Abstract
This thesis work presents the development of the new imaging technique gamma- MRI (gamma-detected Magnetic Resonance Imaging). The fundamentals of gamma-MRI is the positioning of a gamma-emitting, Hyperpolarized (HP) nuclei of spin >1/2 h in a MRI setup complemented by gamma detectors. The experiment in this thesis was performed on two such nuclei, 129mXe and 131mXe, HP by the Spin Exchange Optical Pumping (SEOP) method. The main goal was to observe and maximize the asymmetry of gamma emission. This thesis work includes the responsibility of implementing, operating and troubleshooting the detectors of the setup. Experimental runs were in the period June-August 2019, during which time multiple improvements were made to the setup. After the experimental period the gamma anisotropy of both 129mXe and 131mXe was surprising. Following an initial analysis there were three approaches: a precision analysis of the data [1], while this thesis work focused on simulations of the metastable xenon (mXe) sample and an in-depth literature review of the hyperpolarizing method and its application for a quadrupolar nucleus. The simulations evaluated possible results of the hyperpolarization and their number of gamma counts observed in the detectors. The main conclusion is that the majority of mXe nuclei occupy the central sublevels after the hyperpolarization, based on a comparison of the anisotropy orientation in simulations and experimental data. Also, the relative short distance and large dimensions of the detector crystal compared to the mXe sample was shown to be important for gamma rays radiated from the edges of the mXe sample. Based on this thesis work, the general explanations for a low observed anisotropy are: low alignment of nuclear sublevel occupation, and/or the gamma contributions from the edges of the sample. The in-depth literature review on SEOP presented in this thesis summarizes the most important documented steps concerning SEOP with stable 129Xe and Rb. The largest dierence between the stable and metastable xenon is the nuclear spin and the gamma emission. The hyperpolarization of mXe (with spin 11/2 h) was explored by the aforementioned simulations. Gamma-MRI is still in its early stages, but holds potential as a medical diagnostic tool. Using radioactive Xe allows imaging of physiology similar to other established techniques, yet still maintain anatomical accuracy from the application of MRI. The biomedical applications of stable xenon is believed to be transferable to metastable xenon. At the same time, this thesis work has highlighted some of the complexity of hyperpolarizing 129m/131mXe with SEOP.