19F MRI of Ventilation in Subjects With Cystic Fibrosis Undergoing Treatment for Pulmonary Exacerbation

Inclusion Criteria: * Non-smokers (\<10 pack year history and no active smoking in the past year); * Diagnosis of cystic fibrosis via standard sweat chloride/phenotypic features/genotyping * Able to reproducibly perform lung function testing and have an FEV1 \>30% of predicted at screening. * No requirement for supplemental oxygen * Evidence of a personally signed and dated informed consent document indicating that the subject has been informed of all pertinent aspects of the trial. * Participants must be willing and able to comply with scheduled visits and other trial procedures. * Diagnosis of a pulmonary exacerbation according to Fuchs criteria (4 of the following 12 signs and symptoms) deemed to require antibiotic treatment, and must also include the change in lung function criterion: * Change in sputum * New or increased hemoptysis * Increased cough * Increased dyspnea * Malaise, fatigue, or lethargy * Temperature above 38deg C * Anorexia or weight loss * Sinus pain or tenderness * Change in sinus discharge * Change in physical examination of the chest * Decrease in pulmonary function by 10% or more from a previously recorded value * Radiographic change indicative of pulmonary infection Exclusion Criteria: * Under 18 years of age * Active or former smokers with less than 1 years since quitting, or \>10 pack-year smoking history * Active asthma flare, as perceived by the study physician or unstable asthma characterized by advancement of asthma therapy in the last month or two courses of oral steroids in the past six months. * Unable to undergo a 3.0-Tesla MRI of lungs and chest because of contraindications including 1. Occupation (past or present) of machinist, welder, grinder 2. Injury to the eye involving a metallic object 3. Injury to the body by a metallic object (bullet, BB, shrapnel) 4. Presence of a cardiac pacemaker or defibrillator 5. Presence of aneurysm clips 6. Presence of carotid artery vascular clamp 7. Presence of neurostimulator 8. Presence of insulin or infusion pump 9. Presence of implanted drug infusion device that is not known to be MRI compatible (i.e., was placed outside of University of North Carolina Hospitals (UNCH) or is older than 10 years) 10. Bone growth or fusion simulator 11. Presence of cochlear, otologic or ear implant 12. Any type of prosthesis (eye, penile, etc.) 13. Artificial limb or joint 14. Non-removable electrodes (on body, head or brain) 15. Intravascular stents, filters or coils 16. Shunt (spinal or intraventricular) 17. Swan-Ganz catheter 18. Any implant held in place by a magnet 19. Transdermal delivery system (e.g. Nitro) 20. Intrauterine device (IUD) or diaphragm 21. Tattooed makeup (eyeliner, lips, etc.) or tattoos covering \>25% of body surface area 22. Body piercings (MUST BE REMOVED BEFORE MRI) 23. Any metal fragments 24. Internal pacing wires 25. Metal or wire mesh implants 26. Hearing aid (REMOVE BEFORE MRI) aa. Dentures (REMOVE BEFORE MRI) bb. Claustrophobia * Unable to tolerate inhalation of the gas mixture * Unable to adequately complete other study measures, including spirometry and multiple breath nitrogen washout * Other severe acute or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with trial participation or may interfere with the interpretation of trial results and, in the judgment of the PI, would make the participant inappropriate for enrollment. * Pregnancy; women of childbearing potential must have a confirmed negative serum pregnancy test at screening, and a negative urine test on the day of the MRI scan, prior to the MRI scan (if serum test not performed the same day). * Facial hair preventing a tight fit of the mask used in the study * Allergy or intolerance due to side effects to bronchodilators