The aim of this study is to establish a correlation algorithm between the BA assessment by an ultrasound apparatus (SonicBone) and the X-ray based assessment using Grulich and Pyle method, and to evaluate the validity and reproducibility of the apparatus, The design of the study is to perform a concomitant skeletal maturation assessment by reading of a hand X-ray radiograph by 3 experienced observers using the GP method, and by the ultrasound technique using the SonicBone apparatus. Skeletal maturation assessment will be performed in females and males at various age groups.