University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
Applications of hyperpolarized 129Xe gas are quickly expanding from gas-phase lung ventilation imaging to dissolved-phase imaging in the lungs and in distal organs. The largest barrier to dissolved-phase imaging continues to be the low xenon polarization value that can be obtained with continuous-flow, spin exchange optical pumping (SEOP). While theoretically polarization values should approach 90%, in practice they have been around 30%. Research in our lab on the SEOP process occurring inside the optical pumping cell, using finite element analysis simulations, pointed out major shortcomings in the entire continuous flow SEOP setup. The goal of my work is to improve the SEOP setup. To this end, I have designed and constructed a new continuous flow 129Xe polarizer that is expected to increase xenon residency time inside the optical pumping cell and reduce turbulence. At the same time, the new polarizer will make use of a new narrow laser that is specifically designed to optimize the optical pumping process. One of the applications of gas-phase hyperpolarized 129Xe gas is lung ventilation imaging. Fluorine-19 gas imaging has been proposed as an easier alternative to lung ventilation imaging with hyperpolarized gases. Here we compare the ability of 19F to that of hyperpolarized 129Xe gas MRI to detect ventilation defects in cystic fibrosis patients. One of the applications of dissolved-phase hyperpolarized 129Xe is the detection and thermometry of brown adipose tissue. Brown adipose tissue is a metabolically active fat tissue whose malfunction has been recently associated with the development of obesity and diabetes. Fat fraction MR techniques have also been proposed as a high-resolution alternative method to detect and quantify brown adipose tissue. Here we analyze some of the shortcomings of these techniques, specifically the specificity of fat fraction to brown adipose tissue and the effect of microscopic magnetic susceptibility gradients on fat fraction quantification.Doctor of Philosoph
