PNNL

Abstract

In ³He magnetic resonance images of pulmonary air spaces, the confining architecture of the parenchymal tissue results in a non-Gaussian distribution of signal phase that non-exponentially attenuates image intensity as diffusion weighting is increased. Here, two approaches previously used for the analysis of non-Gaussian effects in the lung are compared and related using diffusion-weighted ³He MR images of mechanically ventilated rats. Total lung coverage is achieved using a hybrid 3D pulse sequence that combines conventional phase encoding with sparse radial sampling for efficient gas usage. This enables the acquisition of nine 3D images using a total of only ~ 1 L of hyperpolarized ³He gas. Diffusion weighting ranges from 0 s/cm² to 40 s/cm². Results show that the non-Gaussian effects of ³He gas diffusion in healthy rat lungs are directly attributed to the anisotropic geometry of lung microstructure, and that quantitative analysis over the entire lung can be reliably repeated in time-course studies of the same animal.