Date of Award

2011

Degree Type

Thesis

Department

Chemical and Biomedical Engineering

First Advisor

Chatzimavroudis, George

Subject Headings

Fluid dynamic measurements, Heart valve prosthesis, Nuclear magnetic resonance, Arteries -- Stenosis, Blood flow, MRPVM, Orifice, Signal loss

Abstract

Magnetic resonance phase velocity mapping (MRPVM) is an established clinical technique to measure blood flow. The acquired information can be used to diagnose a variety of cardiovascular disease. One of the main limitations of MRPVM is that it cannot quantify the flow under turbulent flow conditions. Such conditions develop in certain cases such as in heart valve stenosis and arterial stenosis. Specifically, heart valve stenosis is a serious disease in which the valve does not open as much as necessary for blood to pass through. As a result, the heart has to overwork to overcome the increased resistance. If untreated, the disease can lead to death. One of the diagnostic problems related to stenosis is that the flow through the stenotic orifice becomes turbulent, associated with velocity fluctuations, flow separation and recirculation downstream of the stenosis. Clinically, it is difficult to quantify turbulent flow. Especially in the case of MRPVM, turbulent flow leads to signal loss in the images, resulting in loss of valuable diagnostic information. This study aimed at investigating the effects of imaging parameters on the ability of MRPVM for turbulent flow quantification. Two orifice models were used, one with a 75 area reduction and another with a 94 area reduction. Axial MRPVM acquisitions were performed (flow rate: 1.2-10.5 L/min upstream Re: 1271-11124, orifice Re: 2542-44497) inside a 1.5 Tesla whole-body clinical MRI scanner. Three in-plane spatial resolutions (0.9 x 0.9, 1.5 x 1.5, and 2.0 x 2.0 mm2) and five echo times (2.65, 3.5, 5.0, 7.5, 10.0 msec) were studied. Images were acquired in both models at five locations: 6.0 cm upstream from the orifice at the orifice 1.0 cm downstream from the orifice 3.0 cm downstream from the orifice and 5.0 cm downstream from the orifice. The MRPVM-measured flow rates were compared with the true flow rates known from rotameters to determine the accuracy. The results confirmed that MRPVM is highly accurate under laminar flow conditions, but under turbulent fl

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