Bio

Bio

I split my time between the medical device industry and academic research. For my day job, I run the Global Science & Technology - Medical Division, focusing on medical device consulting and services for healthcare agencies. At Stanford, my research is focused on the interaction between vascular implants and the dynamic anatomy. I advise companies on device design, biomechanics, mechanical testing, preclinical and cadaver testing, regulatory strategy, and entrepreneurship.

Academic Appointments

Professional Education

  • PhD, Stanford University, Biomechanical Engineering (2002)
  • MS, Stanford University, Biomechanical Engineering (2000)
  • BSE, Duke University, Biomedical Engineering (1998)
  • BSE, Duke University, Electrical Engineering (1998)

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Research & Scholarship

Current Research and Scholarly Interests

Our research laboratory focuses on understanding the mechanics of the cardiovascular system, especially with respect to interactions between medical devices and the dynamic cardiovascular environment. We use medical imaging, 3D geometric modeling, and custom deformation quantification techniques to investigate disease processes and medical device performance. We are interested in the dynamics of the heart, aorta, and peripheral vasculature, and are always seeking ways to apply our research to current and emerging therapies. While our research pursuits seek to add to the fundamental understanding of cardiovascular biomechanics, all of our projects are directly related to improving medical device design, evaluation, regulation, and their use in clinical practice.

Teaching

2018-19 Courses

Graduate and Fellowship Programs

Publications

All Publications

  • Cardiopulmonary-induced deformations of the thoracic aorta following thoracic endovascular aortic repair. Vascular Suh, G., Ullery, B. W., Lee, J. T., Dake, M. D., Fleischmann, D., Cheng, C. 2018: 1708538118811204

    Abstract

    OBJECTIVES: Thoracic endovascular aortic repair has become a preferred treatment strategy for thoracic aortic aneurysms and dissections. Yet, it is not well understood if the performance of endografts is affected by physiologic strain due to cyclic aortic motion during cardiac pulsation and respiration. We aim to quantify cardiac- and respiratory-induced changes of the postthoracic endovascular aortic repair thoracic aorta and endograft geometries.METHODS: Fifteen thoracic endovascular aortic repair patients (66±10 years) underwent cardiac-resolved computed tomography angiographies during inspiratory/expiratory breath holds. The computed tomography angiography images were utilized to build models of the aorta, and lumen centerlines and cross-sections were extracted. Arclength and curvature were computed from the lumen centerline. Effective diameter was computed from cross-sections of the thoracic aorta. Deformation was computed from the mid-diastole to end-systole (cardiac deformation) and expiration to inspiration (respiratory deformation).RESULTS: Cardiac pulsation induced significant changes in arclength, mean curvature, maximum curvature change, and effective diameter of the ascending aorta, as well as effective diameter of the stented aortic segment. Respiration, however, induced significant change in mean curvature and effective diameter of the ascending aorta only. Cardiac-induced arclength change of the ascending aorta was significantly greater than respiratory-induced arclength change.CONCLUSIONS: Deformations are present across the thoracic aorta due to cardiopulmonary influences after thoracic endovascular aortic repair. The geometric deformations are greatest in the ascending aorta and decline at the stented thoracic aorta. Additional investigation is warranted to correlate aortic deformation to endograft performance.

    View details for DOI 10.1177/1708538118811204

    View details for PubMedID 30426849

  • Stabilization of the Abdominal Aorta During the Cardiac Cycle with the Sac-Anchoring Nellix Device. Annals of vascular surgery Itoga, N. K., Suh, G., Cheng, C. P. 2018

    Abstract

    The Nellix device utilizes polymer filled endobags to stabilize the abdominal aortic aneurysm (AAA) sac described as endovascular aneurysm sealing (EVAS). We analyzed cardiac gated CTA scans of repaired AAA with EVAS in four patients to evaluate geometry and cardiac pulsatility-induced deformation. Graft translation and aortic curvature changes were found to be minimal during the cardiac cycle. The mean±SD changes in renal-aorta angles (1.0±0.9°) were less than the changes in the SMA-aorta angle (4.0±2.1°) (P<0.01), during the cardiac cycle, demonstrating greater stabilization of the visceral branches closer to the device. These findings confirm stabilization of the abdominal aorta during the cardiac cycle using EVAS.

    View details for DOI 10.1016/j.avsg.2018.02.039

    View details for PubMedID 29775657

  • Geometric Deformations of the Thoracic Aorta and Supra-Aortic Arch Branch Vessels Following Thoracic Endovascular Aortic Repair VASCULAR AND ENDOVASCULAR SURGERY Ullery, B. W., Suh, G., Hirotsu, K., Zhu, D., Lee, J. T., Dake, M. D., Fleischmann, D., Cheng, C. P. 2018; 52 (3): 173?80

    Abstract

    To utilize 3-D modeling techniques to better characterize geometric deformations of the supra-aortic arch branch vessels and descending thoracic aorta after thoracic endovascular aortic repair.Eighteen patients underwent endovascular repair of either type B aortic dissection (n = 10) or thoracic aortic aneurysm (n = 8). Computed tomography angiography was obtained pre- and postprocedure, and 3-D geometric models of the aorta and supra-aortic branch vessels were constructed. Branch angle of the supra-aortic branch vessels and curvature metrics of the ascending aorta, aortic arch, and stented thoracic aortic lumen were calculated both at pre- and postintervention.The left common carotid artery branch angle was lower than the left subclavian artery angles preintervention ( P < .005) and lower than both the left subclavian and brachiocephalic branch angles postintervention ( P < .05). From pre- to postoperative, no significant change in branch angle was found in any of the great vessels. Maximum curvature change of the stented lumen from pre- to postprocedure was greater than those of the ascending aorta and aortic arch ( P < .05).Thoracic endovascular aortic repair results in relative straightening of the stented aortic region and also accentuates the native curvature of the ascending aorta when the endograft has a more proximal landing zone. Supra-aortic branch vessel angulation remains relatively static when proximal landing zones are distal to the left common carotid artery.

    View details for DOI 10.1177/1538574417753452

    View details for Web of Science ID 000429975600002

    View details for PubMedID 29400263

  • A Lagrangian cylindrical coordinate system for characterizing dynamic surface geometry of tubular anatomic structures. Medical & biological engineering & computing Lundh, T., Suh, G., DiGiacomo, P., Cheng, C. 2018

    Abstract

    Vascular morphology characterization is useful for disease diagnosis, risk stratification, treatment planning, and prediction of treatment durability. To quantify the dynamic surface geometry of tubular-shaped anatomic structures, we propose a simple, rigorous Lagrangian cylindrical coordinate system to monitor well-defined surface points. Specifically, the proposed system enables quantification of surface curvature and cross-sectional eccentricity. Using idealized software phantom examples, we validate the method's ability to accurately quantify longitudinal and circumferential surface curvature, as well as eccentricity and orientation of eccentricity. We then apply the method to several medical imaging data sets of human vascular structures to exemplify the utility of this coordinate system for analyzing morphology and dynamic geometric changes in blood vessels throughout the body. Graphical abstract Pointwise longitudinal curvature of a thoracic aortic endograft surface for systole and diastole, with their absolute difference.

    View details for DOI 10.1007/s11517-018-1801-8

    View details for PubMedID 29500737

  • Optimization of three-dimensional modeling for geometric precision and efficiency for healthy and diseased aortas COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING Cheng, C. P., Zhu, Y. D., Suh, G. 2018; 21 (1): 65?74

    Abstract

    The study purpose is to optimize modeling parameters, specifically segmentation spacing and centerline extraction, to efficiently construct accurate 3D aortic models. Models are constructed by centerline extraction and orthogonal 2D segmentations. We examine the effect of segmentation interval spacing (2, 1, 0.5, 0.25 cm) and orthogonal segmentation and centerline extraction iteration (one, two, three iterations) for constructing models of Healthy, Tortuous, Aneurysmal, and Dissected human thoracic aortas. Aortic arclength, curvature, and cross-sectional axis ratio were computed to compare variations in modeling parameters. Centerline arclength is precisely characterized for all aortas with a single iteration of centerline extraction (?1% deviation), however, complex anatomies required 1 cm segmentation intervals whereas the Healthy aorta only required 2 cm intervals. Centerline curvature is more sensitive to modeling methods, requiring 1 cm intervals for ?5% deviation in peak curvature for the three diseased anatomies, and two iterations of segmentation and centerline extraction for the Aneurysmal and Dissected aortas. Accurate lumen cross-sectional characterization required 1 or 0.5 cm segmentation intervals, and two or three segmentation and centerline iterations, with greater refinement needed for more complex geometries. Depending on the geometric characteristic and complexity of anatomy and pathology, different levels of segmentation interval refinement and iterations of segmentation and centerline extraction are required.

    View details for DOI 10.1080/10255842.2017.1423291

    View details for Web of Science ID 000423504400007

    View details for PubMedID 29313372

  • Changes in Geometry and Cardiac Deformation of the Thoracic Aorta after Thoracic Endovascular Aortic Repair. Annals of vascular surgery Hirotsu, K., Suh, G., Lee, J. T., Dake, M. D., Fleischmann, D., Cheng, C. P. 2017

    Abstract

    BACKGROUND: Thoracic endovascular aortic repair (TEVAR) has dramatically expanded treatment options for patients with thoracic aortic pathology. The interaction between endografts and the dynamic anatomy of the thoracic aorta is not well characterized for repetitive physiologic stressors and subsequent issues related to long-term durability. Through three-dimensional (3D) modeling we sought to quantify cardiac-induced aortic deformation before and after TEVAR to assess the impact of endografts on dynamic aortic anatomy.METHODS: Eight patients with acute (n=4) or chronic (n=3) type B dissections, or chronic arch aneurysm (n=1), underwent TEVAR with a single (n=5) or multiple (n=3) Gore C-TAG(s). Cardiac-resolved thoracic CT images were acquired pre- and post-TEVAR. 3D models of thoracic aorta and branch vessels were constructed in systole and diastole. Axial length, mean, and peak curvature of the ascending aorta, arch, and stented lumens were computed from the aortic lumen centerline, delineated with branch vessel landmarks. Cardiac-induced deformation was computed from mid-diastole to end-systole.RESULTS: Pre-TEVAR, there were no significant cardiac-induced changes for aortic axial length or mean curvature. Post-TEVAR, the ascending aorta increased in axial length (2.7±3.1%, P<0.05) and decreased in mean curvature (0.38±0.05 0.36±0.05cm-1, P<0.05) from diastole to systole. From pre- to post-TEVAR, axial length change increased in the ascending aorta (P<0.02), mean curvature decreased in the arch and stented aorta (P<0.03), and peak curvature decreased in the stented aorta (P<0.05).CONCLUSIONS: TEVAR for a range of indications not only causes direct geometric changes to the stented aorta but also results in dynamic changes to the ascending and stented aorta. In our cohort, endograft placement straightens the stented aorta and mutes cardiac-induced bending due to longitudinal stiffness. This is compensated by greater length and curvature changes from diastole to systole in the ascending aorta, relative to pre-TEVAR.

    View details for DOI 10.1016/j.avsg.2017.07.033

    View details for PubMedID 28887263

  • Quantification of motion of the thoracic aorta after ascending aortic repair of type-A dissection INTERNATIONAL JOURNAL OF COMPUTER ASSISTED RADIOLOGY AND SURGERY Suh, G., Fleischmann, D., Beygui, R. E., Cheng, C. P. 2017; 12 (5): 811-819

    View details for DOI 10.1007/s11548-016-1499-8

    View details for Web of Science ID 000400863100012

  • Dynamic Geometric Analysis of the Renal Arteries and Aorta following Complex Endovascular Aneurysm Repair. Annals of vascular surgery Ullery, B. W., Suh, G., Kim, J. J., Lee, J. T., Dalman, R. L., Cheng, C. P. 2017

    Abstract

    Aneurysm regression and target vessel patency during early and mid-term follow-up may be related to the effect of stent-graft configuration on the anatomy. We quantified geometry and remodeling of the renal arteries and aneurysm following fenestrated (F-) or snorkel/chimney (Sn-) endovascular aneurysm repair (EVAR).Twenty-nine patients (mean age, 76.8 ± 7.8 years) treated with F- or Sn-EVAR underwent computed tomography angiography at preop, postop, and follow-up. Three-dimensional geometric models of the aorta and renal arteries were constructed. Renal branch angle was defined relative to the plane orthogonal to the aorta. End-stent angle was defined as the angulation between the stent and native distal artery. Aortic volumes were computed for the whole aorta, lumen, and their difference (excluded lumen). Renal patency, reintervention, early mortality, postoperative renal impairment, and endoleak were reviewed.From preop to postop, F-renal branches angled upward, Sn-renal branches angled downward (P < 0.05), and Sn-renals exhibited increased end-stent angulation (12 ± 15°, P < 0.05). From postop to follow-up, branch angles did not change for either F- or Sn-renals, whereas F-renals exhibited increased end-stent angulation (5 ± 10°, P < 0.05). From preop to postop, whole aortic and excluded lumen volumes increased by 5 ± 14% and 74 ± 81%, whereas lumen volume decreased (39 ± 27%, P < 0.05). From postop to follow-up, whole aortic and excluded lumen volumes decreased similarly (P < 0.05), leaving the lumen volume unchanged. At median follow-up of 764 days (range, 7-1,653), primary renal stent patency was 94.1% and renal impairment occurred in 2 patients (6.7%).Although F- and Sn-EVAR resulted in significant, and opposite, changes to renal branch angle, only Sn-EVAR resulted in significant end-stent angulation increase. Longitudinal geometric analysis suggests that these anatomic alterations are primarily generated early as a consequence of the procedure itself and, although persistent, they show no evidence of continued significant change during the subsequent postoperative follow-up period.

    View details for DOI 10.1016/j.avsg.2016.12.005

    View details for PubMedID 28390918

  • Quantification of motion of the thoracic aorta after ascending aortic repair of type-A dissection. International journal of computer assisted radiology and surgery Suh, G., Fleischmann, D., Beygui, R. E., Cheng, C. P. 2016: -?

    Abstract

    To quantify cardiac and respiratory deformations of the thoracic aorta after ascending aortic graft repair.Eight patients were scanned with cardiac-resolved computed tomography angiography during inspiratory/expiratory breath-holds. Aortic centerlines and lumen were extracted to compute the arclength, curvature, angulation, and cross-section shape.From systole to diastole, the angle of graft [Formula: see text] arch increased by 2.4[Formula: see text] ± 1.8[Formula: see text] (P < 0.01) and the angle of arch [Formula: see text] descending aorta decreased by 2.4[Formula: see text] ± 2.6[Formula: see text] (P < 0.05), while the effective diameter of the proximal arch decreased by 2.4 ± 1.9% (P < 0.01), a greater change than those of the graft or distal arch (P < 0.05). From inspiration to expiration, the angle of graft [Formula: see text] arch increased by 2.8[Formula: see text] ± 2.6[Formula: see text] (P < 0.02) with the peak curvature increase (P < 0.05). Shorter graft length was correlated with greater cardiac-induced graft [Formula: see text] arch angulation, and longer graft length was correlated with greater respiratory-induced arch [Formula: see text] descending aorta angulation (R [Formula: see text] 0.50).The thoracic aorta changed curvature and angulation with cardiac and respiratory influences, driven by aortic root and arch motion. The thoracic aortic geometry and deformation are correlated with the ascending aortic graft length.

    View details for PubMedID 27882488

  • Three-Dimensional Modeling Analysis of Visceral Arteries and Kidneys during Respiration. Annals of vascular surgery Suh, G., Choi, G., Herfkens, R. J., Dalman, R. L., Cheng, C. P. 2016; 34: 250-260

    Abstract

    Visceral arteries are commonly involved in endovascular repair of complex abdominal aortic aneurysms (AAAs). To improve repair techniques and reduce long-term complications involving visceral arteries, it is crucial to understand in vivo arterial geometry and the deformations due to visceral organ movement with respiration. This study quantifies deformation of the celiac, superior mesenteric (SMA), and renal arteries during respiration and correlates the deformations with diaphragmatic excursion.Sixteen patients with small AAAs underwent magnetic resonance angiography during inspiratory and expiratory breathholds. From geometric models of the aorta and visceral arteries, vessel length, branch angle, curvature, and positions were computed, along with degree of diaphragmatic excursion as indicated by kidney translation.From inspiration to expiration, the celiac artery exhibited axial shortening of 4.8 ± 6.4% (P < 0.001) and a mean curvature increase of 0.03 ± 0.02 mm(-1), greater than other visceral arteries (P < 0.01). With expiration, the SMA, left and right renal arteries (LRA and RRA) angled upward by -9.8 ± 6.4°, -6.4 ± 6.4°, and -5.2 ± 5.0°, respectively (P < 0.005). All vessels translated superiorly (P < 0.0005) and posteriorly (P < 0.01), and the SMA translated rightward additionally (P < 0.005). The left and right kidneys translated by 22 ± 9 mm and 21 ± 9 mm, mostly superiorly (P < 0.001). Translations of all visceral arteries were moderately correlated to the right kidney (R > 0.50). Correlation of the LRA with the left kidney was greater than that of the RRA with the right kidney.The celiac artery exhibited less branch angle change, and greater axial and curvature deformations than the other visceral arteries, due to the vicinity to the liver and influence of the median arcuate ligament. Correlation between visceral arteries and kidney translations revealed that diaphragmatic excursion affects vessel mobility. Weaker correlation of the RRA to the right kidney indicates mechanical shielding from the inferior vena cava.

    View details for DOI 10.1016/j.avsg.2016.04.004

    View details for PubMedID 27116907

    View details for PubMedCentralID PMC4930742

  • Comparative geometric analysis of renal artery anatomy before and after fenestrated or snorkel/chimney endovascular aneurysm repair JOURNAL OF VASCULAR SURGERY Ullery, B. W., Suh, G., Lee, J. T., Liu, B., Stineman, R., Daman, R. L., Cheng, C. P. 2016; 63 (4): 922-929

    Abstract

    The durability of stent grafts may be related to how procedures and devices alter native anatomy. We aimed to quantify and compare renal artery geometry before and after fenestrated (F-) or snorkel/chimney (Sn-) endovascular aneurysm repair (EVAR).Forty patients (75 ± 6 years) underwent computed tomographic angiography before and after F-EVAR (n = 21) or Sn-EVAR (n = 19), with a total of 72 renal artery stents. Renal artery geometry was quantified using three-dimensional model-based centerline extraction. The stented length was computed from the vessel origin to the stent end. The branch angle was computed relative to the orthogonal configuration with respect to the aorta. The end-stent angle was computed relative to the distal native renal artery. Peak curvature was defined as the inverse of the radius of the circumscribed circle at the highest curvature within the proximal portion from the origin to the stent end and the distal portion from the stent end to the first renal artery bifurcation.Sn-renals had greater stented length compared to F-renals (P < .05). From the pre- to the postoperative period, the origins of the Sn-left renal artery and right renal artery (RRA) angled increasingly downward by 21 ± 19° and 13 ± 17°, respectively (P < .005). The F-left renal artery and RRA angled upward by 25 ± 15° and 14 ± 15°, respectively (P < .005). From the pre- to the postoperative period, the end-stent angle of the Sn-RRA increased by 17 ± 12° (P < .00001), with greater magnitude change compared to the F-RRA (P < .0005). Peak curvature increased in distal Sn-RRAs by .02 ± .03 mm(-1) (P < .05). Acute renal failure occurred in 12.5% of patients, although none required dialysis following either F- and Sn-EVAR. Renal stent patency was 97.2% at mean follow-up of 13.7 months. Three type IA endoleaks were identified, prompting one secondary procedure, with the remainder resolving at 6-month follow-up. One renal artery reintervention was performed due to a compressed left renal stent in an asymptomatic patient.Stented renal arteries were angled more inferiorly after Sn-EVAR and more superiorly after F-EVAR due to stent configuration. Sn-EVAR induced significantly greater angle change at the stent end and curvature change distal to the stent compared to F-EVAR, although no difference in patency was noted in this small series with relatively short follow-up. Sn-RRAs exhibited greater end-stent angle change from the pre- to the postoperative period as compared to the F-RRA. These differences may exert differential effects on long-term renal artery patency, integrity, and renal function following complex EVAR for juxta- or pararenal abdominal aortic aneurysms.

    View details for DOI 10.1016/j.jvs.2015.10.091

    View details for Web of Science ID 000372958200012

  • Comparative geometric analysis of renal artery anatomy before and after fenestrated or snorkel/chimney endovascular aneurysm repair. Journal of vascular surgery Ullery, B. W., Suh, G., Lee, J. T., Liu, B., Stineman, R., Dalman, R. L., Cheng, C. P. 2016; 63 (4): 922-929

    Abstract

    The durability of stent grafts may be related to how procedures and devices alter native anatomy. We aimed to quantify and compare renal artery geometry before and after fenestrated (F-) or snorkel/chimney (Sn-) endovascular aneurysm repair (EVAR).Forty patients (75 ± 6 years) underwent computed tomographic angiography before and after F-EVAR (n = 21) or Sn-EVAR (n = 19), with a total of 72 renal artery stents. Renal artery geometry was quantified using three-dimensional model-based centerline extraction. The stented length was computed from the vessel origin to the stent end. The branch angle was computed relative to the orthogonal configuration with respect to the aorta. The end-stent angle was computed relative to the distal native renal artery. Peak curvature was defined as the inverse of the radius of the circumscribed circle at the highest curvature within the proximal portion from the origin to the stent end and the distal portion from the stent end to the first renal artery bifurcation.Sn-renals had greater stented length compared to F-renals (P < .05). From the pre- to the postoperative period, the origins of the Sn-left renal artery and right renal artery (RRA) angled increasingly downward by 21 ± 19° and 13 ± 17°, respectively (P < .005). The F-left renal artery and RRA angled upward by 25 ± 15° and 14 ± 15°, respectively (P < .005). From the pre- to the postoperative period, the end-stent angle of the Sn-RRA increased by 17 ± 12° (P < .00001), with greater magnitude change compared to the F-RRA (P < .0005). Peak curvature increased in distal Sn-RRAs by .02 ± .03 mm(-1) (P < .05). Acute renal failure occurred in 12.5% of patients, although none required dialysis following either F- and Sn-EVAR. Renal stent patency was 97.2% at mean follow-up of 13.7 months. Three type IA endoleaks were identified, prompting one secondary procedure, with the remainder resolving at 6-month follow-up. One renal artery reintervention was performed due to a compressed left renal stent in an asymptomatic patient.Stented renal arteries were angled more inferiorly after Sn-EVAR and more superiorly after F-EVAR due to stent configuration. Sn-EVAR induced significantly greater angle change at the stent end and curvature change distal to the stent compared to F-EVAR, although no difference in patency was noted in this small series with relatively short follow-up. Sn-RRAs exhibited greater end-stent angle change from the pre- to the postoperative period as compared to the F-RRA. These differences may exert differential effects on long-term renal artery patency, integrity, and renal function following complex EVAR for juxta- or pararenal abdominal aortic aneurysms.

    View details for DOI 10.1016/j.jvs.2015.10.091

    View details for PubMedID 26755068

  • Quantification of In Vivo Kinematics of Superficial Femoral Artery due to Hip and Knee Flexion Using Magnetic Resonance Imaging JOURNAL OF MEDICAL AND BIOLOGICAL ENGINEERING Choi, G., Cheng, C. P. 2016; 36 (1): 80-86

    View details for DOI 10.1007/s40846-016-0116-1

    View details for Web of Science ID 000372533100009

  • Abdominal Aortic Hemodynamics in Intermittent Claudication Patients at Rest and during Dynamic Pedaling Exercise ANNALS OF VASCULAR SURGERY Cheng, C. P., Taylor, C. A., Dalman, R. L. 2015; 29 (8): 1516-1523

    View details for DOI 10.1016/j.avsg.2015.06.089

    View details for Web of Science ID 000363475300006

    View details for PubMedID 26315797

  • Geometry and respiratory-induced deformation of abdominal branch vessels and stents after complex endovascular aneurysm repair JOURNAL OF VASCULAR SURGERY Ullery, B. W., Suh, G., Lee, J. T., Liu, B., Stineman, R., Dalman, R. L., Cheng, C. P. 2015; 61 (4): 875-884

    Abstract

    This study quantified the geometry and respiration-induced deformation of abdominal branch vessels and stents after fenestrated (F-) and snorkel (Sn-) endovascular aneurysm repair (EVAR).Twenty patients (80% male; mean age, 75.2 ± 7.4 years; mean aneurysm diameter, 6.2 ± 1.8 cm) underwent computed tomography angiography during inspiratory and expiratory breath hold protocols after F-EVAR (n = 11) or Sn-EVAR (n = 9). Centerlines for the aorta and visceral vessels were extracted from three-dimensional models. Branch angles were computed relative to the orthogonal plane at the branch ostia, and end-stent angles of the left renal artery (LRA) and right renal artery (RRA) were computed relative to the distal stent orientation. The radius of peak curvature was defined by the circumscribed circle at the highest curvature.Sn-renal branches were more downward-angled than F-renal branches (P < .04). At the distal ends of the RRA stents, Sn-RRAs were angled greater than F-RRAs (P < .03) and had a smaller radius of peak curvature (P < .03). With expiration, the end-stent angle of Sn-LRAs increased by 4° ± 4° (P < .02) and exhibited a significant reduction of radius of curvature (P < .04). The unstented celiac arteries were more downward-angled (P < .02, inspiration), with a smaller radius of curvature (P < .00001), than the unstented superior mesenteric arteries. With expiration, the celiac arteries angled upwards by 9° ± 9° (P < .0005), which was greater than the superior mesenteric arteries (P < .03). At a median postoperative follow-up of 12.6 months (range, 1.0-37.1 months), branch vessel patency was 100%, serum creatinine levels remained stable, and one reintervention was required for a type III endoleak at the main body-LRA stent interface.Sn-renals were angled more inferiorly at the branch and more angulated at the stent end than F-renals due to stent placement strategies. Sn-LRAs exhibited a significant change in end-stent angle and curvature during respiration, a finding that may compromise long-term durability for parallel stent graft configurations. Further investigation is warranted to better optimize anatomic, patient, and branch vessel stent selection between fenestrated and snorkel strategies and their relationship to long-term patency.

    View details for DOI 10.1016/j.jvs.2014.11.075

    View details for Web of Science ID 000351776100005

    View details for PubMedID 25601499

  • Aortic Arch Vessel Geometries and Deformations in Patients with Thoracic Aortic Aneurysms and Dissections JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY Suh, G., Beygui, R. E., Fleischmann, D., Cheng, C. P. 2014; 25 (12): 1903-1911

    Abstract

    To quantify aortic arch geometry and in vivo cardiac-induced and respiratory-induced arch translations and arch branch angulations using three-dimensional geometric modeling techniques.Scanning with electrocardiogram-gated computed tomography angiography during inspiratory and expiratory breath holds was performed in 15 patients (age, 64 y ± 14) with thoracic aortic aneurysms or dissections. From the lumen models, centerlines of the thoracic aorta, brachiocephalic artery, left common carotid artery, and left subclavian artery and their branching ostia positions were quantified. Three-dimensional translation of vessel ostia, branching angles, and their changes secondary to cardiac pulsation and respiration were computed.During expiration, all ostia translated rightward from systole to diastole (P < .035). Regardless of cardiac phase, all ostia translated posteriorly and superiorly from inspiration to expiration (P < .05). Respiration induced greater posterior and superior translations than cardiac pulsation (P < .03). The left common carotid artery branch angled significantly more toward the aortic arch compared with the brachiocephalic artery and left subclavian artery (P < .03). No significant changes in branching angle were found from systole to diastole or inspiration to expiration.In patients with thoracic aortic aneurysms or dissections, the thoracic aortic arch translated significantly secondary to inspiration and expiration and to a lesser extent secondary to cardiac pulsation. Insignificant branching angle changes suggest that the aortic arch and its branch origins move predominantly in unison.

    View details for DOI 10.1016/j.jvir.2014.06.012

    View details for Web of Science ID 000345676700011

    View details for PubMedID 25066591

  • Methods for Characterizing Human Coronary Artery Deformation From Cardiac-Gated Computed Tomography Data IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING Choi, G., Xiong, G., Cheng, C. P., Taylor, C. A. 2014; 61 (10): 2582-2592

    Abstract

    Accurate quantification of changes in length, curvature, and bifurcation angles of coronary arteries due to cardiac motion is important for the design of coronary stents. A new method is developed to describe the dynamic characteristics of the human coronary artery. From cardiac-gated computed tomography (CT) data, 3-D surface geometry and centerline paths of the coronary arteries were constructed. For quantification of strain and twisting deformation, 3-D distortion-free vessel straightening and landmark matching algorithms were developed to compute the relative translation and rotation of distal landmarks with respect to a proximal landmark. For quantification of bending deformation, change in curvature was measured by computing a best-fit torus in the region of interest within a coronary segment. The optimal torus parameters were estimated by minimizing the standard deviation of distances from the surface mesh to the centerline of the torus. The angle between branch vessels was measured using linear fitting of centroid sets from the cross-sectional vessel lumen. The proposed methods were verified using a software phantom and applied to two patient specific CT datasets. Vascular deformations derived from these methods can provide information for designing bench-top tests for endovascular devices that better replicate the in vivo environment, thereby improving device performance prediction and leading to more durable designs.

    View details for DOI 10.1109/TBME.2014.2323333

    View details for Web of Science ID 000346226300007

    View details for PubMedID 24835123

  • Respiratory-Induced 3D Deformations of the Renal Arteries Quantified With Geometric Modeling During Inspiration and Expiration Breath-Holds of Magnetic Resonance Angiography JOURNAL OF MAGNETIC RESONANCE IMAGING Suh, G., Choi, G., Draney, M. T., Herfkens, R. J., Dalman, R. L., Cheng, C. P. 2013; 38 (6): 1325-1332

    Abstract

    PURPOSE: To quantify renal artery deformation due to respiration using magnetic resonance (MR) image-based geometric analysis. MATERIALS AND METHODS: Five males were imaged with contrast-enhanced MR angiography during inspiratory and expiratory breath-holds. From 3D models of the abdominal aorta, left and right renal arteries (LRA and RRA), we quantified branching angle, curvature, peak curve angle, axial length, and locations of branch points. RESULTS: With expiration, maximum curvature changes were 0.054 ± 0.025 mm(-1) (P < 0.01), and curve angle at the most proximal curvature peak increased by 8.0 ± 4.5° (P < 0.05) in the LRA. Changes in maximum curvature and curve angles were not significant in the RRA. The first renal bifurcation point translated superiorly and posteriorly by 9.7 ± 3.6 mm (P < 0.005) and 3.5 ± 2.1 mm (P < 0.05), respectively, in the LRA, and 10.8 ± 6.1 mm (P < 0.05) and 3.6 ± 2.5 mm (P < 0.05), respectively, in the RRA. Changes in branching angle, axial length, and renal ostia locations were not significant. CONCLUSION: The LRA and RRA deformed and translated significantly. Greater deformation of the LRA as compared to the RRA may be due to asymmetric anatomy and mechanical support by the inferior vena cava. The presented methodology can extend to quantification of deformation of diseased and stented arteries to help renal artery implant development. J. Magn. Reson. Imaging 2013;. © 2013 Wiley Periodicals, Inc.

    View details for DOI 10.1002/jmri.24101

    View details for Web of Science ID 000327756800003

    View details for PubMedID 23553967

  • Respiration-induced Deformations of the Superior Mesenteric and Renal Arteries in Patients with Abdominal Aortic Aneurysms. Journal of vascular and interventional radiology Suh, G., Choi, G., Herfkens, R. J., Dalman, R. L., Cheng, C. P. 2013; 24 (7): 1035-1042

    Abstract

    To quantify respiration-induced deformations of the superior mesenteric artery (SMA), left renal artery (LRA), and right renal artery (RRA) in patients with small abdominal aortic aneurysms (AAAs).Sixteen men with AAAs (age 73 y ± 7) were imaged with contrast-enhanced magnetic resonance angiography during inspiratory and expiratory breath-holds. Centerline paths of the aorta and visceral arteries were acquired by geometric modeling and segmentation techniques. Vessel translations and changes in branching angle and curvature resulting from respiration were computed from centerline paths.With expiration, the SMA, LRA, and RRA bifurcation points translated superiorly by 12.4mm ± 9.5, 14.5mm ± 8.8, and 12.7mm ± 6.4 (P < .001), and posteriorly by 2.2mm ± 2.7, 4.9mm ± 4.2, and 5.6mm ± 3.9 (P < .05), respectively, and the SMA translated rightward by 3.9mm ± 4.9 (P < .01). With expiration, the SMA, LRA, and RRA angled upward by 9.7° ± 6.4, 7.5° ± 7.8, and 4.9° ± 5.3, respectively (P < .005). With expiration, mean curvature increased by 0.02mm(-1) ± 0.01, 0.01mm(-1) ± 0.01, and 0.01mm(-1) ± 0.01 in the SMA, LRA, and RRA, respectively (P < .05). For inspiration and expiration, RRA curvature was greater than in other vessels (P < .025).With expiration, the SMA, LRA, and RRA translated superiorly and posteriorly as a result of diaphragmatic motion, inducing upward angling of vessel branches and increased curvature. In addition, the SMA exhibited rightward translation with expiration. The RRA was significantly more tortuous, but deformed less than the other vessels during respiration.

    View details for DOI 10.1016/j.jvir.2013.04.006

    View details for PubMedID 23796090

    View details for PubMedCentralID PMC3694359

  • Hemodynamic Changes Quantified in Abdominal Aortic Aneurysms with Increasing Exercise Intensity Using MR Exercise Imaging and Image-Based Computational Fluid Dynamics ANNALS OF BIOMEDICAL ENGINEERING Suh, G., Les, A. S., Tenforde, A. S., Shadden, S. C., Spilker, R. L., Yeung, J. J., Cheng, C. P., Herfkens, R. J., Dalman, R. L., Taylor, C. A. 2011; 39 (8): 2186-2202

    Abstract

    Abdominal aortic aneurysm (AAA) is a vascular disease resulting in a permanent, localized enlargement of the abdominal aorta. We previously hypothesized that the progression of AAA may be slowed by altering the hemodynamics in the abdominal aorta through exercise [Dalman, R. L., M. M. Tedesco, J. Myers, and C. A. Taylor. Ann. N.Y. Acad. Sci. 1085:92-109, 2006]. To quantify the effect of exercise intensity on hemodynamic conditions in 10 AAA subjects at rest and during mild and moderate intensities of lower-limb exercise (defined as 33 ± 10% and 63 ± 18% increase above resting heart rate, respectively), we used magnetic resonance imaging and computational fluid dynamics techniques. Subject-specific models were constructed from magnetic resonance angiography data and physiologic boundary conditions were derived from measurements made during dynamic exercise. We measured the abdominal aortic blood flow at rest and during exercise, and quantified mean wall shear stress (MWSS), oscillatory shear index (OSI), and particle residence time (PRT). We observed that an increase in the level of activity correlated with an increase of MWSS and a decrease of OSI at three locations in the abdominal aorta, and these changes were most significant below the renal arteries. As the level of activity increased, PRT in the aneurysm was significantly decreased: 50% of particles were cleared out of AAAs within 1.36 ± 0.43, 0.34 ± 0.10, and 0.22 ± 0.06 s at rest, mild exercise, and moderate exercise levels, respectively. Most of the reduction of PRT occurred from rest to the mild exercise level, suggesting that mild exercise may be sufficient to reduce flow stasis in AAAs.

    View details for DOI 10.1007/s10439-011-0313-6

    View details for Web of Science ID 000292268900008

    View details for PubMedID 21509633

    View details for PubMedCentralID PMC3362397

  • Quantification of Particle Residence Time in Abdominal Aortic Aneurysms Using Magnetic Resonance Imaging and Computational Fluid Dynamics ANNALS OF BIOMEDICAL ENGINEERING Suh, G., Les, A. S., Tenforde, A. S., Shadden, S. C., Spilker, R. L., Yeung, J. J., Cheng, C. P., Herfkens, R. J., Dalman, R. L., Taylor, C. A. 2011; 39 (2): 864-883

    Abstract

    Hemodynamic conditions are hypothesized to affect the initiation, growth, and rupture of abdominal aortic aneurysms (AAAs), a vascular disease characterized by progressive wall degradation and enlargement of the abdominal aorta. This study aims to use magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) to quantify flow stagnation and recirculation in eight AAAs by computing particle residence time (PRT). Specifically, we used gadolinium-enhanced MR angiography to obtain images of the vessel lumens, which were used to generate subject-specific models. We also used phase-contrast MRI to measure blood flow at supraceliac and infrarenal locations to prescribe physiologic boundary conditions. CFD was used to simulate pulsatile flow, and PRT, particle residence index, and particle half-life of PRT in the aneurysms were computed. We observed significant regional differences of PRT in the aneurysms with localized patterns that differed depending on aneurysm geometry and infrarenal flow. A bulbous aneurysm with the lowest mean infrarenal flow demonstrated the slowest particle clearance. In addition, improvements in particle clearance were observed with increase of mean infrarenal flow. We postulate that augmentation of mean infrarenal flow during exercise may reduce chronic flow stasis that may influence mural thrombus burden, degradation of the vessel wall, and aneurysm growth.

    View details for DOI 10.1007/s10439-010-0202-4

    View details for Web of Science ID 000287213300022

    View details for PubMedID 21103933

    View details for PubMedCentralID PMC3066149

  • The NovoStent® SAMBA® stent: A novel alternating helix self-expanding nitinol stent design Interventional Cardiology Zeller T., Braunlich S., Waldo M., Cheng C.P., Macharzina R., Scheinert D., Rastan A. 2011; 3 (2): 247-261
  • The Effect of Aging on Deformations of the Superficial Femoral Artery Resulting from Hip and Knee Flexion: Potential Clinical Implications JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY Cheng, C. P., Choi, G., Herfkens, R. J., Taylor, C. A. 2010; 21 (2): 195-202

    Abstract

    Vessel deformations have been implicated in endoluminal device fractures, and therefore better understanding of these deformations could be valuable for device regulation, evaluation, and design. The purpose of this study is to describe geometric changes of the superficial femoral artery (SFA) resulting from hip and knee flexion in older subjects.The SFAs of seven healthy subjects aged 50-70 years were imaged with magnetic resonance angiography with the legs straight and with hip and knee flexion. From geometric models constructed from these images, axial, twisting, and bending deformations were quantified.There was greater shortening in the bottom third of the SFA than in the top two thirds (top, 5.9% +/- 3.0%; middle, 6.7% +/- 2.1%; bottom, 8.1% +/- 2.0% [mean +/- SD]; P < .05), significant twist in all sections (top, 1.3 degrees /cm +/- 0.8; middle, 1.8 degrees /cm +/- 1.1; bottom, 2.1 degrees /cm +/- 1.3), and greater curvature increase in the bottom third than in the top two thirds (top, 0.15 cm(-1) +/- 0.06; middle, 0.09 cm(-1) +/- 0.07; bottom, 0.41 cm(-1) +/- 0.22; P < .001).The SFA tends to deform more in the bottom third than in the other sections, likely because of less musculoskeletal constraint distal to the adductor canal and vicinity of knee flexion. The SFAs of these older subjects curve off axis with normal joint flexion, probably resulting from known loss of arterial elasticity with age. This slackening of the vessel enables a method for noninvasive quantification of in vivo SFA strain, which may be valuable for treatment planning and device design. In addition, the spatially resolved arterial deformations quantified in this study may be useful for commercial and regulatory device evaluation.

    View details for DOI 10.1016/j.jvir.2009.08.027

    View details for Web of Science ID 000277367600005

    View details for PubMedID 20022767

    View details for PubMedCentralID PMC2818320

  • Quantifying In Vivo Hemodynamic Response to Exercise in Patients With Intermittent Claudication and Abdominal Aortic Aneurysms Using Cine Phase-Contrast MRI JOURNAL OF MAGNETIC RESONANCE IMAGING Tenforde, A. S., Cheng, C. P., Suh, G., Herfkens, R. J., Dalman, R. L., Taylor, C. A. 2010; 31 (2): 425-429

    Abstract

    To evaluate rest and exercise hemodynamics in patients with abdominal aortic aneurysms (AAA) and peripheral occlusive disease (claudicants) using phase-contrast MRI.Blood velocities were acquired by means of cardiac-gated cine phase-contrast in a 0.5 Tesla (T) open MRI. Volumetric flow was calculated at the supraceliac (SC), infrarenal (IR), and mid-aneurysm (MA) levels during rest and upright cycling exercise using an MR-compatible exercise cycle.Mean blood flow increased during exercise (AAA: 130%, Claudicants: 136% of resting heart rate) at the SC and IR levels for AAA participants (2.6 +/- 0.6 versus 5.8 +/- 1.6 L/min, P < 0.001 and 0.8 +/- 0.4 versus 5.1 +/- 1.7 L/min, P < 0.001) and claudicants (2.3 +/- 0.5 versus 4.5 +/- 0.9 L/min, P < 0.005 and 0.8 +/- 0.2 versus 3.3 +/- 0.9 L/min, P < 0.005). AAA participants had a significant decrease in renal and digestive blood flow from rest to exercise (1.8 +/- 0.7 to 0.7 +/- 0.6 L/min, P < 0.01). The decrease in renal and digestive blood flow during exercise correlated with daily activity level for claudicants (R = 0.81).Abdominal aortic hemodynamic changes due to lower extremity exercise can be quantified in patients with AAA and claudication using PC-MRI. The redistribution of blood flow during exercise was significant and different between the two disease states.

    View details for DOI 10.1002/jmri.22055

    View details for Web of Science ID 000274117200019

    View details for PubMedID 20099356

    View details for PubMedCentralID PMC2963312

  • In Vivo Deformation of the Human Abdominal Aorta and Common Iliac Arteries With Hip and Knee Flexion: Implications for the Design of Stent-Grafts JOURNAL OF ENDOVASCULAR THERAPY Choi, G., Shin, L. K., Taylor, C. A., Cheng, C. P. 2009; 16 (5): 531-538

    Abstract

    To quantify in vivo deformations of the abdominal aorta and common iliac arteries (CIAs) caused by musculoskeletal motion.Seven healthy subjects (age 34+/-11 years, range 24-50) were imaged in the supine and fetal positions (hip flexion angle 134.0 degrees +/-9.7 degrees ) using contrast-enhanced magnetic resonance angiography. Longitudinal strain, twisting, and curvature change of the infrarenal aorta and CIAs were computed. The angle between the left and right CIAs and translation of the arteries were also computed.Maximal hip flexion induced shortening (5.2%+/-4.6%), twisting (0.45+/-0.27 degrees /mm), and curvature changes (0.015+/-0.007 mm(-1)) of the CIAs. The angle between the CIAs increased by 17.6 degrees +/-8.6 degrees . The iliac arteries moved predominantly in the superior direction relative to the aortic bifurcation, which would induce compression and bending, thus increasing curvature and angle between the CIAs. The abdominal aorta also exhibited shortening (2.9%+/-2.1%) and twisting (0.07+/-0.05 degrees /mm) deformation associated with the hip flexion.Although this study was limited to a few healthy young adults, musculoskeletal motion, specifically hip flexion, caused significant in vivo morphological changes (shortening, twisting, and bending) of the arteries. Predominant superior translation of the CIAs was observed, which suggests that preclinical testing of cyclic superior-inferior translational motion may aid in predicting stent-graft fractures. In turn, stent-graft design could be improved, decreasing overall stent-graft-related complications.

    View details for Web of Science ID 000271308800001

    View details for PubMedID 19842734

    View details for PubMedCentralID PMC2793421

  • Methods for Quantifying Three-Dimensional Deformation of Arteries due to Pulsatile and Nonpulsatile Forces: Implications for the Design of Stents and Stent Grafts ANNALS OF BIOMEDICAL ENGINEERING Choi, G., Cheng, C. P., Wilson, N. M., Taylor, C. A. 2009; 37 (1): 14-33

    Abstract

    The knowledge of dynamic changes in the vascular system has become increasingly important in ensuring the safety and efficacy of endovascular devices. We developed new methods for quantifying in vivo three-dimensional (3D) arterial deformation due to pulsatile and nonpulsatile forces. A two-dimensional threshold segmentation technique combined with a level set method enabled calculation of the consistent centroid of the cross-sectional vessel lumen, whereas an optimal Fourier smoothing technique was developed to eliminate spurious irregularities of the centerline connecting the centroids. Longitudinal strain and novel metrics for axial twist and curvature change were utilized to characterize 3D deformations of the abdominal aorta, common iliac artery, and superficial femoral artery (SFA) due to musculoskeletal motion and deformations of the coronary artery due to cardiac pulsatile motion. These illustrative applications show the significance of each deformation metric, revealing significant longitudinal strain and axial twist in the SFA and coronary artery, and pronounced changes in vessel curvature in the coronary artery and in the inferior region of the SFA. The proposed methods may aid in designing preclinical tests aimed at replicating dynamic in vivo conditions in the arterial tree for the purpose of developing more durable endovascular devices including stents and stent grafts.

    View details for DOI 10.1007/s10439-008-9590-0

    View details for Web of Science ID 000261401100002

    View details for PubMedID 19002584

  • IN VIVO QUANTIFICATION OF HUMAN CORONARY ARTERY DEFORMATION FROM CARDIAC-GATED COMPUTED TOMOGRAPHY DATA ASME Summer Bioengineering Conference Choi, G., Dusch, M. N., Xiong, G., Xiao, N., Cheng, C. P., Taylor, C. A. AMER SOC MECHANICAL ENGINEERS. 2009: 983?984

    View details for Web of Science ID 000280089000492

  • QUANTIFICATION OF THE DEFORMATION OF THE HUMAN ILIAC ARTERIES WITH HIP AND KNEE FLEXION: IMPLICATIONS FOR STENT-GRAFT DESIGN ASME Summer Bioengineering Conference Choi, G., Shin, L. K., Taylor, C. A., Cheng, C. P. AMER SOC MECHANICAL ENGINEERS. 2009: 239?240

    View details for Web of Science ID 000263364700120

  • Biomechanical Response of Stented Carotid Arteries to Swallowing and Neck Motion JOURNAL OF ENDOVASCULAR THERAPY Robertson, S. W., Cheng, C. P., Razavi, M. K. 2008; 15 (6): 663-671

    Abstract

    To examine the effects of swallowing and side-to-side head turning on stents in the internal carotid artery.Seven patients (4 men; mean age 76.9 years) who underwent carotid artery stenting for the treatment of atherosclerotic cervical carotid artery disease were examined with cine fluoroscopy. Geometric processing techniques were used to quantify carotid stent deformations due to head turning and swallowing forces. The variables measured included radial, axial, and crush deformations, as well as radii of stent curvatures during tested maneuvers.Radial deformations of the stented vessels were significantly less than axial and crush deformations, ranging from -10.2% to 15.5%. Axial deformations in response to both swallowing and head turning were positive (average 4.5%, range -14.5% to 14.1%), indicating a general lengthening of the stented vessel due to biomechanical motions. Crush strains exhibited the largest range of all of the deformation modes during both swallowing and head turning. Strain values ranged from -18.7% to 25.9% in the anteroposterior direction and from -25.6% to 21.9% in the lateral direction. Head turning produced fairly symmetrical crushing of the stent. Conversely, swallowing resulted in a preferential medial crush of the stented artery due to contraction of the pharyngeal constrictor muscles. Curvature measurements revealed a tightest radius of curvature of approximately 1.5 cm during ipsilateral head turning, with average values during both swallowing and head turning of approximately 10 cm.In general, head turning toward the stented artery produced greater deformation in the vessels than swallowing. Since patients are expected to undergo far more swallowing cycles than head turns, however, the accumulated deformations from swallowing may be more significant and should be considered in the design of fatigue resistant stents for carotid arteries.

    View details for Web of Science ID 000261624900004

    View details for PubMedID 19090633

  • Right renal artery in vivo stent fracture JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY Robertson, S. W., Jessup, D. B., Boero, I. J., Cheng, C. P. 2008; 19 (3): 439-442

    Abstract

    The authors describe an incident of a type I single strut fracture in a right renal artery (RRA) stent resulting in approximately 90% restenosis. Fracture was observed just distal to the ostium approximately 1 year after implantation in an 83-year-old man with a history of systemic cardiovascular disease. In addition, a statistical analysis of the clinically reported cases of left renal artery (LRA) and RRA stent fracture is provided, which suggests a greater susceptibility to fracture in LRA stents as demonstrated by the greater occurrence (67%) in the left side.

    View details for DOI 10.1016/j.jvir.2007.11.014

    View details for Web of Science ID 000253788200018

    View details for PubMedID 18295705

  • A Review of Peripheral Vascular Deformations Due to Respiration and Musculoskeletal Influences Journal of ASTM International (Symposium on Fatigue and Fracture of Medical Metallic Materials and Devices) Cheng, C.P. 2008; 5 (10): JAI102074
  • Methods for quantifying vessel deformation due to pulsatile and non-pulsatile forces ASME Summer Bioengineering Conference Choi, G., Cheng, C. P., Wilson, N. M., Taylor, C. A. AMER SOC MECHANICAL ENGINEERS. 2007: 543?544

    View details for Web of Science ID 000252105700272

  • Hemodynamics in human abdominal aortic aneurysms during rest and simulated exercise ASME Summer Bioengineering Conference Les, A. S., Cheng, C. P., Blomme, M. T., Figueroa, C. A., LaDisa, J. F., Park, J. M., Herfkens, R. J., Dalman, R. L., Taylor, C. A. AMER SOC MECHANICAL ENGINEERS. 2007: 169?170

    View details for Web of Science ID 000252105700085

  • Relative lung perfusion distribution in normal lung scans: observations and clinical implications. Congenital heart disease Cheng, C. P., Taur, A. S., Lee, G. S., Goris, M. L., Feinstein, J. A. 2006; 1 (5): 210-216

    Abstract

    While relative lung perfusion distributions are cited in clinical decision making for congenital and acquired pulmonary vascular diseases, normal values and ranges have not been published for a large population of normally perfused lungs. These values of normal relative perfusion will be useful for establishing what is abnormal and for clinical decisions related to various pulmonary vascular diseases.Relative perfusion distributions were quantified for the top, middle, and bottom thirds of the right and left lungs with a semiautomatic algorithm in 206 normal scintigraphy lung studies (45 +/- 18 years, 149 female, 57 male) acquired between January 1, 2000 and March 30, 2004 in the Nuclear Medicine Division at Stanford Hospital and Clinics.The perfusion data were found to be highly non-Gaussian in nature (necessitating the use of Wilcoxon statistical comparisons), and the right/left perfusion ratio was found to be 52.5/47.5 (+/-2.1%) rather than the often quoted 55/45 split. While this right/left split was consistent between the genders, males had proportionally less perfusion in the lower left lung as compared with females (P < .05).The long-standing 55/45 right/left perfusion ratio assumption was found to be more than 1 standard deviation greater than the mean, and the population variance is very small. Relative pulmonary perfusion distribution varies significantly with lung region, gender, and age, and should be considered when making clinical decisions based on pulmonary perfusion.

    View details for DOI 10.1111/j.1747-0803.2006.00037.x

    View details for PubMedID 18377528

  • Abdominal aortic hemodynamics in young healthy adults at rest and during lower limb exercise: quantification using image-based computer modeling AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY Tang, B. T., Cheng, C. P., Draney, M. T., Wilson, N. M., Tsao, P. S., Herfkens, R. J., Taylor, C. A. 2006; 291 (2): H668-H676

    Abstract

    Localization of atherosclerotic lesions in the abdominal aorta has been previously correlated to areas of adverse hemodynamic conditions, such as flow recirculation, low mean wall shear stress, and high temporal oscillations in shear. Along with its many systemic benefits, exercise is also proposed to have local benefits in the vasculature via the alteration of these regional flow patterns. In this work, subject-specific models of the human abdominal aorta were constructed from magnetic resonance angiograms of five young, healthy subjects, and computer simulations were performed under resting and exercise (50% increase in resting heart rate) pulsatile flow conditions. Velocity fields and spatial variations in mean wall shear stress (WSS) and oscillatory shear index (OSI) are presented. When averaged over all subjects, WSS increased from 4.8 +/- 0.6 to 31.6 +/- 5.7 dyn/cm2 and OSI decreased from 0.22 +/- 0.03 to 0.03 +/- 0.02 in the infrarenal aorta between rest and exercise. WSS significantly increased, whereas OSI decreased between rest and exercise at the supraceliac, infrarenal, and suprabifurcation levels, and significant differences in WSS were found between anterior and posterior sections. These results support the hypothesis that exercise provides localized benefits to the cardiovascular system through acute mechanical stimuli that trigger longer-term biological processes leading to protection against the development or progression of atherosclerosis.

    View details for DOI 10.1152/ajpheart.01301.2005

    View details for Web of Science ID 000239020300021

    View details for PubMedID 16603687

  • In vivo MR angiographic quantification of axial and twisting deformations of the superficial femoral artery resulting from maximum hip and knee flexion JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY Cheng, C. P., Wilson, N. M., Hallett, R. L., Herfkens, R. J., Taylor, C. A. 2006; 17 (6): 979-987

    Abstract

    The goal of this study was to quantify in vivo deformations of the superficial femoral artery (SFA) during maximum knee and hip flexion with use of magnetic resonance (MR) angiography to improve description of the complex, dynamic SFA environment.Contrast medium-enhanced MR angiography was performed on the leg vasculature of eight healthy adults in the supine and fetal positions. The SFA was defined as the centerline path of the iliofemoral segment from the profunda femoris to the descending genicular artery. Deformations that resulted from flexion from the supine position to the fetal position were quantified with the SFA path and its branches.Fourteen SFAs shortened from the supine position to fetal position, whereas two lengthened. Six of eight left SFAs twisted counterclockwise, and seven of eight right SFAs twisted clockwise. Straightness percentages for supine and fetal SFAs were 99.1%+/-0.4% and 98.7%+/-0.6%, respectively. From the supine position to the fetal position, the SFA shortened 13%+/-11% (P<.001) and twisted 60 degrees+/-34 degrees (P<.001). SFA arc length and percent shortening were strongly correlated (r>.8) between left and right limbs; however, no significant correlation existed for SFA twist angle.Complex and varying vascular and muscular anatomy among study participants made SFA lengths and deformations from the supine position to the fetal position unpredictable a priori; however, there were strong symmetries between left and right SFAs in terms of arc length, length change, and direction of twist. The data show that, from the supine position to the fetal position, the SFA tended to shorten and twist substantially, suggesting these as possible fracture mechanisms and also providing important parameters for stent design.

    View details for DOI 10.1097/01.RVI.0000220367.62137.E8

    View details for Web of Science ID 000238334500006

    View details for PubMedID 16778231

  • Proximal pulmonary artery blood flow characteristics in healthy subjects measured in an upright posture using MRI: The effects of exercise and age 12th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine Cheng, C. P., Herfkens, R. J., Taylor, C. A., Feinstein, J. A. JOHN WILEY & SONS INC. 2005: 752?58

    Abstract

    To use MRI to quantify blood flow conditions in the proximal pulmonary arteries of healthy children and adults at rest and during exercise in an upright posture.Cine phase-contrast MRI was used to calculate mean flow and reverse flow index (RFI) in the main (MPA), right (RPA), and left (LPA) pulmonary arteries in healthy children and adults in an open-MRI magnet equipped with an upright MRI-compatible ergometer.From rest to exercise (150% resting heart rate), blood flow (liters/minute/m2) increased in the RPA (1.4+/-0.3 vs. 2.5+/-0.4; P<0.001), LPA (1.1+/-0.3 vs. 2.2+/-0.6; P<0.001), and MPA (2.7+/-0.5 vs. 4.9+/-0.5; P<0.001). RFI decreased in the LPA (0.040+/-0.030 vs. 0.017+/-0.018; P<0.02) and MPA (0.025+/-0.024 vs. 0.008+/-0.007; P<0.03). Adults experienced greater retrograde flow in the MPA than the children (0.042+/-0.029 vs. 0.014+/-0.012; P<0.02).It appears that at both rest and during exercise, in children and adults alike, RPA/LPA mean blood flow distribution is predominantly determined by distal vascular resistance, while retrograde flow is affected by proximal pulmonary bifurcation geometry.

    View details for DOI 10.1002/jmri.20333

    View details for Web of Science ID 000229453900012

    View details for PubMedID 15906332

  • Blood flow conditions in the proximal pulmonary arteries and vena cavae: healthy children during upright cycling exercise AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY Cheng, C. P., Herfkens, R. J., Lightner, A. L., Taylor, C. A., Feinstein, J. A. 2004; 287 (2): H921-H926

    Abstract

    Diagnostic testing in patients with congenital heart disease is usually performed supine and at rest, conditions not representative of their typical hemodynamics. Upright exercise measurements of blood flow may prove valuable in the assessment of these patients, but data in normal subjects are first required. With the use of a 0.5-T open magnet, a magnetic resonance-compatible exercise cycle, and cine phase-contrast techniques, time-dependent blood flow velocities were measured in the right (RPA), left (LPA), and main (MPA) pulmonary arteries and superior (SVC) and inferior (IVC) vena cavae of 10 healthy 10- to 14-yr-old subjects. Measurements were made at seated rest and during upright cycling exercise (150% resting heart rate). Mean blood flow (l/min) and reverse flow index were computed from the velocity data. With exercise, RPA and LPA mean flow increased 2.0 +/- 0.5 to 3.7 +/- 0.7 (P < 0.05) and 1.6 +/- 0.4 to 2.9 +/- 0.8 (P < 0.05), respectively. Pulmonary reverse flow index (rest vs. exercise) decreased with exercise as follows: MPA: 0.014 +/- 0.012 vs. 0.006 +/- 0.006 [P = not significant (NS)], RPA: 0.005 +/- 0.004 vs. 0.000 +/- 0.000 (P < 0.05), and LPA: 0.041 +/- 0.019 vs. 0.014 +/- 0.016 (P < 0.05). SVC and IVC flow increased from 1.5 +/- 0.2 to 1.9 +/- 0.6 (P = NS) and 1.6 +/- 0.4 to 4.9 +/- 1.3 (P < 0.05), respectively. A 56/44% RPA/LPA flow distribution at both rest and during exercise suggests blood flow distribution is dominated by distal pulmonary resistance. Reverse flow in the MPA appears to originate solely from the LPA while the RPA is in relative isolation. During seated rest, the SVC-to-IVC venous return ratio is 50/50%. With light/moderate cycling exercise, IVC flow increases by threefold, whereas SVC remains essentially constant.

    View details for DOI 10.1152/ajpheart.00022.2004

    View details for Web of Science ID 000222848000064

    View details for PubMedID 15031121

  • Abdominal aortic hemodynamic conditions in healthy subjects aged 50-70 at rest and during lower limb exercise: in vivo quantification using MR1 ATHEROSCLEROSIS Cheng, C. P., Herfkens, R. J., Taylor, C. A. 2003; 168 (2): 323-331

    Abstract

    The prevalence of atherosclerosis in the abdominal aorta increases with age and is hypothesized to be related to adverse hemodynamic conditions including flow recirculation and low wall shear stress. Exercise has been shown to modulate these adverse conditions observed in the infrarenal aorta of healthy young subjects at rest. A custom magnetic resonance (MR)-compatible stationary cycle, an open MRI, and custom image processing software were used to quantify hemodynamic conditions in the abdominal aorta at rest and during cycling exercise in healthy subjects aged 50-70 years. The subjects increased their heart rate from 63+/-8 bpm at rest to 95+/-12 bpm during cycling exercise. Supraceliac blood flow increased from 2.3+/-0.4 to 6.0+/-1.4 l/min (P<0.001) and infrarenal flow increased from 0.9+/-0.3 to 4.9+/-1.7 l/min (P<0.001) from rest to exercise. Wall shear stress increased from 2.0+/-0.7 to 7.3+/-2.4 dynes/cm(2) at the supraceliac level (P<0.001) and 1.4+/-0.8 to 16.5+/-5.1 dynes/cm(2) at the infrarenal level (P<0.001) from rest to exercise. Flow and shear oscillations present at rest were eliminated during exercise. At rest, these older subjects experienced lower mean wall shear stress at the supraceliac level of the aorta and greater oscillations in wall shear stress as compared to a group of younger subjects (23.6+/-2.2 years). Compared to the younger subjects, the older subjects also experienced greater increases in mean wall shear stress and greater decreases in wall shear stress oscillations from rest to exercise.

    View details for DOI 10.1016/S0021-9150(03)00099-6

    View details for Web of Science ID 000183784900015

    View details for PubMedID 12801616

  • Inferior vena caval hemodynamics quantified in vivo at rest and during cycling exercise using magnetic resonance imaging AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY Cheng, C. P., Herfkens, R. J., Taylor, C. A. 2003; 284 (4): H1161-H1167

    Abstract

    Compared with the abdominal aorta, the hemodynamic environment in the inferior vena cava (IVC) is not well described. With the use of cine phase-contrast magnetic resonance imaging (MRI) and a custom MRI-compatible cycle in an open magnet, we quantified mean blood flow rate, wall shear stress, and cross-sectional lumen area in 11 young normal subjects at the supraceliac and infrarenal levels of the aorta and IVC at rest and during dynamic cycling exercise. Similar to the aorta, the IVC experienced significant increases in blood flow and wall shear stress as a result of exercise, with greater increases in the infrarenal level compared with the supraceliac level. At the infrarenal level during resting conditions, the IVC experienced higher mean flow rate than the aorta (1.2 +/- 0.5 vs. 0.9 +/- 0.4 l/min, P < 0.01) and higher mean wall shear stress than the aorta (2.0 +/- 0.6 vs. 1.3 +/- 0.6 dyn/cm(2), P < 0.005). During exercise, wall shear stress remained higher in the IVC compared with the aorta, although not significantly. It was also observed that, whereas the aorta tapers inferiorly, the IVC tapers superiorly from the infrarenal to the supraceliac location. The hemodynamic and anatomic data of the IVC acquired in this study add to our understanding of the venous circulation and may be useful in a clinical setting.

    View details for DOI 10.1152/ajpheart.00641.2002

    View details for Web of Science ID 000181425900016

    View details for PubMedID 12595296

  • Dynamic exercise imaging with an MR-Compatible stationary cycle within the general electric open magnet MAGNETIC RESONANCE IN MEDICINE Cheng, C. P., Schwandt, D. F., Topp, E. L., Anderson, J. H., Herfkens, R. J., Taylor, C. A. 2003; 49 (3): 581-585

    Abstract

    Many cases of muscular ischemia do not manifest without increased metabolic demand. Hence, diagnosis of intermittent claudication often requires inducing physiologic challenge, such as by exercise. Cine phase-contrast MRI can concurrently acquire cross-sectional vascular anatomy and through-plane blood velocities, enabling blood flow rate quantification. An MR-compatible stationary cycle was designed, constructed, and tested for flow quantification in large arteries during lower-limb exercise in a General Electric Signa SP 0.5 T open magnet. The cycle demonstrated smooth cycling during image acquisition, has freewheeling capability, is adjustable for subject size and strength, and can quantify workload. A healthy 59-year-old male was imaged at the supraceliac and infrarenal levels of the abdominal aorta at rest and during exercise. An exercise workload of 47.9 W was achieved. His heart rate increased from 52 to 78 bpm, supraceliac flow increased from 1.7 to 3.7 L/min, and infrarenal flow increased from 0.4 to 3.2 L/min from rest to exercise.

    View details for DOI 10.1002/mrm.10364

    View details for Web of Science ID 000181297200024

    View details for PubMedID 12594764

  • Comparison of abdominal aortic hemodynamics between men and women at rest and during lower limb exercise JOURNAL OF VASCULAR SURGERY Cheng, C. P., Herfkens, R. J., Taylor, C. A. 2003; 37 (1): 118-123

    Abstract

    Biologic variations between men and women have been hypothesized to contribute to the differences in atherosclerosis epidemiology of the two genders. Hemodynamics are also hypothesized to play an important role in the localization of atherosclerosis in the abdominal aorta. However, the hemodynamics of men and women have not been compared at this location at rest or during lower limb exercise conditions.A magnetic resonance-compatible exercise bicycle, magnetic resonance imaging techniques, and custom data processing software were used to quantify blood flow rate, wall shear stress, and oscillations in flow and wall shear stress at the supraceliac and infrarenal levels of the abdominal aorta of young healthy men and women at rest and during lower limb exercise.Heart rate increased from 73 +/- 6.2 bpm at rest to 110 +/- 8.8 bpm during exercise (P <.0001). No statistical differences were found at the infrarenal level for mean blood flow rate (men, 0.9 +/- 0.4 L/min; women, 0.8 +/- 0.4 L/min) or mean wall shear stress (men, 1.2 +/- 0.5 dynes/cm(2); women, 1.4 +/- 0.7 dynes/cm(2)) at rest or mean blood flow rate (men, 5.9 +/- 1.3 L/min; women, 5.2 +/- 0.8 L/min) or mean wall shear stress (men, 5.1 +/- 0.8 dynes/cm(2); women, 5.4 +/- 2.1 dynes/cm(2)) during exercise. Also, no differences were seen in temporal flow and wall shear stress oscillations between men and women at rest or during exercise. Similarly, no significant hemodynamic differences were found between the genders at the supraceliac level.These similarities suggest that hemodynamics may not play a significant role in abdominal aortic disease differentiation between the genders and that biologic factors may be more important.

    View details for DOI 10.1067/mva.2002.107

    View details for Web of Science ID 000180465200027

    View details for PubMedID 12514587

  • Quantification of wall shear stress in large blood vessels using lagrangian interpolation functions with cine phase-contrast magnetic resonance imaging ANNALS OF BIOMEDICAL ENGINEERING Cheng, C. P., Parker, D., Taylor, C. A. 2002; 30 (8): 1020-1032

    Abstract

    Arterial wall shear stress is hypothesized to be an important factor in the localization of atherosclerosis. Current methods to compute wall shear stress from magnetic resonance imaging (MRI) data do not account for flow profiles characteristic of pulsatile flow in noncircular vessel lumens. We describe a method to quantify wall shear stress in large blood vessels by differentiating velocity interpolation functions defined using cine phase-contrast MRI data on a band of elements in the neighborhood of the vessel wall. Validation was performed with software phantoms and an in vitro flow phantom. At an image resolution corresponding to in vivo imaging data of the human abdominal aorta, time-averaged, spatially averaged wall shear stress for steady and pulsatile flow were determined to be within 16% and 23% of the analytic solution, respectively. These errors were reduced to 5% and 8% with doubling in image resolution. For the pulsatile software phantom, the oscillation in shear stress was predicted to within 5%. The mean absolute error of circumferentially resolved shear stress for the nonaxisymmetric phantom decreased from 28% to 15% with a doubling in image resolution. The irregularly shaped phantom and in vitro investigation demonstrated convergence of the calculated values with increased image resolution. We quantified the shear stress at the supraceliac and infrarenal regions of a human abdominal aorta to be 3.4 and 2.3 dyn/cm2, respectively.

    View details for DOI 10.1114/1.1511239

    View details for Web of Science ID 000179121200004

    View details for PubMedID 12449763

  • In vivo quantification of blood flow and wall shear stress in the human abdominal aorta during lower limb exercise ANNALS OF BIOMEDICAL ENGINEERING Taylor, C. A., Cheng, C. P., Espinosa, L. A., Tang, B. T., Parker, D., Herfkens, R. J. 2002; 30 (3): 402-408

    Abstract

    Magnetic resonance (MR) imaging techniques and a custom MR-compatible exercise bicycle were used to measure, in vivo, the effects of exercise on hemodynamic conditions in the abdominal aorta of eleven young, healthy subjects. Heart rate increased from 73 +/- 6.2 beats/min at rest to 110 +/- 8.8 beats/min during exercise (p<0.0001). The total blood flow through the abdominal aorta increased from 2.9 +/- 0.6 L/min at rest to 7.2 +/- 1.4 L/min during exercise (p <0.0005) while blood flow to the digestive and renal circulations decreased from 2.1 +/- 0.5 L/min at rest to 1.6 +/- 0.7 L/min during exercise (p<0.01). Infrarenal blood flow increased from 0.9 +/- 0.4 L/min at rest to 5.6 +/- 1.1 L/min during exercise (p<0.0005). Wall shear stress increased in the supraceliac aorta from 3.5 +/- 0.8 dyn/cm2 at rest to 6.2 +/- 0.5 dyn/cm2 during exercise (p<0.0005) and increased in the infrarenal aorta from 1.3 +/- 0.8 dyn/cm2 at rest to 5.2 +/- 1.3 dyn/cm2 during exercise (p<0.0005).

    View details for DOI 10.1114/1.1476016

    View details for Web of Science ID 000175849500012

    View details for PubMedID 12051624

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