This study is being done to determine whether MRI can produce high quality lung and airway images in healthy and CF patients and if MRI can be used to evaluate size and shape of the airways with computer assistance. This study will also repeat MRI experiments two years after the initial MRI scan to see if changes to airway size and shape are seen over time. In a subset of participants, we will investigate whether MRI results are repeatable and reproducible in the short-term one week after the initial MRI visit. This study will help understand if MRI based measurements of airway size and shape can be used as a monitoring tool that does not use x-ray radiation in patients with CF.