Long-length tomosynthesis and 3D-2D registration for intraoperative assessment of spine instrumentation

Purpose. A system for long-length intraoperative imaging is reported based on longitudinal motion of an O-arm gantry featuring a multi-slot collimator. We assess the utility of long-length tomosynthesis and the geometric accuracy of 3D image registration for surgical guidance and evaluation of long spinal constructs. Methods. A multi-slot collimator with tilted apertures was integrated into an O-arm system for long-length imaging. The multi-slot projective geometry leads to slight view disparity in both long-length projection images (referred to as 'line scans') and tomosynthesis 'slot reconstructions' produced using a weighted-backprojection method. The radiation dose for long-length imaging was measured, and the utility of long-length, intraoperative tomosynthesis was evaluated in phantom and cadaver studies. Leveraging the depth resolution provided by parallax views, an algorithm for 3D-2D registration of the patient and surgical devices was adapted for registration with line scans and slot reconstructions. Registration performance using single-plane or dual-plane long-length images was evaluated and compared to registration accuracy achieved using standard dual-plane radiographs. Results. Longitudinal coverage of similar to 50-64 cm was achieved with a single long-length slot scan, providing a field-of-view (FOV) up to (40 x 64) cm(2), depending on patient positioning. The dose-area product (reference point air kerma x x-ray field area) for a slot scan ranged from similar to 702-1757 mGycm(2), equivalent to similar to 2.5 s of fluoroscopy and comparable to other long-length imaging systems. Long-length scanning produced high-resolution tomosynthesis reconstructions, covering similar to 12-16 vertebral levels. 3D image registration using dual-plane slot reconstructions achieved median target registration error (TRE) of 1.2 mm and 0.6 degrees in cadaver studies, outperforming registration to dual-plane line scans (TRE = 2.8 mm and 2.2 degrees) and radiographs (TRE = 2.5 mm and 1.1 degrees). 3D registration using single-plane slot reconstructions leveraged the similar to 7-14 degrees angular separation between slots to achieve median TRE similar to 2 mm and Conclusion. The multi-slot configuration provided intraoperative visualization of long spine segments, facilitating target localization, assessment of global spinal alignment, and evaluation of long surgical constructs. 3D-2D registration to long-length tomosynthesis reconstructions yielded a promising means of guidance and verification with accuracy exceeding that of 3D-2D registration to conventional radiographs.