**Using Raman Spectroscopy to Improve Hyperpolarized Noble Gas Production for Clinical Lung Imaging** Provisional chapter Using Raman Spectroscopy to Improve Hyperpolarized

Noble Gas Production for Clinical Lung Imaging

Jonathan Birchall, Nicholas Whiting, Jason Skinner, Techniques

Michael J. Barlow and Boyd M. Goodson Jonathan Birchall, Nicholas Whiting, Jason Skinner,

Michael J. Barlow and Boyd M. Goodson

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/65114

#### Abstract

**Techniques**

Spin-exchange optical pumping (SEOP) can be used to "hyperpolarize" 129Xe for human lung MRI. SEOP involves transfer of angular momentum from light to an alkali metal (Rb) vapor, and then onto 129Xe nuclear spins during collisions; collisions between excited Rb and N2 ensure that incident optical energy is nonradiatively converted into heat. However, because variables that govern SEOP are temperature-dependent, the excess heat can complicate efforts to maximize spin polarization—particularly at high laser fluxes and xenon densities. Ultra-low frequency Raman spectroscopy may be used to perform in situ gas temperature measurements to investigate the interplay of energy thermalization and SEOP dynamics. Experimental configurations include an "orthogonal" pump-and-probe design and a newer "inline" design (with source and detector on the same axis) that has provided a >20-fold improvement in SNR. The relationship between 129Xe polarization and the spatiotemporal distribution of N2 rotational temperatures has been investigated as a function of incident laser flux, exterior cell temperature, and gas composition. Significantly elevated gas temperatures have been observed —hundreds of degrees hotter than exterior cell surfaces—and variances with position and time can indicate underlying energy transport, convection, and Rb mass-transport processes that, if not controlled, can negatively impact 129Xe hyperpolarization.

Keywords: low-frequency Raman, hyperpolarization, spin-exchange optical pumping, xenon NMR/MRI, low-field NMR, remote temperature measurement

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.
