James Carr

University of Texas Southwestern Medical Center, Dallas, Texas, United States

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Publications (218)874.73 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: There exists considerable controversy surrounding the timing and extent of aortic resection for patients with BAV disease. Since abnormal wall shear stress (WSS) is potentially associated with tissue remodeling in BAV-related aortopathy, we propose a methodology that creates patient-specific 'heat maps' of abnormal WSS, based on 4D flow MRI. The heat maps were created by detecting outlier measurements from a volumetric 3D map of ensemble-averaged WSS in healthy controls. 4D flow MRI was performed in 13 BAV patients, referred for aortic resection and 10 age-matched controls. Systolic WSS was calculated from this data, and an ensemble-average and standard deviation (SD) WSS map of the controls was created. Regions of the individual WSS maps of the BAV patients that showed a higher WSS than the mean + 1.96SD of the ensemble-average control WSS map were highlighted. Elevated WSS was found on the greater ascending aorta (35% ± 15 of the surface area), which correlated significantly with peak systolic velocity (R (2) = 0.5, p = 0.01) and showed good agreement with the resected aortic regions. This novel approach to characterize regional aortic WSS may allow clinicians to gain unique insights regarding the heterogeneous expression of aortopathy and may be leveraged to guide patient-specific resection strategies for aorta repair.
    Annals of biomedical engineering. 08/2014;
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    ABSTRACT: The left ventricular outflow tract (LVOT) peak pressure gradient is an important haemodynamic descriptor in patients with hypertrophic cardiomyopathy (HCM); however, secondary alterations in aortic blood flow have not been well described in these patients. Aortic flow derangement is not easily assessed by traditional imaging methods, but may provide unique characterization of this disease. In this study, we demonstrated how four-dimensional (4D) flow MRI can assess LVOT peak pressure gradients in HCM patients and also evaluated the ascending aorta (AAo) haemodynamic derangement associated with HCM.
    European Heart Journal – Cardiovascular Imaging 08/2014; · 2.39 Impact Factor
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    ABSTRACT: We sought to evaluate the feasibility of k-t parallel imaging for accelerated 4D flow MRI in the hepatic vascular system by investigating the impact of different acceleration factors.
    Magma (New York, N.Y.). 08/2014;
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    ABSTRACT: Associations of collateral vessels and lower extremity plaque with functional decline are unknown. Among people with peripheral artery disease (PAD), we determined whether greater superficial femoral artery (SFA) plaque burden combined with fewer lower extremity collateral vessels was associated with faster functional decline, compared to less plaque and/or more numerous collateral vessels. A total of 226 participants with ankle-brachial index (ABI) <1.00 underwent magnetic resonance imaging of lower extremity collateral vessels and cross-sectional imaging of the proximal SFA. Participants were categorized as follows: Group 1 (best), maximum plaque area < median and collateral vessel number ≥6 (median); Group 2, maximum plaque area < median and collateral vessel number <6; Group 3, maximum plaque area > median and collateral vessel number ≥6; Group 4 (worst), maximum plaque area > median and collateral vessel number <6. Functional measures were performed at baseline and annually for 2 years. Analyses adjust for age, sex, race, comorbidities, and other confounders. Annual changes in usual-paced walking velocity were: Group 1, +0.01 m/s; Group 2, -0.02 m/s; Group 3, -0.01 m/s; Group 4, -0.05 m/s (p-trend=0.008). Group 4 had greater decline than Group 1 (p<0.001), Group 2 (p=0.029), and Group 3 (p=0.010). Similar trends were observed for fastest-paced 4-meter walking velocity (p-trend=0.018). Results were not substantially changed when analyses were repeated with additional adjustment for ABI. However, there were no associations of SFA plaque burden and collateral vessel number with decline in 6-minute walk. In summary, a larger SFA plaque burden combined with fewer collateral vessels is associated with a faster decline in usual and fastest-paced walking velocity in PAD.
    Vascular medicine (London, England). 07/2014; 19(4):281-288.
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    ABSTRACT: Paradoxical embolization is frequently posited as a mechanism of ischemic stroke in patients with patent foramen ovale. Several studies have suggested that the deep lower extremity and pelvic veins might be an embolic source in cryptogenic stroke (CS) patients with patent foramen ovale.
    06/2014;
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    ABSTRACT: To test the hypothesis that biomechanical changes are quantitatively related to morphological features of coronary arteries in heart transplant (HTx) recipients.
    European journal of radiology. 05/2014;
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    ABSTRACT: The objective of this study was to evaluate the potential of 4D flow MRI to assess valve effective orifice area (EOA) in patients with aortic stenosis as determined by the jet shear layer detection (JSLD) method.
    Magnetic resonance imaging. 04/2014;
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    ABSTRACT: OBJECTIVE. The objective of our study was to assess the diagnostic performance of quiescent-interval single-shot (QISS) MR angiography (MRA) at 3 T for the evaluation of chronic lower limb ischemia. SUBJECTS AND METHODS. For this prospective study, 25 patients referred for lower extremity angiography for suspected or known chronic peripheral arterial disease were imaged on a 3-T system using QISS MRA. Contrast-enhanced MRA of the lower extremities was acquired at 3 T for each patient at the time of the initial visit and served as the noninvasive reference standard. Two blinded reviewers separately graded the degree of arterial stenosis. The sensitivity and specificity of QISS MRA for the determination of significant (≥ 50%) stenosis were calculated against contrast-enhanced MRA. Subsequent selective digital subtraction angiography (DSA) was performed and reviewed in nine patients. RESULTS. QISS MRA exhibited diagnostic performance nearly equivalent to that of contrast-enhanced MRA and also showed strong correlation with findings on DSA. Segment-based analysis revealed that, for the two reviewers, QISS MRA had sensitivities of 95.9% (142 of 148 segments) and 93.5% (145 of 155 segments) and specificities of 98.5% (595 of 604 segments) and 97.0% (578 of 596 segments) on comparison with contrast-enhanced MRA. CONCLUSION. QISS MRA maintains high diagnostic performance at 3 T despite the challenges inherent to image acquisition at higher field strengths.
    American Journal of Roentgenology 04/2014; 202(4):886-93. · 2.90 Impact Factor
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    ABSTRACT: PurposeTo compute cohort-averaged wall shear stress (WSS) maps in the thoracic aorta of patients with aortic dilatation or valvular stenosis and to detect abnormal regional WSS.Methods Systolic WSS vectors, estimated from four-dimensional flow MRI data, were calculated along the thoracic aorta lumen in 10 controls, 10 patients with dilated aortas, and 10 patients with aortic valve stenosis. Three-dimensional segmentations of each aorta were coregistered by group and used to create a cohort-specific aortic geometry. The WSS vectors of each subject were interpolated onto the corresponding cohort-specific geometry to create cohort-averaged WSS maps. A Wilcoxon rank sum test was used to generate aortic P-value maps (P<0.05) representing regional relative WSS differences between groups.ResultsCohort-averaged systolic WSS maps and P-value maps were successfully created for all cohorts and comparisons. The dilation cohort showed significantly lower WSS on 7% of the ascending aorta surface, whereas the stenosis cohort showed significantly higher WSS on 34% of the ascending aorta surface.Conclusions The findings of this study demonstrated the feasibility of generating cohort-averaged WSS maps for the visualization and identification of regionally altered WSS in the presence of disease, compared with healthy controls. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 04/2014; · 3.27 Impact Factor
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    ABSTRACT: The objective of this study was to assess the evolution of T1 contrast (T1c) between cardiovascular tissues, contrast agents, and magnetic field strengths. This Health Insurance Portability and Accountability Act-compliant study was approved by the institutional review board, and written informed consent was obtained from all participants. Eight healthy volunteers were recruited to undergo 4 consecutive magnetic resonance (MR) scans with the same imaging parameters. Scans 1 and 2 were performed using a 3-T MR scanner, and scans 3 and 4 were performed using a 1.5-T MR scanner. Gadofosveset trisodium (0.03 mmol/kg) was injected for scans 1 and 3, and gadopentetate dimeglumine (Gd-DTPA) (0.1 mmol/kg) was used for scans 2 and 4. Modified Look-Locker inversion recovery T1 maps with a midventricular short-axis view were acquired before contrast and repeated every 5 minutes until 45 minutes after contrast agent administration. T1 contrast tissue (T1myocardium - T1blood), T1c agent (T1Gd-DTPA - T1Gadofosveset), and T1c field (T13T - T11.5T) were calculated and compared using t tests. The T1c tissue of the 3-T scanner was larger than that of the 1.5-T scanner for both contrast agents. In both the myocardium and the blood pool, the T1c agent of the 1.5-T scanner was larger than that of the 3-T scanner. Gadofosveset trisodium exhibited a larger T1c field and T1c tissue than did Gd-DTPA. The T1c tissue induced by Gd-DTPA diminished faster than that induced by gadofosveset trisodium at both 1.5 and 3 T. Our study demonstrates the independent effects of timing, contrast agent type, and magnetic field strength on postcontrast T1c under general physiological conditions. The behaviors of T1c can be used to tailor quantitative MR imaging protocols for various clinical purposes.
    Investigative radiology 01/2014; · 4.85 Impact Factor
  • SCMR; 01/2014
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    ABSTRACT: Aortic 3D blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy. 4D flow MRI measured in vivo 3D blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=15 RL-BAV, mid AAo diameter=39.9±4.4mm; n=15 RN-BAV, 39.6±7.2mm); aorta size controls with tricuspid aortic valves (n=30, 41.1±4.4mm); healthy volunteers (n=15, 24.9±3.0mm). Aortopathy type (0-3), systolic flow angle, flow displacement, and regional wall shear stress (WSS) were determined for all subjects. Eccentric outflow jet patterns in BAV patients resulted in elevated regional WSS (p<0.0125) at the right-anterior walls for RL-BAV and right-posterior walls for RN-BAV compared to aorta size controls. Dilatation of the aortic root only (type 1) or involving the entire AAo and arch (type 3) was found in the majority of RN-BAV patients (87%) but was mostly absent for RL-BAV (87% type 2). Differences in aortopathy type between RL-BAV and RN-BAV were associated with altered flow displacement in the proximal and mid AAo for type 1 (42-81% decrease versus type 2) and distal AAo for type 3 (33-39% increase versus type 2). The presence and type of BAV fusion was associated with changes in regional WSS distribution, systolic flow eccentricity, and expression of BAV aortopathy. Hemodynamic markers suggest a physiologic mechanism by which valve morphology phenotype can influence phenotypes of BAV aortopathy.
    Circulation 12/2013; · 15.20 Impact Factor
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    ABSTRACT: Thoracic aortic aneurysm is one of the most common aorta pathologies worldwide, which is commonly evaluated by computed tomography angiography (CTA). One of the routine methods to improve the image quality of CTA is heart rate reduction prior to study by beta-blockade administration. To assess the effect of beta-blockade on image quality of the ascending aorta in electrocardiography (ECG)-gated dual-source CTA (DSCTA) images. In this retrospective study, ECG-gated thoracic aorta CTA images of 40 patients without beta-blocker administration were compared with ECG-gated images of 40 patients with beta-blockade. Images of the aorta were analyzed objectively and subjectively at three levels: sinus of Valsalva (sinus), sinotubular junction (STJ), and mid ascending aorta (MAA). Quantitative sharpness index (SI) and signal-to-noise ratio (SNR) were calculated and two radiologists evaluated the image quality using a 3-point scale. Mean heart rate in beta-blocker and non-beta-blocker groups was 61.7 beats per minute (bpm) (range, 58.1-63.9 bpm) and 72.9 bpm (range, 69.3-84.1 bpm), respectively (P <0.05). Aorta wall SI, SNR, and subjective grading were comparable between the two groups at all three levels (P >0.05). Beta-blocker premedication may not be necessary for imaging of ascending aorta with ECG-gated DSCTA.
    Acta Radiologica 12/2013; · 1.33 Impact Factor
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    ABSTRACT: To investigate the influence of atherosclerotic plaques on femoral haemodynamics assessed by two-dimensional (2D) phase-contrast (PC) magnetic resonance imaging (MRI) with three-directional velocity encoding. During 1 year, patients with peripheral artery disease and an ankle brachial index <1.00 were enrolled. After institutional review board approval and written informed consent, 44 patients (age, 70 ± 12 years) underwent common femoral artery MRI. Patients with contra-indications for MRI were excluded. Sequences included 2D time-of-flight, proton-density, T1-weighted and T2-weighted MRI. Electrocardiogram (ECG)-gated 2D PC-MRI with 3D velocity encoding was acquired. A radiologist classified images in five categories. Blood flow, velocity and wall shear stress (WSS) along the vessel circumference were quantified from the PC-MRI data. The acquired images were of good quality for interpretation. There were no image quality problems related to poor ECG-gating or slice positioning. Velocities, oscillatory shear stress and total flow were similar between patients with normal arteries and wall thickening/plaque. Patients with plaques demonstrated regionally increased peak systolic WSS and enhanced WSS eccentricity. Combined multi-contrast morphological imaging of the peripheral arterial wall with PC-MRI with three-directional velocity encoding is a feasible technique. Further study is needed to determine whether flow is an appropriate marker for altered endothelial cell function, vascular remodelling and plaque progression. • Femoral plaques are associated with altered dynamics of peripheral blood flow. • Multi-contrast MRI can investigate the presence and type of atherosclerotic plaques. • Three-dimensional velocity-encoding phase-contrast MRI can investigate flow and wall shear stress. • Atherosclerotic peripheral arteries demonstrate increased systolic velocities and wall shear stress.
    European Radiology 12/2013; · 4.34 Impact Factor
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    ABSTRACT: To provide a more complete characterization of aortic blood flow in patients following valve-sparing aortic root replacement (VSARR) compared with presurgical cohorts matched by tricuspid and bicuspid valve morphology, age and presurgical aorta size. Four-dimensional (4D) flow magnetic resonance imaging (MRI) was performed to analyse three-dimensional (3D) blood flow in the thoracic aorta of n = 13 patients after VSARR with reimplantation of native tricuspid aortic valve (TAV, n = 6) and bicuspid aortic valve (BAV, n = 7). Results were compared with presurgical age and aortic size-matched control cohorts with TAV (n = 10) and BAV (n = 10). Pre- and post-surgical aortic flow was evaluated using time-resolved 3D pathlines using a blinded grading system (0-2, 0 = small, 1 = moderate and 2 = prominent) analysing ascending aortic (AAo) helical flow. Systolic flow profile uniformity in the aortic root, proximal and mid-AAo was evaluated using a four-quadrant model. Further analysis in nine analysis planes distributed along the thoracic aorta quantified peak systolic velocity, retrograde fraction and peak systolic flow acceleration. Pronounced AAo helical flow in presurgical control subjects (both BAV and TAV: helix grading = 1.8 ± 0.4) was significantly reduced (0.2 ± 0.4, P < 0.001) in cohorts after VSARR independent of aortic valve morphology. Presurgical AAo flow was highly eccentric for BAV patients but more uniform for TAV. VSARR resulted in less eccentric flow profiles. Systolic peak velocities were significantly (P < 0.05) increased in post-root repair BAV patients throughout the aorta (six of nine analysis planes) and to a lesser extent in TAV patients (three of nine analysis planes). BAV reimplantation resulted in significantly increased peak velocities in the proximal AAo compared with root repair with TAV (2.3 ± 0.6 vs 1.6 ± 0.4 m/s, P = 0.017). Post-surgical patients showed a non-significant trend towards higher systolic flow acceleration as a surrogate measure of reduced aortic compliance. VSARR restored a cohesive flow pattern independent of native valve morphology but resulted in increased peak velocities throughout the aorta. 4D flow MRI methods can assess the clinical implications of altered aortic flow dynamics in patients undergoing VSARR.
    European journal of cardio-thoracic surgery: official journal of the European Association for Cardio-thoracic Surgery 12/2013; · 2.40 Impact Factor
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    ABSTRACT: To assess the impact of aortic valve morphology on aortic hemodynamics between normal tricuspid and congenitally anomalous aortic valves ranging from unicuspid to quadricuspid morphology. Aortic three-dimensional (3D) blood flow was evaluated by 4D flow MRI in 14 healthy volunteers with normal trileaflet valves and 14 patients with unicuspid (n = 3), bicuspid (n = 9, 3 "true" bicuspid, 3 right-left (RL), 3 right-noncoronary (RN) leaflet fusion, and quadricuspid aortic valves (n = 2). Data analysis included the co-registered visualization of aortic valve morphology with systolic 3D blood flow. The influence of valve morphology on aortic hemodynamics was quantified by valve flow angle. All RL-bicuspid aortic valve (BAV) were associated with flow jets directed toward the right anterior aortic wall while RN-fusion and unicuspid valves resulted in flow jet patterns toward the right-posterior or posterior wall. Flow angles were clearly influenced by valve morphology (47° ± 10, 28° ± 2, 29° ± 18, 18° ± 12, 15° ± 2 for unicuspid, true BAV, RN-BAV, RL-BAV, quadricuspid valves) and increased compared with controls (7.2° ± 1.1, P = 0.001). Altered 3D aortic hemodynamics are impacted by the morphology of congenitally malformed aortic valves.J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.
    Journal of Magnetic Resonance Imaging 11/2013; · 2.57 Impact Factor
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    ABSTRACT: The aim of the present study was to assess the incremental benefit of compensating asynchronous cardiac quiescence in coronary wall MR imaging. With the approval of IRB, black-blood coronary wall MR imaging was performed on 30 older subjects (90 coronary wall segments). For round 1 coronary wall MR imaging, acquisition windows were traditionally set within rest period4-chamber. Totally 51 of 90 images were ranked as "good" images and resulted in an interpretability rate of 57 %. Then, an additional cine-MR was centered at coronary segments to obtain rest periodcross-sectional. The rest periodoverlap (the intersection between rest period4-chamber and rest periodcross-sectional) was measured for each coronary segment. The "good" images had a longer rest periodoverlap and higher acquisition coincidence rate (the percentage of acquisition window covered by the rest periodoverlap) than "poor" images. Coronary wall rescans (round 2) were completed at 39 coronary segments that were judged as having "poor" images in round 1 scans. The acquisition window was set within the rest periodoverlap. For the round 2 images, 17 of 39 (44 %) coronary segments were ranked as "good" images. The overall interpretability rate (68 of 90, 76 %) was significantly higher than that of the round 1 images alone. Our data demonstrated that asynchronous cardiac quiescence adversely affects the performance of coronary wall MR imaging. Individualizing acquisition windows based on multi-plane cine-MR helps to compensate for this motion discrepancy and to improve image quality.
    The international journal of cardiovascular imaging 10/2013; · 2.15 Impact Factor
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    ABSTRACT: To use four-dimensional (4D)-flow MRI for the comprehensive in vivo analysis of hemodynamics and its relationship to size and morphology of different intracranial aneurysms (IA). We hypothesize that different IA groups, defined by size and morphology, exhibit different velocity fields, wall shear stress, and vorticity. The 4D-flow MRI (spatial resolution = 0.99-1.8 × 0.78-1.46 × 1.2-1.4 mm(3) , temporal resolution = 44-48 ms) was performed in 19 IAs (18 patients, age = 55.4 ± 13.8 years) with saccular (n = 16) and fusiform (n = 3) morphology and different sizes ranging from small (n = 8; largest dimension = 6.2 ± 0.4 mm) to large and giant (n = 11; 25 ± 7 mm). Analysis included quantification of volumetric spatial-temporal velocity distribution, vorticity, and wall shear stress (WSS) along the aneurysm's 3D surface. The 4D-flow MRI revealed distinct hemodynamic patterns for large/giant saccular aneurysms (Group 1), small saccular aneurysms (Group 2), and large/giant fusiform aneurysms (Group 3). Saccular IA (Groups 1, 2) demonstrated significantly higher peak velocities (P < 0.002) and WSS (P < 0.001) compared with fusiform aneurysms. Although intra-aneurysmal 3D velocity distributions were similar for Group 1 and 2, vorticity and WSS was significantly (P < 0.001) different (increased in Group 1 by 54%) indicating a relationship between IA size and hemodynamics. Group 3 showed reduced velocities (P < 0.001) and WSS (P < 0.001). The 4D-flow MRI demonstrated the influence of lesion size and morphology on aneurysm hemodynamics suggesting the potential of 4D-flow MRI to assist in the classification of individual aneurysms. J. Magn. Reson. Imaging 2013;. © 2013 Wiley Periodicals, Inc.
    Journal of Magnetic Resonance Imaging 10/2013; · 2.57 Impact Factor
  • Circulation 10/2013; 128(17):e341-3. · 15.20 Impact Factor
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    ABSTRACT: Type 2 diabetes mellitus (T2DM) is a prevalent condition in aged populations. Cardiovascular diseases are leading causes of death and disability in patients with T2DM. Traditional strategies for controlling the cardiovascular complications of diabetes primarily target a cluster of well-defined risk factors, such as hyperglycemia, lipid disorders and hypertension. However, there is controversy over some recent clinical trials aimed at evaluating efficacy of intensive treatments for T2DM. As a powerful tool for quantitative cardiovascular risk estimation, multi-disciplinary cardiovascular imaging have been applied to detect and quantify morphological and functional abnormalities in the cardiovascular system. Quantitative imaging biomarkers acquired with advanced imaging procedures are expected to provide new insights to stratify absolute cardiovascular risks and reduce the overall costs of health care for people with T2DM by facilitating the selection of optimal therapies. This review discusses principles of state-of-the-art cardiovascular imaging techniques and compares applications of those techniques in various clinical circumstances. Individuals measurements of cardiovascular disease burdens from multiple aspects, which are closely related to existing biomarkers and clinical outcomes, are recommended as promising candidates for quantitative imaging biomarkers to assess the responses of the cardiovascular system during diabetic regimens.
    Journal of diabetes and its complications 10/2013; · 2.11 Impact Factor

Publication Stats

2k Citations
874.73 Total Impact Points

Institutions

  • 2014
    • University of Texas Southwestern Medical Center
      Dallas, Texas, United States
  • 2001–2014
    • Northwestern University
      • Department of Radiology
      Evanston, Illinois, United States
    • Washington University in St. Louis
      San Luis, Missouri, United States
  • 2013
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 2002–2013
    • Northwestern Memorial Hospital
      • Department of Radiology
      Chicago, Illinois, United States
    • University of Tuebingen
      • Department of Internal Medicine
      Tübingen, Baden-Wuerttemberg, Germany
  • 2001–2013
    • University of Illinois at Chicago
      Chicago, Illinois, United States
  • 2011
    • Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center
      Torrance, California, United States
    • Cedars-Sinai Medical Center
      • Cedars Sinai Medical Center
      Los Angeles, California, United States
  • 2008
    • University of Chicago
      Chicago, Illinois, United States