Patients with cystic fibrosis are at risk of developing low bone mineral density (BMD) potentially leading to pathological fractures at adult age. Recent data from our center and others have suggested that low BMD could be observed very early in life. However, quantitative bone abnormalities found out by Dual X-ray absorptiometry (DXA) need to be confronted to qualitative evaluation of bone microarchitecture (surrogate of bone strength).

High-Resolution peripheral quantitative computed tomography (HR-pQCT) is a recent technology with very high spatial resolution. Images obtained with this technic are considered as virtual bone biopsies. It enables an accurate bones' cortical and trabecular surfaces exploration in a three-dimensional manner, and therefore provides informations on bone microarchitecture as well as bone density.

The aim of this study is to evaluate bone microarchitecture of paediatric patients matched to sex-age-pubertal status-healthy volunteers. In the meantime, biological markers will be collected and DXA (Dual-energy x-ray absorptiometry) will be performed in order to explore potential correlations HR-pQCT parameters.

Inclusion Criteria:

• Cystic Fibrosis patient of both sex
• Pubertal patient
• Age ≥10 years and ≤18 years on the date of informed consent
• FEV1(forced expiratory volume at one second ) ≥ 60% of predicted normal for age, gender and height
• Patient on a clinical stable period

Exclusion Criteria:

• Unable to maintain arm and/or leg immobile for 3 minutes
• History of solid organ transplantation
• Participation in the same time to a clinical trial
• Acute pulmonary exacerbation at the time of evaluation