Fig. 1.
Calculation of bone mass deposited by periosteal apposition (ΔBMCPA) and of endosteal bone loss (ΔBMCEBL) between baseline (t0) and follow-up (t1). Long semi-axes of the ellipse at baseline (R0) and during the followup (R1) are equal to half the external diameter of the region of interest (ROI). Bone mass deposited by periosteal apposition (ΔBMCPA) is the product of the ellipsoid volume and the vBMD of cortical bone (d = 1.15 g/cm3). Coefficient 0.75 reflects bone flattening in the anteroposterior projection in comparison with its diameter in the frontal projection. Endosteal bone loss (ΔBMCEBL) is presented graphically as the brighter colour of the entire cross-sectional area of bone (black at baseline and light grey at follow-up) in order to indicate that the “endosteal bone loss” makes no distinction as to the morphological basis (cortical thninning, increase in cortical porosity, trabecular bone loss)