The goal of the study is to develop a quantitative imaging biomarker based on MRI for the assessment of lung disease severity and monitoring disease progression. Fibrotic changes increase lung stiffness and induce a restrictive lung disease with decreased lung volumes on PFT. Thus, the investigators hypothesized that the assessment of lung elasticity would allow differentiating between fibrotic and healthy lung parenchyma. For each subject, they will examine an overall "elasticity index" (based on the total disease volume), as well as the spatial distribution of elastic properties. These properties will be calculated using a deformable registration between expiratory and inspiratory MR images. For the representation of lung tissue expansion they will examine several surrogates based on the determinant of the Jacobian of the deformation field.