Mehrdad Pourfathi1, Nicholas N. Kuzma1, Rajat Kumar Ghosh1, Stephen J. Kadlececk1, Rahim Rizi1
1Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States
Dynamic Nuclear Polarization (DNP) of 129Xe lags far behind that of [1-13C]pyruvate under similar experimental conditions. Understanding the interplay between DNP, spin diffusion and nuclear relaxation at the microscopic scale requires theoretical modeling as well as experimental probes of the local DNP parameters. We use the recently reported measurements in micro-clustered 129Xe/1-propanol/trityl solid mixtures to validate our first-principles theory of the observed spin-diffusion bottleneck at the cluster boundaries. In our self-contained model, the factor of ~ 30 apparent drop in the local 129Xe polarization at the cluster boundary is obtained analytically across a thin insulating layer of the matrix immediately surrounding the cluster, in good agreement with the measurements. We estimate cluster size, intrinsic temperature, and T1 relaxation rates by fitting the model to the data. These findings have enabled us to increase the achievable 129Xe polarization from 5% to 21%.