Evaluation of a quantitative method for carpal motion analysis using clinical 3D and 4D CT protocols.

For wrist complaints related to motion, a 2D radiograph or CT scan of the static wrist may not always be considered diagnostic. Three-dimensional motion imaging, i.e., multiple 3DCT scans in time (4DCT), enables quantifying carpal motion and comparing motion patterns of the affected wrist with those of the healthy contralateral side. The accuracy and precision of the method however, is limited by noise and motion artifacts. Although the technique is considered promising in existing literature, the accuracy and precision of carpal motion analysis has never been investigated systematically.

METHODS: In this paper we introduce and evaluate a semi-automatic segmentation- and registration-based method for 3D carpal motion analysis. We investigate the accuracy and precision of the method, and its dependency on motion and scan parameters (angular velocity, dose, gantry revolution angle for image reconstruction, scanner type) using a wrist phantom.

RESULTS: During standstill the positioning error was ≤ 0.23 mm and ≤ 0.78°. A partial gantry revolution for 3D reconstruction introduced image deformation, contributing to a positioning error of approx. 0.8 mm. This error increased with reduced dose, and with increasing angular velocity of the wrist phantom. In cases where the phantom was rotating about an axis parallel to the rotation axis of the gantry, and in a direction opposite to the gantry, the positioning error increased, probably because of the apparent increase in angular velocity with respect to the gantry.

CONCLUSION: Slow carpal motion 4DCT analysis is feasible using a regular CT scanner. A partial gantry revolution angle for 3D reconstruction may introduce image deformation, which decreases the accuracy of carpal motion analysis.

SIGNIFICANCE: Knowing the positioning error in 4DCT imaging with the proposed method is considered valuable when investigating wrist injury since it enables discrimination of actual motion from apparent motion caused by methodological error.