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

Xiaoxuan Zhang, Ali Uneri, Pengwei Wu, Michael Daniel Ketcha, Craig Jones, Yixuan Huang, Sheng-Fu L Lo, Patrick A Helm, Jeffrey H Siewerdsen
Physics in Medicine and Biology 2021 January 21

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 biplane radiographs.

RESULTS: Longitudinal coverage of ~50-64 cm was achieved with a single long-length slot scan, providing a field-of-view up to (40 × 64) cm2 , depending on patient positioning. The dose-area product (reference point air kerma × x-ray field area) for a slot scan ranged from ~702-1757 mGy ⋅ cm2 , equivalent to ~2.5 s of fluoroscopy and comparable to other long-length imaging systems. Long-length scanning produced high-resolution tomosynthesis reconstructions, covering ~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° in cadaver studies, outperforming registration to line scans (TRE = 2.8 mm and 2.2°) and biplane radiographs (TRE = 2.5 mm and 1.1°). 3D registration using single-plane slot reconstructions leveraged the ~7-14° angular separation between slots to achieve median TRE ~2 mm and < 2° from a single scan.

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.

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