaculum (P < 0.05), where 2D was preferred. Typical imaging time for T2 Sh and the conventional exam was 7 and 13 minutes, respectively.A single-sequence pediatric knee exam is feasible with T2 Sh, providing multiplanar, reformattable 4D images. Level of Evidence 2 J. Magn. Reson. Imaging 2016;00:000-000.

    View details for DOI 10.1002/jmri.25508

    View details for PubMedID 27726251

  • Cloud-processed 4D CMR flow imaging for pulmonary flow quantification. European journal of radiology Chelu, R. G., Wanambiro, K. W., Hsiao, A., Swart, L. E., Voogd, T., van den Hoven, A. T., van Kranenburg, M., Coenen, A., Boccalini, S., Wielopolski, P. A., Vogel, M. W., Krestin, G. P., Vasanawala, S. S., Budde, R. P., Roos-Hesselink, J. W., Nieman, K. 2016; 85 (10): 1849-1856

    Abstract

    In this study, we evaluated a cloud-based platform for cardiac magnetic resonance (CMR) four-dimensional (4D) flow imaging, with fully integrated correction for eddy currents, Maxwell phase effects, and gradient field non-linearity, to quantify forward flow, regurgitation, and peak systolic velocity over the pulmonary artery.We prospectively recruited 52 adult patients during one-year period from July 2014. The 4D flow and planar (2D) phase-contrast (PC) were acquired during same scanning session, but 4D flow was scanned after injection of a gadolinium-based contrast agent. Eddy-currents were semi-automatically corrected using the web-based software. Flow over pulmonary valve was measured and the 4D flow values were compared against the 2D PC ones.The mean forward flow was 92 (±30) ml/cycle measured with 4D flow and 86 (±29) ml/cycle measured with 2D PC, with a correlation of 0.82 and a mean difference of -6ml/cycle (-41-29). For the regurgitant fraction the correlation was 0.85 with a mean difference of -0.95% (-17-15). Mean peak systolic velocity measured with 4D flow was 92 (±49) cm/s and 108 (±56) cm/s with 2D PC, having a correlation of 0.93 and a mean difference of 16cm/s (-24-55).4D flow imaging post-processed with an integrated cloud-based application accurately quantifies pulmonary flow. However, it may underestimate the peak systolic velocity.

    View details for DOI 10.1016/j.ejrad.2016.07.018

    View details for PubMedID 27666627

  • Feasibility of ferumoxytol-enhanced neonatal and young infant cardiac MRI without general anesthesia. Journal of magnetic resonance imaging : JMRI Lai, L. M., Cheng, J. Y., Alley, M. T., Zhang, T., Lustig, M., Vasanawala, S. S. 2016

    Abstract

    To assess the feasibility of ferumoxytol-enhanced anesthesia-free cardiac MRI in neonates and young infants for complex congenital heart disease (CHD).With Institutional Review Board approval, 21 consecutive neonates and young infants (1 day to 11 weeks old; median age of 3 days) who underwent a rapid two-sequence (MR angiography [MRA] and four-dimensional [4D] flow) MRI protocol with intravenous ferumoxytol without sedation (n = 17) or light sedation (n = 4) at 3 Tesla (T) (except one case at 1.5T) between June 2014 and February 2016 were retrospectively identified. Medical records were reviewed for indication, any complications, if further diagnostic imaging was performed after MRI, and surgical findings. Two radiologists scored the images in two sessions on a 5-point scale for overall image quality and delineation of various anatomical structures. Confidence interval of proportions for likelihood of requiring additional diagnostic imaging after MRI was determined. For the possibility of reducing the protocol to a single rapid sequence, Wilcoxon-rank sum test was used to assess whether 4D flow and MRA significantly differed in anatomical delineation.One of 21 patients (4.8%, 80% confidence interval 0-11%) required additional imaging, a computed tomography angiography to assess lung parenchyma and peripheral pulmonary arteries. Only 1 of 13 patients (7.7%) with operative confirmation had a minor discrepancy between radiology and operative reports (80% confidence interval 0-17%). 4D flow was significantly superior to MRA (P < 0.05) for the evaluation of systemic arteries, valves, ventricular trabeculae, and overall quality. Using Cohen's kappa coefficient, there was good interobserver agreement for the evaluation of systemic arteries by 4D flow (κ = 0.782), and systemic veins and pulmonary arteries by MRA (κ > 0.6). Overall 4D flow measurements (mean κ = 0.64-0.74) had better internal agreement compared with MRA (mean κ = 0.30-0.64).Ferumoxytol-enhanced cardiac MRI, without anesthesia, is feasible for the evaluation of complex CHD in neonates and young infants, with a low likelihood of need for additional diagnostic studies. The decreased risk by avoiding anesthesia must be balanced against the potential for adverse reactions with ferumoxytol.2 J. Magn. Reson. Imaging 2016.

    View details for DOI 10.1002/jmri.25482

    View details for PubMedID 27678106

  • A semiflexible 64-channel receive-only phased array for pediatric body MRI at 3T. Magnetic resonance in medicine Zhang, T., Grafendorfer, T., Cheng, J. Y., Ning, P., Rainey, B., Giancola, M., Ortman, S., Robb, F. J., Calderon, P. D., Hargreaves, B. A., Lustig, M., Scott, G. C., Pauly, J. M., Vasanawala, S. S. 2016; 76 (3): 1015-1021

    Abstract

    To design, construct, and validate a semiflexible 64-channel receive-only phased array for pediatric body MRI at 3T.A 64-channel receive-only phased array was developed and constructed. The designed flexible coil can easily conform to different patient sizes with nonoverlapping coil elements in the transverse plane. It can cover a field of view of up to 44 × 28 cm(2) and removes the need for coil repositioning for body MRI patients with multiple clinical concerns. The 64-channel coil was compared with a 32-channel standard coil for signal-to-noise ratio and parallel imaging performances on different phantoms. With IRB approval and informed consent/assent, the designed coil was validated on 21 consecutive pediatric patients.The pediatric coil provided higher signal-to-noise ratio than the standard coil on different phantoms, with the averaged signal-to-noise ratio gain at least 23% over a depth of 7 cm along the cross-section of phantoms. It also achieved better parallel imaging performance under moderate acceleration factors. Good image quality (average score 4.6 out of 5) was achieved using the developed pediatric coil in the clinical studies.A 64-channel semiflexible receive-only phased array has been developed and validated to facilitate high quality pediatric body MRI at 3T. Magn Reson Med 76:1015-1021, 2016. © 2015 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.25999

    View details for PubMedID 26418283

    View details for PubMedCentralID PMC4811745

  • Assessment of the precision and reproducibility of ventricular volume, function, and mass measurements with ferumoxytol-enhanced 4D flow MRI JOURNAL OF MAGNETIC RESONANCE IMAGING Hanneman, K., Kino, A., Cheng, J. Y., Alley, M. T., Vasanawala, S. S. 2016; 44 (2): 383-392

    Abstract

    To compare the precision and interobserver agreement of ventricular volume, function, and mass quantification by 3D time-resolved (4D) flow MRI relative to cine steady-state free precession (SSFP).With Institutional Research Board approval, informed consent, and HIPAA compliance, 22 consecutive patients with congenital heart disease (CHD) (10 males, 6.4 ± 4.8 years) referred for 3T ferumoxytol-enhanced cardiac MRI were prospectively recruited. Complete ventricular coverage with standard 2D short-axis cine SSFP and whole chest coverage with axial 4D flow were obtained. Two blinded radiologists independently segmented images for left ventricular (LV) and right ventricular (RV) myocardium at end systole (ES) and end diastole (ED). Statistical analysis included linear regression, analysis of variance (ANOVA), Bland-Altman (BA) analysis, and intraclass correlation (ICC).Significant positive correlations were found between 4D flow and SSFP for ventricular volumes (r = 0.808-0.972, P < 0.001), ejection fraction (EF) (r = 0.900-928, P < 0.001), and mass (r = 0.884-0.934, P < 0.001). BA relative limits of agreement for both ventricles were between -52% to 34% for volumes, -29% to 27% for EF, and -41% to 48% for mass, with wider limits of agreement for the RV compared to the LV. There was no significant difference between techniques with respect to mean square difference of ED-ES mass for either LV (F = 2.05, P = 0.159) or RV (F = 0.625, P = 0.434). Interobserver agreement was moderate to good with both 4D flow (ICC 0.523-0.993) and SSFP (ICC 0.619-0.982), with overlapping confidence intervals.Quantification of ventricular volume, function, and mass can be accomplished with 4D flow MRI with precision and interobserver agreement comparable to that of cine SSFP. J. Magn. Reson. Imaging 2016;44:383-392.

    View details for DOI 10.1002/jmri.25180

    View details for Web of Science ID 000380068100014

    View details for PubMedID 26871420

  • Robust self-navigated body MRI using dense coil arrays. Magnetic resonance in medicine Zhang, T., Cheng, J. Y., Chen, Y., Nishimura, D. G., Pauly, J. M., Vasanawala, S. S. 2016; 76 (1): 197-205

    Abstract

    To develop a robust motion estimation method for free-breathing body MRI using dense coil arrays.Self-navigating pulse sequences can measure subject motion without using external motion monitoring devices. With dense coil arrays, individual coil elements can provide localized motion estimates. An averaged motion estimate over all coils is often used for motion compensation. However, this motion estimate may not accurately represent the dominant motion within the imaging volume. In this work, a coil clustering method is proposed to automatically determine the dominant motion for dense coil arrays. The feasibility of the proposed method is investigated in free-breathing abdominal MRI and cardiac MRI, and compared with manual motion estimate selection for respiratory motion estimation and electrocardiography for cardiac motion estimation.Automated motion estimation achieved similar respiratory motion estimation compared to manual selection (averaged correlation coefficient 0.989 and 0.988 for abdominal MRI and cardiac MRI, respectively), and accurate cardiac triggering compared to electrocardiography (averaged temporal variability 17.5 ms).The proposed method can provide accurate automated motion estimation for body MRI using dense coil arrays. It can enable self-navigated free-breathing abdominal and cardiac MRI without the need for external motion monitoring devices. Magn Reson Med 76:197-205, 2016. © 2015 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.25858

    View details for PubMedID 26220204

  • Comprehensive motion-compensated highly accelerated 4D flow MRI with ferumoxytol enhancement for pediatric congenital heart disease. Journal of magnetic resonance imaging Cheng, J. Y., Hanneman, K., Zhang, T., Alley, M. T., Lai, P., Tamir, J. I., Uecker, M., Pauly, J. M., Lustig, M., Vasanawala, S. S. 2016; 43 (6): 1355-1368

    Abstract

    To develop and evaluate motion-compensation and compressed-sensing techniques in 4D flow MRI for anatomical assessment in a comprehensive ferumoxytol-enhanced congenital heart disease (CHD) exam.A Cartesian 4D flow sequence was developed to enable intrinsic navigation and two variable-density sampling schemes: VDPoisson and VDRad. Four compressed-sensing methods were developed: A) VDPoisson scan reconstructed using spatial wavelets; B) added temporal total variation to A; C) VDRad scan using the same reconstruction as in B; and D) added motion compensation to C. With Institutional Review Board (IRB) approval and Health Insurance Portability and Accountability Act (HIPAA) compliance, 23 consecutive patients (eight females, mean 6.3 years) referred for ferumoxytol-enhanced CHD 3T MRI were recruited. Images were acquired and reconstructed using methods A-D. Two cardiovascular radiologists independently scored the images on a 5-point scale. These readers performed a paired wall motion and functional assessment between method D and 2D balanced steady-state free precession (bSSFP) CINE for 16 cases.Method D had higher diagnostic image quality for most anatomical features (mean 3.8-4.8) compared to A (2.0-3.6), B (2.2-3.7), and C (2.9-3.9) with P < 0.05 with good interobserver agreement (κ ≥ 0.49). Method D had similar or better assessment of myocardial borders and cardiac motion compared to 2D bSSFP (P < 0.05, κ ≥ 0.77). All methods had good internal agreement in comparing aortic with pulmonic flow (BA mean < 0.02%, r > 0.85) and compared to method A (BA mean < 0.13%, r > 0.84) with P < 0.01.Flow, functional, and anatomical assessment in CHD with ferumoxytol-enhanced 4D flow is feasible and can be significantly improved using motion compensation and compressed sensing. J. Magn. Reson. Imaging 2016;43:1355-1368.

    View details for DOI 10.1002/jmri.25106

    View details for PubMedID 26646061

  • Resolving phase ambiguity in dual-echo dixon imaging using a projected power method. Magnetic resonance in medicine Zhang, T., Chen, Y., Bao, S., Alley, M. T., Pauly, J. M., Hargreaves, B. A., Vasanawala, S. S. 2016

    Abstract

    To develop a fast and robust method to resolve phase ambiguity in dual-echo Dixon imaging.A major challenge in dual-echo Dixon imaging is to estimate the phase error resulting from field inhomogeneity. In this work, a binary quadratic optimization program was formulated to resolve the phase ambiguity. A projected power method was developed to efficiently solve the optimization problem. Both the 1-peak fat model and 6-peak fat model were applied to three-dimensional (3D) datasets. Additionally, the proposed method was extended to dynamic magnetic resonance imaging (MRI) applications using the 6-peak fat model. With institutional review board (IRB) approval and patient consent/assent, the proposed method was evaluated and compared with region growing on 29 consecutive 3D high-resolution patient datasets.Fast and robust water/fat separation was achieved by the proposed method in different representative 3D datasets and dynamic 3D datasets. Superior water/fat separation was achieved using the 6-peak fat model compared with the 1-peak fat model. Compared to region growing, the proposed method reduced water/fat swaps from 76 to 7% of the patient cohort.The proposed method can achieve fast and robust phase error estimation in dual-echo Dixon imaging. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26287

    View details for PubMedID 27221766

  • Safety and technique of ferumoxytol administration for MRI. Magnetic resonance in medicine Vasanawala, S. S., Nguyen, K., Hope, M. D., Bridges, M. D., Hope, T. A., Reeder, S. B., Bashir, M. R. 2016; 75 (5): 2107-2111

    Abstract

    Ferumoxytol is an ultrasmall superparamagnetic iron oxide agent marketed for the treatment of anemia. There has been increasing interest in its properties as an MRI contrast agent as well as greater awareness of its adverse event profile. This mini-review summarizes the current state of knowledge of the risks of ferumoxytol and methods of administration. Magn Reson Med 75:2107-2111, 2016. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26151

    View details for PubMedID 26890830

  • 3D Cartesian MRI with compressed sensing and variable view sharing using complementary poisson-disc sampling. Magnetic resonance in medicine Levine, E., Daniel, B., Vasanawala, S., Hargreaves, B., Saranathan, M. 2016: -?

    Abstract

    To enable robust, high spatio-temporal-resolution three-dimensional Cartesian MRI using a scheme incorporating a novel variable density random k-space sampling trajectory allowing flexible and retrospective selection of the temporal footprint with compressed sensing (CS).A complementary Poisson-disc k-space sampling trajectory was designed to allow view sharing and varying combinations of reduced view sharing with CS from the same prospective acquisition. These schemes were used for two-point Dixon-based dynamic contrast-enhanced MRI (DCE-MRI) of the breast and abdomen. Results were validated in vivo with a novel approach using variable-flip-angle data, which was retrospectively accelerated using the same methods but offered a ground truth.In breast DCE-MRI, the temporal footprint could be reduced 2.3-fold retrospectively without introducing noticeable artifacts, improving depiction of rapidly enhancing lesions. Further, experiments with variable-flip-angle data showed that reducing view sharing improved accuracy in reconstruction and T1 mapping. In abdominal MRI, 2.3-fold and 3.6-fold reductions in temporal footprint allowed reduced motion artifacts.The complementary-Poisson-disc k-space sampling trajectory allowed a retrospective spatiotemporal resolution tradeoff using CS and view sharing, imparting robustness to motion and contrast enhancement. The technique was also validated using a novel approach of fully acquired variable-flip-angle acquisition. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26254

    View details for PubMedID 27097596

    View details for PubMedCentralID PMC5074926

  • Combined parenchymal and vascular imaging: High spatiotemporal resolution arterial evaluation of hepatocellular carcinoma JOURNAL OF MAGNETIC RESONANCE IMAGING Hope, T. A., Petkovska, I., Saranathan, M., Hargreaves, B. A., Vasanawala, S. S. 2016; 43 (4): 859-865

    Abstract

    To assess the ability of high-resolution arterial phase imaging of hepatocellular carcinoma (HCC) to provide combined vascular characterization and parenchymal evaluation.Thirty-eight consecutive studies in cirrhotic patients with HCC scanned with a view-shared 2-point-Dixon-based Differential Subsampling with Cartesian Ordering (DISCO) sequence were analyzed. Lesion contrast relative to precontrast and adjacent parenchyma was evaluated and compared using a Fisher's exact test. Visibility of hepatic arteries and tumor feeding vessels were graded on a 5-point scale. Catheter angiography was used as a reference standard for arterial anatomy.The high spatiotemporal multiphasic acquisition allowed imaging of both the angiographic and late arterial phase in 30 of 38 studies with good image quality. Maximal lesion enhancement compared to precontrast occurred more frequently during the late arterial phase compared to maximal lesion-to-adjacent, which occurred more frequently during the early arterial phase (P < 0.001). Common and proper hepatic arteries were visualized adequately in 100%, right hepatic artery in 94-97%, left hepatic artery in 94%, and segmental vessel in 83% of cases. Arterial variants were detected with sensitivity of 87-100% and specificity of 100%.High spatiotemporal resolution arterial phase imaging provides multiple angiographic and arterial phases in a single breath-hold, enabling accurate depiction of vascular anatomy while maintain optimal arterial phase imaging for characterization of focal lesions. J. Magn. Reson. Imaging 2016;43:859-865.

    View details for DOI 10.1002/jmri.25042

    View details for Web of Science ID 000373000500009

  • Pilot Comparison of Ga-68-RM2 PET and Ga-68-PSMA-11 PET in Patients with Biochemically Recurrent Prostate Cancer JOURNAL OF NUCLEAR MEDICINE Minamimoto, R., Hancock, S., Schneider, B., Chin, F. T., Jamali, M., Loening, A., Vasanawala, S., Gambhir, S. S., Iagaru, A. 2016; 57 (4): 557-562

    Abstract

    Glu-NH-CO-NH-Lys-(Ahx)-[(68)Ga(HBED-CC)] ((68)Ga-PSMA-11) is a PET tracer that can detect prostate cancer relapses and metastases by binding to the extracellular domain of PSMA.(68)Ga-labeled DOTA-4-amino-1-carboxymethyl-piperidine-d-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 ((68)Ga-RM2) is a synthetic bombesin receptor antagonist that targets gastrin-releasing peptide receptors. We present pilot data on the biodistribution of these PET tracers in a small cohort of patients with biochemically recurrent prostate cancer.Seven men (mean age ± SD, 74.3 ± 5.9 y) with biochemically recurrent prostate cancer underwent both(68)Ga-PSMA-11 PET/CT and(68)Ga-RM2 PET/MRI scans. SUVmaxand SUVmeanwere recorded for normal tissues and areas of uptake outside the expected physiologic biodistribution.All patients had a rising level of prostate-specific antigen (mean ± SD, 13.5 ± 11.5) and noncontributory results on conventional imaging.(68)Ga-PSMA-11 had the highest physiologic uptake in the salivary glands and small bowel, with hepatobiliary and renal clearance noted, whereas(68)Ga-RM2 had the highest physiologic uptake in the pancreas, with renal clearance noted. Uptake outside the expected physiologic biodistribution did not significantly differ between(68)Ga-PSMA-11 and(68)Ga-RM2; however,(68)Ga-PSMA-11 localized in a lymph node and seminal vesicle in a patient with no abnormal(68)Ga-RM2 uptake. Abdominal periaortic lymph nodes were more easily visualized by(68)Ga-RM2 in two patients because of lack of interference by radioactivity in the small intestine.(68)Ga-PSMA-11 and(68)Ga-RM2 had distinct biodistributions in this small cohort of patients with biochemically recurrent prostate cancer. Additional work is needed to understand the expression of PSMA and gastrin-releasing peptide receptors in different types of prostate cancer.

    View details for DOI 10.2967/jnumed.115.168393

    View details for Web of Science ID 000373627800022

    View details for PubMedID 26659347

  • Combined parenchymal and vascular imaging: High spatiotemporal resolution arterial evaluation of hepatocellular carcinoma. Journal of magnetic resonance imaging Hope, T. A., Petkovska, I., Saranathan, M., Hargreaves, B. A., Vasanawala, S. S. 2016; 43 (4): 859-865

    Abstract

    To assess the ability of high-resolution arterial phase imaging of hepatocellular carcinoma (HCC) to provide combined vascular characterization and parenchymal evaluation.Thirty-eight consecutive studies in cirrhotic patients with HCC scanned with a view-shared 2-point-Dixon-based Differential Subsampling with Cartesian Ordering (DISCO) sequence were analyzed. Lesion contrast relative to precontrast and adjacent parenchyma was evaluated and compared using a Fisher's exact test. Visibility of hepatic arteries and tumor feeding vessels were graded on a 5-point scale. Catheter angiography was used as a reference standard for arterial anatomy.The high spatiotemporal multiphasic acquisition allowed imaging of both the angiographic and late arterial phase in 30 of 38 studies with good image quality. Maximal lesion enhancement compared to precontrast occurred more frequently during the late arterial phase compared to maximal lesion-to-adjacent, which occurred more frequently during the early arterial phase (P < 0.001). Common and proper hepatic arteries were visualized adequately in 100%, right hepatic artery in 94-97%, left hepatic artery in 94%, and segmental vessel in 83% of cases. Arterial variants were detected with sensitivity of 87-100% and specificity of 100%.High spatiotemporal resolution arterial phase imaging provides multiple angiographic and arterial phases in a single breath-hold, enabling accurate depiction of vascular anatomy while maintain optimal arterial phase imaging for characterization of focal lesions. J. Magn. Reson. Imaging 2016;43:859-865.

    View details for DOI 10.1002/jmri.25042

    View details for PubMedID 26340309

  • High temporal resolution dynamic MRI and arterial input function for assessment of GFR in pediatric subjects. Magnetic resonance in medicine Yoruk, U., Saranathan, M., Loening, A. M., Hargreaves, B. A., Vasanawala, S. S. 2016; 75 (3): 1301-1311

    Abstract

    To introduce a respiratory-gated high-spatiotemporal-resolution dynamic-contrast-enhanced MRI technique and a high-temporal-resolution aortic input function (HTR-AIF) estimation method for glomerular filtration rate (GFR) assessment in children.A high-spatiotemporal-resolution DCE-MRI method with view-shared reconstruction was modified to incorporate respiratory gating, and an AIF estimation method that uses a fraction of the k-space data from each respiratory period was developed (HTR-AIF). The method was validated using realistic digital phantom simulations and demonstrated on clinical subjects. The GFR estimates using HTR-AIF were compared with estimates obtained by using an AIF derived directly from the view-shared images.Digital phantom simulations showed that using the HTR-AIF technique gives more accurate AIF estimates (RMSE = 0.0932) compared with the existing estimation method (RMSE = 0.2059) that used view-sharing (VS). For simulated GFR > 27 mL/min, GFR estimation error was between 32% and 17% using view-shared AIF, whereas estimation error was less than 10% using HTR-AIF. In all clinical subjects, the HTR-AIF method resulted in higher GFR estimations than the view-shared method.The HTR-AIF method improves the accuracy of both the AIF and GFR estimates derived from the respiratory-gated acquisitions, and makes GFR estimation feasible in free-breathing pediatric subjects. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.25731

    View details for PubMedID 25946307

  • Qualitative grading of aortic regurgitation: a pilot study comparing CMR 4D flow and echocardiography INTERNATIONAL JOURNAL OF CARDIOVASCULAR IMAGING Chelu, R. G., van den Bosch, A. E., van Kranenburg, M., Hsiao, A., van den Hoven, A. T., Ouhlous, M., Budde, R. P., Beniest, K. M., Swart, L. E., Coenen, A., Lubbers, M. M., Wielopolski, P. A., Vasanawala, S. S., Roos-Hesselink, J. W., Nieman, K. 2016; 32 (2): 301-307
  • Hemodynamic safety and efficacy of ferumoxytol as an intravenous contrast agents in pediatric patients and young adults MAGNETIC RESONANCE IMAGING Ning, P., Zucker, E. J., Wong, P., Vasanawala, S. S. 2016; 34 (2): 152-158
  • T2 shuffling: Sharp, multicontrast, volumetric fast spin-echo imaging. Magnetic resonance in medicine Tamir, J. I., Uecker, M., Chen, W., Lai, P., Alley, M. T., Vasanawala, S. S., Lustig, M. 2016

    Abstract

    A new acquisition and reconstruction method called T2 Shuffling is presented for volumetric fast spin-echo (three-dimensional [3D] FSE) imaging. T2 Shuffling reduces blurring and recovers many images at multiple T2 contrasts from a single acquisition at clinically feasible scan times (6-7 min).The parallel imaging forward model is modified to account for temporal signal relaxation during the echo train. Scan efficiency is improved by acquiring data during the transient signal decay and by increasing echo train lengths without loss in signal-to-noise ratio (SNR). By (1) randomly shuffling the phase encode view ordering, (2) constraining the temporal signal evolution to a low-dimensional subspace, and (3) promoting spatio-temporal correlations through locally low rank regularization, a time series of virtual echo time images is recovered from a single scan. A convex formulation is presented that is robust to partial voluming and radiofrequency field inhomogeneity.Retrospective undersampling and in vivo scans confirm the increase in sharpness afforded by T2 Shuffling. Multiple image contrasts are recovered and used to highlight pathology in pediatric patients. A proof-of-principle method is integrated into a clinical musculoskeletal imaging workflow.The proposed T2 Shuffling method improves the diagnostic utility of 3D FSE by reducing blurring and producing multiple image contrasts from a single scan. Magn Reson Med 77:180-195, 2017. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26102

    View details for PubMedID 26786745

  • High-resolution diffusion-weighted imaging of the breast with multiband 2D radiofrequency pulses and a generalized parallel imaging reconstruction. Magnetic resonance in medicine Taviani, V., Alley, M. T., Banerjee, S., Nishimura, D. G., Daniel, B. L., Vasanawala, S. S., Hargreaves, B. A. 2016

    Abstract

    To develop a technique for high-resolution diffusion-weighted imaging (DWI) and to compare it with standard DWI methods.Multiple in-plane bands of magnetization were simultaneously excited by identically phase modulating each subpulse of a two-dimensional (2D) RF pulse. Several excitations with the same multiband pattern progressively shifted in the phase-encode direction were used to cover the prescribed field of view (FOV). The phase-encoded FOV was limited to the width of a single band to reduce off-resonance-induced distortion and blurring. Parallel imaging (PI) techniques were used to resolve aliasing from the other bands and to combine the different excitations. Following validation in phantoms and healthy volunteers, a preliminary study in breast cancer patients (N=14) was performed to compare the proposed method to conventional DWI with PI and to reduced-FOV DWI.The proposed method gave high-resolution diffusion-weighted images with minimal artifacts at the band intersections. Compared to PI alone, higher phase-encoded FOV-reduction factors and reduced noise amplification were obtained, which translated to higher resolution images than conventional (non-multiband) DWI. The same resolution and image quality achievable over targeted regions using existing reduced-FOV methods was obtained, but the proposed method also enables complete bilateral coverage.We developed an in-plane multiband technique for high-resolution DWI and compared its performance with other standard DWI methods. Magn Reson Med 77:209-220, 2017. © 2016 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.26110

    View details for PubMedID 26778549

  • Prospective Comparison of 99mTc-MDP Scintigraphy, Combined 18F-NaF and 18F-FDG PET/CT, and Whole-Body MRI in Patients with Breast and Prostate Cancer. Journal of nuclear medicine Minamimoto, R., Loening, A., Jamali, M., Barkhodari, A., Mosci, C., Jackson, T., Obara, P., Taviani, V., Gambhir, S. S., Vasanawala, S., Iagaru, A. 2015; 56 (12): 1862-1868

    Abstract

    We prospectively evaluated the combined (18)F-NaF/(18)F-FDG PET/CT in patients with breast and prostate cancers, and compared the results to (99m)Tc MDP bone scintigraphy (BS) and whole-body MRI (WBMRI).30 patients (15 women with breast cancer and 15 men with prostate cancer) referred for standard of care BS were prospectively enrolled in this study. (18)F-NaF/(18)F-FDG PET/CT and WBMRI were performed following BS. WBMRI protocol consisted of both non-contrast enhanced and contrast enhanced sequences. Lesions detected with each test were tabulated and the results were compared.For extra skeletal lesions, (18)F-/(18)F-FDG PET/CT and WBMRI had no statistically significant differences in sensitivity (92.9% vs 92.9%, P = 1.00), PPV (81.3% vs 86.7%, P = 0.68) and accuracy (76.5% vs 82.4%, P = 0.56). However, (18)F-/(18)F-FDG PET/CT showed significantly higher sensitivity and accuracy than WBMRI (96.2% vs 81.4%, P<0.001, 89.8% vs 74.7%, P = 0.01) and BS (96.2% vs 64.6%, P<0.001, 89.8% vs 65.9%, P<0.001) for the detection of skeletal lesions. Overall, (18)F-/(18)F-FDG PET/CT showed higher sensitivity and accuracy than WBMRI (95.7% vs 83.3%, P<0.002, 87.6% vs 76.0%, P< 0.02), but not statistically significant when compared to a combination of WBMRI and BS (95.7% vs 91.6%, P = 0.17, 87.6% vs 83.0%, P = 0.53). (18)F-/(18)F-FDG PET/CT showed no significant difference with a combination of (18)F-/(18)F-FDG PET/CT and WBMRI. No statistically significant differences in PPV were noted among the 3 examinations.The (18)F NaF/(18)F FDG PET/CT is superior to WBMRI and (99m)Tc-MDP scintigraphy for evaluation of skeletal disease extent. Further, (18)F NaF/(18)F FDG PET/CT and WBMRI detected extra-skeletal disease that may change the management of these patients. The (18)F NaF/(18)F FDG PET/CT provide similar diagnostic ability with combination of WBMRI and BS in patients with breast and prostate cancers. Larger cohorts are needed in order to confirm these preliminary findings, ideally using the newly introduced simultaneous PET/MRI scanners.

    View details for DOI 10.2967/jnumed.115.162610

    View details for PubMedID 26405167

  • Improved Quantification and Mapping of Anomalous Pulmonary Venous Flow With Four-Dimensional Phase-Contrast MRI and Interactive Streamline Rendering JOURNAL OF MAGNETIC RESONANCE IMAGING Hsiao, A., Yousaf, U., Alley, M. T., Lustig, M., Chan, F. P., Newman, B., Vasanawala, S. S. 2015; 42 (6): 1765-1776

    View details for DOI 10.1002/jmri.24928

    View details for Web of Science ID 000368258100034

  • Whole-body simultaneous time-of-flight PET-MRI: early experience with clinical studies. EJNMMI physics Minamimoto, R., Iagaru, A., Jamali, M., Barkodhodari, A., Holley, D., Vasanawala, S., Zaharchuk, G. 2015; 2: A64-?

    View details for DOI 10.1186/2197-7364-2-S1-A64

    View details for PubMedID 26956324

    View details for PubMedCentralID PMC4798693

  • Increased Speed and Image Quality in Single-Shot Fast Spin Echo Imaging Via Variable Refocusing Flip Angles JOURNAL OF MAGNETIC RESONANCE IMAGING Loening, A. M., Saranathan, M., Ruangwattanapaisarn, N., Litwiller, D. V., Shimakawa, A., Vasanawala, S. S. 2015; 42 (6): 1747-1758

    Abstract

    To develop and validate clinically a single-shot fast spin echo (SSFSE) sequence utilizing variable flip angle refocusing pulses to shorten acquisition times via reductions in specific absorption rate (SAR) and improve image quality.A variable refocusing flip angle SSFSE sequence (vrfSSFSE) was designed and implemented, with simulations and volunteer scans performed to determine suitable flip angle modulation parameters. With Institutional Review Board (IRB) approval/informed consent, patients referred for 3T abdominal magnetic resonance imaging (MRI) were scanned with conventional SSFSE and either half-Fourier (n = 25) or full-Fourier vrfSSFSE (n = 50). Two blinded radiologists semiquantitatively scored images on a scale from -2 to 2 for contrast, noise, sharpness, artifacts, cardiac motion-related signal loss, and the ability to evaluate the pancreas and kidneys.vrfSSFSE demonstrated significantly increased speed (∼2-fold, P < 0.0001). Significant improvements in image quality parameters with full-Fourier vrfSSFSE included increased contrast, sharpness, and visualization of pancreatic and renal structures with higher bandwidth technique (mean scores 0.37, 0.83, 0.62, and 0.31, respectively, P ≤ 0.001), and decreased image noise and improved visualization of renal structures when used with an equal bandwidth technique (mean scores 0.96 and 0.35, respectively, P < 0.001). Increased cardiac motion-related signal loss with full-Fourier vrfSSFSE was seen in the pancreas but not the kidney.vrfSSFSE increases speed at 3T over conventional SSFSE via reduced SAR, and when combined with full-Fourier acquisition can improve image quality, although with some increased sensitivity to cardiac motion-related signal loss. J. Magn. Reson. Imaging 2015.

    View details for DOI 10.1002/jmri.24941

    View details for Web of Science ID 000368258100032

  • Imaging patients with breast and prostate cancers using combined 18F NaF/18F FDG and TOF simultaneous PET/ MRI. EJNMMI physics Iagaru, A., Minamimoto, R., Jamali, M., Barkodhodari, A., Gambhir, S. S., Vasanawala, S. 2015; 2: A65-?

    View details for DOI 10.1186/2197-7364-2-S1-A65

    View details for PubMedID 26956325

    View details for PubMedCentralID PMC4798635

  • Congenital heart disease assessment with 4D flow MRI. Journal of magnetic resonance imaging Vasanawala, S. S., Hanneman, K., Alley, M. T., Hsiao, A. 2015; 42 (4): 870-886

    Abstract

    With improvements in surgical and medical management, patients with congenital heart disease (CHD) are often living well into adulthood. MRI provides critical data for diagnosis and monitoring of these patients, yielding information on cardiac anatomy, blood flow, and cardiac function. Though historically these exams have been complex and lengthy, four-dimensional (4D) flow is emerging as a single fast technique for comprehensive assessment of CHD. The 4D flow consists of a volumetric time-resolved acquisition that is gated to the cardiac cycle, providing a time-varying vector field of blood flow as well as registered anatomic images. In this article, we provide an overview of MRI evaluation of congenital heart disease by means of example of three relatively common representative conditions: tetralogy of Fallot, aortic coarctation, and anomalous pulmonary venous drainage. Then 4D flow data acquisition, data correction, and postprocessing techniques are reviewed. We conclude with several examples that highlight the comprehensive nature of the evaluation of congenital heart disease with 4D flow. J. Magn. Reson. Imaging 2015;42:870-886.

    View details for DOI 10.1002/jmri.24856

    View details for PubMedID 25708923

  • Clinical performance of a free-breathing spatiotemporally accelerated 3-D time-resolved contrast-enhanced pediatric abdominal MR angiography. Pediatric radiology Zhang, T., Yousaf, U., Hsiao, A., Cheng, J. Y., Alley, M. T., Lustig, M., Pauly, J. M., Vasanawala, S. S. 2015; 45 (11): 1635-1643

    Abstract

    Pediatric contrast-enhanced MR angiography is often limited by respiration, other patient motion and compromised spatiotemporal resolution.To determine the reliability of a free-breathing spatiotemporally accelerated 3-D time-resolved contrast-enhanced MR angiography method for depicting abdominal arterial anatomy in young children.With IRB approval and informed consent, we retrospectively identified 27 consecutive children (16 males and 11 females; mean age: 3.8 years, range: 14 days to 8.4 years) referred for contrast-enhanced MR angiography at our institution, who had undergone free-breathing spatiotemporally accelerated time-resolved contrast-enhanced MR angiography studies. A radio-frequency-spoiled gradient echo sequence with Cartesian variable density k-space sampling and radial view ordering, intrinsic motion navigation and intermittent fat suppression was developed. Images were reconstructed with soft-gated parallel imaging locally low-rank method to achieve both motion correction and high spatiotemporal resolution. Quality of delineation of 13 abdominal arteries in the reconstructed images was assessed independently by two radiologists on a five-point scale. Ninety-five percent confidence intervals of the proportion of diagnostically adequate cases were calculated. Interobserver agreements were also analyzed.Eleven out of 13 arteries achieved acceptable image quality (mean score range: 3.9-5.0) for both readers. Fair to substantial interobserver agreement was reached on nine arteries.Free-breathing spatiotemporally accelerated 3-D time-resolved contrast-enhanced MR angiography frequently yields diagnostic image quality for most abdominal arteries in young children.

    View details for DOI 10.1007/s00247-015-3384-y

    View details for PubMedID 26040509

  • Free-breathing pediatric MRI with nonrigid motion correction and acceleration JOURNAL OF MAGNETIC RESONANCE IMAGING Cheng, J. Y., Zhang, T., Ruangwattanapaisarn, N., Alley, M. T., Uecker, M., Pauly, J. M., Lustig, M., Vasanawala, S. S. 2015; 42 (2): 407-420

    Abstract

    To develop and assess motion correction techniques for high-resolution pediatric abdominal volumetric magnetic resonance images acquired free-breathing with high scan efficiency.First, variable-density sampling and radial-like phase-encode ordering were incorporated into the 3D Cartesian acquisition. Second, intrinsic multichannel butterfly navigators were used to measure respiratory motion. Lastly, these estimates are applied for both motion-weighted data-consistency in a compressed sensing and parallel imaging reconstruction, and for nonrigid motion correction using a localized autofocusing framework. With Institutional Review Board approval and informed consent/assent, studies were performed on 22 consecutive pediatric patients. Two radiologists independently scored the images for overall image quality, degree of motion artifacts, and sharpness of hepatic vessels and the diaphragm. The results were assessed using paired Wilcoxon test and weighted kappa coefficient for interobserver agreements.The complete procedure yielded significantly better overall image quality (mean score of 4.7 out of 5) when compared to using no correction (mean score of 3.4, P < 0.05) and to using motion-weighted accelerated imaging (mean score of 3.9, P < 0.05). With an average scan time of 28 seconds, the proposed method resulted in comparable image quality to conventional prospective respiratory-triggered acquisitions with an average scan time of 91 seconds (mean score of 4.5).With the proposed methods, diagnosable high-resolution abdominal volumetric scans can be obtained from free-breathing data acquisitions. J. Magn. Reson. Imaging 2015;42:407-420.

    View details for DOI 10.1002/jmri.24785

    View details for Web of Science ID 000358258600019

  • Ferumoxytol as an off-label contrast agent in body 3T MR angiography: a pilot study in children PEDIATRIC RADIOLOGY Ruangwattanapaisarn, N., Hsiao, A., Vasanawala, S. S. 2015; 45 (6): 831-839

    Abstract

    Ferumoxytol is an ultrasmall superparamagnetic iron oxide (USPIO) nanoparticle agent used to treat iron deficiency anemia in adults with chronic kidney disease.We aim to determine the feasibility of using ferumoxytol for clinical pediatric cardiac and vascular imaging.We retrospectively identified 23 consecutive children who underwent MRI with ferumoxytol (11 males; mean age: 7.4 years, range: 3 days-18 years), yielding 12 abdominal MR angiography and 15 cardiac MRI studies. Medical records were reviewed for the clinical indication, ferumoxytol dose, injection rate, sedation and any complication. A two-reader consensus scored the images on a five-point scale for overall image quality and delineation of various anatomical structures. Signal-to-background ratios for abdominal aorta and inferior vena cava for abdominal cases and blood pool-myocardium contrast ratios for cardiac cases were calculated. The confidence intervals for obtaining a score of three or above for each image parameter were calculated by using adjusted Wald method.For abdominal MR angiography, average scores for overall image quality, as well as delineation of the hepatic artery, superior mesenteric artery, renal artery and veins were 4.5, 4.3, 4.3, 3.7 and 4.7, respectively. For cardiac exams, the average scores for overall image quality, systemic arteries, pulmonary arteries, pulmonary veins, valves and ventricles were 4.4, 4.6, 4.1, 4.8, 4.1 and 4.7, respectively. For all parameters, the lower bound for the proportion of cases to have a score of 3 or above was 65%. Signal-to-background ratios for aorta and abdominal veins averaged 86 +/- 74 and 86 +/- 77 for full-dose images, and 23 and 18 for half-dose images, respectively. Mean blood pool to myocardium contrast ratio was 3:3.Ferumoxytol can provide excellent image quality for pediatric body MR angiography/MR venography at a dose of 1.5 or 3 mg Fe/kg. Further investigation should be directed toward understanding the lowest dose that can be administered.

    View details for DOI 10.1007/s00247-014-3226-3

    View details for Web of Science ID 000355345800007

    View details for PubMedID 25427433

  • Faster pediatric 3-T abdominal magnetic resonance imaging: comparison between conventional and variable refocusing flip-angle single-shot fast spin-echo sequences. Pediatric radiology Ruangwattanapaisarn, N., Loening, A. M., Saranathan, M., Litwiller, D. V., Vasanawala, S. S. 2015; 45 (6): 847-854

    Abstract

    Single-shot fast spin echo (SSFSE) is particularly appealing in pediatric patients because of its motion robustness. However radiofrequency energy deposition at 3 tesla forces long pauses between slices, leading to longer scans, longer breath-holds and more between-slice motion.We sought to learn whether modulation of the SSFSE refocusing flip-angle train could reduce radiofrequency energy deposition without degrading image quality, thereby reducing inter-slice pauses and overall scan times.We modulated the refocusing flip-angle train for SSFSE to minimize energy deposition while minimizing blurring and motion-related signal loss. In a cohort of 50 consecutive patients (25 boys, mean age 5.5 years, range 1 month to 17 years) referred for abdominal MRI we obtained standard SSFSE and variable refocusing flip-angle (vrfSSFSE) images and recorded sequence scan times. Two readers independently scored the images in blinded, randomized order for noise, tissue contrast, sharpness, artifacts and left lobe hepatic signal uniformity on a four-point scale. The null hypothesis of no difference between SSFSE and vrfSSFSE image-quality was assessed with a Mann-Whitney U test, and the null hypothesis of no scan time difference was assessed with the paired t-test.SSFSE and vrfSSFSE mean acquisition times were 54.3 and 26.2 s, respectively (P-value <0.0001). For each reader, SSFSE and vrfSSFSE noise, tissue contrast, sharpness and artifacts were not significantly different (P-values 0.18-0.86). However, SSFSE had better left lobe hepatic signal uniformity (P < 0.01, both readers).vrfSSFSE is twice as fast as SSFSE, with equivalent image quality with the exception of left hepatic lobe signal heterogeneity.

    View details for DOI 10.1007/s00247-014-3227-2

    View details for PubMedID 25433510

    View details for PubMedCentralID PMC4449830

  • Classification of Hypervascular Liver Lesions Based on Hepatic Artery and Portal Vein Blood Supply Coefficients Calculated from Triphasic CT Scans JOURNAL OF DIGITAL IMAGING Boas, F. E., Kamaya, A., Do, B., Desser, T. S., Beaulieu, C. F., Vasanawala, S. S., Hwang, G. L., Sze, D. Y. 2015; 28 (2): 213-223

    Abstract

    Perfusion CT of the liver typically involves scanning the liver at least 20 times, resulting in a large radiation dose. We developed and validated a simplified model of tumor blood supply that can be applied to standard triphasic scans and evaluated whether this can be used to distinguish benign and malignant liver lesions. Triphasic CTs of 46 malignant and 32 benign liver lesions were analyzed. For each phase, regions of interest were drawn in the arterially enhancing portion of each lesion, as well as the background liver, aorta, and portal vein. Hepatic artery and portal vein blood supply coefficients for each lesion were then calculated by expressing the enhancement curve of the lesion as a linear combination of the enhancement curves of the aorta and portal vein. Hepatocellular carcinoma (HCC) and hypervascular metastases, on average, both had increased hepatic artery coefficients compared to the background liver. Compared to HCC, benign lesions, on average, had either a greater hepatic artery coefficient (hemangioma) or a greater portal vein coefficient (focal nodular hyperplasia or transient hepatic attenuation difference). Hypervascularity with washout is a key diagnostic criterion for HCC, but it had a sensitivity of 72 % and specificity of 81 % for diagnosing malignancy in our diverse set of liver lesions. The sensitivity for malignancy was increased to 89 % by including enhancing lesions that were hypodense on all phases. The specificity for malignancy was increased to 97 % (p = 0.039) by also examining hepatic artery and portal vein blood supply coefficients, while maintaining a sensitivity of 76 %.

    View details for DOI 10.1007/s10278-014-9725-9

    View details for Web of Science ID 000351242500012

    View details for PubMedID 25183580

  • Robust 4D Flow Denoising Using Divergence-Free Wavelet Transform MAGNETIC RESONANCE IN MEDICINE Ong, F., Uecker, M., Tariq, U., Hsiao, A., Alley, M. T., Vasanawala, S. S., Lustig, M. 2015; 73 (2): 828-842

    Abstract

    To investigate four-dimensional flow denoising using the divergence-free wavelet (DFW) transform and compare its performance with existing techniques.DFW is a vector-wavelet that provides a sparse representation of flow in a generally divergence-free field and can be used to enforce "soft" divergence-free conditions when discretization and partial voluming result in numerical nondivergence-free components. Efficient denoising is achieved by appropriate shrinkage of divergence-free wavelet and nondivergence-free coefficients. SureShrink and cycle spinning are investigated to further improve denoising performance.DFW denoising was compared with existing methods on simulated and phantom data and was shown to yield better noise reduction overall while being robust to segmentation errors. The processing was applied to in vivo data and was demonstrated to improve visualization while preserving quantifications of flow data.DFW denoising of four-dimensional flow data was shown to reduce noise levels in flow data both quantitatively and visually. Magn Reson Med 73:828-842, 2015. © 2014 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.25176

    View details for Web of Science ID 000348139500043

    View details for PubMedID 24549830

  • Inlet and outlet valve flow and regurgitant volume may be directly and reliably quantified with accelerated, volumetric phase-contrast MRI. Journal of magnetic resonance imaging Hsiao, A., Tariq, U., Alley, M. T., Lustig, M., Vasanawala, S. S. 2015; 41 (2): 376-385

    Abstract

    To determine whether it is feasible to use solely an accelerated 4D phase-contrast magnetic resonance imaging (4D-PC MRI) acquisition to quantify net and regurgitant flow volume through each of the cardiac valves.Accelerated, 4D-PC MRI examinations performed between March 2010 through June 2011 as part of routine MRI examinations for congenital, structural heart disease were retrospectively reviewed and analyzed using valve-tracking visualization and quantification algorithms developed in Java and OpenGL. Excluding patients with transposition or single ventricle physiology, a total of 34 consecutive pediatric patients (19 male, 15 female; mean age 6.9 years; age range 10 months to 15 years) were identified. 4D-PC flow measurements were compared at each valve and against routine measurements from conventional cardiac MRI using Bland-Altman and Pearson correlation analysis.Inlet and outlet valve net flow were highly correlated between all valves (P = 0.940-0.985). The sum of forward flow at the outlet valve and regurgitant flow at the inlet valve were consistent with volumetric displacements in each ventricle (P = 0.939-0.948). These were also highly consistent with conventional planar MRI measurements with net flow (P = 0.923-0.935) and regurgitant fractions (P = 0.917-0.972) at the outlet valve and ventricular volumes (P = 0.925-0.965).It is possible to obtain consistent measurements of net and regurgitant blood flow across the inlet and outlet valves relying solely on accelerated 4D-PC. This may facilitate more efficient clinical quantification of valvular regurgitation. J. Magn. Reson. Imaging 2015;41:376-385.© 2013 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24578

    View details for PubMedID 24677253

  • Fast pediatric 3D free-breathing abdominal dynamic contrast enhanced MRI with high spatiotemporal resolution. Journal of magnetic resonance imaging Zhang, T., Cheng, J. Y., Potnick, A. G., Barth, R. A., Alley, M. T., Uecker, M., Lustig, M., Pauly, J. M., Vasanawala, S. S. 2015; 41 (2): 460-473

    Abstract

    To develop a method for fast pediatric 3D free-breathing abdominal dynamic contrast enhanced (DCE) magnetic resonance imaging (MRI) and investigate its clinical feasibility.A combined locally low rank parallel imaging method with soft gating is proposed for free-breathing DCE MRI acquisition. With Institutional Review Board (IRB) approval and informed consent/assent, 23 consecutive pediatric patients were recruited for this study. Free-breathing DCE MRI with ∼1 mm(3) spatial resolution and a 6.5-sec frame rate was acquired on a 3T scanner. Undersampled data were reconstructed with a compressed sensing method without motion correction (FB-CS) and the proposed method (FB-LR). A follow-up respiratory-triggered acquisition (RT-CS) was performed as a reference standard. The reconstructed images were evaluated independently by two radiologists. Wilcoxon tests were performed to test the hypothesis that there was no significant difference between different reconstructions. Quantitative evaluation of contrast dynamics was also performed.The mean score of overall image quality of FB-LR was 4.0 on a 5-point scale, significantly better (P < 0.05) than FB-CS reconstruction (mean score 2.9), and similar to RT-CS (mean score 4.1). FB-LR also matched the temporal fidelity of contrast dynamics with a root mean square error less than 5%.Fast 3D free-breathing DCE MRI with high scan efficiency and image quality similar to respiratory-triggered acquisition is feasible in a pediatric clinical setting.J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24551

    View details for PubMedID 24375859

  • Simultaneous Whole-Body Time-of-Flight F-18-FDG PET/MRI A Pilot Study Comparing SUVmax With PET/CT and Assessment of MR Image Quality CLINICAL NUCLEAR MEDICINE Iagaru, A., Mittra, E., Minamimoto, R., Jamali, M., Levin, C., Quon, A., Gold, G., Herfkens, R., Vasanawala, S., Gambhir, S. S., Zaharchuk, G. 2015; 14 (1): 1-8

    Abstract

    The recent introduction of hybrid PET/MRI scanners in clinical practice has shown promising initial results for several clinical scenarios. However, the first generation of combined PET/MRI lacks time-of-flight (TOF) technology. Here we report the results of the first patients to be scanned on a completely novel fully integrated PET/MRI scanner with TOF.We analyzed data from patients who underwent a clinically indicated F FDG PET/CT, followed by PET/MRI. Maximum standardized uptake values (SUVmax) were measured from F FDG PET/MRI and F FDG PET/CT for lesions, cerebellum, salivary glands, lungs, aortic arch, liver, spleen, skeletal muscle, and fat. Two experienced radiologists independently reviewed the MR data for image quality.Thirty-six patients (19 men, 17 women, mean [±standard deviation] age of 61 ± 14 years [range: 27-86 years]) with a total of 69 discrete lesions met the inclusion criteria. PET/CT images were acquired at a mean (±standard deviation) of 74 ± 14 minutes (range: 49-100 minutes) after injection of 10 ± 1 mCi (range: 8-12 mCi) of F FDG. PET/MRI scans started at 161 ± 29 minutes (range: 117 - 286 minutes) after the F FDG injection. All lesions identified on PET from PET/CT were also seen on PET from PET/MRI. The mean SUVmax values were higher from PET/MRI than PET/CT for all lesions. No degradation of MR image quality was observed.The data obtained so far using this investigational PET/MR system have shown that the TOF PET system is capable of excellent performance during simultaneous PET/MR with routine pulse sequences. MR imaging was not compromised. Comparison of the PET images from PET/CT and PET/MRI show no loss of image quality for the latter. These results support further investigation of this novel fully integrated TOF PET/MRI instrument.

    View details for Web of Science ID 000346633400023

  • Simultaneous whole-body time-of-flight 18F-FDG PET/MRI: a pilot study comparing SUVmax with PET/CT and assessment of MR image quality. Clinical nuclear medicine Iagaru, A., Mittra, E., Minamimoto, R., Jamali, M., Levin, C., Quon, A., Gold, G., Herfkens, R., Vasanawala, S., Gambhir, S. S., Zaharchuk, G. 2015; 40 (1): 1-8

    Abstract

    The recent introduction of hybrid PET/MRI scanners in clinical practice has shown promising initial results for several clinical scenarios. However, the first generation of combined PET/MRI lacks time-of-flight (TOF) technology. Here we report the results of the first patients to be scanned on a completely novel fully integrated PET/MRI scanner with TOF.We analyzed data from patients who underwent a clinically indicated F FDG PET/CT, followed by PET/MRI. Maximum standardized uptake values (SUVmax) were measured from F FDG PET/MRI and F FDG PET/CT for lesions, cerebellum, salivary glands, lungs, aortic arch, liver, spleen, skeletal muscle, and fat. Two experienced radiologists independently reviewed the MR data for image quality.Thirty-six patients (19 men, 17 women, mean [±standard deviation] age of 61 ± 14 years [range: 27-86 years]) with a total of 69 discrete lesions met the inclusion criteria. PET/CT images were acquired at a mean (±standard deviation) of 74 ± 14 minutes (range: 49-100 minutes) after injection of 10 ± 1 mCi (range: 8-12 mCi) of F FDG. PET/MRI scans started at 161 ± 29 minutes (range: 117 - 286 minutes) after the F FDG injection. All lesions identified on PET from PET/CT were also seen on PET from PET/MRI. The mean SUVmax values were higher from PET/MRI than PET/CT for all lesions. No degradation of MR image quality was observed.The data obtained so far using this investigational PET/MR system have shown that the TOF PET system is capable of excellent performance during simultaneous PET/MR with routine pulse sequences. MR imaging was not compromised. Comparison of the PET images from PET/CT and PET/MRI show no loss of image quality for the latter. These results support further investigation of this novel fully integrated TOF PET/MRI instrument.

    View details for DOI 10.1097/RLU.0000000000000611

    View details for PubMedID 25489952

  • High resolution multi-arterial phase MRI improves lesion contrast in chronic liver disease. Clinical and investigative medicine. Médecine clinique et experimentale Clarke, S. E., Saranathan, M., Rettmann, D. W., Hargreaves, B. A., Vasanawala, S. S. 2015; 38 (3): E90-9

    View details for PubMedID 26026643

  • High resolution multi-arterial phase MRI improves lesion contrast in chronic liver disease. Clinical and investigative medicine. Me´decine clinique et experimentale Clarke, S. E., Saranathan, M., Rettmann, D. W., Hargreaves, B. A., Vasanawala, S. S. 2015; 38 (3): E90-9

    Abstract

    To determine the reliability of arterial phase capture and evaluate hypervascular lesion contrast kinetics with a combined view-sharing and parallel imaging dynamic contrast-enhanced acquisition, DIfferential Sub-sampling with Cartesian Ordering (DISCO), in patients with known chronic liver disease.A retrospective review of 3T MR images from 26 patients with known chronic liver disease referred for hepatocellular carcinoma surveillance or post-treatment follow up was performed. After administration of a gadolinium-based contrast agent, a multiphasic acquisition was obtained in a 28 s breath-hold, from which seven sequential post-contrast image volumes were reconstructed.The late arterial phase was successfully captured in all cases (26/26, 95% CI 87-100%). Images obtained 26 s post-injection had the highest frequency of late arterial phase capture (20/26) and lesion detection (23/26) of any individual post-contrast time; however, the multiphasic data resulted in a significantly higher frequency of late arterial phase capture (26/26, p=0.03) and a higher relative contrast (5.37+/-0.97 versus 7.10+/-0.98, p < 0.01).Multiphasic acquisition with combined view-sharing and parallel imaging reliably captures the late arterial phase and provides sufficient temporal resolution to characterize hepatic lesion contrast kinetics in patients with chronic liver disease while maintaining high spatial resolution.

    View details for PubMedID 26026643

  • Enhancement of Respiratory Navigator-Gated Three-Dimensional Spoiled Gradient-Recalled Echo Sequence with Variable Flip Angle Scheme MAGNETIC RESONANCE IN MEDICINE Iwadate, Y., Brau, A. C., Vasanawala, S. S., Kabasawa, H. 2014; 72 (1): 172-177

    Abstract

    To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection.A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners.Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts.The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study.

    View details for DOI 10.1002/mrm.24902

    View details for Web of Science ID 000337624400020

    View details for PubMedID 23904390

  • Clinical performance of contrast enhanced abdominal pediatric MRI with fast combined parallel imaging compressed sensing reconstruction. Journal of magnetic resonance imaging : JMRI Zhang, T., Chowdhury, S., Lustig, M., Barth, R. A., Alley, M. T., Grafendorfer, T., Calderon, P. D., Robb, F. J., Pauly, J. M., Vasanawala, S. S. 2014; 40 (1): 13-25

    Abstract

    To deploy clinically, a combined parallel imaging compressed sensing method with coil compression that achieves a rapid image reconstruction, and assess its clinical performance in contrast-enhanced abdominal pediatric MRI.With Institutional Review Board approval and informed patient consent/assent, 29 consecutive pediatric patients were recruited. Dynamic contrast-enhanced MRI was acquired on a 3 Tesla scanner using a dedicated 32-channel pediatric coil and a three-dimensional SPGR sequence, with pseudo-random undersampling at a high acceleration (R = 7.2). Undersampled data were reconstructed with three methods: a traditional parallel imaging method and a combined parallel imaging compressed sensing method with and without coil compression. The three sets of images were evaluated independently and blindly by two radiologists at one siting, for overall image quality and delineation of anatomical structures. Wilcoxon tests were performed to test the hypothesis that there was no significant difference in the evaluations, and interobserver agreement was analyzed.Fast reconstruction with coil compression did not deteriorate image quality. The mean score of structural delineation of the fast reconstruction was 4.1 on a 5-point scale, significantly better (P < 0.05) than traditional parallel imaging (mean score 3.1). Fair to substantial interobserver agreement was reached in structural delineation assessment.A fast combined parallel imaging compressed sensing method is feasible in a pediatric clinical setting. Preliminary results suggest it may improve structural delineation over parallel imaging. J. Magn. Reson. Imaging 2014;40:13-25. © 2013 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24333

    View details for PubMedID 24127123

    View details for PubMedCentralID PMC3984374

  • An open-label study to evaluate sildenafil for the treatment of lymphatic malformations. Journal of the American Academy of Dermatology Danial, C., Tichy, A. L., Tariq, U., Swetman, G. L., Khuu, P., Leung, T. H., Benjamin, L., Teng, J., Vasanawala, S. S., Lane, A. T. 2014; 70 (6): 1050-1057

    Abstract

    Lymphatic malformations can be challenging to treat. Mainstay interventions including surgery and sclerotherapy are invasive and can result in local recurrence and complications.We sought to assess the effect of 20 weeks of oral sildenafil on reducing lymphatic malformation volume and symptoms in children.Seven children (4 boys, 3 girls; ages 13-85 months) with lymphatic malformations were given oral sildenafil for 20 weeks in this open-label study. The volume of the lymphatic malformation was calculated blindly using magnetic resonance imaging performed before and after 20 weeks of sildenafil. Lymphatic malformations were assessed clinically on weeks 4, 12, 20, and 32. Both the physician and parents evaluated the lymphatic malformation in comparison with baseline.Four subjects had a lymphatic malformation volume decrease (1.0%-31.7%). In 2 subjects, despite a lymphatic malformation volume increase (1.1%-3.7%), clinical improvement was noted while on sildenafil. One subject had a 29.6% increase in lymphatic malformation volume and no therapeutic response. Lymphatic malformations of all 6 subjects who experienced a therapeutic response on sildenafil softened and became easily compressible. Adverse events were minimal.A randomized controlled trial will be necessary to verify the effects of sildenafil on lymphatic malformations.Sildenafil can reduce lymphatic malformation volume and symptoms in some children.

    View details for DOI 10.1016/j.jaad.2014.02.005

    View details for PubMedID 24656411

  • Perforated appendicitis: an underappreciated mimic of intussusception on ultrasound. Pediatric radiology Newman, B., Schmitz, M., Gawande, R., Vasanawala, S., Barth, R. 2014; 44 (5): 535-541

    Abstract

    We encountered multiple cases in which the US appearance of ruptured appendicitis mimicked intussusception, resulting in diagnostic and therapeutic delay and multiple additional imaging studies.To explore the clinical and imaging discriminatory features between the conditions.Initial US images in six children (age 16 months to 8 years; 4 boys, 2 girls) were reviewed independently and by consensus by three pediatric radiologists. These findings were compared and correlated with the original reports and subsequent US, fluoroscopic, and CT images and reports.All initial US studies demonstrated a multiple-ring-like appearance (target sign, most apparent on transverse views) with diagnostic consensus supportive of intussusception. In three cases, US findings were somewhat discrepant with clinical concerns. Subsequently, four of the six children had contrast enemas; two were thought to have partial or complete intussusception reduction. Three had a repeat US examination, with recognition of the correct diagnosis. None of the US examinations demonstrated definite intralesional lymph nodes or mesenteric fat, but central echogenicity caused by debris/appendicolith was misinterpreted as fat. All showed perilesional hyperechogenicity that, in retrospect, represented inflamed fat "walling off" of the perforated appendix. There were four CTs, all of which demonstrated a double-ring appearance that correlated with the US target appearance, with inner and outer rings representing the dilated appendix and walled-off appendiceal rupture, respectively. All six children had surgical confirmation of perforated appendicitis.Contained perforated appendicitis can produce US findings closely mimicking intussusception. Clinical correlation and careful multiplanar evaluation should allow for sonographic suspicion of perforated appendicitis, which can be confirmed on CT if necessary.

    View details for DOI 10.1007/s00247-014-2873-8

    View details for PubMedID 24463638

  • ESPIRiT-An Eigenvalue Approach to Autocalibrating Parallel MRI: Where SENSE Meets GRAPPA MAGNETIC RESONANCE IN MEDICINE Uecker, M., Lai, P., Murphy, M. J., Virtue, P., Elad, M., Pauly, J. M., Vasanawala, S. S., Lustig, M. 2014; 71 (3): 990-1001

    View details for DOI 10.1002/mrm.24751

    View details for Web of Science ID 000331614600011

  • ESPIRiT--an eigenvalue approach to autocalibrating parallel MRI: where SENSE meets GRAPPA. Magnetic resonance in medicine Uecker, M., Lai, P., Murphy, M. J., Virtue, P., Elad, M., Pauly, J. M., Vasanawala, S. S., Lustig, M. 2014; 71 (3): 990-1001

    Abstract

    Parallel imaging allows the reconstruction of images from undersampled multicoil data. The two main approaches are: SENSE, which explicitly uses coil sensitivities, and GRAPPA, which makes use of learned correlations in k-space. The purpose of this work is to clarify their relationship and to develop and evaluate an improved algorithm.A theoretical analysis shows: (1) The correlations in k-space are encoded in the null space of a calibration matrix. (2) Both approaches restrict the solution to a subspace spanned by the sensitivities. (3) The sensitivities appear as the main eigenvector of a reconstruction operator computed from the null space. The basic assumptions and the quality of the sensitivity maps are evaluated in experimental examples. The appearance of additional eigenvectors motivates an extended SENSE reconstruction with multiple maps, which is compared to existing methods.The existence of a null space and the high quality of the extracted sensitivities are confirmed. The extended reconstruction combines all advantages of SENSE with robustness to certain errors similar to GRAPPA.In this article the gap between both approaches is finally bridged. A new autocalibration technique combines the benefits of both.

    View details for DOI 10.1002/mrm.24751

    View details for PubMedID 23649942

  • Investigating the feasibility of rapid MRI for image-guided motion management in lung cancer radiotherapy. BioMed research international Sawant, A., Keall, P., Pauly, K. B., Alley, M., Vasanawala, S., Loo, B. W., Hinkle, J., Joshi, S. 2014; 2014: 485067-?

    Abstract

    Cycle-to-cycle variations in respiratory motion can cause significant geometric and dosimetric errors in the administration of lung cancer radiation therapy. A common limitation of the current strategies for motion management is that they assume a constant, reproducible respiratory cycle. In this work, we investigate the feasibility of using rapid MRI for providing long-term imaging of the thorax in order to better capture cycle-to-cycle variations. Two nonsmall-cell lung cancer patients were imaged (free-breathing, no extrinsic contrast, and 1.5 T scanner). A balanced steady-state-free-precession (b-SSFP) sequence was used to acquire cine-2D and cine-3D (4D) images. In the case of Patient 1 (right midlobe lesion, ~40 mm diameter), tumor motion was well correlated with diaphragmatic motion. In the case of Patient 2, (left upper-lobe lesion, ~60 mm diameter), tumor motion was poorly correlated with diaphragmatic motion. Furthermore, the motion of the tumor centroid was poorly correlated with the motion of individual points on the tumor boundary, indicating significant rotation and/or deformation. These studies indicate that image quality and acquisition speed of cine-2D MRI were adequate for motion monitoring. However, significant improvements are required to achieve comparable speeds for truly 4D MRI. Despite several challenges, rapid MRI offers a feasible and attractive tool for noninvasive, long-term motion monitoring.

    View details for DOI 10.1155/2014/485067

    View details for PubMedID 24524077

  • Investigating the Feasibility of Rapid MRI for Image-Guided Motion Management in Lung Cancer Radiotherapy BIOMED RESEARCH INTERNATIONAL Sawant, A., Keall, P., Pauly, K. B., Alley, M., Vasanawala, S., Loo, B. W., Hinkle, J., Joshi, S. 2014

    View details for DOI 10.1155/2014/485067

    View details for Web of Science ID 000330472600001

    View details for PubMedID 24524077

  • Improvement of gadoxetate arterial phase capture with a high spatio-temporal resolution multiphase three-dimensional SPGR-dixon sequence. Journal of magnetic resonance imaging Hope, T. A., Saranathan, M., Petkovska, I., Hargreaves, B. A., Herfkens, R. J., Vasanawala, S. S. 2013; 38 (4): 938-945

    Abstract

    PURPOSE: To determine whether a multiphase method with high spatiotemporal resolution (STR) by means of a combination of parallel imaging, pseudorandom sampling and temporal view sharing improves the capture and intensity of gadoxetate arterial phase images as well as lesion enhancement. MATERIALS AND METHODS: Thirty-seven patients were imaged with a conventional spoiled gradient echo acquisition and 48 with a high STR multiphase acquisition after the administration of gadoxetate. Arterial phase capture, image quality, and quality of fat suppression were qualitatively graded. Fourteen lesions in the conventional group and 28 in the high STR multiphase group were imaged, including 34 focal nodular hyperplasias. The ratio of lesion to parenchyma enhancement as well as relative hepatic artery enhancement were calculated. Chi-squared, Mann-Whitney U and student t-tests were used to compare differences. RESULTS: The high STR multiphase acquisition included the arterial phase more frequently than conventional acquisitions (P < 0.001), with the arterial phase missed in 17% (95% CI of 4-28%) of patients with conventional acquisition compared with 2% (95% CI of 0-6%) with the high STR multiphase acquisition. There was no loss of image quality or degree of fat saturation. Additionally, there was increased relative intensity of the hepatic arteries (P < 0.001) as well as lesion enhancement (P = 0.01). CONCLUSION: The high STR multiphase acquisition resulted in more reliable gadoxetate arterial phase capture compared with a conventional acquisition while preserving image quality with robust fat saturation J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24048

    View details for PubMedID 23371926

  • Noncontrast-enhanced renal angiography using multiple inversion recovery and alternating TR balanced steady-state free precession MAGNETIC RESONANCE IN MEDICINE Dong, H. Z., Worters, P. W., Wu, H. H., Ingle, R. R., Vasanawala, S. S., Nishimura, D. G. 2013; 70 (2): 527-536

    Abstract

    Noncontrast-enhanced renal angiography techniques based on balanced steady-state free precession avoid external contrast agents, take advantage of high inherent blood signal from the $T_2/T_1$ contrast mechanism, and have short steady-state free precession acquisition times. However, background suppression is limited; inflow times are inflexible; labeling region is difficult to define when tagging arterial flow; and scan times are long. To overcome these limitations, we propose the use of multiple inversion recovery preparatory pulses combined with alternating pulse repetition time balanced steady-state free precession to produce renal angiograms. Multiple inversion recovery uses selective spatial saturation followed by four nonselective inversion recovery pulses to concurrently null a wide range of background $T_1$ species while allowing for adjustable inflow times; alternating pulse repetition time steady-state free precession maintains vessel contrast and provides added fat suppression. The high level of suppression enables imaging in three-dimensional as well as projective two-dimensional formats, the latter of which has a scan time as short as one heartbeat. In vivo studies at 1.5 T demonstrate the superior vessel contrast of this technique. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

    View details for DOI 10.1002/mrm.24480

    View details for Web of Science ID 000322128300025

    View details for PubMedID 23172805

  • Pediatric Hepatobiliary Magnetic Resonance Imaging RADIOLOGIC CLINICS OF NORTH AMERICA Vy Thao Tran, V. T., Vasanawala, S. 2013; 51 (4): 599-?

    Abstract

    Magnetic resonance (MR) imaging is an effective and noninvasive modality for evaluating hepatobiliary pathologic conditions. This article provides an up-to-date review of anatomy, indications, and imaging goals and protocols, including patient preparation, pulse sequences, and contrast agents used in pediatric MR hepatobiliary imaging. This article also highlights some of the common MR features of pediatric liver pathologic conditions, including tumors, congenital biliary ductal plate malformations, trauma, fibrosis, and infection.

    View details for DOI 10.1016/j.rcl.2013.03.005

    View details for Web of Science ID 000322847100004

    View details for PubMedID 23830788

  • Venous and arterial flow quantification are equally accurate and precise with parallel imaging compressed sensing 4D phase contrast MRI. Journal of magnetic resonance imaging Tariq, U., Hsiao, A., Alley, M., Zhang, T., Lustig, M., Vasanawala, S. S. 2013; 37 (6): 1419-1426

    Abstract

    To evaluate the precision and accuracy of parallel-imaging compressed-sensing 4D phase contrast (PICS-4DPC) magnetic resonance imaging (MRI) venous flow quantification in children with patients referred for cardiac MRI at our children's hospital.With Institutional Review Board (IRB) approval and Health Insurance Portability and Accountability Act (HIPAA) compliance, 22 consecutive patients without shunts underwent 4DPC as part of clinical cardiac MRI examinations. Flow measurements were obtained in the superior and inferior vena cava, ascending and descending aorta, and the pulmonary trunk. Conservation of flow to the upper, lower, and whole body was used as an internal physiologic control. The arterial and venous flow rates at each location were compared with paired t-tests and F-tests to assess relative accuracy and precision.Arterial and venous flow measurements were strongly correlated with the upper (ρ = 0.89), lower (ρ = 0.96), and whole body (ρ = 0.97); net aortic and pulmonary trunk flow rates were also tightly correlated (ρ = 0.97). There was no significant difference in the value or precision of arterial and venous flow measurements in upper, lower, or whole body, although there was a trend toward improved precision with lower velocity-encoding settings.With PICS-4DPC MRI, the accuracy and precision of venous flow quantification are comparable to that of arterial flow quantification at velocity-encodings appropriate for arterial vessels. J. Magn. Reson. Imaging 2013;37:1419-1426. © 2012 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.23936

    View details for PubMedID 23172846

  • Abdominal MR Imaging in Children: Motion Compensation, Sequence Optimization, and Protocol Organization RADIOGRAPHICS Chavhan, G. B., Babyn, P. S., Vasanawala, S. S. 2013; 33 (3): 703-719

    Abstract

    Familiarity with basic sequence properties and their trade-offs is necessary for radiologists performing abdominal magnetic resonance (MR) imaging. Acquiring diagnostic-quality MR images in the pediatric abdomen is challenging due to motion, inability to breath hold, varying patient size, and artifacts. Motion-compensation techniques (eg, respiratory gating, signal averaging, suppression of signal from moving tissue, swapping phase- and frequency-encoding directions, use of faster sequences with breath holding, parallel imaging, and radial k-space filling) can improve image quality. Each of these techniques is more suitable for use with certain sequences and acquisition planes and in specific situations and age groups. Different T1- and T2-weighted sequences work better in different age groups and with differing acquisition planes and have specific advantages and disadvantages. Dynamic imaging should be performed differently in younger children than in older children. In younger children, the sequence and the timing of dynamic phases need to be adjusted. Different sequences work better in smaller children and in older children because of differing breath-holding ability, breathing patterns, field of view, and use of sedation. Hence, specific protocols should be maintained for younger children and older children. Combining longer-higher-resolution sequences and faster-lower-resolution sequences helps acquire diagnostic-quality images in a reasonable time.

    View details for DOI 10.1148/rg.333125027

    View details for Web of Science ID 000319111700009

    View details for PubMedID 23674770

  • An investigational study to evaluate sildenafil for the treatment of lymphatic malformations International Investigative Dermatology Meeting Danial, C., Tichy, A., Tariq, U., Swetman, G. L., Khuu, P., Leung, T., Teng, J., VASANAWALA, S., Lane, A. NATURE PUBLISHING GROUP. 2013: S175–S175
  • Coil compression for accelerated imaging with Cartesian sampling MAGNETIC RESONANCE IN MEDICINE Zhang, T., Pauly, J. M., Vasanawala, S. S., Lustig, M. 2013; 69 (2): 571-582

    Abstract

    MRI using receiver arrays with many coil elements can provide high signal-to-noise ratio and increase parallel imaging acceleration. At the same time, the growing number of elements results in larger datasets and more computation in the reconstruction. This is of particular concern in 3D acquisitions and in iterative reconstructions. Coil compression algorithms are effective in mitigating this problem by compressing data from many channels into fewer virtual coils. In Cartesian sampling there often are fully sampled k-space dimensions. In this work, a new coil compression technique for Cartesian sampling is presented that exploits the spatially varying coil sensitivities in these nonsubsampled dimensions for better compression and computation reduction. Instead of directly compressing in k-space, coil compression is performed separately for each spatial location along the fully sampled directions, followed by an additional alignment process that guarantees the smoothness of the virtual coil sensitivities. This important step provides compatibility with autocalibrating parallel imaging techniques. Its performance is not susceptible to artifacts caused by a tight imaging field-of-view. High quality compression of in vivo 3D data from a 32 channel pediatric coil into six virtual coils is demonstrated.

    View details for DOI 10.1002/mrm.24267

    View details for Web of Science ID 000314059500031

    View details for PubMedID 22488589

  • IMPROVED VISUALIZATION AND QUANTIFICATION OF 4D FLOW MRI DATA USING DIVERGENCE-FREE WAVELET DENOISING IEEE 10th International Symposium on Biomedical Imaging - From Nano to Macro (ISBI) Ong, F., Uecker, M., Tariq, U., Hsiao, A., Alley, M. T., Vasanawala, S. S., Lustig, M. IEEE. 2013: 1186–1189
  • Nonrigid motion correction in 3D using autofocusing withlocalized linear translations MAGNETIC RESONANCE IN MEDICINE Cheng, J. Y., Alley, M. T., Cunningham, C. H., Vasanawala, S. S., Pauly, J. M., Lustig, M. 2012; 68 (6): 1785-1797

    Abstract

    MR scans are sensitive to motion effects due to the scan duration. To properly suppress artifacts from nonrigid body motion, complex models with elements such as translation, rotation, shear, and scaling have been incorporated into the reconstruction pipeline. However, these techniques are computationally intensive and difficult to implement for online reconstruction. On a sufficiently small spatial scale, the different types of motion can be well approximated as simple linear translations. This formulation allows for a practical autofocusing algorithm that locally minimizes a given motion metric--more specifically, the proposed localized gradient-entropy metric. To reduce the vast search space for an optimal solution, possible motion paths are limited to the motion measured from multichannel navigator data. The novel navigation strategy is based on the so-called "Butterfly" navigators, which are modifications of the spin-warp sequence that provides intrinsic translational motion information with negligible overhead. With a 32-channel abdominal coil, sufficient number of motion measurements were found to approximate possible linear motion paths for every image voxel. The correction scheme was applied to free-breathing abdominal patient studies. In these scans, a reduction in artifacts from complex, nonrigid motion was observed.

    View details for DOI 10.1002/mrm.24189

    View details for Web of Science ID 000311398600012

    View details for PubMedID 22307933

  • Evaluation of Valvular Insufficiency and Shunts with Parallel-imaging Compressed-sensing 4D Phase-contrast MR Imaging with Stereoscopic 3D Velocity-fusion Volume-rendered Visualization RADIOLOGY Hsiao, A., Lustig, M., Alley, M. T., Murphy, M. J., Vasanawala, S. S. 2012; 265 (1): 87-95

    Abstract

    To assess the potential of compressed-sensing parallel-imaging four-dimensional (4D) phase-contrast magnetic resonance (MR) imaging and specialized imaging software in the evaluation of valvular insufficiency and intracardiac shunts in patients with congenital heart disease.Institutional review board approval was obtained for this HIPAA-compliant study. Thirty-four consecutive retrospectively identified patients in whom a compressed-sensing parallel-imaging 4D phase-contrast sequence was performed as part of routine clinical cardiac MR imaging between March 2010 and August 2011 and who had undergone echocardiography were included. Multiplanar, volume-rendered, and stereoscopic three-dimensional velocity-fusion visualization algorithms were developed and implemented in Java and OpenGL. Two radiologists independently reviewed 4D phase-contrast studies for each of 34 patients (mean age, 6 years; age range, 10 months to 21 years) and tabulated visible shunts and valvular regurgitation. These results were compared with color Doppler echocardiographic and cardiac MR imaging reports, which were generated without 4D phase-contrast visualization. Cohen κ statistics were computed to assess interobserver agreement and agreement with echocardiographic results.The 4D phase-contrast acquisitions were performed, on average, in less than 10 minutes. Among 123 valves seen in 34 4D phase-contrast studies, 29 regurgitant valves were identified, with good agreement between observers (k=0.85). There was also good agreement with the presence of at least mild regurgitation at echocardiography (observer 1, κ=0.76; observer 2, κ=0.77) with high sensitivity (observer 1, 75%; observer 2, 82%) and specificity (observer 1, 97%; observer 2, 95%) relative to the reference standard. Eight intracardiac shunts were identified, four of which were not visible with conventional cardiac MR imaging but were detected with echocardiography. No intracardiac shunts were found with echocardiography alone.With velocity-fusion visualization, the compressed-sensing parallel-imaging 4D phase-contrast sequence can augment conventional cardiac MR imaging by improving sensitivity for and depiction of hemodynamically significant shunts and valvular regurgitation.

    View details for DOI 10.1148/radiol.12120055

    View details for Web of Science ID 000309517600011

    View details for PubMedID 22923717

  • DIfferential subsampling with cartesian ordering (DISCO): A high spatio-temporal resolution dixon imaging sequence for multiphasic contrast enhanced abdominal imaging JOURNAL OF MAGNETIC RESONANCE IMAGING Saranathan, M., Rettmann, D. W., Hargreaves, B. A., Clarke, S. E., Vasanawala, S. S. 2012; 35 (6): 1484-1492

    Abstract

    To develop and evaluate a multiphasic contrast-enhanced MRI method called DIfferential Sub-sampling with Cartesian Ordering (DISCO) for abdominal imaging.A three-dimensional, variable density pseudo-random k-space segmentation scheme was developed and combined with a Dixon-based fat-water separation algorithm to generate high temporal resolution images with robust fat suppression and without compromise in spatial resolution or coverage. With institutional review board approval and informed consent, 11 consecutive patients referred for abdominal MRI at 3 Tesla (T) were imaged with both DISCO and a routine clinical three-dimensional SPGR-Dixon (LAVA FLEX) sequence. All images were graded by two radiologists using quality of fat suppression, severity of artifacts, and overall image quality as scoring criteria. For assessment of arterial phase capture efficiency, the number of temporal phases with angiographic phase and hepatic arterial phase was recorded.There were no significant differences in quality of fat suppression, artifact severity or overall image quality between DISCO and LAVA FLEX images (P > 0.05, Wilcoxon signed rank test). The angiographic and arterial phases were captured in all 11 patients scanned using the DISCO acquisition (mean number of phases were two and three, respectively).DISCO effectively captures the fast dynamics of abdominal pathology such as hyperenhancing hepatic lesions with a high spatio-temporal resolution. Typically, 1.1 × 1.5 × 3 mm spatial resolution over 60 slices was achieved with a temporal resolution of 4-5 s.

    View details for DOI 10.1002/jmri.23602

    View details for Web of Science ID 000304035100028

    View details for PubMedID 22334505

    View details for PubMedCentralID PMC3354015

  • Fast l(1)-SPIRiT Compressed Sensing Parallel Imaging MRI: Scalable Parallel Implementation and Clinically Feasible Runtime IEEE TRANSACTIONS ON MEDICAL IMAGING Murphy, M., Alley, M., Demmel, J., Keutzer, K., Vasanawala, S., Lustig, M. 2012; 31 (6): 1250-1262

    Abstract

    We present l₁-SPIRiT, a simple algorithm for auto calibrating parallel imaging (acPI) and compressed sensing (CS) that permits an efficient implementation with clinically-feasible runtimes. We propose a CS objective function that minimizes cross-channel joint sparsity in the wavelet domain. Our reconstruction minimizes this objective via iterative soft-thresholding, and integrates naturally with iterative self-consistent parallel imaging (SPIRiT). Like many iterative magnetic resonance imaging reconstructions, l₁-SPIRiT's image quality comes at a high computational cost. Excessively long runtimes are a barrier to the clinical use of any reconstruction approach, and thus we discuss our approach to efficiently parallelizing l₁-SPIRiT and to achieving clinically-feasible runtimes. We present parallelizations of l₁-SPIRiT for both multi-GPU systems and multi-core CPUs, and discuss the software optimization and parallelization decisions made in our implementation. The performance of these alternatives depends on the processor architecture, the size of the image matrix, and the number of parallel imaging channels. Fundamentally, achieving fast runtime requires the correct trade-off between cache usage and parallelization overheads. We demonstrate image quality via a case from our clinical experimentation, using a custom 3DFT spoiled gradient echo (SPGR) sequence with up to 8× acceleration via Poisson-disc undersampling in the two phase-encoded directions.

    View details for DOI 10.1109/TMI.2012.2188039

    View details for Web of Science ID 000304911300008

    View details for PubMedID 22345529

  • Images in clinical medicine. Splenic spirals. New England journal of medicine Patadia, S., Vasanawala, S. S. 2012; 366 (22): 2111-?

    View details for DOI 10.1056/NEJMicm1105154

    View details for PubMedID 22646633

  • Inversion-recovery-prepared dixon bSSFP: Initial clinical experience with a novel pulse sequence for renal MRA within a breathhold JOURNAL OF MAGNETIC RESONANCE IMAGING Worters, P. W., Saranathan, M., Xu, A., Vasanawala, S. S. 2012; 35 (4): 875-881

    Abstract

    To evaluate the capability of a new breathhold non-contrast-enhanced MRA method (Non-contrast Outer Radial Inner Square k-space Scheme, NORISKS) to visualize renal arteries by comparing the method with a routine clinical but significantly longer non-contrast-enhanced (non-CE) MRA technique.Eighteen subjects referred for abdominal MRI were examined with NORISKS and a routine non-contrast-enhanced MRA technique. Two versions of NORISKS were evaluated: with and without ECG gating. The images were then scored independently and in blinded manner by two radiologists on 5-point scales for visualization of the proximal and distal renal arteries and quality of fat suppression.No statistically significant difference was detected between NORISKS and routine clinical non-CE MRA in all categories except for visualization of the distal renal arteries where ungated NORISKS performed poorer than the routine non-CE MRA (P < 10(-4) ).We have demonstrated a promising non-CE MRA method for acquiring renal angiograms within a breathhold without any compromise in spatial resolution or coverage. ECG-gated NORISKS is able to acquire renal angiograms that are comparable to a routine clinical non-CE MRA method (Inhance IFIR, GE Healthcare), which requires approximately seven times the scan time of NORISKS.

    View details for DOI 10.1002/jmri.23503

    View details for Web of Science ID 000301712400015

    View details for PubMedID 22095672

  • Rapid Pediatric Cardiac Assessment of Flow and Ventricular Volume With Compressed Sensing Parallel Imaging Volumetric Cine Phase-Contrast MRI AMERICAN JOURNAL OF ROENTGENOLOGY Hsiao, A., Lustig, M., Alley, M. T., Murphy, M., Chan, F. P., Herfkens, R. J., Vasanawala, S. S. 2012; 198 (3): W250-W259

    Abstract

    The quantification of cardiac flow and ventricular volumes is an essential goal of many congenital heart MRI examinations, often requiring acquisition of multiple 2D phase-contrast and bright-blood cine steady-state free precession (SSFP) planes. Scan acquisition, however, is lengthy and highly reliant on an imager who is well-versed in structural heart disease. Although it can also be lengthy, 3D time-resolved (4D) phase-contrast MRI yields global flow patterns and is simpler to perform. We therefore sought to accelerate 4D phase contrast and to determine whether equivalent flow and volume measurements could be extracted.Four-dimensional phase contrast was modified for higher acceleration with compressed sensing. Custom software was developed to process 4D phase-contrast images. We studied 29 patients referred for congenital cardiac MRI who underwent a routine clinical protocol, including cine short-axis stack SSFP and 2D phase contrast, followed by contrast-enhanced 4D phase contrast. To compare quantitative measurements, Bland-Altman analysis, paired Student t tests, and F tests were used.Ventricular end-diastolic, end-systolic, and stroke volumes obtained from 4D phase contrast and SSFP were well correlated (ρ = 0.91-0.95; r(2) = 0.83-0.90), with no statistically significant difference. Ejection fractions were well correlated in a subpopulation that underwent higher-resolution compressed-sensing 4D phase contrast (ρ = 0.88; r(2) = 0.77). Four-dimensional phase contrast and 2D phase contrast flow rates were also well correlated (ρ = 0.90; r(2) = 0.82). Excluding ventricles with valvular insufficiency, cardiac outputs derived from outlet valve flow and stroke volumes were more consistent by 4D phase contrast than by 2D phase contrast and SSFP.Combined parallel imaging and compressed sensing can be applied to 4D phase contrast. With custom software, flow and ventricular volumes may be extracted with comparable accuracy to SSFP and 2D phase contrast. Furthermore, cardiac outputs were more consistent by 4D phase contrast.

    View details for DOI 10.2214/AJR.11.6969

    View details for Web of Science ID 000301069000006

    View details for PubMedID 22358022

  • Rapid MR venography in children using a blood pool contrast agent and multi-station fat-water-separated volumetric imaging PEDIATRIC RADIOLOGY Ghanouni, P., Walters, S. G., Vasanawala, S. S. 2012; 42 (2): 242-248

    Abstract

    A rapid, reliable radiation-free method of pediatric body venography might complement US by evaluating veins in the abdomen and pelvis and by providing a global depiction of venous anatomy. We describe a MR venography technique utilizing gadofosveset, a blood pool contrast agent, in children. The technique allows high-spatial-resolution imaging of the veins from the diaphragm to the knees in less than 15 min of total exam time.

    View details for DOI 10.1007/s00247-011-2254-5

    View details for Web of Science ID 000301664100015

    View details for PubMedID 21989981

  • Sildenafil for Severe Lymphatic Malformations NEW ENGLAND JOURNAL OF MEDICINE Swetman, G. L., Berk, D. R., Vasanawala, S. S., Feinstein, J. A., Lane, A. T., Bruckner, A. L. 2012; 366 (4): 384-386

    View details for Web of Science ID 000299464100029

    View details for PubMedID 22276841

  • Estimation of liver T*2 in transfusion-related iron overload in patients with weighted least squares T*2 IDEAL MAGNETIC RESONANCE IN MEDICINE Vasanawala, S. S., Yu, H., Shimakawa, A., Jeng, M., Brittain, J. H. 2012; 67 (1): 183-190

    Abstract

    MRI imaging of hepatic iron overload can be achieved by estimating T(2) values using multiple-echo sequences. The purpose of this work is to develop and clinically evaluate a weighted least squares algorithm based on T(2) Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation (IDEAL) technique for volumetric estimation of hepatic T(2) in the setting of iron overload. The weighted least squares T(2) IDEAL technique improves T(2) estimation by automatically decreasing the impact of later, noise-dominated echoes. The technique was evaluated in 37 patients with iron overload. Each patient underwent (i) a standard 2D multiple-echo gradient echo sequence for T(2) assessment with nonlinear exponential fitting, and (ii) a 3D T(2) IDEAL technique, with and without a weighted least squares fit. Regression and Bland-Altman analysis demonstrated strong correlation between conventional 2D and T(2) IDEAL estimation. In cases of severe iron overload, T(2) IDEAL without weighted least squares reconstruction resulted in a relative overestimation of T(2) compared with weighted least squares.

    View details for DOI 10.1002/mrm.22986

    View details for Web of Science ID 000298482800021

    View details for PubMedID 21574184

  • Combined respiratory and cardiac triggering improves blood pool contrast-enhanced pediatric cardiovascular MRI PEDIATRIC RADIOLOGY Vasanawala, S. S., Chan, F. P., Newman, B., Alley, M. T. 2011; 41 (12): 1536-1544

    Abstract

    Contrast-enhanced cardiac MRA suffers from cardiac motion artifacts and often requires a breath-hold.This work develops and evaluates a blood pool contrast-enhanced combined respiratory- and ECG-triggered MRA method.An SPGR sequence was modified to enable combined cardiac and respiratory triggering on a 1.5-T scanner. Twenty-three consecutive children referred for pediatric heart disease receiving gadofosveset were recruited in HIPAA-compliant fashion with IRB approval and informed consent. Children underwent standard non-triggered contrast-enhanced MRA with or without suspended respiration. Additionally, a free-breathing-triggered MRA was acquired. Triggered and non-triggered studies were presented in blinded random order independently to two radiologists twice. Anatomical structure delineation was graded for each triggered and non-triggered acquisition and the visual quality on triggered MRA was compared directly to that on non-triggered MRA.Triggered images received higher scores from each radiologist for all anatomical structures on each of the two reading sessions (Wilcoxon rank sum test, P < 0.05). In direct comparison, triggered images were preferred over non-triggered images for delineating cardiac structures, with most comparisons reaching statistical significance (binomial test, P < 0.05).Combined cardiac and respiratory triggering, enabled by a blood pool contrast agent, improves delineation of most anatomical structures in pediatric cardiovascular MRA.

    View details for DOI 10.1007/s00247-011-2196-y

    View details for Web of Science ID 000297621800005

    View details for PubMedID 21786125

  • Functional hepatobiliary MR imaging in children PEDIATRIC RADIOLOGY Tamrazi, A., Vasanawala, S. S. 2011; 41 (10): 1250-1258

    Abstract

    Clinical application efforts for the hepatocyte-specific MRI contrast agent gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) have mainly been directed toward detection and characterization of various hepatic masses in the adult population.Here we report our initial experience with Gd-EOB-DTPA for evaluating congenital and acquired hepatobiliary pathologies in the pediatric population.Twenty-one consecutive children receiving Gd-EOB-DTPA for functional hepatobiliary evaluation at our institution were retrospectively identified with IRB approval. The use of Gd-EOB-DTPA was classified in each case as definite, potential, or no clinical utility, focusing on the clinical value gained beyond traditional noncontrast fluid-sensitive MR cholangiopancreatography (FS-MRCP) and other imaging modalities.Definite added value of Gd-EOB-DTPA was found in 12 patients, with potential value in 4 patients, and no value in 5 patients. Benefit was seen in cases of iatrogenic and non-iatrogenic biliary strictures, perihepatic fluid collections for biliary leak, hepatobiliary dysfunction in the absence of hyperbilirubinemia, and in the functional exclusion of cystic duct occlusion that can be seen in acute cholecystitis.This is the first reported series of children with Gd-EOB-DTPA and this early work suggests potential pediatric applications.

    View details for DOI 10.1007/s00247-011-2086-3

    View details for Web of Science ID 000294690500005

    View details for PubMedID 21553038

  • Point/counterpoint: dose-related issues in cardiac CT imaging. Pediatric radiology Newman, B., Vasanawala, S. S. 2011; 41: 528-533

    Abstract

    This manuscript reviews some of the more controversial dose-related issues in cardiac CT imaging. Discussion covers the relative merits of cardiac CT versus MR, advantages and concerns regarding gated versus nongated cardiac CT and advantages and concerns regarding the use of breast shields in girls undergoing cardiac CT imaging.

    View details for DOI 10.1007/s00247-011-2153-9

    View details for PubMedID 21847735

  • Advances in pediatric body MRI. Pediatric radiology Vasanawala, S. S., Lustig, M. 2011; 41: 549-554

    Abstract

    MRI offers an alternative to CT, and thus is central to an ALARA strategy. However, long exam times, limited magnet availability, and motion artifacts are barriers to expanded use of MRI. This article reviews developments in pediatric body MRI that might reduce these barriers: high field systems, acceleration, navigation and newer contrast agents.

    View details for DOI 10.1007/s00247-011-2103-6

    View details for PubMedID 21847737

  • Active gastrointestinal hemorrhage identification by blood pool contrast-enhanced magnetic resonance angiography PEDIATRIC RADIOLOGY Williams, J., Vasanawala, S. S. 2011; 41 (9): 1198-1200

    Abstract

    Localization of the source of gastrointestinal hemorrhage can be challenging. Currently, this is often accomplished with tagged red blood cell scintigraphy, with attendant ionizing radiation and relatively poor spatial resolution. We describe an analogous method of detecting acute gastrointestinal hemorrhage by enhanced MRI with blood pool contrast agent. Briefly, following precontrast fat-suppressed volumetric T1-weighted image acquisition, single-dose gadofosveset trisodium, a blood pool agent, is administered. Then serial post-T1-weighted images are obtained. This technique is a novel method for evaluating gastrointestinal hemorrhage.

    View details for DOI 10.1007/s00247-011-2139-7

    View details for Web of Science ID 000293979800013

    View details for PubMedID 21594539

  • Volumetric fat-water separated T2-weighted MRI PEDIATRIC RADIOLOGY Vasanawala, S. S., Madhuranthakam, A. J., Venkatesan, R., Sonik, A., Lai, P., Brau, A. C. 2011; 41 (7): 875-883

    Abstract

    Pediatric body MRI exams often cover multiple body parts, making the development of broadly applicable protocols and obtaining uniform fat suppression a challenge. Volumetric T2 imaging with Dixon-type fat-water separation might address this challenge, but it is a lengthy process.We develop and evaluate a faster two-echo approach to volumetric T2 imaging with fat-water separation.A volumetric spin-echo sequence was modified to include a second shifted echo so two image sets are acquired. A region-growing reconstruction approach was developed to decompose separate water and fat images. Twenty-six children were recruited with IRB approval and informed consent. Fat-suppression quality was graded by two pediatric radiologists and compared against conventional fat-suppressed fast spin-echo T2-W images. Additionally, the value of in- and opposed-phase images was evaluated.Fat suppression on volumetric images had high quality in 96% of cases (95% confidence interval of 80-100%) and were preferred over or considered equivalent to conventional two-dimensional fat-suppressed FSE T2 imaging in 96% of cases (95% confidence interval of 78-100%). In- and opposed-phase images had definite value in 12% of cases.Volumetric fat-water separated T2-weighted MRI is feasible and is likely to yield improved fat suppression over conventional fat-suppressed T2-weighted imaging.

    View details for DOI 10.1007/s00247-010-1963-5

    View details for Web of Science ID 000292167300011

    View details for PubMedID 21243349

  • Improved cardiovascular flow quantification with time-resolved volumetric phase-contrast MRI PEDIATRIC RADIOLOGY Hsiao, A., Alley, M. T., Massaband, P., Herfkens, R. J., Chan, F. P., Vasanawala, S. S. 2011; 41 (6): 711-720

    Abstract

    Cardiovascular flow is commonly assessed with two-dimensional, phase-contrast MRI (2-D PC-MRI). However, scan prescription and acquisition over multiple planes is lengthy, often requires direct physician oversight and has inconsistent results. Time-resolved volumetric PC-MRI (4-D flow) may address these limitations.We assess the degree of agreement and internal consistency between 2-D and 4-D flow quantification in our clinical population.Software enabling flow calculation from 4-D flow was developed in Java. With IRB approval and HIPAA compliance, 18 consecutive patients without shunts were identified who underwent both (1) conventional 2-D PC-MRI of the aorta and main pulmonary artery and (2) 4-D flow imaging. Aortic and pulmonary flow rates were assessed with both techniques.Both methods showed general agreement in flow rates (ρ: 0.87-0.90). Systemic and pulmonary arterial flow rates were well-correlated (ρ: 4-D 0.98-0.99, 2-D 0.93), but more closely matched with 4-D (P < 0.05, Brown-Forsythe). Pulmonary flow rates were lower than systemic rates for 2-D (P < 0.05, two-sample t-test). In a sub-analysis of patients without pulmonary or aortic regurgitation, 2-D showed improved correlation of flow rates while 4-D phase-contrast remained tightly correlated (ρ: 4-D 0.99-1.00, 2-D 0.99).4-D PC-MRI demonstrates greater consistency than conventional 2-D PC-MRI for flow quantification.

    View details for DOI 10.1007/s00247-010-1932-z

    View details for Web of Science ID 000290544500005

    View details for PubMedID 21221566

  • An Approach to Pediatric Liver MRI AMERICAN JOURNAL OF ROENTGENOLOGY Mitchell, C. L., Vasanawala, S. S. 2011; 196 (5): W519-W526

    Abstract

    This article illustrates an approach to MRI for hepatobiliary imaging in children. The indications, patient preparation, protocols, pulse sequences, and contrast agents will be highlighted.Significant advances in hepatobiliary MRI have allowed reliable, high quality imaging in a pediatric population.

    View details for DOI 10.2214/AJR.10.6076

    View details for Web of Science ID 000289769000004

    View details for PubMedID 21512040

  • Adrenal and renal corticomedullary junction iron deposition in red cell aplasia PEDIATRIC RADIOLOGY Rakow-Penner, R., Glader, B., Yu, H., Vasanawala, S. 2010; 40 (12): 1955-1957

    Abstract

    Iron deposition can occur in the kidneys as a result of hemolysis or extensive iron overload from transfusions. With T2* MRI, renal iron deposition can be visualized. In this report, renal corticomedullary junction iron deposition is noted using T2* MRI in a boy with red cell aplasia. The renal corticomedullary junction iron deposition is an indication of the severity of his iron overload. This is an unusual finding and brings clinical attention to the boy's renal function for further evaluation.

    View details for DOI 10.1007/s00247-010-1824-2

    View details for Web of Science ID 000284375300013

    View details for PubMedID 20852855

  • A method of rapid robust respiratory synchronization for MRI PEDIATRIC RADIOLOGY Vasanawala, S. S., Jackson, E. 2010; 40 (10): 1690-1692

    Abstract

    Respiratory motion degrades MRI exams. Adequate detection of respiratory motion with pneumatic respiratory belts in small children is challenging and time-consuming.

    View details for DOI 10.1007/s00247-010-1755-y

    View details for Web of Science ID 000281907100014

    View details for PubMedID 20567966

  • Respiratory Navigated Free Breathing 3D Spoiled Gradient-Recalled Echo Sequence for Contrast-Enhanced Examination of the Liver: Diagnostic Utility and Comparison With Free Breathing and Breath-Hold Conventional Examinations AMERICAN JOURNAL OF ROENTGENOLOGY Young, P. M., Brau, A. C., Iwadate, Y., Vasanawala, S., Daniel, B. L., Tamrazi, A., Herfkens, R. J. 2010; 195 (3): 687-691

    Abstract

    The purpose of our study was to evaluate image quality in a 3D spoiled gradient-recalled echo (SPGR) sequence that was modified to incorporate respiratory navigation to limit the deleterious effects of respiratory motion and to compare it with conventional scanning during breath-holding and free breathing.Respiratory navigation of 3D SPGR sequences is technically feasible, and image quality is modestly improved over free breathing acquisitions using conventional 3D SPGR sequences. This may represent a promising imaging alternative for patients who cannot hold their breath.

    View details for DOI 10.2214/AJR.09.3892

    View details for Web of Science ID 000281180500022

    View details for PubMedID 20729447

  • Improved Pediatric MR Imaging with Compressed Sensing RADIOLOGY Vasanawala, S. S., Alley, M. T., Hargreaves, B. A., Barth, R. A., Pauly, J. M., Lustig, M. 2010; 256 (2): 607-616

    Abstract

    To develop a method that combines parallel imaging and compressed sensing to enable faster and/or higher spatial resolution magnetic resonance (MR) imaging and show its feasibility in a pediatric clinical setting.Institutional review board approval was obtained for this HIPAA-compliant study, and informed consent or assent was given by subjects. A pseudorandom k-space undersampling pattern was incorporated into a three-dimensional (3D) gradient-echo sequence; aliasing then has an incoherent noiselike pattern rather than the usual coherent fold-over wrapping pattern. This k-space-sampling pattern was combined with a compressed sensing nonlinear reconstruction method that exploits the assumption of sparsity of medical images to permit reconstruction from undersampled k-space data and remove the noiselike aliasing. Thirty-four patients (15 female and 19 male patients; mean age, 8.1 years; range, 0-17 years) referred for cardiovascular, abdominal, and knee MR imaging were scanned with this 3D gradient-echo sequence at high acceleration factors. Obtained k-space data were reconstructed with both a traditional parallel imaging algorithm and the nonlinear method. Both sets of images were rated for image quality, radiologist preference, and delineation of specific structures by two radiologists. Wilcoxon and symmetry tests were performed to test the hypothesis that there was no significant difference in ratings for image quality, preference, and delineation of specific structures.Compressed sensing images were preferred more often, had significantly higher image quality ratings, and greater delineation of anatomic structures (P < .001) than did images obtained with the traditional parallel reconstruction method.A combination of parallel imaging and compressed sensing is feasible in a clinical setting and may provide higher resolution and/or faster imaging, addressing the challenge of delineating anatomic structures in pediatric MR imaging.

    View details for DOI 10.1148/radiol.10091218

    View details for Web of Science ID 000280272100032

    View details for PubMedID 20529991

    View details for PubMedCentralID PMC2909438

  • T-2 relaxation times of C-13 metabolites in a rat hepatocellular carcinoma model measured in vivo using C-13-MRS of hyperpolarized [1-C-13]pyruvate NMR IN BIOMEDICINE Yen, Y., Le Roux, P., Mayer, D., King, R., Spielman, D., Tropp, J., Pauly, K. B., Pfefferbaum, A., Vasanawala, S., Hurd, R. 2010; 23 (4): 414-423

    Abstract

    A single-voxel Carr-Purcell-Meibloom-Gill sequence was developed to measure localized T(2) relaxation times of (13)C-labeled metabolites in vivo for the first time. Following hyperpolarized [1-(13)C]pyruvate injections, pyruvate and its metabolic products, alanine and lactate, were observed in the liver of five rats with hepatocellular carcinoma and five healthy control rats. The T(2) relaxation times of alanine and lactate were both significantly longer in HCC tumors than in normal livers (p < 0.002). The HCC tumors also showed significantly higher alanine signal relative to the total (13)C signal than normal livers (p < 0.006). The intra- and inter-subject variations of the alanine T(2) relaxation time were 11% and 13%, respectively. The intra- and inter-subject variations of the lactate T(2) relaxation time were 6% and 7%, respectively. The intra-subject variability of alanine to total carbon ratio was 16% and the inter-subject variability 28%. The intra-subject variability of lactate to total carbon ratio was 14% and the inter-subject variability 20%. The study results show that the signal level and relaxivity of [1-(13)C]alanine may be promising biomarkers for HCC tumors. Its diagnostic values in HCC staging and treatment monitoring are yet to be explored.

    View details for DOI 10.1002/nbm.1481

    View details for Web of Science ID 000277525800011

    View details for PubMedID 20175135

    View details for PubMedCentralID PMC2891253

  • State-of-the-Art in Pediatric Body and Musculoskeletal Magnetic Resonance Imaging SEMINARS IN ULTRASOUND CT AND MRI MacKenzie, J. D., Vasanawala, S. S. 2010; 31 (2): 86-99

    Abstract

    Pediatric body and musculoskeletal MRI has seen tremendous advances over the past few years. These advances have enabled high-quality imaging in even the smallest children and expanded the range of clinical problems amenable to MRI. In this review, we highlight some advances: transition to 3 Tesla, parallel imaging, motion compensation, and new contrast agents. Given the increasing saliency of concerns regarding ionizing radiation from computed tomography, these advances could not be more welcome.

    View details for DOI 10.1053/j.sult.2010.01.005

    View details for Web of Science ID 000276295500004

    View details for PubMedID 20304318

  • MRI of the liver-how to do it PEDIATRIC RADIOLOGY Vasanawala, S. S. 2010; 40 (4): 431-437

    Abstract

    This article details indications, patient preparation, pulse sequences/protocols, and contrast agents for pediatric hepatobiliary MRI. When performed well, MRI provides superior diagnostic information relative to CT for evaluation of hepatic tumors, liver transplants, and biliary disease.

    View details for DOI 10.1007/s00247-009-1522-0

    View details for Web of Science ID 000275555900008

    View details for PubMedID 20225098

  • Navigated abdominal T1-W MRI permits free-breathing image acquisition with less motion artifact PEDIATRIC RADIOLOGY Vasanawala, S. S., Iwadate, Y., Church, D. G., Herfkens, R. J., Brau, A. C. 2010; 40 (3): 340-344

    Abstract

    T1-W imaging of the pediatric abdomen is often limited by respiratory motion artifacts. Although navigation has been commonly employed for coronary MRA and T2-W imaging, navigation for T1-W imaging is less developed. Thus, we incorporated a navigator pulse into a fat-suppressed T1-W SPGR sequence such that steady-state contrast was not disrupted. Ten children were scanned after gadolinium administration three times in immediate succession: breath-hold with no navigation, free-breathing with navigation, and free-breathing without navigation. Motion artifacts were scored for each sequence by two radiologists,showing fewer motion artifacts with navigation compared to free-breathing and greater motion artifacts than with breath-holding. This work demonstrates the feasibility and potential utility of navigation for pediatric abdominal T1-W imaging.

    View details for DOI 10.1007/s00247-009-1502-4

    View details for Web of Science ID 000274386700008

    View details for PubMedID 20066407

  • Magnetic resonance imaging for uterine and vaginal anomalies CURRENT OPINION IN OBSTETRICS & GYNECOLOGY Church, D. G., Vancil, J. M., Vasanawala, S. S. 2009; 21 (5): 379-389

    Abstract

    Pediatric pelvic MRI has had dramatic advances in the past few years. This review documents studies demonstrating the accuracy of MRI for the evaluation of uterine and vaginal anomalies and discusses the salient changes to MRI methods that are particularly applicable to evaluating the pediatric patient with these developmental anomalies.MRI has high accuracy for evaluation of uterine and vaginal anomalies. Significant advances, such as volumetric imaging, increased resolution, decreased motion artifacts, and shorter examination time, have increased the access and utility of MRI for pediatric patients.MRI techniques have evolved markedly in the past several years, providing a robust method of evaluating uterine and vaginal anomalies in the pediatric patient.

    View details for DOI 10.1097/GCO.0b013e3283307c3e

    View details for Web of Science ID 000270062100003

    View details for PubMedID 19623067

  • Appendiceal hyperemia and/or distention is not always appendicitis: appendicitis mimicry in the pediatric population CLINICAL IMAGING Price, R. O., Jeffrey, R. B., Vasanawala, S. S. 2009; 33 (5): 402-405

    Abstract

    Appendicitis is the most common surgical cause of acute abdominal pain in the pediatric population. Several conditions can mimic the clinical presentation of appendicitis, leaving imaging as an essential modality to uncover the etiology, yet under certain circumstances, it can be misleading. Here, we present three cases where findings on multidetector computerized tomography scans supported the diagnosis of appendicitis, yet an alternate cause was found. These cases highlight a particular pitfall of satisfaction of search.

    View details for DOI 10.1016/j.clinimag.2009.01.010

    View details for Web of Science ID 000269764400014

    View details for PubMedID 19712824

  • MR Voiding Cystography for Evaluation of Vesicoureteral Reflux AMERICAN JOURNAL OF ROENTGENOLOGY Vasanawala, S. S., Kennedy, W. A., Ganguly, A., Fahrig, R., Rieke, V., Daniel, B., Barth, R. A. 2009; 192 (5): W206-W211

    Abstract

    The purpose of our study is to present a real-time interactive continuous fluoroscopy MRI technique for vesicoureteral reflux (VUR) diagnosis.MR voiding cystography with a real-time interactive MR fluoroscopic technique on an open MRI magnet is feasible for the evaluation of VUR in children.

    View details for DOI 10.2214/AJR.08.1251

    View details for Web of Science ID 000265387300045

    View details for PubMedID 19380524

  • Advances in Pediatric MR Imaging MAGNETIC RESONANCE IMAGING CLINICS OF NORTH AMERICA MacKenzie, J. D., Vasanawala, S. S. 2008; 16 (3): 385-?

    Abstract

    This article describes the considerable technical achievements that have been made in MR imaging in the evaluation of pediatric patients. The latest techniques in improving signal intensity, resolution, and speed are discussed. The multitude of new options for pediatric MR imaging are illustrated, including higher field strength imaging, multi-channel coil technology coupled with parallel imaging, and new pulse sequence designs. Several future directions in the field of pediatric body and musculoskeletal imaging also are highlighted.

    View details for DOI 10.1016/j.mric.2008.04.008

    View details for Web of Science ID 000264835900002

    View details for PubMedID 18585595

  • Balanced SSFP imaging of the musculoskeletal system JOURNAL OF MAGNETIC RESONANCE IMAGING Gold, G. E., Hargreaves, B. A., Reeder, S. B., Block, W. F., Kijowski, R., Vasanawala, S. S., Kornaat, P. R., Bammer, R., Newbould, R., Bangerter, N. K., Beaulieu, C. F. 2007; 25 (2): 270-278

    Abstract

    Magnetic resonance imaging (MRI), with its unique ability to image and characterize soft tissue noninvasively, has emerged as one of the most accurate imaging methods available to diagnose bone and joint pathology. Currently, most evaluation of musculoskeletal pathology is done with two-dimensional acquisition techniques such as fast spin echo (FSE) imaging. The development of three-dimensional fast imaging methods based on balanced steady-state free precession (SSFP) shows great promise to improve MRI of the musculoskeletal system. These methods may allow acquisition of fluid sensitive isotropic data that can be reformatted into arbitrary planes for improved detection and visualization of pathology. Sensitivity to fluid and fat suppression are important issues in these techniques to improve delineation of cartilage contours, for detection of marrow edema and derangement of other joint structures.

    View details for DOI 10.1002/jmri.20819

    View details for Web of Science ID 000244133000006

    View details for PubMedID 17260387

  • Value of delayed imaging in MDCT of the abdomen and pelvis AMERICAN JOURNAL OF ROENTGENOLOGY Vasanawala, S. S., Desser, T. 2006; 187 (1): 154-163

    Abstract

    Our objective was to illustrate the benefits of obtaining delayed CT images.There are several clinical scenarios in which delayed CT images may improve diagnostic specificity.

    View details for DOI 10.2214/AJR.05.0148

    View details for Web of Science ID 000238659600027

    View details for PubMedID 16794170

  • Articular cartilage of the knee: Evaluation with fluctuating equilibrium MR imaging - Initial experience in healthy volunteers RADIOLOGY Gold, G. E., Hargreaves, B. A., Vasanawala, S. S., Webb, J. D., Shimakawa, A. S., Brittain, J. H., Beaulieu, C. F. 2006; 238 (2): 712-718

    Abstract

    Institutional review board approval and informed consent were obtained for this HIPAA-compliant study, whose purpose was to prospectively compare three magnetic resonance (MR) imaging techniques-fluctuating equilibrium, three-dimensional (3D) spoiled gradient-recalled acquisition in the steady state (SPGR), and two-dimensional (2D) fast spin echo (SE)-for evaluating articular cartilage in the knee. The study cohort consisted of 10 healthy volunteers (four men, six women; age range, 26-42 years). Cartilage signal-to-noise ratio (SNR), SNR efficiency, cartilage-fluid contrast-to-noise ratio (CNR), CNR efficiency, image quality, cartilage visibility, and fat suppression were compared. Cartilage volume was compared for the fluctuating equilibrium and 3D SPGR techniques. Compared with 3D SPGR and 2D fast SE, fluctuating equilibrium yielded the highest cartilage SNR efficiency and cartilage-fluid CNR efficiency (P < .01 for both). Image quality was similar with all sequences. Fluctuating equilibrium imaging yielded higher cartilage visibility than did 2D fast SE imaging (P <. 01) but worse fat suppression than did 3D SPGR and 2D fast SE imaging (P < .04). Cartilage volume measurements with fluctuating equilibrium and 3D SPGR were similar. Fluctuating equilibrium MR imaging is a promising method for evaluating articular cartilage in the knee.

    View details for DOI 10.1148/radiol.2381042183

    View details for Web of Science ID 000234859100040

    View details for PubMedID 16436826

  • Dual-acquisition phase-sensitive fat-water separation using balanced steady-state free precession MAGNETIC RESONANCE IMAGING Hargreaves, B. A., Bangerter, N. K., Shimakawa, A., Vasanawala, S. S., Brittain, J. H., Nishimura, D. G. 2006; 24 (2): 113-122

    Abstract

    Balanced steady-state free precession (SSFP) sequences use fully re-focussed gradient waveforms to achieve a high signal and useful image contrast in short scan times. Despite these strengths, the clinical feasibility of balanced SSFP is still limited both by bright fat signal and by the signal voids that result from off-resonance effects such as field or susceptibility variations. A new method, dual-acquisition phase-sensitive SSFP, combines the signals from two standard balanced SSFP acquisitions to separate fat and water while simultaneously reducing the signal voids. The acquisitions are added in quadrature and then phase corrected using a simple algorithm before fat and water can be identified simply by the sign of the signal. This method is especially useful for applications at high field, where the RF power deposition, spatial resolution requirements and gradient strength limit the minimum repetition times. Finally, dual-acquisition phase-sensitive SSFP can be combined with other magnetization preparation schemes to produce specific image contrast in addition to separating fat and water signals.

    View details for DOI 10.1016/j.mri.2005.10.013

    View details for Web of Science ID 000235506400002

    View details for PubMedID 16455400

  • Controversies in protocol selection in the Imaging of articular cartilage SEMINARS IN MUSCULOSKELETAL RADIOLOGY Gold, G. E., Hargreaves, B. A., Reeder, S. B., Vasanawala, S. S., Beaulieu, C. F. 2005; 9 (2): 161-172

    Abstract

    Magnetic resonance (MR) imaging, with its unique ability to noninvasively image and characterize soft tissue, has shown promise in assessment of cartilage. The development of new, fast imaging methods with high contrast will improve the MR evaluation of cartilage morphology. In addition to morphological MR imaging methods, MR imaging contrast mechanisms under development may reveal detailed information regarding the physiology of cartilage. However, many of these methods remain to be tested in the clinical setting. Protocol selection for cartilage imaging requires understanding of the patient population and the advantages and limitations of these techniques.

    View details for Web of Science ID 000230039200008

    View details for PubMedID 16044384

  • Rapid musculoskeletal MRI with phase-sensitive steady-state free precession: Comparison with routine knee MRI AMERICAN JOURNAL OF ROENTGENOLOGY Vasanawala, S. S., Hargreaves, B. A., Pauly, J. M., Nishimura, D. G., Beaulieu, C. F., Gold, G. E. 2005; 184 (5): 1450-1455

    Abstract

    The aim of this work was to show the potential utility of a novel rapid 3D fat-suppressed MRI method for joint imaging.Phase-sensitive steady-state free precession provides rapid 3D joint imaging with robust fat suppression and excellent cartilage delineation.

    View details for Web of Science ID 000228875300013

    View details for PubMedID 15855095

  • Accommodation of requests for emergency US and CT: Applications of queueing theory to scheduling of urgent studies RADIOLOGY Vasanawala, S. S., Desser, T. S. 2005; 235 (1): 244-249

    Abstract

    The purpose of this study was to determine whether queueing theory would allow prediction of optimal number of schedule slots to be reserved for urgent computed tomography (CT) and ultrasonography (US). Institutional review board approval was obtained; informed consent was exempted. Emergency studies were modeled as a Poisson process; slots were reserved such that rate of rescheduling of routine studies to accommodate emergencies was predicted to be below a certain level. Model was tested with 3 years of emergency US and CT requests. US and CT requests showed Poisson distribution. US rescheduling was near that predicted. CT rescheduling exceeded that predicted, which reflected increasing CT use. By using more recent CT data for prediction, a more concordant rescheduling rate resulted.

    View details for DOI 10.1148/radiol.2351040289

    View details for Web of Science ID 000227952600036

    View details for PubMedID 15716391

  • Analysis of multiple-acquisition SSFP MAGNETIC RESONANCE IN MEDICINE Bangerter, N. K., Hargreaves, B. A., Vasanawala, S. S., Pauly, J. M., Gold, G. E., Nishimura, D. G. 2004; 51 (5): 1038-1047

    Abstract

    Refocused steady-state free precession (SSFP) is limited by its high sensitivity to local field variation, particularly at high field strengths or the long repetition times (TRs) necessary for high resolution. Several methods have been proposed to reduce SSFP banding artifact by combining multiple phase-cycled SSFP acquisitions, each differing in how individual signal magnitudes and phases are combined. These include maximum-intensity SSFP (MI-SSFP) and complex-sum SSFP (CS-SSFP). The reduction in SSFP banding is accompanied by a loss in signal-to-noise ratio (SNR) efficiency. In this work a general framework for analyzing banding artifact reduction, contrast, and SNR of any multiple-acquisition SSFP combination method is presented. A new sum-of-squares method is proposed, and a comparison is performed between each of the combination schemes. The sum-of-squares SSFP technique (SOS-SSFP) delivers both robust banding artifact reduction and higher SNR efficiency than other multiple-acquisition techniques, while preserving SSFP contrast.

    View details for DOI 10.1002/mrm.20052

    View details for Web of Science ID 000221239000022

    View details for PubMedID 15122688

  • Knee cartilage volume with fluctuating equilibrium MRI 9th World Congress of the OsteoArthritis-Research-Society-International Gold, G. E., Hargreaves, B. A., Vasanawala, S. S., Webb, J., Shimakawa, A., Brittain, J. H., Pauly, J. M., Beaulieu, C. F. W B SAUNDERS CO LTD. 2004: S1–S1
  • Fat-suppressed steady-state free precession imaging using phase detection MAGNETIC RESONANCE IN MEDICINE Hargreaves, B. A., Vasanawala, S. S., Nayak, K. S., Hu, B. S., Nishimura, D. G. 2003; 50 (1): 210-213

    Abstract

    Fully refocused steady-state free precession (SSFP) is a rapid, efficient imaging sequence that can provide diagnostically useful image contrast. In SSFP, the signal is refocused midway between excitation pulses, much like in a spin-echo experiment. However, in SSFP, the phase of the refocused spins alternates for each resonant frequency interval equal to the reciprocal of the sequence repetition time (TR). Appropriate selection of the TR results in a 180 degrees phase difference between lipid and water signals. This phase difference can be used for fat-water separation in SSFP without any increase in scan time. The technique is shown to produce excellent non-contrast-enhanced, flow-independent angiograms of the peripheral vasculature.

    View details for DOI 10.1002/mrm.10488

    View details for Web of Science ID 000183961800028

    View details for PubMedID 12815698

  • Comparison of new sequences for high-resolution cartilage imaging MAGNETIC RESONANCE IN MEDICINE Hargreaves, B. A., Gold, G. E., Beaulieu, C. F., Vasanawala, S. S., Nishimura, D. G., Pauly, J. M. 2003; 49 (4): 700-709

    Abstract

    The high prevalence of osteoarthritis continues to demand improved accuracy in detecting cartilage injury and monitoring its response to different treatments. MRI is the most accurate noninvasive method of diagnosing cartilage lesions. However, MR imaging of cartilage is limited by scan time, signal-to-noise ratio (SNR), and image contrast. Recently, there has been renewed interest in SNR-efficient imaging sequences for imaging cartilage, including various forms of steady-state free-precession as well as driven-equilibrium imaging. This work compares several of these sequences with existing methods, both theoretically and in normal volunteers. Results show that the new steady-state methods increase SNR-efficiency by as much as 30% and improve cartilage-synovial fluid contrast by a factor of three. Additionally, these methods markedly decrease minimum scan times, while providing 3D coverage without the characteristic blurring seen in fast spin-echo images.

    View details for DOI 10.1002/mrm.10424

    View details for Web of Science ID 000182007200013

    View details for PubMedID 12652541

  • Characterization and reduction of the transient response in steady-state MR imaging MAGNETIC RESONANCE IN MEDICINE Hargreaves, B. A., Vasanawala, S. S., Pauly, J. M., Nishimura, D. G. 2001; 46 (1): 149-158

    Abstract

    Refocused steady-state free precession (SSFP) imaging sequences have recently regained popularity as faster gradient hardware has allowed shorter repetition times, thereby reducing SSFP's sensitivity to off-resonance effects. Although these sequences offer fast scanning with good signal-to-noise efficiency, the "transient response," or time taken to reach a steady-state, can be long compared with the total imaging time, particularly when using 2D sequences. This results in lost imaging time and has made SSFP difficult to use for real-time and cardiac-gated applications. A linear-systems analysis of the steady-state and transient response for general periodic sequences is shown. The analysis is applied to refocused-SSFP sequences to generate a two-stage method of "catalyzing," or speeding up the progression to steady-state by first scaling, then directing the magnetization. This catalyzing method is compared with previous methods in simulations and experimentally. Although the second stage of the method exhibits some sensitivity to B(1) variations, our results show that the transient time can be significantly reduced, allowing imaging in a shorter total scan time. Magn Reson Med 46:149-158, 2001.

    View details for Web of Science ID 000169561000019

    View details for PubMedID 11443721

  • Linear combination steady-state free precession MRI MAGNETIC RESONANCE IN MEDICINE Vasanawala, S. S., Pauly, J. M., Nishimura, D. G. 2000; 43 (1): 82-90

    Abstract

    A new, fast, spectrally selective steady-state free precession (SSFP) imaging method is presented. Combining k-space data from SSFP sequences with certain phase schedules of radiofrequency excitation pulses permits manipulation of the spectral selectivity of the image. For example, lipid and water can be resolved. The contrast of each image depends on both T1 and T2, and the relative contribution of the two relaxation mechanisms to image contrast can be controlled by adjusting the flip angle. Several potential applications of the technique, referred to as linear combination steady-state free precession (LCSSFP), are demonstrated: fast musculoskeletal, abdominal, angiographic, and brain imaging.

    View details for Web of Science ID 000084538500010

    View details for PubMedID 10642734

  • Fluctuating equilibrium MRI MAGNETIC RESONANCE IN MEDICINE Vasanawala, S. S., Pauly, J. M., Nishimura, D. G. 1999; 42 (5): 876-883

    Abstract

    A new fast, spectrally selective imaging method called fluctuating equilibrium magnetic resonance is presented. With all gradients refocused over a repetition interval, certain phase schedules of radiofrequency excitation pulses produce an equilibrium magnetization that fluctuates from excitation to excitation, thus permitting simultaneous acquisition of several images with different contrast features. For example, lipid and water images can be rapidly acquired. The effective echo time can be adjusted using the flip angle, thus providing control over the T(2) contribution to the contrast. Several applications of the technique are presented, including fast musculoskeletal, abdominal, breast, and brain imaging, in addition to MR angiography. A technique for combining lipid and water images generated with this sequence for angiography is described and other potential applications are suggested. Magn Reson Med 42:876-883, 1999.

    View details for Web of Science ID 000083447900006

    View details for PubMedID 10542345

  • Prospective MR signal-based cardiac triggering MAGNETIC RESONANCE IN MEDICINE Vasanawala, S. S., Sachs, T. S., Brittain, J. H., Meyer, C. H., Nishimura, D. G. 1999; 42 (1): 82-86

    Abstract

    A cardiac motion compensation method using magnetic resonance signal-based triggering is presented. The method interlaces a triggering pulse sequence with an imaging sequence. The triggering sequence is designed to measure aortic blood velocity, from which cardiac phase can be inferred. The triggering sequence is executed repeatedly and the acquired data processed after each sequence iteration. When the desired phase of the cardiac cycle is detected, data are acquired using the imaging sequence. A signal-processing unit of a conventional scanner is used to process the triggering data in real time and issue triggering commands. Alternatively, a workstation, with a bus adaptor, can access data as they are acquired, process and display the data, and issue triggering commands. With a graphical user interface, the triggering pulse sequence and data-processing techniques can be modified instantaneously to optimize triggering. The technique is demonstrated with coronary artery imaging using both conventional two-dimensional Fourier transform scans and spiral trajectories.

    View details for Web of Science ID 000081433800012

    View details for PubMedID 10398953