Publications

Associate Professor of Radiology (Veterans Affairs)

Bio

Daniel Ennis (Ph.D.) is an Associate Professor in the Department of Radiology. As an MRI scientist for nearly twenty years, he has worked to develop advanced translational cardiovascular MRI methods for quantitatively assessing structure, function, flow, and remodeling in both adult and pediatric populations. He began his research career as a Ph.D. student in the Department of Biomedical Engineering at Johns Hopkins University during which time he formed an active collaboration with investigators in the Laboratory of Cardiac Energetics at the National Heart, Lung, and Blood Institute (NIH/NHLBI). Thereafter, he joined the Departments of Radiological Sciences and Cardiothoracic Surgery at Stanford University as a post doc and began to establish an independent research program with an NIH K99/R00 award focused on “Myocardial Structure, Function, and Remodeling in Mitral Regurgitation.” For ten years he led a group of clinicians and scientists at UCLA working to develop and evaluate advanced cardiovascular MRI exams as PI of several NIH funded studies. In 2018 he returned to Stanford Radiology and the Radiological Sciences Lab to bolster programs in cardiovascular MRI. He is also the Director of Radiology Research for the Veterans Administration Palo Alto Health Care System where he oversees a growing radiology research program.

Publications

  • A gradient optimization toolbox for general purpose time-optimal MRI gradient waveform design MAGNETIC RESONANCE IN MEDICINE Loecher, M., Middione, M. J., Ennis, D. B. 2020

    View details for DOI 10.1002/mrm.28384

    View details for Web of Science ID 000545612400001

  • INTRA-MYOCARDIAL ALGINATE HYDROGEL INJECTION ACTS AS A LEFT VENTRICULAR MID-WALL CONSTRAINT IN SWINE. Acta biomaterialia Sack, K. L., Aliotta, E., Choy, J. S., Ennis, D. B., Davies, N., Franz, T., Kassab, G. S., Guccione, J. M. 2020

    Abstract

    Despite positive initial outcomes emerging from preclinical and early clinical investigation of alginate hydrogel injection therapy as a treatment for heart failure, the lack of knowledge about the mechanism of action remains a major shortcoming that limits the efficacy of treatment design. To identify the mechanism of action, we examined previously unobtainable measurements of cardiac function from in vivo, ex vivo, and in silico states of clinically relevant heart failure (HF) in large animals. High-resolution ex vivo magnetic resonance imaging and histological data were used along with state-of-the-art subject-specific computational model simulations. Ex vivo data were incorporated in detailed geometric computational models for swine hearts in health (n=5), ischemic HF (n=5), and ischemic HF treated with alginate hydrogel injection therapy (n=5). Hydrogel injection therapy mitigated elongation of sarcomere lengths (1.66 ± 0.15mum [treated] vs. 1.79 ± 0.16mum [untreated], p<0.001). Systolic contractility in treated animals improved substantially (ejection fraction = 43.9 ± 2.6% [treated] vs. 34.7 ± 2.7% [untreated], p<0.01). The in silico models realistically simulated in vivo function with >99% accuracy and predicted small myofiber strain in the vicinity of the solidified hydrogel that was sustained for up to 13 mm away from the implant. These findings suggest that the solidified alginate hydrogel material acts as an LV mid-wall constraint that significantly reduces adverse LV remodeling compared to untreated HF controls without causing negative secondary outcomes to cardiac function. [229 words].

    View details for DOI 10.1016/j.actbio.2020.04.033

    View details for PubMedID 32428678

  • 4D Flow MR Imaging to Improve Microwave Ablation Prediction Models: A Feasibility Study in an InVivo Porcine Liver. Journal of vascular and interventional radiology : JVIR Chiang, J., Loecher, M., Moulin, K., Meloni, M. F., Raman, S. S., McWilliams, J. P., Ennis, D. B., Lee, E. W. 2020

    Abstract

    PURPOSE: To characterize the effect of hepatic vessel flow using 4-dimensional (4D) flow magnetic resonance (MR) imaging and correlate their effect on microwave ablation volumes in an invivo non-cirrhotic porcine liver model.MATERIALS AND METHODS: Microwave ablation antennas were placed under ultrasound guidance in each liver lobe of swine (n= 3 in each animal) for a total of 9 ablations. Pre- and post-ablation 4D flow MR imaging was acquired to quantify flow changes in the hepatic vasculature. Flow measurements, along with encompassed vessel size and vessel-antenna spacing, were then correlated with final ablation volume from segmented MR images.RESULTS: The linear regression model demonstrated that the preablation measurement of encompassed hepatic vein size (beta= -0.80 ±0.25, 95% confidence interval [CI] -1.15 to -0.22; P= .02) was significantly correlated to final ablation zone volume. The addition of hepatic vein flow rate found via 4D flow MRI (beta= -0.83 ± 0.65, 95% CI -2.50 to 0.84; P= .26), and distance from antenna to hepatic vein (beta= 0.26 ±0.26, 95% CI -0.40 to 0.92; P= .36) improved the model accuracy but not significantly so (multivariate adjusted R2= 0.70 vs univariate (vessel size) adjusted R2= 0.63, P= .24).CONCLUSIONS: Hepatic vein size in an encompassed ablation zone was found to be significantly correlated with final ablation zone volume. Although the univariate 4D flow MR imaging-acquired measurements alone were not found to be statistically significant, its addition to hepatic vein size improved the accuracy of the ablation volume regression model. Pre-ablation 4D flow MR imaging of the liver may assist in prospectively optimizing thermal ablation treatment.

    View details for DOI 10.1016/j.jvir.2019.11.034

    View details for PubMedID 32178944

  • Evaluation of a Workflow to Define Low Specific Absorption Rate MRI Protocols for Patients With Active Implantable Medical Devices. Journal of magnetic resonance imaging : JMRI Martinez, J. A., Moulin, K., Yoo, B., Shi, Y., Kim, H. J., Villablanca, P. J., Ennis, D. B. 2020

    Abstract

    MRI exams for patients with MR-conditional active implantable medical devices (AIMDs) are contraindicated unless specific conditions are met. This limits the maximum specific absorption rate (SAR, W/kg). Currently, there is no general framework to guide meeting a lower SAR limit.To design and evaluate a workflow for modifying MRI protocols to whole-body SAR (WB-SAR ≤0.1 W/kg) and local-head SAR (LH-SAR ≤0.3 W/kg) limits while mitigating the impact on image quality and exam time.Prospective.Twenty healthy volunteers on head (n = 5), C-spine (n = 5), T-spine (n = 5), and L-spine (n = 5) with IRB consent.Vendor-provided head, C-spine, T-spine, and L-spine protocols (SARRT ) were modified to meet both low SAR targets (SARLOW ) using the proposed workflow. in vitro SNR and CNR were evaluated with a T1 -T2 phantom. in vivo image quality and clinical acceptability were scored using a 5-point Likert scale for two blinded readers.1.5T/spin-echoes, gradient-echoes.In vitro SNR and CNR values were evaluated with a repeated measures general linear model. in vivo image quality and clinical acceptability were evaluated using a generalized estimating equation analysis (GEE). The two reader's level of agreement was analyzed using Cohen's kappa statistical analysis.Using the workflow, SAR limits were met.0.12 ± 0.02 W/kg, median (SD) values for LH-SAR were 0.12 (0.02) W/kg and WB-SAR: 0.09 (0.01) W/kg. Examination time did not increase ≤2x the initial time. SARRT SNR values were higher and significantly different than SARLOW (P < 0.05). However, no significant difference was observed between the CNR values (value = 0.21). Median (IQR) CNR values were 14.2 (25.0) vs. 15.1 (9.2) for head, 12.1 (16.9) vs. 25.3 (14.2) for C-spine, 81.6 (70.1) vs. 71.0 (26.6) for T-spine, and 51.4 (52.6) vs. 37.7 (27.3) for L-spine. Image quality scores were not significantly different between SARRT and SARLOW (median [SD] scores were 4.0 [0.01] vs. 4.3 [0.2], P > 0.05).The proposed workflow provides guidance for modifying routine MRI exams to achieve low SAR limits. This can benefit patients referred for an MRI exam with low SAR MR-conditional AIMDs.1 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2020.

    View details for DOI 10.1002/jmri.27044

    View details for PubMedID 31922311

  • Motion-Induced Signal Loss in In Vivo Cardiac Diffusion-Weighted Imaging JOURNAL OF MAGNETIC RESONANCE IMAGING Stoeck, C. T., Scott, A. D., Ferreira, P. F., Tunnicliffe, E. M., Teh, I., Nielles-Vallespin, S., Moulin, K., Sosnovik, D. E., Viallon, M., Croisille, P., Kozerke, S., Firmin, D. N., Ennis, D. B., Schneider, J. E. 2020; 51 (1): 319–20

    View details for DOI 10.1002/jmri.26767

    View details for Web of Science ID 000530627200031