The safety and accuracy of radiation-free spinal navigation using a short, scoliosis-specific BoneMRI-protocol, compared to CT

Abstract

Purpose: Spinal navigation systems require pre- and/or intra-operative 3-D imaging, which expose young patients to harmful radiation. We assessed a scoliosis-specific MRI-protocol that provides T2-weighted MRI and AI-generated synthetic-CT (sCT) scans, through deep learning algorithms. This study aims to compare MRI-based synthetic-CT spinal navigation to CT for safety and accuracy of pedicle screw planning and placement at thoracic and lumbar levels.

Methods: Spines of 5 cadavers were scanned with thin-slice CT and the scoliosis-specific MRI-protocol (to create sCT). Preoperatively, on both CT and sCT screw trajectories were planned. Subsequently, four spine surgeons performed surface-matched, navigated placement of 2.5 mm k-wires in all pedicles from T3 to L5. Randomization for CT/sCT, surgeon and side was performed (1:1 ratio). On postoperative CT-scans, virtual screws were simulated over k-wires. Maximum angulation, distance between planned and postoperative screw positions and medial breach rate (Gertzbein-Robbins classification) were assessed.

Results: 140 k-wires were inserted, 3 were excluded. There were no pedicle breaches > 2 mm. Of sCT-guided screws, 59 were grade A and 10 grade B. For the CT-guided screws, 47 were grade A and 21 grade B (p = 0.022). Average distance (± SD) between intraoperative and postoperative screw positions was 2.3 ± 1.5 mm in sCT-guided screws, and 2.4 ± 1.8 mm for CT (p = 0.78), average maximum angulation (± SD) was 3.8 ± 2.5° for sCT and 3.9 ± 2.9° for CT (p = 0.75).

Conclusion: MRI-based, AI-generated synthetic-CT spinal navigation allows for safe and accurate planning and placement of thoracic and lumbar pedicle screws in a cadaveric model, without significant differences in distance and angulation between planned and postoperative screw positions compared to CT.

Keywords: AI-generated; MRI; Navigation; Pedicle screws; Radiation-free; Synthetic CT.

Fig. 1

Representation of the maximum angle and distance. At one third of the planned screw (green trajectory), a virtual circle perpendicular to the screw was expanded till it touched the other screw axis (orange trajectory), and the distance (D) between these was measured. The maximum angle (a) between both screw trajectories was also calculated

Fig. 2

(a) Example of planned intraoperative screw position in thoracic vertebra on a CT-scan; (b) example of planned intraoperative screw position in thoracic vertebra on a sCT scan; (c) axial postoperative CT-scan with a virtual screw positioned over the k-wire. The dotted circles could be used to adapt the screw position to exactly overlay the k-wire (d) sagittal reconstruction of all postoperative screw positions in the navigation software