Bio

Bio


Currently, I split my time between the medical device industry and academic research. For my day job, I am the CEO of a medical device start up developing a novel implantable device to treat gallstone disease. 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 clinical trials, regulatory affairs, and clinical affairs.

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)

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

2013-14 Courses


Postdoctoral Advisees


Graduate and Fellowship Programs


Publications

Journal Articles


  • 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

  • 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

  • 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

  • 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

  • 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

  • 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

  • IN VIVO QUANTIFICATION OF HUMAN CORONARY ARTERY DEFORMATION FROM CARDIAC-GATED COMPUTED TOMOGRAPHY DATA PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2009, PT A AND B Choi, G., Dusch, M. N., Xiong, G., Xiao, N., Cheng, C. P., Taylor, C. A. 2009: 983-984
  • 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

  • QUANTIFICATION OF THE DEFORMATION OF THE HUMAN ILIAC ARTERIES WITH HIP AND KNEE FLEXION: IMPLICATIONS FOR STENT-GRAFT DESIGN PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE 2008, PTS A AND B Choi, G., Shin, L. K., Taylor, C. A., Cheng, C. P. 2009: 239-240
  • 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 PROCEEDING OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2007 Choi, G., Cheng, C. P., Wilson, N. M., Taylor, C. A. 2007: 543-544
  • Hemodynamics in human abdominal aortic aneurysms during rest and simulated exercise PROCEEDING OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2007 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. 2007: 169-170
  • 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 JOURNAL OF MAGNETIC RESONANCE IMAGING Cheng, C. P., Herfkens, R. J., Taylor, C. A., Feinstein, J. A. 2005; 21 (6): 752-758

    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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