Accuracy analysis for triangulation and tracking based on time‐multiplexed structured light

• Published in: Medical physics (Lancaster) Vol. 41; no. 8Part1; pp. 082701 - n/a
• Main Authors: Wagner, Benjamin, Stüber, Patrick, Wissel, Tobias, Bruder, Ralf, Schweikard, Achim, Ernst, Floris
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01.08.2014
• Subjects: Biological material, e.g. blood, urine; Haemocytometers; biomedical equipment; Calibration; cameras; Computed tomography; Details of cameras or camera bodies; Accessories therefor; Digital computing or data processing equipment or methods, specially adapted for specific applications; Equipment Design; General statistical methods; Head - surgery; Humans; ICP; Image data processing or generation, in general; image reconstruction; image registration; laser applications in medicine; Laser beams; Laser imaging; Lasers; least squares approximations; Least-Squares Analysis; Linear Models; medical image processing; Medical imaging; Nonlinear Dynamics; object tracking; optical head tracking; Optical Imaging - instrumentation; Optical Imaging - methods; optical tracking; PCA; Radiation therapy; Radiosurgery - instrumentation; Reconstruction; Registration; Robotics; Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems; skin; Surface reconstruction; Surface structure; surgery; Surgery, Computer-Assisted - instrumentation; Surgical instruments, devices or methods, e.g. tourniquets; Therapeutic applications; time‐multiplexed structured light; Tissues; triangulation
• ISSN: 0094-2405; 2473-4209; 2473-4209
• DOI: 10.1118/1.4890093

Purpose: The authors’ research group is currently developing a new optical head tracking system for intracranial radiosurgery. This tracking system utilizes infrared laser light to measure features of the soft tissue on the patient's forehead. These features are intended to offer highly accurate registration with respect to the rigid skull structure by means of compensating for the soft tissue. In this context, the system also has to be able to quickly generate accurate reconstructions of the skin surface. For this purpose, the authors have developed a laser scanning device which uses time‐multiplexed structured light to triangulate surface points. Methods: The accuracy of the authors’ laser scanning device is analyzed and compared for different triangulation methods. These methods are given by the Linear‐Eigen method and a nonlinear least squares method. Since Microsoft's Kinect camera represents an alternative for fast surface reconstruction, the authors' results are also compared to the triangulation accuracy of the Kinect device. Moreover, the authors' laser scanning device was used for tracking of a rigid object to determine how this process is influenced by the remaining triangulation errors. For this experiment, the scanning device was mounted to the end‐effector of a robot to be able to calculate a ground truth for the tracking. Results: The analysis of the triangulation accuracy of the authors' laser scanning device revealed a root mean square (RMS) error of 0.16 mm. In comparison, the analysis of the triangulation accuracy of the Kinect device revealed a RMS error of 0.89 mm. It turned out that the remaining triangulation errors only cause small inaccuracies for the tracking of a rigid object. Here, the tracking accuracy was given by a RMS translational error of 0.33 mm and a RMS rotational error of 0.12°. Conclusions: This paper shows that time‐multiplexed structured light can be used to generate highly accurate reconstructions of surfaces. Furthermore, the reconstructed point sets can be used for high‐accuracy tracking of objects, meeting the strict requirements of intracranial radiosurgery.