Xinyang Liu1, Christina E Rice1,2, Raj Shekhar3. 1. Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, 111 Michigan Avenue NW, Washington, DC, 20010, USA. 2. Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, 08544, USA. 3. Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Health System, 111 Michigan Avenue NW, Washington, DC, 20010, USA. rshekhar@childrensnational.org.
Abstract
PURPOSE: The oblique-viewing (i.e., angled) rigid endoscope is a commonly used tool in conventional endoscopic surgeries. The relative rotation between its two moveable parts, the telescope and the camera head, creates a rotation offset between the actual and the projection of an object in the camera image. A calibration method tailored to compensate such offset is needed. METHODS: We developed a fast calibration method for oblique-viewing rigid endoscopes suitable for clinical use. In contrast to prior approaches based on optical tracking, we used electromagnetic (EM) tracking as the external tracking hardware to improve compactness and practicality. Two EM sensors were mounted on the telescope and the camera head, respectively, with considerations to minimize EM tracking errors. Single-image calibration was incorporated into the method, and a sterilizable plate, laser-marked with the calibration pattern, was also developed. Furthermore, we proposed a general algorithm to estimate the rotation center in the camera image. Formulas for updating the camera matrix in terms of clockwise and counterclockwise rotations were also developed. RESULTS: The proposed calibration method was validated using a conventional [Formula: see text], 5-mm laparoscope. Freehand calibrations were performed using the proposed method, and the calibration time averaged 2 min and 8 s. The calibration accuracy was evaluated in a simulated clinical setting with several surgical tools present in the magnetic field of EM tracking. The root-mean-square re-projection error averaged 4.9 pixel (range 2.4-8.5 pixel, with image resolution of [Formula: see text] for rotation angles ranged from [Formula: see text] to [Formula: see text]. CONCLUSIONS: We developed a method for fast and accurate calibration of oblique-viewing rigid endoscopes. The method was also designed to be performed in the operating room and will therefore support clinical translation of many emerging endoscopic computer-assisted surgical systems.
PURPOSE: The oblique-viewing (i.e., angled) rigid endoscope is a commonly used tool in conventional endoscopic surgeries. The relative rotation between its two moveable parts, the telescope and the camera head, creates a rotation offset between the actual and the projection of an object in the camera image. A calibration method tailored to compensate such offset is needed. METHODS: We developed a fast calibration method for oblique-viewing rigid endoscopes suitable for clinical use. In contrast to prior approaches based on optical tracking, we used electromagnetic (EM) tracking as the external tracking hardware to improve compactness and practicality. Two EM sensors were mounted on the telescope and the camera head, respectively, with considerations to minimize EM tracking errors. Single-image calibration was incorporated into the method, and a sterilizable plate, laser-marked with the calibration pattern, was also developed. Furthermore, we proposed a general algorithm to estimate the rotation center in the camera image. Formulas for updating the camera matrix in terms of clockwise and counterclockwise rotations were also developed. RESULTS: The proposed calibration method was validated using a conventional [Formula: see text], 5-mm laparoscope. Freehand calibrations were performed using the proposed method, and the calibration time averaged 2 min and 8 s. The calibration accuracy was evaluated in a simulated clinical setting with several surgical tools present in the magnetic field of EM tracking. The root-mean-square re-projection error averaged 4.9 pixel (range 2.4-8.5 pixel, with image resolution of [Formula: see text] for rotation angles ranged from [Formula: see text] to [Formula: see text]. CONCLUSIONS: We developed a method for fast and accurate calibration of oblique-viewing rigid endoscopes. The method was also designed to be performed in the operating room and will therefore support clinical translation of many emerging endoscopic computer-assisted surgical systems.
Authors: Alfred M Franz; Tamás Haidegger; Wolfgang Birkfellner; Kevin Cleary; Terry M Peters; Lena Maier-Hein Journal: IEEE Trans Med Imaging Date: 2014-05-05 Impact factor: 10.048
Authors: Xinyang Liu; William Plishker; Timothy D Kane; David A Geller; Lung W Lau; Jun Tashiro; Karun Sharma; Raj Shekhar Journal: Int J Comput Assist Radiol Surg Date: 2020-04-22 Impact factor: 2.924
Authors: Andrea Teatini; Egidijus Pelanis; Davit L Aghayan; Rahul Prasanna Kumar; Rafael Palomar; Åsmund Avdem Fretland; Bjørn Edwin; Ole Jakob Elle Journal: Sci Rep Date: 2019-12-10 Impact factor: 4.379