Fig. 3

Schematic diagram of HU value measurement. HU values were measured in CT axial slice images of the patient’s L1 vertebrae (D) below the upper endplate (A), in the middle (B) and above the lower endplate (C), respectively, and averaged as the patient’s BMD. In each measurement, the largest possible elliptical region of interest was plotted, but the cortical margin was excluded to prevent volume averaging