High Speed, High Density Intraoperative 3D Optical Topographical Imaging with Efficient Registration to MRI and CT for Craniospinal Surgical Navigation

Abstract

Intraoperative image-guided surgical navigation for craniospinal procedures has significantly improved accuracy by providing an avenue for the surgeon to visualize underlying internal structures corresponding to the exposed surface anatomy. Despite the obvious benefits of surgical navigation, surgeon adoption remains relatively low due to long setup and registration times, steep learning curves, and workflow disruptions. We introduce an experimental navigation system utilizing optical topographical imaging (OTI) to acquire the 3D surface anatomy of the surgical cavity, enabling visualization of internal structures relative to exposed surface anatomy from registered preoperative images. Our OTI approach includes near instantaneous and accurate optical measurement of >250,000 surface points, computed at >52,000 points-per-second for considerably faster patient registration than commercially available benchmark systems without compromising spatial accuracy. Our experience of 171 human craniospinal surgical procedures, demonstrated significant workflow improvement (41 s vs. 258 s and 794 s, p < 0.05) relative to benchmark navigation systems without compromising surgical accuracy. Our advancements provide the cornerstone for widespread adoption of image guidance technologies for faster and safer surgeries without intraoperative CT or MRI scans. This work represents a major workflow improvement for navigated craniospinal procedures with possible extension to other image-guided applications.

Figure 1

Ideal thoracic pedicle screw entry point and trajectory. Ideal thoracic pedicle screw entry point (dark red circle) and trajectory (dashed red cylinder) in the coronal (A), axial (B) and sagittal (C) planes. Ideal entry point distance (d) and trajectory angle (∅) shown on axial and sagittal planes. Example of a misplaced thoracic pedicle screw via freehand technique (D), Heary Grade V, with tip (arrowhead) abutting the aorta.

Figure 2

Clinical prototype of the experimental navigational system. (A) Design model of the surgical light head with embedded navigation. Designed to inconspicuously serve as traditional boom-supported surgical light head comprised of 64 high intensity surgical light LEDs to provide standard lighting with minimal spectral overlap with the navigation optics. Binocular infrared cameras utilizing provide real-time tracking of passive-reflective markers mounted on surgical tools. A digital mirror device centered around binocular structured light cameras forming an epipolar baseline provide intra-operative surface imaging for registration to the pre-operative images. Co-ordinates of the tracked tools are easily matched to the acquired structured light surface image. (B) Design model of the surgical light head with embedded navigation: Technical specifications: Field of view of the infrared tracking volume (outer pyramid) and the structured light imaging volume (inner pyramid). All measurements are in millimeters. (C) Prototype navigation system in clinical use. (D) Comparison of total setup time (median and IQR) for cranial and spine applications of experimental and benchmark navigation systems (cranial: StealthStation; spine A: Nav3/3i; spine B: O-arm).

Figure 3

Optical topographical imaging (OTI) experimental navigation system. (A) Structured light patterns projected into the open surgical field. Structured light patterns deflect and deform upon reaching the surface of the target. Pattern deformations reflect height variations (along the optical axis) of the surface. (B) Registered reconstructed surface data to pre-acquired imaging data with tool tracking capabilities. Verification of the system’s accuracy is conducted by sliding a passively tracked probe along boney landmarks of the anatomy and confirming the system is reporting the tool’s spatial location correctly. (C) Grey-scale stereoscopic cameras acquire surface images: light patterns are projected onto the surface, images are captured and 3D reconstructions and thresholded point-clouds are created representing the bony surface of the spine. (D) Registration of the acquired 3D-point cloud to pre-acquired imaging data (i.e. CT, MRI, OTI) using an iterative closest point (ICP) algorithm based on a three-point picking protocol.

Figure 4

Engineering analysis quantifying cranial translational error. Comparison of postoperative cranial screw co-ordinates to intraoperative co-ordinates base on the location of the tracked probe. (A) Axial CT representation, (B) Coronal CT representation (C) Multiplanar reformatted CT image (2 cranial fixation screws), (D) 3-dimensional volume rendered CT.

Figure 5

Engineering analysis quantifying absolute translational and angular deviation in the axial and sagittal planes. Example shown of a patient with hypoplastic pedicles at L2. (A) Intraoperative predicted screw trajectory (red) as visualized on a preoperative axial CT. (B) Postoperative actual screw trajectory (red) as visualized on a multiplanar reformatted postoperative CT. Axial distances (d) were measured at 90° relative to midsagittal axis (green line). Angle (Ø) represents corresponding trajectory angles. (C) Intraoperative predicted screw trajectory (red) as visualized on a preoperative sagittal CT. (D) Postoperative actual screw trajectory (red) as visualized on a multiplanar reformatted postoperative CT. Sagittal distances (d) were measured at 90° relative to the inferior or superior endplate (green line). Angle (Ø) represents corresponding trajectory angles. Errors in each plane were calculated as d₁-d (translational) and Ø₁-Ø (angular).

Figure 6

Bland Altman analysis. Left Panel: Correlation plots with corresponding boxplots comparing predicted intraoperative screw trajectory with actual postoperative screw trajectory for benchmark (blue) and experimental (red) navigation systems. Right Panel: Bland-Altman plots comparing actual screw trajectory with distance and angular deviations for (A) Axial Distance, (B) Sagittal Distance, (C) Axial Angle, (D) Sagittal Angle. No statistically significant differences were found.