MRI equilibrium signal mapping is a quantitative and reproducible alternative to CT for the estimation of lung density in COPD

In MRI, the equilibrium tissue magnetisation is proportional to tissue water density. This study aimed to explore the feasibility and reproducibility of mapping the signal (S 0 ) associated with the equilibrium magnetisation in the assessment of structural abnormalities in COPD. MR images were acquired in 12 COPD subjects twice within 1 week for T 1 and S 0 mapping. Lung S 0 was normalized by dividing by muscle S 0 to obtain a quantitative S 0 (qS 0 ). Matched CT slices were selected to calculate PD 15 and RA -950 . Lung qS 0 maps were reproducible with reduced values seen in regions comparable to CT detected emphysema regions. The mean and 15 th , 50 th , 75 th percentile qS 0 showed strong correlations with PD 15 and RA -950 . Equilibrium signal maps of MRI correlate strongly with CT density estimates, indicating that qS 0 may be a reproducible, non-invasive/-ionising measure for quantifying lung density changes in COPD.