Clinical Focus

  • Diagnostic Radiology
  • Interventional Radiology
  • Cardiovascular Diseases

Academic Appointments

Professional Education

  • Medical Education:UCSD School of Medicine (06/3/2007) CA
  • Fellowship:Stanford University Medical Center - Radiology (03/31/2014) CA
  • Fellowship:Stanford University Medical Center - Radiology (06/30/2013) CA
  • Residency:Stanford University - Dept of Radiology (06/30/2012) CA
  • Internship:Stanford University (06/30/2008) CA
  • Board Certification: Diagnostic Radiology, American Board of Radiology (2012)

Research & Scholarship

Current Research and Scholarly Interests

My current focus is the development and clinical translation of advanced computational techniques for cardiovascular MRI, particularly the development of 4D Flow MRI for clinical use. This technology and those like it have potential for revolutionizing the current practice of cardiovascular MRI.


Journal Articles

  • 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


    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 ? 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, ?=0.76; observer 2, ?=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

  • 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


    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 (? = 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 (? = 0.88; r(2) = 0.77). Four-dimensional phase contrast and 2D phase contrast flow rates were also well correlated (? = 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

  • 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


    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 (?: 0.87-0.90). Systemic and pulmonary arterial flow rates were well-correlated (?: 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 (?: 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

  • 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


    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 (? = 0.89), lower (? = 0.96), and whole body (? = 0.97); net aortic and pulmonary trunk flow rates were also tightly correlated (? = 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

  • Extracranial Venous Drainage Patterns in Patients with Multiple Sclerosis and Healthy Controls AMERICAN JOURNAL OF NEURORADIOLOGY McTaggart, R. A., Fischbein, N. J., Elkins, C. J., Hsiao, A., Cutalo, M. J., Rosenberg, J., Dake, M. D., Zaharchuk, G. 2012; 33 (8): 1615-1620


    CCSVI hypothesizes an association between impaired extracranial venous drainage and MS. Published sonographic criteria for CCSVI are controversial, and no MR imaging data exist to support the CCSVI hypothesis. Our purpose was to evaluate possible differences in the extracranial venous drainage of MS and healthy controls using both TOF and contrast-enhanced TRICKS MRV.Healthy subjects (n = 20) and patients with MS (n = 19) underwent axial 2D-TOF neck MRV (to assess flattening) and TRICKS MRV (to assess collaterals) at 3T. Two neuroradiologists blinded to cohort status scored IJV flattening and the severity of non-IJV collaterals by using a 4-point qualitative scale (normal = 0, mild = 1, moderate = 2, severe = 3). ? was used to assess reader agreement. Comparisons between groups were performed by using the Wilcoxon rank sum test. The Spearman rank correlation was used to assess the relationship between IJV flattening and collateral scores and, in patients with MS, EDSS scores.The 2 groups were matched for age and sex (MS, 45 ± 8 years, 79% female; healthy controls, 47 ± 10 years, 65% female). Reader agreement for IJV flattening and collateral severity was good (? = 0.74) and moderate (? = 0.58), respectively. While IJV flattening was seen in both patients with MS and healthy controls, scores for the patients with MS were significantly higher (P = .002). Despite a trend, there was no significant difference in collateral scores between groups (P = .063). There was a significant positive correlation between flattening and collateral scores (? = 0.32, P = .005) and EDSS and flattening scores (? = 0.45, P = .004) but not between EDSS and collateral scores (? = 0.01, P = .97).These results indicate that patients with MS have greater IJV flattening and a trend toward more non-IJV collaterals than healthy subjects. The role that this finding plays in the pathogenesis or progression of MS, if any, requires further study.

    View details for DOI 10.3174/ajnr.A3097

    View details for Web of Science ID 000309489800034

    View details for PubMedID 22517280

Stanford Medicine Resources: