Multi-slot intraoperative imaging and 3D-2D registration for evaluation of long surgical constructs in spine surgery

Purpose. Initial prototype for an intraoperative slot-scan imaging and registration technique is reported for 3D guidance and confirmation of surgical constructs in spine surgery - specifically, involving placement of pedicle screws in multilevel spinal fusion or deformity correction. The unique projection geometry provided by a multi-slot collimator is exploited to produce parallax views of the radiographic scene for accurate 3D registration from a single scan. Methods. The approach takes advantage of the collimator apertures that form disparate fan-beam views to perform 3D- 2D registration of 3D implant models (pedicle screws) and 2D raw detector slot-scan measurements acquired via linear motion of the gantry. Experiments using a prototype O-arm (Medtronic, Littleton MA) were conducted in a cadaver specimen to evaluate the geometric accuracy of multi-slot registration to that of conventional 3D-2D registration from multiple fluoroscopic views. Results. Cadaver studies showed the multi-slot apertures to provide a sufficient degree of parallax to estimate the 3D location of implants. Spinal pedicle screws were registered from a single slot-scan, with mean target registration error of <1.5 mm, comparable to the margins of errors for optical surgical tracking and dual radiograph (AP + Lat) registration. Conclusions. Presented work demonstrates the feasibility of using a multi-slot collimator to perform 3D pose estimation of the patient and surgical implants in intraoperative images. The method is particularly suitable to evaluating the quality of long surgical constructs, as in spinal deformity correction. Ongoing work includes radiation dosimetry in comparison to conventional radiography and streamlined integration with tools for automatic analysis of global spinal alignment.