Intraoperative CT as a registration benchmark for intervertebral motion compensation in image-guided open spinal surgery

Abstract

Purpose

An accurate and reliable benchmark of registration accuracy and intervertebral motion compensation is important for spinal image guidance. In this study, we evaluated the utility of intraoperative CT (iCT) in place of bone-implanted screws as the ground-truth registration and illustrated its use to benchmark the performance of intraoperative stereovision (iSV).

Methods

A template-based, multi-body registration scheme was developed to individually segment and pair corresponding vertebrae between preoperative CT and iCT of the spine. Intervertebral motion was determined from the resulting vertebral pair-wise registrations. The accuracy of the image-driven registration was evaluated using surface-to-surface distance error (SDE) based on segmented bony features and was independently verified using point-to-point target registration error (TRE) computed from bone-implanted mini-screws. Both SDE and TRE were used to assess the compensation accuracy using iSV.

Results

The iCT-based technique was evaluated on four explanted porcine spines (20 vertebral pairs) with artificially induced motion. We report a registration accuracy of 0.57 $\pm$ 0.32 mm (range 0.34–1.14 mm) and 0.29 $\pm$ 0.15 mm (range 0.14–0.78 mm) in SDE and TRE, respectively, for all vertebrae pooled, with an average intervertebral rotation of $4.9^{\circ } \pm 1.2^{\circ }$ (range 1.5$^{\circ }$–7.9$^{\circ }$). The iSV-based compensation accuracy for one sample (four vertebrae) was 1.32 $\pm$ 0.19 mm and 1.72 $\pm$ 0.55 mm in SDE and TRE, respectively, exceeding the recommended accuracy of 2 mm.

Conclusion

This study demonstrates the effectiveness of iCT in place of invasive fiducials as a registration ground truth. These findings are important for future development of on-demand spinal image guidance using radiation-free images such as stereovision and ultrasound on human subjects.