MR Quantitative Equilibrium Signal Mapping: A Reliable Alternative to CT in the Assessment of Emphysema in Patients with Chronic Obstructive Pulmonary Disease

Abstract

Purpose: To compare magnetic resonance (MR) quantitative equilibrium signal (qS0) mapping with quantitative computed tomography (CT) in the estimation of emphysema in patients with chronic obstructive pulmonary disease (COPD).

Materials and methods: Written informed consent of the original study permitted future reanalysis of data. This study was a retrospective analysis of data from an institutional review board-approved study. Twenty-four patients with COPD and 12 healthy patients who did not smoke underwent spirometry and two separate 1.5-T MR imaging examinations. All patients with COPD underwent additional chest CT. Lung MR qS0 maps were generated from MR images obtained with multiple inversion times by fitting the inversion recovery signal equation. Mean, 15th percentile, and standard deviation of whole-lung qS0 and relative lung area with a qS0 value below 0.20 (RA0.20) were measured and compared between groups with an unpaired t test. Reproducibility between two examinations was tested with intraclass correlation coefficients (ICCs), and their associations with spirometry and CT measurements of 15th percentile attenuation (PA15) and relative lung area with attenuation below -950 HU (RA-950) were assessed with the Pearson correlation coefficient.

Results: Whole-lung mean qS0 and 15th percentile of qS0 were significantly lower, whereas RA0.20 and standard deviation of qS0 were significantly higher in patients with COPD than in healthy control subjects (P = .014, P = .002, P = .005, and P < .001, respectively). Whole-lung mean qS0, the 15th percentile of qS0, and RA0.20 strongly correlated with RA-950 (r = -0.78, r = -0.81, and r = 0.86, respectively; P < .001) and PA15 (r = 0.78, r = 0.79, and r = -0.71, respectively; P < .001) and moderately correlated with the ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (r = 0.63, r = 0.67, and r = -0.60, respectively; P < .001) and percentage predicted FEV1 (r = 0.54, r = 0.62, and r = -0.56, respectively; P ≤ .001). Good reproducibility of qS0 readouts was found in both groups (ICC range, 0.89-0.98).

Conclusion: Lung MR qS0 mapping may be a reliable noncontrast nonradiation alternative to CT in the assessment of emphysema in patients with COPD.