RecruitingCombination productQuantitation and Spatial Registration of Airways Dysfunction With Dynamic 19F MRI in Cystic FibrosisThe purpose of this study is to look at lung ventilation in people with cystic fibrosis over time (1 year) using magnetic resonance imaging (MRI) with an inhaled contrast gas, and compare these measures to lung function assessed by spirometry and multiple breath nitrogen washout. This study also looks at how these measures change in response to a pulmonary exacerbation and treatment (if applicable). Over the span of a year, participants would be asked to complete 3-5 visits to the University of North Carolina at Chapel Hill (UNC). with each lasting up to 4 hours. If participants do not have a pulmonary exacerbation during the year they would be asked to complete 3 visits (one at enrollment, a second roughly 2 weeks later, and the third approximately a year later). If participants do experience a CF pulmonary exacerbation they would complete 5 visits (Visit 1, Visit 2, two exacerbation visits with one before treatment and the other after, and Visit 3 at one year after Visit 1). Only one exacerbation per participant will be tracked. Participants are eligible for this study if they are 18 years old or older, have Cystic Fibrosis (CF) with mild lung disease (FEV1 \>/= 60%), and can undergo an MRI. There are no known benefits for participating in this study.