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 3 He MRI with five diffusion sensitizations (b-value ¼ 0, 1.6, 3.2, 4.8, and 6.4 s/cm 2 ) was used, and signal intensities were fit using a cylindrical and single-compartment acinar-duct model to estimate MRIderived mean linear intercept (L m ) and surface-to-volume ratio (S/V). A stretched exponential model was also developed to estimate the mean airway length and L m . Results: We evaluated 42 participants, including 15 elderly never-smokers (69 6 5 years), 12 ex-smokers without COPD (67 6 11 years), 9 COPD ex-smokers (80 6 6 years), and 6 AATD patients (59 6 6 years). In the never-and ex-smokers, the diffusing capacity of the lung for carbon monoxide (DL CO ) and computed tomography relative area of less than 2950 Hounsfield units (RA 950 ) 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 L m 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 L m and S/V in the AATD and COPD subgroups compared with the never-and exsmokers without emphysema. Conclusions: Differences in airspace enlargement may be estimated using L m and S/V, generated using MRI and a stretchedexponential or cylindrical model of the acinar ducts. Magn Reson Med 79:439-448,

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

“…Lung morphometry parameters were significantly increased (ADC, DDC, Lm D , R , L Alv , and Lm ) or decreased (α and h ) ( P < .05) between healthy subjects and COPD patients. These significant differences reflect enlarged acinar airspaces associated with emphysematous destruction and loss of alveolar elasticity in COPD . To our knowledge, in vivo DW‐MRI metrics from lungs of patients with IPF have not been reported before.…”

“…Mean 3 He CM‐derived parameters of R , h, and Lm (Table ) were comparable to the values reported in the literature for healthy ( R = 304 µm, h = 154 µm, Lm = 186 µm), ex‐smokers ( R = 304, h = 130, Lm = 220), and COPD patients ( R = 450, Lm = 450) . Mean 3 He SEM metrics for healthy and COPD subjects also matched previously reported DDC (healthy = 0.14 cm 2 /s, COPD = 0.39 cm 2 /s), α (healthy = 0.86, COPD = 0.69), and Lm D (healthy = 210 µm, COPD = 293 µm) values .…”

“…Mean 3 He SEM metrics for healthy and COPD subjects also matched previously reported DDC (healthy = 0.14 cm 2 /s, COPD = 0.39 cm 2 /s), α (healthy = 0.86, COPD = 0.69), and Lm D (healthy = 210 µm, COPD = 293 µm) values . Ex‐smoker SEM metrics were also comparable to reported values (DDC = 0.21 cm 2 /s, α = 0.81) . The 129 Xe α value was the same for all groups, and was larger than the equivalent 3 He α value.…”

Rapid single‐breath hyperpolarized noble gas MRI‐based biomarkers of airspace enlargement

“…[] was not validated with histology or morphometry methods and this is in contrast to Eq. [] . However, we note that Eq.…”

“…[] to 129 Xe gas, the empirical relationship in Eq. [] was previously determined and proposed: where is the diffusion coefficient of 3 He (0.88 cm 2 /s) in gas mixture, Δ He = 1.46 msec, D Xe 0 is the diffusion coefficient of 129 Xe (0.12 cm 2 s ‐1 /0.14 cm 2 s ‐1 ) in a gas mixture and Δ Xe is the diffusion time.…”