• Written informed consent (and assent where appropriate) obtained from the subject or subject's legal representative.

• Willingness to adhere to the study-visit schedule and other protocol requirements.

• Ages 6-8 years old at baseline MRI visit (may be enrolled up to 60 days before 6th birthday).

• Documentation of CF diagnosis as evidenced by one or more clinical features consistent with the CF phenotype and one or more of the following criteria:

‣ Sweat chloride equal to or greater than 60 mEq/liter by quantitative pilocarpine iontophoresis test

⁃ Two well-characterized mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene

• Physician intent to prescribe triple-combination therapy

• Clinically-stable with no respiratory tract infection at the time of enrollment.

• No change in chronic maintenance therapies in the 28 days prior to enrollment.

• Ability to cooperate with MRI procedures