In this phantom study, rotations of a vertebral body calculated from computerized tomography (CT) were compared to the actual rotations provided by a specially designed device incorporating a reduction gear.Objective.
The objective was to measure the accuracy of the CT and an automated software program to calculate rotations of lumbar vertebral bodies.Background.
Rotations of individual vertebrae secondary to a change in position or load can be measured in select patients by roentgen stereophotogrammetry or by using CT and a specially constructed table that creates the rotation of the torso. The purpose of this study was to measure the precision and accuracy of rotation measurements made with a CT scanner and an automated program to calculate rotation.Methods.
We constructed a phantom with a lumbar vertebra that can be rotated within a CT scanner. CT of the vertebra were obtained at angular positions of 0, 0.360°, 1.080°, 2.520°, 5.400°, 11.160°, 29.160°, 29.340°, 29.520°, 29.610°, 29.700°, 29.790°, 29.880°, and 29.889°. With an automated program based on a pixel-shift algorithm, we calculated rotations of the vertebra between pairs of images. Accuracy was calculated as mean difference between the actual and the calculated rotation, and precision was calculated as the standard deviation of the differences.Results.
Differences between actual and calculated rotations varied from −0.083° to 0.132°. For rotations less than 15°, mean error (accuracy) was −0.039°, and the standard deviation (precision) was 0.029°. For rotations greater than 15°, the accuracy was 0.086°, and the precision was 0.023°.Conclusions.
This study shows that rotations of lumbar vertebrae may be measured with CT, and an automated program to an accuracy and precision better than 0.1°, comparable to that of roentgen stereophotogrammetry.