The 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.

Inclusion Criteria:

1. Subjects must be ≥18 years of age
2. Non-smokers (<10 pack/year history and no active smoking in the past year)
3. Diagnosis of cystic fibrosis via standard sweat chloride/phenotypic features/genotyping
4. No use of supplemental oxygen
5. Stable lung function (within 10% of personal best in the last 6 months) with no pulmonary exacerbations in the past 4 weeks and baseline FEV1≥60% of predicted
6. Evidence of a personally signed and dated consent indicating that the subject has been informed of all pertinent aspects of the trial
7. Subjects must be willing and able to comply with scheduled visits and other trial procedures

Exclusion Criteria:

Subjects presenting with any of the following will not be included in the trial:

1. Active or past smokers or vapers with less than 1 year since quitting or >10 pack-year smoking history

2. Unable to undergo a 3.0-Tesla MRI exam of the lungs and chest because of contraindications including

   1. Occupation (past or present) of machinist, welder, or grinder;
   2. Injury to the eye involving a metallic object
   3. Injury to the body by a metallic object (bullet, bullet ball, 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 UNC 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. An intrauterine device or diaphragm that is not MRI compatible
   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

3. Unable to tolerate inhalation of gas mixture

4. Presence of facial hair that may interfere with the fit of the mask (and unwillingness to shave prior to each MRI)

5. Any changes in medications that may affect CF lung disease in the past 28 days, including any experimental therapies

6. 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 investigator, would make the subject inappropriate for entry into this trial.

7. Pregnancy; women of childbearing potential must have a confirmed negative urine pregnancy test on the day of the MR scan, prior to the MRI scan.

Adults with cystic fibrosis and stable lung disease at the time of enrollment