Pulmonary MRI morphometry modeling of airspace enlargement in chronic obstructive pulmonary disease and alpha-1 antitrypsin deficiency

Abstract

Purpose: We generated lung morphometry measurements using single-breath diffusion-weighted MRI and three different acinar duct models in healthy participants and patients with emphysema stemming from chronic obstructive lung disease (COPD) and alpha-1 antitrypsin deficiency (AATD). Methods: Single-breath-inhaled 3He MRI with five diffusion sensitizations (b-value = 0, 1.6, 3.2, 4.8, and 6.4 s/cm2) was used, and signal intensities were fit using a cylindrical and single-compartment acinar-duct model to estimate MRI-derived mean linear intercept (Lm) and surface-to-volume ratio (S/V). A stretched exponential model was also developed to estimate the mean airway length and Lm. Results: We evaluated 42 participants, including 15 elderly never-smokers (69 ± 5 years), 12 ex-smokers without COPD (67 ± 11 years), 9 COPD ex-smokers (80 ± 6 years), and 6 AATD patients (59 ± 6 years). In the never- and ex-smokers, the diffusing capacity of the lung for carbon monoxide (DLCO) and computed tomography relative area of less than −950 Hounsfield units (RA950) were normal, but these were abnormal in the COPD and AATD patients, which is reflective of emphysema. Although cylindrical and stretched-exponential-model estimates of Lm and S/V were not significantly different, the single-compartment-model estimates were significantly different (P < 0.05) for the never- and ex-smoker subgroups. All models estimated significantly worse Lm and S/V in the AATD and COPD subgroups compared with the never- and ex-smokers without emphysema. Conclusions: Differences in airspace enlargement may be estimated using Lm and S/V, generated using MRI and a stretched-exponential or cylindrical model of the acinar ducts. Magn Reson Med 79:439–448, 2018. © 2017 International Society for Magnetic Resonance in Medicine.