Currently, patients with CF are evaluated annually for bone disease with dual X-ray absorptiometry (DXA), and screening usually starts at age 12. However, this may not be sufficient to detect early bone changes that may impact fracture risk. Furthermore, bone disease in children may manifest earlier than adolescence, which would suggest that screening should start at an earlier age in these vulnerable patients. The following study is therefore proposed to examine the potential role of peripheral quantitative computed tomography (pQCT) as a screening approach for bone disease in children with CF. The investigators expect to find bone problems by pQCT but not DXA.