Christopher Cheng

All Publications

• Stent deformations in the common iliac and iliofemoral veins as a result of hip flexion and extension JOURNAL OF VASCULAR SURGERY-VENOUS AND LYMPHATIC DISORDERS Cheng, C. P., Suh, G., Jalaie, H., Barbati, M. E. 2023; 11 (5): 1014-1022

  View details for DOI 10.1016/j.j.vsv2023.02.010

  View details for Web of Science ID 001067706600001

• Pulsatile Deformations of a Conformable Descending Thoracic Aortic Endograft in Aneurysm, Dissection, and Blunt Traumatic Aortic Injury Patients. Journal of endovascular therapy : an official journal of the International Society of Endovascular Specialists Cheng, C. P., Suh, G. Y., Moainie, S. L., Stern, J. R., Szeto, W. Y. 2023: 15266028231187741

  Abstract

  This study presents analytic techniques to quantify cardiac pulsatility-induced deformations of thoracic aortic endografts in patients with thoracic aortic aneurysm (TAA), dissection (TAD), and blunt thoracic aortic injury (BTAI) after thoracic endovascular aortic repair (TEVAR).We analyzed 19 image data sets from 14 patients treated for TAA, TAD, and BTAI with cardiac-gated post-TEVAR CTs. Systolic and diastolic geometric models were constructed and diametric, axial, and bending deformations were quantified. For patients with cardiac-gated pre-op scans, the damping of pulsatile diametric distension was computed. Maximum localized diametric distension was 2.4±1.0%, 4.2±1.7%, and 5.5±1.6%, and axial deformation was 0.0±0.1%, -0.1±0.3%, and 1.1±0.6% in the endografts of TAA, TAD, and BTAI cohorts, respectively. Diametric distension damping from pre- to post-TEVAR was ~50%. Diametric and bending deformations were localized at certain axial positions on the endograft, and the inner curve bends more than the centerline, especially adjacent to overlapping regions.The presented techniques support investigation of multi-axial endograft deformations between disease causes and geometric locations on the device. Discretized quantification of deformation is needed to define device fatigue testing conditions and predict device durability in patients.This study demonstrates analytic techniques to quantify discretized deformation of thoracic endografts. Cardiac-resolved computed tomography is sometimes acquired for surgical planning and follow-up, however, the dynamic data are not typically used to quantify pulsatile deformations. Our analytic techniques extract the centerline and surface geometry of the stented thoracic aorta during the cardiac cycle, which are used to quantify diametric, axial, and bending deformations to provide better understanding of device durability and impact on the native anatomy.

  View details for DOI 10.1177/15266028231187741

  View details for PubMedID 37485662

• Cardiac Pulsatile Helical Deformation of the Thoracic Aorta Before and After Thoracic Endovascular Aortic Repair of Type B Dissections. Journal of endovascular therapy : an official journal of the International Society of Endovascular Specialists Bondesson, J., Suh, G., Dake, M. D., Lee, J. T., Cheng, C. P. 2023: 15266028231179592

  Abstract

  PURPOSE: Type B aortic dissections propagate with either achiral (nonspiraling) or right-handed chiral (spiraling) morphology, have mobile dissection flaps, and are often treated with thoracic endovascular aortic repair (TEVAR). We aim to quantify cardiac-induced helical deformation of the true lumen of type B aortic dissections before and after TEVAR.MATERIAL AND METHODS: Retrospective cardiac-gated computed tomography (CT) images before and after TEVAR of type B aortic dissections were used to construct systolic and diastolic 3-dimensional (3D) surface models, including true lumen, whole lumen (true+false lumens), and branch vessels. This was followed by extraction of true lumen helicity (helical angle, twist, and radius) and cross-sectional (area, circumference, and minor/major diameter ratio) metrics. Deformations between systole and diastole were quantified, and deformations between pre- and post-TEVAR were compared.RESULTS: Eleven TEVAR patients (59.9±4.6 years) were included in this study. Pre-TEVAR, there were no significant cardiac-induced deformations of helical metrics; however, post-TEVAR, significant deformation was observed for the true lumen proximal angular position. Pre-TEVAR, cardiac-induced deformations of all cross-sectional metrics were significant; however, only area and circumference deformations remained significant post-TEVAR. There were no significant differences of pulsatile deformation from pre- to post-TEVAR. Variance of proximal angular position and cross-sectional circumference deformation decreased after TEVAR.CONCLUSION: Pre-TEVAR, type B aortic dissections did not exhibit significant helical cardiac-induced deformation, indicating that the true and false lumens move in unison (do not move with respect to each other). Post-TEVAR, true lumens exhibited significant cardiac-induced deformation of proximal angular position, suggesting that exclusion of the false lumen leads to greater rotational deformations of the true lumen and lack of true lumen major/minor deformation post-TEVAR means that the endograft promotes static circularity. Population variance of deformations is muted after TEVAR, and dissection acuity influences pulsatile deformation while pre-TEVAR chirality does not.CLINICAL IMPACT: Description of thoracic aortic dissection helical morphology and dynamics, and understanding the impact of thoracic endovascular aortic repair (TEVAR) on dissection helicity, are important for improving endovascular treatment. These findings provide nuance to the complex shape and motion of the true and false lumens, enabling clinicians to better stratify dissection disease. The impact of TEVAR on dissection helicity provides a description of how treatment alters morphology and motion, and may provide clues for treatment durability. Finally, the helical component to endograft deformation is important to form comprehensive boundary conditions for testing and developing new endovascular devices.

  View details for DOI 10.1177/15266028231179592

  View details for PubMedID 37300396

• Renovisceral Artery Alterations due to Branched Endovascular Aortic Repair and Respiratory-induced Deformations. Journal of vascular surgery Cheng, C. P., Bondesson, J., Bendavid, J., Haulon, S. 2023

  Abstract

  OBJECTIVE: This study quantified respiratory-induced dynamics of branch vessels before and after thoracoabdominal aortic aneurysm (TAAA) branched endovascular aneurysm repair (bEVAR).METHODS: TAAA patients were prospectively recruited and treated with bEVAR, predominantly with Zenith t-Branch and BeGraft Peripheral PLUS bridging stents. Using SimVascular software, 3D geometric models of the vessels and implants were constructed from CT angiograms during both inspiratory and expiratory breath-holds, pre- and post-operatively. From these models, branch take-off angles, end-stent angles (transition from distal end of stent to native artery), and curvatures were computed. Paired, two-tailed t-tests were performed to compare inspiratory vs. expiratory geometry and pre- vs. post-operative deformations.RESULTS: N=52 (12 celiac (CA), 15 superior mesenteric (SMA), 25 renal arteries (RA)) branched renovisceral vessels with bridging stents were evaluated in 15 patients. Implantation of bridging stents caused branch take-off angle to shift inferiorly in the SMA (p=0.015) and RA (p=0.014), and decreased respiratory-induced branch angle motion in the CA and SMA by 50%. End-stent angle increased from pre- to post-bEVAR for the CA (p=0.005), SMA (p=0.020), and RA (p<0.001), however, respiratory-induced deformation was unchanged. Bridging stents did not experience significant bending due to respiration.CONCLUSIONS: The reduction in respiratory-induced deformation of branch take-off angle from pre- to post-bEVAR should reduce the risk of device disengagement and endoleak. The unchanging respiratory-induced end-stent bending, from pre- to post-bEVAR, means that bEVAR maintains native vessel dynamics distal to the bridging stents. This minimizes the risk of tissue irritation due to respiratory cycles, boding well for branch vessel patency. The longer bridging stent paths associated with bEVAR may enable smoother paths subject to less dynamic bending, and potentially lower fatigue risk, compared to fEVAR.

  View details for DOI 10.1016/j.jvs.2023.05.032

  View details for PubMedID 37236516

• Stent Deformations in the Common Iliac and Iliofemoral Veins as a Result of Hip Flexion and Extension. Journal of vascular surgery. Venous and lymphatic disorders Cheng, C. P., Suh, G. Y., Jalaie, H., Barbati, M. E. 2023

  Abstract

  Characterize deformations of venous stents implanted into common iliac veins (for Non-thrombotic iliac vein lesion) and iliofemoral veins (for deep vein thrombosis) due to hip movements commensurate with everyday activities such as walking, sitting, and stair-climbing.Patients treated with iliofemoral venous stents were recruited from three centers and imaged with two orthogonal 2D projection X-rays. Stents in the common iliac veins and iliofemoral veins crossing the hip joint were imaged in 0°/30°/90° and -15°/0°/30° hip positions, respectively. Using the X-ray images, 3D geometries of the stents were constructed for each hip position and diametric and bending deformations between those positions were quantified.Twelve patients were included and showed that common iliac vein stents experienced approximately 2-fold more local diametric compression with 90° hip flexion compared to 30° flexion, and iliofemoral vein stents crossing the hip joint experienced significant bending with hip hyperextension (-15°) but not with hip flexion. In both anatomic locations, maximum local diametric and bending deformations were in proximity with each other.Stents implanted in the common iliac and iliofemoral veins exhibit greater deformation during high hip flexion and hyperextension, respectively, and iliofemoral venous stents interact with the superior ramus of the pubis during hyperextension. This suggests that device fatigue could be influenced by the type and level of patient physical activity, as well as anatomic positioning, opening up the potential benefit of activity modification and careful implantation strategy. The proximity of maximum diametric and bending deformations means that simultaneous multimodal deformations need to be considered for device design and evaluation.

  View details for DOI 10.1016/j.jvsv.2023.02.010

  View details for PubMedID 37172935

• Ascending Aortic Endograft and Thoracic Aortic Deformation After Ascending Thoracic Endovascular Aortic Repair. Journal of endovascular therapy : an official journal of the International Society of Endovascular Specialists Suh, G. K., Bondesson, J., Zhu, Y. D., Nilson, M. C., Roselli, E. E., Cheng, C. P. 2023: 15266028231168351

  Abstract

  We aim to quantify multiaxial cardiac pulsatility-induced deformation of the thoracic aorta after ascending thoracic endovascular aortic repair (TEVAR) as a part of the GORE ARISE Early Feasibility Study.Fifteen patients (7 females and 8 males, age 73±9 years) with ascending TEVAR underwent computed tomography angiography with retrospective cardiac gating. Geometric modeling of the thoracic aorta was performed; geometric features including axial length, effective diameter, and centerline, inner surface, and outer surface curvatures were quantified for systole and diastole; and pulsatile deformations were calculated for the ascending aorta, arch, and descending aorta.From diastole to systole, the ascending endograft exhibited straightening of the centerline (0.224±0.039 to 0.217±0.039 cm-1, p<0.05) and outer surface (0.181±0.028 to 0.177±0.029 cm-1, p<0.05) curvatures. No significant changes were observed for inner surface curvature, diameter, or axial length in the ascending endograft. The aortic arch did not exhibit any significant deformation in axial length, diameter, or curvature. The descending aorta exhibited small but significant expansion of effective diameter from 2.59±0.46 to 2.63±0.44 cm (p<0.05).Compared with the native ascending aorta (from prior literature), ascending TEVAR damps axial and bending pulsatile deformations of the ascending aorta similar to how descending TEVAR damps descending aortic deformations, while diametric deformations are damped to a greater extent. Downstream diametric and bending pulsatility of the native descending aorta was muted compared with that in patients without ascending TEVAR (from prior literature). Deformation data from this study can be used to evaluate the mechanical durability of ascending aortic devices and inform physicians about the downstream effects of ascending TEVAR to help predict remodeling and guide future interventional strategies.This study quantified local deformations of both stented ascending and native descending aortas to reveal the biomechanical impact of ascending TEVAR on the entire thoracic aorta, and reported that the ascending TEVAR muted cardiac-induced deformation of the stented ascending aorta and native descending aorta. Understanding of in vivo deformations of the stented ascending aorta, aortic arch and descending aorta can inform physicians about the downstream effects of ascending TEVAR. Notable reduction of compliance may lead to cardiac remodeling and long-term systemic complications. This is the first report which included dedicated deformation data regarding ascending aortic endograft from clinical trial.

  View details for DOI 10.1177/15266028231168351

  View details for PubMedID 37144300

• Longitudinal Mapping of True Lumen Morphology for Accurate Endograft Oversizing in Patients with Type B Aortic Dissections Bondesson, J., Raja, S., Suh, G., Dake, M. D., Lee, J. T., Cheng, C. P. MOSBY-ELSEVIER. 2023: 64S-65S

  View details for Web of Science ID 000994639100142

• Boundary Conditions and Long-Term Implantation Effects with Cardiovascular Nitinol Implants SHAPE MEMORY AND SUPERELASTICITY Suh, G., Frakes, D., Kamali, R., Cheng, C. P. 2022

  View details for DOI 10.1007/s40830-022-00376-z

  View details for Web of Science ID 000824826600001

• Impact of renal chimney intra-aortic stent length on branch and end-stent angle in chimney endovascular aneurysm repair and endovascular aneurysm sealing configurations. Vascular Ullery, B. W., Suh, G., Thompson, P., Lee, J. T., Holden, A., Dalman, R. L., Cheng, C. P. 1800: 17085381211059978

  Abstract

  OBJECTIVE: Practice patterns and durability of parallel stent graft techniques in complex endovascular aneurysm repair (EVAR) remain poorly defined. We aimed to quantify and compare the impact of renal chimney intra-aortic stent length (IASL) on geometric deformations of renal arteries in complex EVAR.METHODS: Thirty-eight nonconsecutive patients underwent EVAR utilizing parallel stent graft techniques (chimney EVAR [chEVAR], n = 28; chimney endovascular aneurysm sealing [chEVAS], n = 10) between 2010 and 2016. A total of 59 renal chimney stent grafts were used. Geometric quantification was derived from three-dimensional model-based centerline extraction. Renal chimney intra-aortic stent length (IASL) was defined as the length of chimney stent that extended from the proximal edge of the chimney stent to the ostium of the corresponding renal artery.RESULTS: Mean IASL for both left and right renal arteries in the cohort was 35.7mm. Renal arteries containing chimney IASL <30mm trended toward a greater branch angle (135.4 vs. 127.8°, p = .06). Left renal arteries showed significantly greater branch angle among those with IASL <40mm (135.5 vs. 121.7°, p = .045). Mean IASL for renal arteries in chEVAR was significantly longer compared to chEVAS (39.2 vs. 26.3mm, p = .003). No difference was noted in overall branch angle or end-stent angle based on procedure type. ChEVAR with IASL <30mm had significantly greater end-stent angle (48.2 vs. 33.5°, p = .03). In contrast, chEVAS patients showed no difference in end-stent angle based on IASL thresholds, but did have significantly greater branch angle among those with IASL <30mm when grouped by both all renal arteries (133.5 vs. 113.5°, p = .004) and right renal arteries (134.3 vs. 111.6°, p = .02).CONCLUSIONS: Renal chimney stents with longer IASL appear to exhibit less renal artery deformation, suggesting a more gradual and perpendicular transition of the chimney stent across the renal ostium.

  View details for DOI 10.1177/17085381211059978

  View details for PubMedID 34963378

• Influence of Thoracic Endovascular Aortic Repair on True Lumen Helical Morphology for Stanford Type B Dissections. Journal of vascular surgery Bondesson, J., Suh, G., Marks, N., Dake, M. D., Lee, J. T., Cheng, C. P. 2021

  Abstract

  OBJECTIVE: Thoracic endovascular aortic repair (TEVAR) can change the morphology of the flow lumen in aortic dissections, which may affect aortic hemodynamics and function. This study characterizes how helical morphology of the true lumen in type B aortic dissections is altered by TEVAR.METHODS: Patients with type B aortic dissection who underwent computed tomography angiography pre- and post-TEVAR were retrospectively reviewed. Images were used to construct 3D stereolithographic (STL) surface models of the true lumen and whole aorta using custom software. STL models were segmented and co-registered to determine helical morphology of the true lumen with respect to the whole aorta. The true lumen region covered by the endograft was defined based on fiducial markers pre- and post-TEVAR. Helical angle, average helical twist, peak helical twist, and cross-sectional eccentricity, area, and circumference were quantified in this region for pre- and post-TEVAR geometries.RESULTS: Sixteen patients (61.3±8.0 years, 12.5% female) were treated successfully for type B dissection (five acute and eleven chronic) with TEVAR and scans pre- and post-TEVAR were retrospectively obtained (follow-up interval 52±91 days). From pre- to post-TEVAR, true lumen helical angle (-70.0±71.1 to -64.9±75.4 deg, p=0.782), average helical twist (-4.1±4.0 to -3.7±3.8 deg/cm, p=0.674) and peak helical twist (-13.2±15.2 to -15.4±14.2 deg/cm, p=0.629) did not change. However, true lumen helical radius (1.4±0.5 to 1.0±0.6 cm, p<0.05) and eccentricity (0.9±0.1 to 0.7±0.1, p<0.05) decreased, and cross-sectional area (3.0±1.1 to 5.0±2.0 cm2, p<0.05) and circumference (7.1±1.0 to 8.0±1.4 cm, p<0.05) increased significantly from pre- to post-TEVAR. The distinct bimodal distribution of chiral and achiral native dissections disappeared post-TEVAR, and subgroup analyses showed that the true lumen circumference of acute dissections increased with TEVAR, while it did not for chronic dissections.CONCLUSIONS: The unchanged helical angle and average and peak helical twists as a result of TEVAR suggest that angular positions of the true lumen are constrained and that the endografts were helically conformable in the angular direction. The decrease of helical radius indicated a straightening of the "corkscrew" shape of the true lumen, and in combination with more circular and expanded lumen cross-sections, TEVAR produced luminal morphology that theoretically allows for lower flow resistance through the endografted portion. The impact of TEVAR on dissection flow lumen morphology and the interaction between endografts and aortic tissue can provide insight for improving device design, implantation technique, and long-term clinical outcomes.

  View details for DOI 10.1016/j.jvs.2021.04.029

  View details for PubMedID 33940073

• Thoracic aortic parallel stent-graft behaviour when subjected to radial loading. Journal of the mechanical behavior of biomedical materials Kwiecinski, J., Cheng, C. P., Uberoi, R., Hadi, M., Hempel, P., Degel, C., You, Z. 2021; 118: 104407

  Abstract

  To manage complex aortic arch disease using minimally invasive techniques, interventionalists have reported the use of multiple stent-graft devices deployed in a parallel configuration. The structural device-device and device-artery interactions arising during aortic arch parallel endografting, also known as chimney thoracic endovascular aortic repair (ch-TEVAR), is not well understood. Through the use of a radial force testing system we sought to characterise both the loading and deformation behaviour of parallel endografts in representative ch-TEVAR configurations. Four commercially available devices (Bentley BeGraft, Gore TAG, Gore Viabahn, and Medtronic Valiant) were subjected to uniform radial load individually, and in six combinations, to quantify loading profiles. Image data collected during testing were analysed to evaluate mechanical deformations in terms of gutters, chimney and main endograft compression, as well as graft infolding. Parallel endografting was found to increase radial loads when compared to standard TEVAR. Chronic outward force during ch-TEVAR was dependent on main endograft manufacturer, with TAG combinations leading to consistently higher loads than Valiant, but independent of chimney graft type. Endograft deformations were dependent on chimney graft type, with Viabahn combinations presenting with lower gutter areas and increased lumen compression than BeGraft. Chimney graft deformations were also influenced by deployment arrangement in the case of double ch-TEVAR. This study emphasizes the significant variability in both radial loads and mechanical deformations between clinically relevant ch-TEVAR configurations.

  View details for DOI 10.1016/j.jmbbm.2021.104407

  View details for PubMedID 33740690

• Multiaxial pulsatile dynamics of the thoracic aorta and impact of thoracic endovascular repair. European journal of radiology open Suh, G., Bondesson, J., Zhu, Y. D., Lee, J. T., Dake, M. D., Cheng, C. P. 2021; 8: 100333

  Abstract

  Purpose: The thoracic aorta is a highly mobile organ whose dynamics are altered by thoracic endovascular aorta repair (TEVAR). The aim of this study was to quantify cardiac pulsatility-induced multi-axial deformation of the thoracic aorta before and after descending aortic TEVAR.Methods: Eleven TEVAR patients (8 males and 3 females, age 57-89) underwent retrospective cardiac-gated CT angiography before and after TEVAR. 3D geometric models of the thoracic aorta were constructed, and lumen centerlines, inner and outer surface curves, and cross-sections were extracted to measure aortic arclength, centerline, inner surface, and outer surface longitudinal curvatures, as well as cross-sectional effective diameter and eccentricity for the ascending and stented aortic portions.Results: From pre- to post-TEVAR, arclength deformation was increased at the ascending aorta from 5.9 ± 3.1 % to 8.8 ± 4.4 % (P < 0.05), and decreased at the stented aorta from 7.5 ± 5.1 % to 2.7 ± 2.5 % (P < 0.05). Longitudinal curvature and diametric deformations were reduced at the stented aorta. Centerline curvature, inner surface curvature, and cross-sectional eccentricity deformations were increased at the distal ascending aorta.Conclusions: Deformations were reduced in the stented thoracic aorta after TEVAR, but increased in the ascending aorta near the aortic arch, possibly as a compensatory mechanism to maintain overall thoracic compliance in the presence of reduced deformation in the stiffened stented aorta.

  View details for DOI 10.1016/j.ejro.2021.100333

  View details for PubMedID 33748348

• Respiratory-induced changes in renovisceral branch vessel morphology after fenestrated thoracoabdominal aneurysm repair with the BeGraft balloon-expandable covered stent. Journal of vascular surgery Tran, K., Suh, G. Y., Mougin, J., Haulon, S., Cheng, C. 2021

  Abstract

  We evaluated the respiratory-induced changes in branch vessel geometry after thoracoabdominal fenestrated endovascular aneurysm repair (fEVAR) with the Bentley BeGraft graft (Innomed GmbH, Hechingen, Germany) as the covered bridging stent.Patients treated with fEVAR for thoracoabdominal aortic aneurysms with a custom-made Zenith fenestrated endograft (Cook Medical Europe Ltd, Limerick, Ireland) and Bentley BeGraft peripheral stents were prospectively recruited. Using SimVascular software (Open-Source Medical Software Corp, San Diego, CA), the pre- and postoperative aortic and branch contours were segmented from computed tomography angiograms performed during inspiratory and expiratory breath-holds. The centerlines were extracted from the lumen contours, from which the branch take-off angles, distal stent angles, and peak branch curvature changes were computed. Paired, two-tailed t tests were performed to compare the pre- and postoperative deformations.Renovisceral vessel geometry was evaluated in 12 patients undergoing fEVAR with a total of 46 target vessels (10 celiac arteries, 12 superior mesenteric arteries [SMAs], 24 renal arteries). Implantation of BeGraft bridging stents was associated with a significant reduction in respiration-induced changes in vessel branch angulation (Δ5.3° ± 3.9° vs Δ12.0° ± 8.3° [postoperative vs preoperative]; P = .001) and mean curvature (0.72 ± 0.22 cm-1 vs 0.53 ± 0.18 cm-1) in the renal arteries, without significant changes in the celiac arteries or SMAs. No significant difference was found in end-stent angle motion in the renal arteries (P = .77), celiac arteries (P = .34), or SMAs (P = .55). The maximum local vessel curvature change decreased after fEVAR in the SMAs (Δ0.28 cm-1 vs Δ0.47 cm-1; P = .04) but was unchanged in the celiac (P = .61) and renal (P = .51) arteries.Implantation of the BeGraft as a bridging stent in fEVAR was associated with decreased respiratory-induced deformation in the renal branch take-off angulation and mean renal artery curvature, with reduced maximum curvature bending in the SMA compared with the preoperative anatomy. However, the BeGraft allowed for celiac and renal artery bending similar to that in the native preoperative state. These findings suggest that the use of BeGraft peripheral stents with fEVAR will closely mimic the native arterial branch geometry and vessel conformability caused by relatively aggressive respiratory motion.

  View details for DOI 10.1016/j.jvs.2020.12.093

  View details for PubMedID 33548438

• The Triple-Wire Technique for Delivery of Endovascular Components in Difficult Anatomy. Annals of vascular surgery Stern, J. R., Cheng, C. P., Colvard, B. D., Paranjape, H., Lee, J. T. 2020

  Abstract

  We describe a novel endovascular technique in which three 0.014" guidewires are placed in parallel through a 0.035" lumen catheter, in order to create a stiff platform to allow for delivery of 0.035" profile devices through challenging anatomy. Three illustrative cases are presented: a difficult aortic bifurcation during lower extremity intervention, a tortuous internal iliac artery during placement of an iliac branch device, and salvage of a renal artery after inadvertent coverage during proximal cuff deployment for type 1a endoleak. We also quantify the relative stiffness of the triple 0.014" wire configuration, using several well-known 0.035" wires for comparison. The "triple-wire technique" is an effective method for tracking endovascular devices through difficult tortuous anatomy, and can be used in a variety of clinical settings. The technique is especially useful when a traditional, stiff 0.035" wire will not track without "kicking out." Each 0.014" wire is reasonably soft and traverses the tortuous vessel easily, but when the three wires are used together as a rail it provides a stiff enough platform for delivery.

  View details for DOI 10.1016/j.avsg.2020.04.021

  View details for PubMedID 32335254

• The biomechanical impact of hip movement on iliofemoral venous anatomy and stenting for deep venous thrombosis. Journal of vascular surgery. Venous and lymphatic disorders Cheng, C. P., Dua, A., Suh, G., Shah, R. P., Black, S. A. 2020

  Abstract

  BACKGROUND: Stenting of the iliofemoral vein may be an effective treatment to improve post-thrombotic symptoms. Iliofemoral vein stents have requirements different from those of lower extremity artery stents, and there is a paucity of literature regarding the biomechanical motion of the iliofemoral vein.METHODS: In a novel cadaveric model, stents were bilaterally inserted into the veins in the iliofemoral region. The veins were pressurized and underwent computed tomography angiography at various hip angle positions. In addition, 21 patients with iliofemoral vein disease had supine computed tomography angiography before and after stenting. The stents and vasculature were reconstructed into three-dimensional geometric models to quantify stent deformations and the interaction between the iliofemoral vein, inguinal ligament, and pubis bone due to hip flexion-extension.RESULTS: In the cadavers, from supine to 30 to 45 degrees and 50 to 75 degrees of hip flexion, iliofemoral vein stents became less compressed (4.5% minor diameter expansion), and the inguinal ligament was separated from the iliofemoral veins by 1 to 3cm in all hip positions. In the patients, the pubis compressed 47% of femoral veins; 78% were within 3mm of the pubis. There was also evidence of contrast-enhanced flow disruption at the superior ramus.CONCLUSIONS: The cadaver and clinical evidence shows that contrary to widely accepted dogma, the common femoral vein is not compressed by the inguinal ligament during hip flexion but rather by the superior ramus of the pubis during hip extension, which may have an impact on future stent design and influence deep venous thrombosis treatment strategies.

  View details for DOI 10.1016/j.jvsv.2020.01.022

  View details for PubMedID 32321693

• Thoracic aortic geometry correlates with endograft bird-beaking severity. Journal of vascular surgery Frohlich, M. M., Suh, G., Bondesson, J., Leineweber, M., Lee, J. T., Dake, M. D., Cheng, C. P. 2020

  Abstract

  OBJECTIVE: Aortic geometry has been shown to influence the development of endograft malapposition (bird-beaking) in thoracic endovascular aortic repair (TEVAR), but the extent of this relationship lacks clarity. The aim of this study was to develop a reproducible method of measuring bird-beak severity and to investigate preoperative geometry associated with bird-beaking.METHODS: The study retrospectively analyzed 20 patients with thoracic aortic aneurysms or type B dissections treated with TEVAR. Computed tomography scans were used to construct three-dimensional geometric models of the preoperative and postoperative aorta and endograft. Postoperative bird-beaking was quantified with length, height, and angle; categorized into a bird-beak group (BBG; n= 10) and no bird-beak group (NBBG; n= 10) using bird-beak height ≥5mm as a threshold; and correlated to preoperative metrics including aortic cross-sectional area, inner curvature, diameter, and inner curvature*diameter as well as graft diameter and oversizing at the proximal landing zone.RESULTS: Aortic area (1002± 118mm2 vs 834± 248mm2), inner curvature (0.040± 0.014mm-1 vs 0.031± 0.012mm-1), and diameter (35.7± 2.1mm vs 32.2± 4.9mm) were not significantly different between BBG and NBBG; however, inner curvature*diameter was significantly higher in BBG (1.4± 0.5 vs 1.0± 0.3; P= .030). Inner curvature and curvature*diameter were significantly correlated with bird-beak height (R= 0.462, P= .041; R= 0.592, P= .006) and bird-beak angle (R= 0.680, P< .001; R= 0.712, P< .001).CONCLUSIONS: TEVAR bird-beak severity can be quantified and predicted with geometric modeling techniques, and the combination of high preoperative aortic inner curvature and diameter increases the risk for development of TEVAR bird-beaking.

  View details for DOI 10.1016/j.jvs.2019.11.045

  View details for PubMedID 32035770

• Quantification of True Lumen Helical Morphology and Chirality in Type B Aortic Dissections. American journal of physiology. Heart and circulatory physiology Bondesson, J. n., Suh, G. Y., Lundh, T. n., Dake, M. D., Lee, J. T., Cheng, C. P. 2020

  Abstract

  Chirality is a fundamental property in many biologic systems. Motivated by previous observations of helical aortic blood flow, aortic tissue fibers, and propagation of aortic dissections, we introduce methods to characterize helical morphology of aortic dissections. After validation on computer generated phantoms, the methods were applied to patients with type B dissection. For this cohort, there was a distinct bimodal distribution of helical propagation of the dissection with either achiral or exclusively right-handed chirality, with no intermediate cases or left-handed cases. This clear grouping indicates that dissection propagation favors these two modes, potentially due to the right-handedness of helical aortic blood flow and cell orientation. The characterization of dissection chirality and quantification of helical morphology advances our understanding of dissection pathology and lays a foundation for applications in clinical research and treatment practice. For example, the chirality and magnitude of helical metrics of dissections may indicate risk of dissection progression, help define treatment and surveillance strategies, and enable development of novel devices that account for various helical morphologies.

  View details for DOI 10.1152/ajpheart.00778.2020

  View details for PubMedID 33382638

• Effects of Heat Treatment on the Magnetic Properties of Nitinol Devices SHAPE MEMORY AND SUPERELASTICITY Combs, J., Levin, E., Cheng, C., Daly, S., Yeralan, S., Duerig, T. 2019; 5 (4): 429–35

  View details for DOI 10.1007/s40830-019-00258-x

  View details for Web of Science ID 000511684400014

• Automated Quantification of Diseased Thoracic Aortic Longitudinal Centerline and Surface Curvatures. Journal of biomechanical engineering Bondesson, J. H., Suh, G., Lundh, T., Lee, J. T., Dake, M. D., Cheng, C. 2019

  Abstract

  Precise description of vascular morphometry is crucial to support medical device manufacturers and clinicians for improving device development and interventional outcomes. A compact and intuitive method is presented to automatically characterize the surface geometry of tubular anatomic structures and quantify surface curvatures starting from generic stereolithographic surfaces. The method was validated with software phantoms and used to quantify the longitudinal surface curvatures of 37 human thoracic aortas with aneurysm or dissection. The quantification of surface curvatures showed good agreement with analytic solutions from the software phantoms, and demonstrated better agreement as compared to estimation methods using only centerline geometry and cross-sectional radii. For the human thoracic aortas, longitudinal inner surface curvature was significantly higher than centerline curvature (0.33±0.06 vs. 0.16±0.02 cm-1 for mean; 1.38±0.48 vs. 0.45±0.11 cm-1 for peak; both p<0.001). These findings show the importance of quantifying surface curvatures in order to better describe the geometry and biomechanical behavior of the thoracic aorta, which can assist in treatment planning and supplying device manufactures with more precise boundary conditions for mechanical evaluation.

  View details for DOI 10.1115/1.4045271

  View details for PubMedID 31633168

• Iliofemoral Vein Compression Is Caused by the Pubic Bone, Not the Inguinal Ligament Cheng, C., Suh, G., Shah, R., Black, S., Chinubhai, A. ELSEVIER SCIENCE INC. 2019: B558

  View details for Web of Science ID 000487306300559

• Cardiac Pulsatility- and Respiratory-Induced Deformations of the Renal Arteries and Snorkel Stents After Snorkel Endovascular Aneurysm Sealing. Journal of endovascular therapy : an official journal of the International Society of Endovascular Specialists Cheng, C. P., Suh, G., Kim, J. J., Holden, A. 2019: 1526602819856363

  Abstract

  Purpose: To quantify deformations of renal arteries and snorkel stents after snorkel endovascular aneurysm sealing (Sn-EVAS) resulting from cardiac pulsatility and respiration and compare these deformations to patients with untreated abdominal aortic aneurysms (AAA) and snorkel endovascular aneurysm repair (Sn-EVAR). Materials and Methods: Ten Sn-EVAS patients (mean age 75±6 years; 8 men) were scanned with cardiac-gated, respiration-resolved computed tomography angiography. From 3-dimensional geometric models, changes in renal artery and stent angulation and curvature due to cardiac pulsatility and respiration were quantified. Respiration-induced motions were compared with those of 16 previously reported untreated AAA patients and 11 Sn-EVAR patients. Results: Renal artery bending at the stent end was greater for respiratory vs cardiac influences (6°±7° vs -1°±2°, p<0.025). Respiration caused a 3-fold greater deformation on the left renal artery as compared with the right side. Maximum curvature change was higher for respiratory vs cardiac influences (0.49±0.29 vs 0.24±0.17 cm-1, p<0.025), and snorkel renal stents experienced similar maximum curvature change due to cardiac pulsatility and respiration (0.14±0.10 vs 0.19±0.09 cm-1, p=0.142). When comparing the 3 patient cohorts for respiratory-induced deformation, there was significant renal branch angulation in untreated AAAs, but not in Sn-EVAR or Sn-EVAS, and there was significant bending at the stent end in Sn-EVAR and Sn-EVAS. Maximum curvature change due to respiration was ~10-fold greater in Sn-EVAR and Sn-EVAS compared to untreated AAAs. Conclusion: The findings suggest that cardiac and respiratory influences may challenge the mechanical durability of snorkel stents of Sn-EVAS; similarly, however, respiration may be the primary culprit for tissue irritation, increasing the risk for stent-end thrombosis, especially in the left renal artery. The bending stiffness of snorkel stents in both the Sn-EVAR and Sn-EVAS cohorts damped renal branch angulation while it intensified bending of the artery distal to the snorkel stent. Understanding these device-to-artery interactions is critical as they may affect mechanical durability of branch stents and quality and durability of treatment.

  View details for DOI 10.1177/1526602819856363

  View details for PubMedID 31210077

• Length Redundancy and Twist Improve the Biomechanical Properties of Polytetrafluoroethylene Bypass Grafts. Annals of vascular surgery Lee, R. n., Stoddart, M. n., Dyson, I. n., Cassimjee, I. n., Handa, A. n., Cheng, C. P. 2019

  Abstract

  The iliofemoropopliteal artery significantly changes path length during normal hip and knee flexion. Prosthetic bypass grafts, such as polytetrafluroethelene (PTFE) grafts, are relatively stiff and thus can subject graft anastomoses to high tension when the path length increases. The aim of this study was to examine the influence of length redundancy and twist on the biomechanical properties of PTFE bypass grafts.Unreinforced and ring-reinforced PTFE grafts were loaded in an axial mechanical testing machine to measure the tensile and compressive axial forces with varying levels of length redundancy and axial twist.Adding 5-15% length redundancy to a graft decreases the force to cause 5% extension by >90% without substantially increasing shortening forces. Adding 4.5 °/cm of axial twist imparts a corkscrew shape to the graft without increasing extension or shortening forces in the presence of length redundancy. Ring-reinforced PTFE grafts require more length redundancy to experience these reduction in forces especially in the presence of axial twist.A modest amount of length redundancy and twist (i.e. a cork-screwed condition) confers improved biomechanical properties in a PTFE graft, especially in ring-reinforced grafts. This should be taken into consideration when fashioning an arterial bypass graft in the ilio-femoral-popliteal segment.

  View details for DOI 10.1016/j.avsg.2019.04.007

  View details for PubMedID 31319171

• 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 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 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 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 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 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 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

• If You Build It, They Will Come: How to Establish an Academic Innovation Enterprise TECHNIQUES IN VASCULAR AND INTERVENTIONAL RADIOLOGY Srimathveeravalli, G., Balesh, E., Cheng, C. P., Chen, D. 2017; 20 (2): 121–26

  Abstract

  The rapid growth of minimally invasive, image-guided intervention has redefined the procedural management of multiple disease entities. The process of innovation which has characterized the growth of interventional radiology can be best described as "needs-based," whereby practicing interventionalists identify unmet clinical needs and subsequently invent solutions to achieve desired technical and clinical outcomes. Historically, catheters and other percutaneous devices were developed with rudimentary manufacturing techniques and subsequently translated to patients with relatively little regulatory oversight. Since then, the resources required and financial costs of interventional technology development have grown exponentially. Fortunately, advances in software development, new methods of rapid prototyping, and commoditization of hardware components have made in-house engineering feasible once again. This has created an opportunity for academic medical centers to translate their research into testable prototypes in humans sooner and at reduced costs, and academic interventional radiology divisions are now leveraging these developments to create collaborative centers of innovation. This article describes five such organizational formats for collaboration and innovation in the academic setting, describing the structure, opportunities, requirements, and caveats of each model.

  View details for PubMedID 28673649

• 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

  Abstract

  Lower-extremity exercise has been shown to eliminate adverse hemodynamics conditions, such as low and oscillating blood flow and wall shear stress, in the abdominal aortas of healthy young and older adults.We use cine phase-contrast magnetic resonance imaging and a custom MRI-compatible exercise cycle to quantify hemodynamic changes because of pedaling exercise in patients diagnosed with intermittent claudication.With only an average heart increase of 35 ± 18% and exercise workload of 36 ± 16 watts, the patients experienced approximately 3- and 6-fold increases in blood flow, and 4- and 16-fold increases in wall shear stress at the supraceliac and infrarenal aortic locations, respectively. Also, all oscillations in flow and shear stress at rest were eliminated with exercise.Claudication patients experience 3- to 4-fold lower oscillations in flow and shear stress at rest as compared with healthy age-matched controls, likely because of reduced distal arterial compliance as a result of distal atherosclerosis. The magnitude of flow and shear oscillatory indices may be good indicators of distal arterial compliance and health, and may provide predictive power for the efficacy of focal interventions.

  View details for DOI 10.1016/j.avsg.2015.06.089

  View details for Web of Science ID 000363475300006

  View details for PubMedID 26315797

  View details for PubMedCentralID PMC4631628

• 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 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

• 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 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 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