UNC-CH PHYSICS AND ASTRONOMY COLLOQUIUM
Boyd Goodson, Southern Illinois University Carbondale
“Enhancing NMR and MRI with Hyperpolarized Xenon and Signal Amplification by Reversible Exchange”
Nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) enjoy wide applicability but suffer from poor detection sensitivity due to inherently low nuclear spin polarization—and hence weak nuclear magnetization. For example, most of the signal in conventional MRI comes from the body’s water molecules because they are available in such high concentration. Imaging low-concentration species—such as gases in lung spaces, or metabolites in tissues—is much more difficult. One way to combat such problems is to employ “hyperpolarization”, a process by which nuclear spin populations are driven far from equilibrium, thereby increasing their polarization—and hence detection sensitivity—by orders of magnitude. We are pursuing two such hyperpolarization methods: (1) spin-exchange optical pumping (SEOP); and (2) parahydrogen-induced polarization via “SABRE” (Signal Amplification by Reversible Exchange). For (1), we have studied SEOP under “extreme” conditions of high xenon densities and resonant laser flux. As an extension of this work, our “consortium” has recently created clinical-scale open-source xenon “hyperpolarizers”. The devices can endow 129Xe with near-unity polarization and imaging of human subjects has begun. For (2), we are investigating SABRE, which utilizes organometallic catalysts that transiently bind both parahydrogen (pH2, a “spin isomer” of ordinary molecular hydrogen with pure spin order) and the target substrate molecule, thereby allowing the target spins to be hyperpolarized. In collaboration with others, we are studying SABRE with heterogeneous catalysts, in aqueous environments, and in variable magnetic fields in order to create hyperpolarized metabolic contrast agents for in vivo NMR and MRI that may ultimately probe responses to treatment of various diseases, including cancer.