Contact-less stylus for surgical navigation: registration without digitization
International Journal of Computer Assisted Radiology and Surgery
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© 2017, CARS. Purpose: We present a laser-based, contact-less, stylus for the purpose of fiducial registration and digitization in the context of surgical navigation. Methods: 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. Results: 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. Conclusion: An inexpensive contact-less stylus can be used to obtain accurate fiducial registration, which can be performed without explicit fiducial digitization.