Objective: Diffusion-weighted, hyperpolarized 129Xe MRI is useful for the characterization of microstructural changes in the lung. A stretched exponential model was proposed for morphometric extraction of the mean chord length (Lm) from diffusion-weighted data. The stretched exponential model enables accelerated mapping of Lm in a single-breathhold using compressed sensing. Our purpose was to compare Lm maps obtained from stretched-exponential model analysis of accelerated versus unaccelerated diffusion-weighted 129Xe MRI data obtained from healthy/injured rat lungs.
Material and methods: Lm maps were generated using a stretched-exponential model analysis of previously acquired fully sampled diffusion-weighted 129Xe rat data (b values = 0 … 110 s/cm2) and compared to Lm maps generated from retrospectively undersampled data simulating acceleration factors of 7/10. The data included four control rats and five rats receiving whole-lung irradiation to mimic radiation-induced lung injury. Mean Lm obtained from the accelerated/unaccelerated maps were compared to histological mean linear intercept.
Results: Accelerated Lm estimates were similar to unaccelerated Lm estimates in all rats, and similar to those previously reported (< 12% different). Lm was significantly reduced (p < 0.001) in the irradiated rat cohort (90 ± 20 µm/90 ± 20 µm) compared to the control rats (110 ± 20 µm/100 ± 15 µm) and agreed well with histological mean linear intercept.
Discussion: Accelerated mapping of Lm using a stretched-exponential model analysis is feasible, accurate and agrees with histological mean linear intercept. Acceleration reduces scan time, thus should be considered for the characterization of lung microstructural changes in humans where breath-hold duration is short.
Keywords: Compressed sensing; Cylindrical model; Diffusion; Lung; Morphometry; Rats; Stretched-exponential model; Xenon-129.