Contour and paired-point registration in a model for image-guided surgery

This study assesses target registration error (TRE) of contour-based registration (CBR) and paired-point registration (PPR) for endoscopic sinus surgery.

The experimental registration model consisted of a replica of a human head (Sawbones #1345-27; Pacific Research Laboratories, Vashon, WA). Twelve surface fiducial markers were affixed to the simulated skin on the model, and titanium screws were placed in the regions of the anterior ethmoid (AE) and sphenoid face (SF). An axial computed tomography scan (1-mm slice thickness) was then obtained.

Registration was then performed on the InstaTrak 3500 Plus (GE Surgical Navigation & Visualization, Lawrence, MA) with the standard PPR protocol with 12 points and CBR protocol with 500, 250, 125, 50, and 4 points. TRE was then calculated at the AE and SF targets.

Target registration error was significantly lower for paired-point registration compared with contour-based registration (AE, 0.5 mm vs. 1.5 mm, P < .0001; SF, 0.8 mm vs. 1.5 mm, P < .0001). Among contour-based registration protocols, target registration error at the sphenoid face was lowest with 50 points (1.5 mm, P < .02). At the anterior ethmoid, contour-based registration with 50 points produced a lower target registration error than contour-based registration with 125 points (1.5 vs. 1.8 mm, P < .01). Other target registration error values for CBR were similar at both regions. The target registration error interquartile range was lowest with CBR-125 at both regions.

Paired-point registration provided significantly lower target registration error. Contour-based registration with 125 points (and possibly as few as 50 points) produces clinically acceptable target registration error. This registration model elucidates important concepts about registration for surgical navigation for sinus surgery.