Investigating short-time diffusion of hyperpolarized 129 Xe in lung air spaces and tissue: A feasibility study in chronic obstructive pulmonary disease patients.

Purpose: To investigate the diffusion of hyperpolarized ¹²⁹ Xe in air spaces at short-time scales for determination of lung surface-to-gas-volume ratio in comparison to results from chemical shift saturation recovery, CT, and established clinical measures.
Methods: A pulse sequence for measurement of time-dependent diffusion of ¹²⁹ Xe in air spaces at short diffusion times was developed. Gas uptake into lung tissue was measured in the same breathhold using chemical shift saturation recovery spectroscopy in the short-time regime. The potential to obtain the surface-to-gas-volume ratio using a first-order and second-order approximation of the short-time expansion of time-dependent diffusion according to Mitra et al ¹¹ and its diagnostic relevance were tested in a study with 9 chronic obstructive pulmonary diseases patients.
Results: Surface-to-gas-volume ratios obtained from time-dependent diffusion were correlated with results from chemical shift saturation recovery, r = 0.840, P = .005 (first-order fits), and r = 0.923, P < .001 (second-order fits), and from CT results for second-order fits, r = 0.729, P = .026. Group means ± SD were 75.0 ± 15.5 cm ^-1 (first-order fits) and 122.3 ± 32.8 cm ^-1 (second-order fits) for time-dependent diffusion, 125.9 ± 43.3 cm ^-1 for chemical shift saturation recovery, and 159.5 ± 50.9 cm ^-1 for CT. Surface-to-gas-volume ratios from time-dependent diffusion with first-order fits correlated significantly with carbon monoxide diffusing capacity as percent of prediction, r = 0.724, P = .028.
Conclusion: Time-dependent diffusion measurements of ¹²⁹ Xe at short-time scales down to ~1 ms are feasible in chronic obstructive pulmonary patients and provide clinically relevant information on lung microstructure.
(© 2020 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.)