Date on Master's Thesis/Doctoral Dissertation
Electrical and Computer Engineering
Sharp, Michael Keith
Stenotic flow; Pressure-Poisson equation; Phase-contrast MRI; Harmonics-based; Particle image velocimetry; Orthogonal projection
Blood flow--Measurement; Magnetic resonance imaging
Peripheral Arterial Disease (PAD) is a progressive atherosclerotic disorder which is defined as any pathologic process obstructing the blood flow of the arteries supplying the lower extremities. Moderate stenoses mayor may not be hemodynamically significant, and intravascular pressure measurements have been recommended to evaluate whether these lesions are clinically significant. Phase-contrast MRI (PC-MRI) provides a powerful and non-invasive method to acquire spatially registered blood velocity. The velocity field, then, can be used to derive other clinically useful hemodynamic parameters, such as blood flow and blood pressure gradients. Herein, a series of detailed experiments are reported for the validation of MR measurements of steady and pulsatile flows with stereoscopic particle image velocimetry (SPIV). Agreement between PC-MRI and SPIV was demonstrated for both steady and pulsatile flow measurements at the inlet by evaluating the linear regression between the two methods, which showed a correlation coefficient of> 0.99 and> 0.96 for steady and pulsatile flows, respectively. Experiments revealed that the most accurate measures of flow by PC-MRI are found at the throat of the stenosis (error < 5% for both steady and pulsatile mean flows). The flow rate error distal to the stenosis was shown to be a function of narrowing severity. Furthermore, pressure differences across an axisymmetric stenotic phantom model were estimated by solving the pressure-Poisson equation (iterative method) and a non-iterative method based on harmonics-based orthogonal projection using PC-MRI velocity data. Results were compared with the values obtained from other techniques including SPIV, computational fluid dynamic (CFD) simulations, and direct pressure measurements. Using the pressure obtained from CFD as the ground truth and PC-MRI velocity data as the input, the relative error in pressure drop for iterative and non-iterative techniques were 13.1 % and 12.5% for steady flow, 4.0% and 22.1 % for pulsatile flow at peak-systole, and 194.5% and 155.2% at end-diastole, respectively. It was concluded that pressure drop calculation using PC-MRI is more promising for steady cases and pulsatile cases at peak-systole compared to pulsatile flow cases at end-diastole.
Khodarahmi, Iman, "Flow and pressure measurement using phase-contrast MRI : experiments in stenotic phantom models." (2012). Electronic Theses and Dissertations. Paper 744.