Cystic fibrosis (CF) is the most common severe autosomal recessive genetic disease in Caucasians. severe structural alterations in the airways and parenchyma, such as bronchiectasis, mucus plugging, air trapping and infiltrations. These in turn result in focal or heterogeneous abnormalities in regional lung ventilation. End-stage lung disease remains the main cause of morbidity and mortality in CF patients. Currently, new targeted CFTR correctors and potentiators are under trial. The quantitative assessment of structural and functional alterations in the lung is of great importance for the phenotyping and follow-up of CF patients, and for the assessment of targeted therapeutic interventions. Computed tomography (CT) is considered as the technology of choice for lung imaging in CF. However, CT requires exposure to significant ionizing radiation, which is a major concern in the pediatric population because children are more radiosensitive than adults and there is an increased risk of radiation-induced cancer from the cumulative dose related to repeated CT investigations. Recent improvements in magnetic resonance imaging (MRI) technology offer a non-ionizing alternative to CT for imaging the lung parenchyma. 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. If the regional changes in proton density in the lung parenchyma during the respiratory cycle prove to be measurable in healthy volunteers, then MRI can be used to quantify regional lung ventilation. This would offer a unique non-invasive, radiation- and contrast media-free alternative to CT for phenotyping and follow-up of CF patients.