Registration accuracy and practicability of laser-directed surface matching

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Abstract
The aim of our study was to evaluate the registration accuracy and practicability of a new laser registration technique in comparison to marker registration. From January to. August 2001, 36 patients (23 male, 13 female) with brain lesions were operated with navigational guidance. Thirty-five patients were registered by paired-point registration. In 16 patients, a second registration was carried out using a special laser pointer for surface matching (z-touch™, BrainLab, Heimstetten, Germany). Accuracy was evaluated by touching seven anatomic landmarks and a target fiducial with the nonsterile pointer. The distance from the virtual pointer tip to these points was determined on the monitor display (600% zoom). Laser registration is fully retrospective and allows registrations when no markers are applied, z-touch™ registration is more sophisticated and time-consuming than marker-based registration (registration time for z-touch™=7.4 ±3.7 min; for markers=4.1 ± 1.7 min; p < 0.005). Marker registration proved to be more accurate than z-touch™ registration with regard to localization of anatomical landmarks and target fiducials (precision with z-touch™=2.77 ± 1.64 mm; with markers=1.31 ± 0.87 mm; p < 0.01). Although the registration error was increased and preparation time prolonged with the z-touch™ technique, it proved to be a valuable option, especially in children.