John N. Oshinski

Association of coronary wall shear stress with atherosclerotic plaque burden, composition, and distribution in patients with coronary artery disease.

Background Extremes of wall shear stress (WSS) have been associated with plaque progression and transformation, which has raised interest in the clinical assessment of WSS. We hypothesized that calculated coronary WSS is predicted only partially by luminal geometry and that WSS is related to plaque composition. Methods and Results Twenty‐seven patients with coronary artery disease underwent virtual histology intravascular ultrasound and Doppler velocity measurement for computational fluid dynamics modeling for WSS calculation in each virtual histology intravascular ultrasound segment (N=3581 segments). We assessed the association of WSS with plaque burden and distribution and with plaque composition. WSS remained relatively constant across the lower 3 quartiles of plaque burden (P=0.08) but increased in the highest quartile of plaque burden (P<0.001). Segments distal to lesions or within bifurcations were more likely to have low WSS (P<0.001). However, the majority of segments distal to lesions (80%) and within bifurcations (89%) did not exhibit low WSS. After adjustment for plaque burden, there was a negative association between WSS and percent necrotic core and calcium. For every 10 dynes/cm2 increase in WSS, percent necrotic core decreased by 17% (P=0.01), and percent dense calcium decreased by 17% (P<0.001). There was no significant association between WSS and percent of fibrous or fibrofatty plaque components (P=NS). Conclusions In patients with coronary artery disease: (1) Luminal geometry predicts calculated WSS only partially, which suggests that detailed computational techniques must be used to calculate WSS. (2) Low WSS is associated with plaque necrotic core and calcium, independent of plaque burden, which suggests a link between WSS and coronary plaque phenotype. (J Am Heart Assoc. 2012;1:e002543 doi: 10.1161/JAHA.112.002543.)

Optimum fuzzy filters for phase‐contrast magnetic resonance imaging segmentation

To develop and validate a multidimensional segmentation and filtering methodology for accurate blood flow velocity field reconstruction from phase‐contrast magnetic resonance imaging (PC MRI).

Framework to Co-register Longitudinal Virtual Histology-Intravascular Ultrasound Data in the Circumferential Direction

Considerable efforts have been directed at identifying prognostic markers for rapidly progressing coronary atherosclerotic lesions that may advance into a high-risk (vulnerable) state. Intravascular ultrasound (IVUS) has become a valuable clinical tool to study the natural history of coronary artery disease (CAD). While prospectively IVUS studies have provided tremendous insight on CAD progression, and its association with independent markers (e.g., wall shear stress), they are limited by the inability to examine the focal association between spatially heterogeneous variables (in both circumferential and axial directions). Herein, we present a framework to automatically co-register longitudinal (in-time) virtual histology-intravascular ultrasound (VH-IVUS) imaging data in the circumferential direction (i.e., rotate follow-up image so circumferential basis coincides with corresponding baseline image). Multivariate normalized cross correlation was performed on paired images (n = 636) from five patients using three independent VH-IVUS defined parameters: artery thickness, VH-IVUS defined plaque constituents, and VH-IVUS perivascular imaging data. Results exhibited high correlation between co-registration rotation angles determined automatically versus manually by an expert reader (r2 = 0.90). Furthermore, no significant difference between automatic and manual co-registration angles was observed (91.31 ±1.04° and 91.07 ±1.04°, respectively; p = 0.48) and Bland-Altman analysis yielded excellent agreement (bias = 0.24°, 95% CI +/- 16.33°). In conclusion, we have developed, verified, and validated an algorithm that automatically co-registers VH-IVUS imaging data that will allow for the focal examination of CAD progression.

A left ventricle model to predict post-revascularization ejection fraction based on cine magnetic resonance images

The left ventricular ejection fraction (LVEF) is an important clinical indicator of the cardiac function and long-term outcome for patients with coronary artery disease. A biomechanical model of the left ventricle was developed to quantitatively predict post-revascularization LVEF based on noninvasive magnetic resonance imaging. The myocardium was categorized into normal, hibernating, and infarcted regions from the ventricular short-axis images. Assuming that hibernating tissue would potentially regain contractility after revascularization, the expected maximum post-revascularization LVEF was calculated for four patients with chronic left ventricular dysfunction. The predictions were within three ejection fraction points of the follow-up LVEFs. This model may be useful to estimate the outcome and efficacy of revascularization plans.

Predicting ejection fraction improvement by mechanical model and cine magnetic resonance images

A mechanical model based on cine magnetic resonance images was developed to predict left ventricle ejection fraction improvement after revascularization. This fast and accurate prediction can assist cardiologists in making decisions for revascularization. Accurate prediction would also reduce patient risk and health care cost by eliminating unnecessary operations.

Potential Hemodynamic Mechanisms for Gender Differences in AAA Formation

Abdominal aortic aneurysms (AAA) are a major cause of morbidity and mortality in the US. It is classically thought of as a disease of older men with the incidence approaching 30%. The most common place of AAA is infrarenal abdominal aorta where oscillatory shear stress (OSS) is present. OSS is known to initiate an inflammatory response in the endothelium. It is also known that females are at lower risk for developing AAA. The explanation for this difference is lacking. We recruited 8 healthy volunteers, 4 males and 4 females who underwent infrarenal abdominal aortic Magnetic Resonance angiography and phase contrast imaging. The collected data was used to calculate systolic forward and diastolic retrograde blood flow. Our results suggest that female infrarenal aortas are exposed to a 3-fold lower degree of OSS. It appears that the low resistance internal iliac arterial system may be in part responsible for such flow patterns. We conclude that female aortas are subjected to lower OSS and that low resistance internal iliac arterial system appears to play a protective role.Copyright

Computational Analyses of an In-Vitro Aneurysm Model Based on Three-Dimensional Angiography With Comparison to Phase Contrast Magnetic Resonance Imaging and Dye Injection Studies

Computational fluid dynamic simulation (CFD) is a valuable tool that has been used to understand some of the fundamental conditions of cerebrovascular flow. Current methods include anatomic modeling of cerebral aneurysms derived from vascular imaging such as MRA, CTA, and three-dimensional angiography. The input blood flow waveforms can be represented from either mathematical models or physiologic sampling of flow with phase contrast MR techniques or particle image velocimetry (1). While there has been general acceptance of the validity of computational fluid dynamics, some research suggests that there can be poor correlation between CFD flow calculations and directly measured flow (2). Therefore, the purpose of this study is to qualitatively compare flow patterns in a cerebral aneurysm model using data derived from three sources: (i) direct phase contrast MRA measurement in the model; (ii) CFD simulation using computer models created from three dimensional angiography, and (iii) previously published high speed injection dye studies.Copyright

1065 Three-directional myocardial motion in patients with univentricular hearts using velocity-encoded phase contrast MRI

Introduction Patients with univentricular hearts rely on a single functioning ventricle to provide blood flow to both the systemic and pulmonary circuits following completion of the Fontan circulation. Tracking the function of the remaining ventricle in these patients is of interest as their long-term survival continues to improve and the ability of this single ventricle to sustain an increased load or serve an atypical role, as in the case of systemic right ventricles, is continually tested. Velocity-encoded phase contrast magnetic resonance imaging (PC MRI) may provide an efficient technique with high spatial resolution to attain threecomponent myocardial tissue velocities in addition to flow information throughout the cardiac cycle which could be useful in the monitoring of these patients.