[An experimental study on the computed tomography of the cervical spinal canal (author's transl)]

A study was carried out to investigate how accurately CT could delineate the vertebral canal, vertebral body, lamina, intervertebral foramen and transverse process, and which factor influences the size of the vertebral canal, using cervical vertebrae obtained from four cadavers and one skeleton. EMI CT 5005 scanner was used. CT picture depicted accurate shapes of the vertebral canal, body and transverse process. The sagittal diameter of the vertebral canal of CT picture varied by various conditions, such as difference of scanning chance, scanning angle, window width and level, but variations due to different absorption coefficients of the bone surrounding the vertebral canal were negligible. It was most significantly changed by scanning angle. Permissible scanning angle was within 5 degrees, and morphological findings were not influenced up to 15 degrees. In repeated scan to measure diameter at window width 400 and level 100, difference was observed from 0.8 mm to 0 mm with a mean of 0.3 mmn. Window width and level also gave influence to the outline of the vertebral canal. The size of the vertebral canal was most accurately measured under the condition of 400 in width and 250 in level. The optimal condition for delineation of the spine seemed to be 400 in width and 100--200 in level. Under the condition at width 400 and level 100, the vertebral canal was delineated narrower by an average 0.6 mm and 0.2 mm in the sagittal and transverse diameter respectively. In CT picture of the imitational ossified posterior longitudinal ligament made of plastic and alginate, the average narrowing rate of the vertebral canal was 4.4% greater than the one obtained by lateral view of radiograph, but both correlated well with each other. The narrowing rate of the vertebral canal by CT tended to increase in proportion to the increase in scanning angle. Further, the narrowing rate was not significantly different at window level from 0--300 as long as width was maintained at 400.