Speaker:
Ross W. Mair, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA

Title:
Laser Polarized Noble Gas NMR and its application to biomedical and materials science

Abstract:
Gas phase NMR was, for many years, a nearly-ignored topic, due to the devastating > 103 decrease in spin density when compared to most condensed phases. In the early 1990’s, Alex Pines began using the spin-exchange/optical-pumping method, to enhance by ~ 3 –4 orders of magnitude, the spin polarizations in samples xenon gas, to permit sensitive NMR spectroscopy studies of adsorbed layers on solid surfaces. Since that time, similar techniques have been applied to medical MRI to enable exquisitely sensitive, and detailed high-resolution images of inhaled gas in the human or animal lung space. Because this very high polarization is achieved with laser-light external to the MRI magnet, our recent biomedical studies have focused on optimizing a very-low-applied-field, open-access and lightweight human MRI system. There are numerous potential benefits of such a system. For instance, it is known that the human lung and its functions are extremely sensitive to gravity, yet few methods of any type exist that allow spatial visualization of the lung or its functions. While laser-polarized helium MRI provides a window to such visualization for the first time, subjects are restricted to lying horizontally in a traditional clinical MRI scanner. Our novel MRI system allows subjects to lie horizontally, sit vertically, and be rotated at angles in between, and will permit detailed studies of lung behavior as a function of the subject’s orientation in the earth’s gravitational field. Highly-polarized noble gases also provide a sensitive probe of heterogeneous samples of interest in many fields of material science. The high diffusion coefficients of gases permits the probing of much longer diffusion distances in porous materials than are possible with liquids. This allows for a simple measurement of sample tortuosity. Also, the ease with which the gases can be pumped or flowed through a porous or granular system allows us to address, via gas-phase NMR or MRI, fundamental questions in fluid flow in porous materials, specifically at very low Peclet numbers, determine the permeability of porous samples in a non-invasive or destructive manner, and study the gas phase behavior in fluidized granular systems.

 

Host:
Joseph Seymour, MSU Dept. of Chemical and Biological Engineering.