EFFECTS OF DIFFUSION ON MAGNETIC-RESONANCE-IMAGING OF LASER-POLARIZEDXENON GAS

Molecular diffusion during the application of magnetic field gradients can distort magnetic resonance images. A systematic characterization of these distortions in one dimension was performed using highly spin- polarized xenon gas. By varying the strength of the applied gradient a nd the geometric dimension of the sample, the evolution of these image distortions between the regimes of strong and weak diffusion was obse rved. These results are compared with numerical simulations. By direct ly measuring the displacement distribution of the polarized xenon atom s, it is shown that in the weak-diffusion regime the image distortions originate from the restricted diffusive motion near the sample bounda ries, in agreement with previous theoretical work. Additionally, it is shown that the effects of diffusion can be utilized to enhance the co ntrast between the boundaries and bulk in the images of polarized gas samples, and thus may be exploited as a means of boundary detection in such systems. (C) 1998 American Institute of Physics. [S0021-9606(98) 02915-8].