Figure 2

CT with low radiation dose performed in prone position. Axial images at the level of L2 (A and C), and at the level of T6 (B and D). (E-F) Axial images at the level of the femoral heads for the measurements of pelvic tilt. To obtain the corrected value of vertebral rotation, the degree of the pelvic tilt was subtracted from the measured degree of the rotation of the vertebral body when the vertebral body and the pelvis were tilted at the same direction (A/E and D/F). On the other hand, the degree of the pelvic tilt was added to the degree of the rotation of the vertebral body when the vertebral body and the pelvis were tilted at the different directions (B/E and C/F). Thus the corrected degree of vertebral rotation will be: A-E for example A, B+E in example B, C+F for example C, and D-F in example D.