Ultra-short echo-time pulmonary MRI: Evaluation and reproducibility in COPD subjects with and without bronchiectasis
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BACKGROUND: To evaluate ultra-short-echo-time (UTE) MRI pulmonary signal-intensity measurements and reproducibility in chronic obstructive pulmonary disease (COPD). METHODS: A 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 (RA950 ) 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 ). RESULTS: In 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 RA950 (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). CONCLUSION: Pulmonary 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.
