Regional Monitoring of CF Lung Disease

Inclusion Criteria: * 1 Written informed consent (and assent when applicable) obtained from subject or subject's legal representative. 2 Use of highly effective modulators for more than 30 days (ie. Trikafta) 3 Willingness and ability to adhere to the study visit schedule and other protocol requirements. 4 Documentation of a CF diagnosis with prescription of Mechanical ACT 5 Ages 12-21 inclusive, at the time of consent. 6 Clinically stable with no respiratory tract infection or recent exacerbations. 7 Treating CF physician agreeable to study procedures. Only applicable to Aim 3. 8 No change in chronic maintenance therapies in the 28 days prior to enrollment. 9 Ability to cooperate with MRI procedures. Exclusion Criteria: 1. Standard MRI exclusions (metal implants, claustrophobia). 2. For females of childbearing potential: Positive urine pregnancy test or Lactating. 3. Acute respiratory symptoms (e.g., wheezing) at the time of the MRI 4. Chronic lung or liver or pancreatic disease not related to CF. 5. Any other condition that, in the opinion of the Investigator, would preclude informed consent or assent, make study participation unsafe, complicate interpretation of study outcome data, or otherwise interfere with achieving the study objectives.