Charles V. Taylor - US grants

ITR/AP: Simulation-Based Medical Planning for Cardiovascular Disease

The current paradigm for interventional and surgery planning for the treatment of congenital and acquired cardiovascular disease relies exclusively on diagnostic imaging data to define the present state of the patient, empirical data to evaluate the efficacy of prior treatments for similar patients, and the judgement of the surgeon to decide on a preferred treatment. The individual variability and inherent complexity of human biological systems is such that diagnostic imaging and empirical data alone are insufficient to predict the outcome of a given treatment for an individual patient.

The specific objectives described in the present proposal are to develop a Problem Solving Environment for Simulation-Based Medical Planning combining (i) the construction of patient-specific preoperative geometric models of the human vascular system directly from medical imaging data, (ii) the modification of these models to incorporate multiple potential interventional and surgical plans, (iii) the generation of finite element meshes of the treatment plans, (iv) the simulation of blood flow in these patient-specific models, and (v) the visualization and quantification of resulting physiologic information. Techniques for identifying vessel boundaries from computed tomography (CT) and magnetic resonance imaging (MRI) data using two- and three-dimensional level set methods will be improved to enhance accuracy and efficiency.
The ultimate result of the successful completion of the outlined tasks will be the development of an integrated Problem Solving Environment for Simulation-Based Medical Planning incorporating image segmentation, geometric modeling, mesh generation, computational mechanics, and scientific visualization techniques.

Abstract Not Provided.

The goal of this project is to quantify the acute and chronic effects of exercise on hemodynamic conditions[unreadable] in the infrarenal aorta of human subjects with small AAA (AAA diameter equal to or > 3, equal to or < 5 cm). The subjects will be a subset of the patients in the standard therapy arm and exercise intervention arm described in Specific Aim 2 of Project IV: Evaluation of Exercise Therapy for Small AAA. We will test the hypotheses that: (i) Shape matters: Differences in shear and dynamic tensile forces acting on the vessel wall, resulting from differences in[unreadable] aneurysm shape, are predictive of AAA growth rate, (ii) Size matters: As AAA enlarge, adverse hemodynamic[unreadable] conditions (including regions of low mean wall shear stress and high particle residence time) are exacerbated[unreadable] under resting conditions, (iii) Structure and motion matter: Differences in wall thickness, tissue composition,[unreadable] cyclic wall motion, and fluid-solid interactions affect AAA enlargement, (iv) Exercise matters: Increased[unreadable] infrarenal blood flow resulting from acute lower limb exercise, eliminates regions of adverse hemodynamic[unreadable] conditions, dramatically increasing wall shear stress and reducing particle residence time in all subjects[unreadable] regardless of AAA shape or size, (v) Persistence matters: Regular exercise slows AAA progression affecting[unreadable] size and shape, and results in more favorable hemodynamics and vessel wall motion. We will test these[unreadable] hypotheses by quantifying hemodynamics and wall tensile stresses under resting and exercise conditions in[unreadable] the abdominal aorta of patients with small AAA randomized to chronic exercise therapy or standard therapy.[unreadable] Our specific aims are: (1) Quantify time-varying abdominal aortic anatomy in AAA patients, (2) Quantify[unreadable] abdominal aortic blood flow at rest and during dynamic exercise using a custom MR-compatible bike in a 0.5T[unreadable] open MRI, and (3) Develop and validate computational methods to model blood flow, pressure, and wall[unreadable] motion in "patient-specific" computational models of the abdominal aorta of patients with small AAA[unreadable] randomized to chronic exercise therapy or standard therapy.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our work focuses on characterizing the hemodynamic environment of the abdominal aorta in the setting of chronic spinal cord injury (SCI), an independent risk factor for abdominal aortic aneurysm. We have hypothesized that a unique, pro-aneurysmal, hemodynamic environment exists in the SCI abdominal aorta as a result of chronic non-ambulation, lower-extremity arterial atrophy, and high distal resistance. We image the abdominal aorta in supine, resting non-ambulatory SCI and ambulatory control subjects in the Lucas Center's 1.5T GE magnet, using magnetic resonance angiography (MRA), phase contrast MRI (PC-MRI), and fast gradient echo sequences to evaluate aortic wall motion. Since June 2008 we have scanned two SCI patients, bringing our total to 6 SCI and 6 control subjects with adequate scan data, and since then have focused our efforts primarily on data analysis.