This is an observational cohort study building on an existing protocol at our institution recruiting CF patients who are 6-21 years old with one or two copies of the F508del CFTR mutation. That existing protocol seeks to enroll a total of 38 subjects; it includes three to four (three scheduled, with a fourth optional) study visits, with spirometry, LCI, UTE MRI, and 129Xe MRI being performed at each visit. This present study will utilize existing study visits for the NHLBI study, with a sub-set of 20 subjects opting-in to have all of the procedures performed twice, with an intervening ACT, during one of their study visits.

This is an observational cohort study building on an existing protocol at our institution recruiting CF patients who are 6-21 years old with one or two copies of the F508del CFTR mutation. The existing protocol is funded by the NHLBI under R01-11863962 (PIs Woods, Clancy, and hereafter referred to as "the NHLBI study" for simplicity), and seeks to enroll a total of 38 subjects; it includes three to four (three scheduled, with a fourth optional) study visits, with spirometry, LCI, UTE MRI, and 129Xe MRI being performed at each visit. This present study will utilize existing study visits for the NHLBI study, with patients opting-in to have all of the procedures performed twice, with an intervening ACT, during one their study visits. The target enrollment is 20 subjects.

Airway clearance therapy (ACT) is used for treating cystic fibrosis (CF). It is known to impact measures of lung function, and while an increasing number of lung function measures are used in clinical trials, there has been no direct comparison of the effects of ACT across the different modalities. This study is actively investigating the relationship between different measures of lung function, comparing a spirometric measure (FEV1 percent-predicted) with measures of whole-lung ventilation (lung clearance index, or LCI) and regional assessments of both structure (with ultra-short echo time magnetic resonance imaging, or UTE MRI) and function (with hyperpolarized xenon, or 129Xe, MRI). Performing these assessments on CF patients will help to elucidate the relative sensitivity of each measure to intra-individual changes within the lung and will help guide the selection of lung function measures in future studies.

Inclusion Criteria:

• Male or female between the ages of 6 through 21 years
• CFTR genotypes as specified in NHLBI study:

Two copies of the F508del CFTR mutation, OR Two non-functional CFTR mutations with one of them being F508del CFTR mutation

• Able to perform acceptable and repeatable spirometry

Exclusion Criteria:

• FEV1 percent predicted of <60%
• standard MRI exclusions (metal implants, claustrophobia)
• pregnancy

Male or female ages 6 through 21 with CF