Examining lung microstructure using ¹⁹ F MR diffusion imaging in COPD patients

To examine the time-dependent diffusion of fluorinated (¹⁹ F) gas in human lungs for determination of surface-to-volume ratio in comparison to results from hyperpolarized ¹²⁹ Xe and lung function testing in healthy volunteers and patients with chronic obstructive pulmonary disease.

Diffusion of fluorinated gas in the short-time regime was measured using multiple gradient-echo sequences with a single pair of trapezoidal gradient pulses. Pulmonary surface-to-volume ratio was calculated using a first-order approximation of the time-dependent diffusion in a study with 20 healthy volunteers and 22 patients with chronic obstructive pulmonary disease. The repeatability after 7 days as well as the correlation with hyperpolarized ¹²⁹ Xe diffusion MRI and lung function testing was analyzed.

Using ¹⁹ F diffusion MRI, the median surface-to-volume ratio is significantly decreased in chronic obstructive pulmonary disease patients (S/V = 126 cm^-1 [87-144 cm^-1 ]) compared with healthy volunteers (S/V = 164 cm^-1 [160-84 cm^-1 ], p < 0.0001). No significant difference was found between measurements within 7 days for healthy (p = 0.88, median coefficient of variation = 4.3%) and diseased subjects (p = 0.58, median coefficient of variation= 6.7%). Linear correlations were found with S/V from ¹²⁹ Xe diffusion MRI (r = 0.85, p = 0.001) and the forced expiratory volume in 1 second (r = 0.68, p < 0.0001).

Examination of lung microstructure using time-dependent diffusion measurement of inhaled ¹⁹ F is feasible, repeatable, and correlates with established measurements.