Does the angle of the computed tomographic scan change spinal canal measurements?

Computed tomographic scanning at 0 degrees, 10 degrees, and 20 degrees was used on two human cadaver cervical spines to determine whether altering the scan angle affects spinal canal measurement. Maximum anteroposterior diameter, cross-sectional area, and transverse diameter were determined by digitization of the scans. Both spines exhibited a regular sinusoidal pattern of variation in anteroposterior diameter and cross-sectional area, with less of a pattern for transverse diameter. The maximum values occurred around the discs in the normal spine, moving to just below the pedicle in the spondylotic spine. Minimum values were at the pedicle in the normal spine and near the discs in the spondylotic spine. Changing the computed tomographic scan angle to 10 degrees in either a cephalad or caudad direction had a negligible effect on the pattern or absolute values for any dimension in either spine. Changing the angle to 20 degrees in either direction significantly and irregularly altered both the pattern and values of anteroposterior diameter and cross-sectional area in both spines. There was little effect on transverse diameter. It was concluded that comparison of different scans should be interpreted with caution unless the change in angulation is 10 degrees or less.