Ultra-short Echo-Time Pulmonary MRI: Evaluation and Reproducibility in COPD Subjects With and Without Bronchiectasis

BackgroundTo evaluate ultra-short-echo-time (UTE) MRI pulmonary signal-intensity measurements and reproducibility in chronic obstructive pulmonary disease (COPD). MethodsA two-dimensional sequence (echo-time=0.05 ms; acquisition-time=13 s) with interleaved half-pulse excitation and radial ramp-sampling was used with compressed-sensing to reconstruct UTE images from under-sampled data. Five healthy volunteers and 15 subjects with COPD provided written informed consent to imaging and pulmonary-function-tests. Healthy volunteers underwent MRI at four lung volumes: full-expiration, functional-residual-capacity (FRC), FRC+1L, and full-inhalation; COPD patients underwent computed-tomography (CT) and MRI at FRC+1L. Three-week reproducibility was evaluated and the relative area of the density histogram-950 HU (RA(950)) was compared with mean MRI signal-intensity. The 15th percentile of signal-intensity-histogram (SI15) was compared with the 15th percentile of the CT-density-histogram (HU15). ResultsIn healthy subjects, signal-intensity correlated with the inverse of lung volume (r=0.99; P=0.007). Contrast-to-noise and signal-to-noise ratios were significantly improved for 32-channel UTE (P<0.01). The coefficient of variation for 3-week repeated measurements was 4%. There were significant correlations for signal-intensity with RA(950) (r=-0.71; P=0.005), FEV1/FVC (r=0.59; P=0.02), and for SI15 with HU15 (r=0.62; P=0.01). ConclusionPulmonary signal-intensity is reproducible and related to tissue density. In COPD subjects with and without bronchiectasis, signal-intensity was also related to pulmonary function and CT measurements. J. Magn. Reson. Imaging 2015;41:1465-1474. (c) 2014 Wiley Periodicals, Inc.