The investigators are developing a new nuclear medicine imaging technique for measuring liquid absorption in the airways that can be applied to screen new medications being developed to treat cystic fibrosis (CF). The investigators believe that the absorption of the small molecule radiopharmaceutical Indium 111 diethylene triamine pentaacetic acid (In-DTPA) will indicate changes in liquid absorption in the airways and demonstrate whether new CF medications will be effective. In this study the investigators will determine whether the imaging technique will demonstrate similar results when it is repeated on different days. They will also determine how their results change when subjects utilize several common CF medications.

Cystic Fibrosis (CF) is an autosomal recessive genetic disease, caused by mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) that impairs ion transport at epithelial surfaces. This results in the accumulation of dehydrated secretions in the airways and chronic infection and inflammation in the lungs, leading to significant morbidity and mortality. The investigators understanding of CF pathogenesis has increased substantially and many new targeted therapies are being developed to treat this disease, however, the measurements of clinical efficacy used to evaluate these therapies require long trials to demonstrate an effect. New translational techniques are needed to assess changes in the most basic aspects of the disease and allow for the rapid screening of disease-altering therapies. The investigators have recently developed a novel aerosol-based imaging technique to measure liquid absorption in the airways - a central pathophysiological process related to CFTR dysfunction. The investigators propose that airway liquid hyper-absorption is a key link between cellular defects in ion and fluid transport and progressive airway dysfunction in CF. Thus The investigators technique may provide a measure of disease severity and rapid indication of therapeutic correction in advance of currently available outcome measures.

Inclusion Criteria:

• subjects 18 years old or older with a diagnosis of cystic fibrosis as determined by sweat test or genotype and clinical symptoms who are clinically stable as determined by a physician co-investigator

Exclusion Criteria:

• one second forced expiratory volume (FEV1) <50% of predicted
• nursing mother
• positive urine pregnancy test or unwilling to test
• cigarette smoker
• unwilling to stop hypertonic saline therapy for 72 hours prior to each test day
• are intolerant to hypertonic saline (response only)
• are intolerant to any inhaled therapies (response only)
• fail mannitol tolerance testing (response only)
• have a history of excessive (uncontrollable) coughing after an osmotic stimulus (response only)
• have a history of hemoptysis (response only)