1.1 Primary Objective Compare bone measurements (by pQCT of the radius and DXA scan of the lumbar spine and total body) in children with CF 6-12 years of age to healthy children. Measurements by pQCT to be compared will include cortex width, trabecular bone mineral density (BMD), and volumetric BMD. Measurements by DXA to be compared will include total body bone mineral density and lumbar spine (L1-L4) BMD.