Morphological and quantitative evaluation of emphysema in chronic obstructive pulmonary disease patients: A comparative study of MRI with CT

Abstract

Purpose: To further validate the ability of ultrashort echo-time (UTE) magnetic resonance imaging (MRI) in quantifying lung density in patients diagnosed with chronic obstructive pulmonary disease (COPD) and to develop an MRI-based emphysema index (EI).

Materials and methods: Ten subjects clinically diagnosed with COPD (5M/5F, age 62.6 ± 8.5 years) and ten healthy subjects (2M/8F, age 48.9 ± 19.2 years) were imaged via UTE MRI at 3T (4 mm slices, 1.39 × 1.39 mm² pixels). Chest computed tomography (CT) images (generally 5 mm slices, ≈0.55 × 0.55 mm² pixels), acquired retrospectively, were compared to UTE MRI. CT lung densities, MR lung-signal density, and EI were quantified from both CT and UTE MR images via a quantitative automated analysis and compared to the percent predicted forced expiratory volume in 1 second (FEV₁ % predicted).

Results: EI quantified in controls via CT and UTE MRI was 0.23 ± 0.78% and 2.40 ± 1.50%, respectively; in COPD subjects it was 13.3 ± 14.9% (P = 0.021) and 12.0 ± 9.8% (P = 0.013), respectively. Bland-Altman determined the mean differences and 95% limits of agreement for COPD subjects and healthy controls were 0.06 (12.50 to -12.38). Strong correlation (R² = 0.79, P < 0.0001) existed between EIs quantified from both CT and UTE MRI. There was a slightly higher correlation between FEV₁ % predicted and the UTE MRI EI (R² = 0.65, P < 0.0001) compared to CT EI (R² = 0.49, P < 0.0001).

Conclusion: Our results demonstrate a significant positive correlation between lung density and EI assessed with CT and MRI. Furthermore, UTE MRI exhibits its potential as a diagnostic alternative to CT for assessing the extent and the severity of emphysema, particularly for longitudinal studies. J. Magn. Reson. Imaging 2016;44:1656-1663.

Keywords: COPD; emphysema; pulmonary imaging; ultrashort echo-time MRI.