Structural lung and airway alterations in CF lead to focal or heterogeneous abnormalities in regional lung ventilation. The quantitative assessment of structural and functional alterations in the lung is of great importance for the phenotyping and follow-up of CF patients. The goal of this study is to assess the feasibility of measuring the changes in proton density in the lung parenchyma with inflation and deflation during the respiratory cycle, using ultrashort echo time (UTE) pulse sequence MRI, in healthy adult volunteers.