RecruitingDiagnostic testSkeletal Health and Bone Marrow Composition in Adolescents With Cystic FibrosisThe investigators will be evaluating bone marrow composition via magnetic resonance imaging in adolescents diagnosed with cystic fibrosis (CF) compared to healthy, matched controls. The investigators will also be assessing their bone mineral density via other imaging modalities, including dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). This longitudinal project will focus on abnormalities in bone marrow composition, and specifically whether adolescents with diagnosed with CF exhibit increased bone marrow fat, its association with bone mineral density (BMD) and the underlying pathophysiology, including glycemic control, inflammation, and bone turnover markers.