Contact-less stylus for surgical navigation: registration without digitization.

Abstract

We present a laser-based, contact-less, stylus for the purpose of fiducial registration and digitization in the context of surgical navigation. We augmented a laser pointer with a spatial measurement device and used the laser beam as a means to locate a fiducial in 3D space. We developed a method for calibrating the orientation of the laser beam with respect to its attached tracking target. Digitization of a fiducial was formulated as a line intersection problem, and registration was formulated as a point-to-line registration problem. We achieved an RMS fiducial localization error of 0.63 mm for 151 measurements of 12 fiducial markers. Mean TRE values of less than 1.5 mm over the entire surface of a lumbar vertebra were achievable using 4 fiducial markers. We found that contact-based rigid registration performed carefully under near-ideal conditions outperforms contact-less registration in terms of TRE. An inexpensive contact-less stylus can be used to obtain accurate fiducial registration, which can be performed without explicit fiducial digitization.