Fig. 1

Technique of obtaining HU values is demonstrated (a-d). b The three arrow directions indicated the head tilt, parallel endplate and tail tilt in the direction of screw placement, and the circle indicated the area where the screw head was located. c At the level of the upper, middle and lower body, the vertebral body (L3) was equally divided into three parts (white dotted line) in the craniocaudal direction. A median line was taken from each of the three sections of the sagittal image to select the transects measured (yellow line). d Two elliptical regions of interest (ROI) were placed on the vertebral cross-sectional images on the left and right sides, and the software automatically calculated the mean HU value of the ROI. The vertebra’s bone density was measured in the cancellous bone surrounded by an oval contour (green oval) excluding cortical bone and posterior venous plexus at the level of the middle body. e Example of the measurement of HU value to help assess osteoporosis: In a cross-sectional image at the level of the midbody, the mean HU value of L1 ROI was 187.7