2021 Volume 70 Issue 2 Pages 120-128
The technology for processing and analyzing tangential X-ray images of intervertebral disc spaces is advancing rapidly with the development of medical imaging information technology. However, geometric measurements of the intervertebral disc space angle and the tangential X-ray incident angle have not yet been evaluated. This study examined these using a lumbar spine phantom and an X-ray flat panel detector. Depiction of the intervertebral disc spaces on frontal images of the lumbar spine was visually evaluated and compared in terms of deviation of the tangential X-ray incident angle in order to reveal whether there was an effective tangential X-ray incident angle index to improve the depiction accuracy. Tangential X-ray incident angle deviation was in the range of 0° to ±9.0°, and images were examined in ±2.0° increments of angle deviation (5 classes in total). Evaluation of the intervertebral disc spaces and the cartilage end plates revealed extremely clear depiction of the disc spaces with tangential depiction with angle deviation of ±2.0° or less and clear depiction of the disc spaces with a thin oval appearance of the cartilage end plates with angle deviation of ±3.0°-4.0°. However, there was unclear depiction of the disc spaces with a slightly thick oval appearance of the cartilage end plates with angle deviation of ±5.0°-6.0°, unclear depiction of the disc spaces and the cartilage end plates with angle deviation of ±7.0°-8.0°, and inadequate quality for observation of both the disc spaces and the cartilage end plates with deviation of ±9.0° or more. Therefore, it is considered that the allowable deviation of the tangential X-ray incident angle needs to be ±5.0°-6.0° or less. Setting of the tangential X-ray incident angle to the intervertebral disc space by geometric measurement can be achieved easily and accurately by use of the flat panel detector and the image processing function. It can also be a new index for improving the accuracy of image depiction ability.
