Abstract
PURPOSE: To quantitatively analyze lung elasticity in idiopathic pulmonary fibrosis (IPF) using elastic registration based on 3-dimensional pulmonary magnetic resonance imaging (3D-PMRI) and to assess its' correlations with the severity of IPF patients. MATERIAL AND METHODS: Thirty male patients with IPF (mean age: 62±6 y) and 30 age-matched male healthy controls (mean age: 62±6 y) were prospectively enrolled. 3D-PMRI was acquired with a 3-dimensional ultrashort echo time sequence in end-inspiration and end-expiration. MR images were registered from end-inspiration to end-expiration with the elastic registration algorithm. Jacobian determinants were calculated from deformation fields on color maps. The log means of the Jacobian determinants (Jac-mean) and Dice similarity coefficient were used to describe lung elasticity between 2 groups. Then, the correlation of lung elasticity with dyspnea Medical Research Council (MRC) score, exercise tolerance, health-related quality of life, lung function, and the extent of pulmonary fibrosis on chest computed tomography were analyzed. RESULTS: The Jac-mean of IPF patients (-0.19, [IQR: -0.22, -0.15]) decreased (absolute value), compared with healthy controls (-0.28, [IQR: -0.31, -0.24], P <0.001). The lung elasticity in IPF patients with dyspnea MRC≥3 (Jac-mean: -0.15; Dice: 0.06) was significantly lower than MRC 1 (Jac-mean: -0.22, P =0.001; Dice: 0.10, P =0.001) and MRC 2 (Jac-mean: -0.21, P =0.007; Dice: 0.09, P <0.001). In addition, the Jac-mean negatively correlated with forced vital capacity % ( r =-0.487, P <0.001), forced expiratory volume 1% ( r =-0.413, P =0.004), TLC% ( r =-0.488, P <0.001), diffusing capacity of the lungs for carbon monoxide % predicted ( r =-0.555, P <0.001), 6-minute walk distance ( r =-0.441, P =0.030) and positively correlated with respiratory symptoms ( r =0.430, P =0.042). Meanwhile, the Dice similarity coefficient positively correlated with forced vital capacity % ( r =0.577, P =0.004), forced expiratory volume 1% ( r =0.526, P =0.012), diffusing capacity of the lungs for carbon monoxide % predicted ( r =0.435, P =0.048), 6-minute walk distance ( r =0.473, P =0.016), final peripheral oxygen saturation ( r =0.534, P =0.004), the extent of fibrosis on chest computed tomography ( r =-0.421, P =0.021) and negatively correlated with activity ( r =-0.431, P =0.048). CONCLUSION: Lung elasticity decreased in IPF patients and correlated with dyspnea, exercise tolerance, health-related quality of life, lung function, and the extent of pulmonary fibrosis. The lung elasticity based on elastic registration of 3D-PMRI may be a new nonradiation imaging biomarker for quantitative evaluation of the severity of IPF.