Comparison of in vivo lung morphometry models from 3D multiple b‐value 3He and 129Xe diffusion‐weighted MRI

Purpose To compare in vivo lung morphometry parameters derived from theoretical gas diffusion models, the cylinder model and stretched exponential model, in a range of acinar microstructural length scales encountered in healthy and diseased lungs with 3He and 129Xe diffusion‐weighted MRI. Methods Three‐dimensional multiple b‐value 3He and 129Xe diffusion‐weighted MRI was acquired with compressed sensing at 1.5 T from 51 and 31 subjects, respectively, including healthy volunteers, ex‐smokers, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease patients. For each subject, the stretched exponential model–derived mean diffusive length scale (LmD) was calculated from the diffusion signal decay, and was compared with the cylinder model–derived mean chord length (Lm) and mean alveolar diameter (LAlv) in order to determine the relationships among the different lung morphometry parameters. Results For both 3He and 129Xe diffusion‐weighted MRI, the mean global LmD value was significantly related (P < .001) to Lm in a nonlinear power relationship, whereas the LAlv demonstrated excellent linear correlation (P < .001) with LmD. A mean bias of +1.0% and 2.6% toward LmD was obtained for Bland‐Altman analyses of 3He and 129Xe LmD and LAlv values, suggesting that the two morphometric parameters are equivalent measures of mean acinar dimensions. Conclusion Within the experimental range of parameters considered here for both 3He and 129Xe, the stretched exponential model–derived LmD is related nonlinearly to cylinder model–derived Lm, and demonstrates excellent agreement with the cylinder model–derived LAlv.