University of Twente Student Theses


Camera calibration for oblique viewing laparoscopes

Snaauw, G. (2017) Camera calibration for oblique viewing laparoscopes.

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Abstract:Expansion of surgical navigation (SN) to laparoscopic procedures can be achieved by implementation of augmented reality (AR). In AR, the patient model of SN is overlaid on the laparoscopic images to provide the surgeon with a ‘roadmap’ for the procedure. AR requires a camera model to link the patient model to the images, and requires all systems to be synchronized to prevent a delay in visualization of the patient model. A delay estimation procedure is created based on phase differences between fitted sinusoidal functions of a rotating object that is tracked by both systems. The procedure allows estimation of the delay within an accuracy of 5 ms. All intrinsic and extrinsic camera parameters are evaluated independently, and are compared against assumptions in available literature. From this, an angle dependent camera model is developed for the Olympus EndoEye HD 10 mm oblique viewing laparoscope under investigation. The proposed camera model uses a fixed focal length and radial distortion, and describes the principal point and decentering distortion as an elliptical motion during rotation of the laparoscope. The position of the camera is defined in relation to a reference sensor attached to the cylinder of the laparoscope. A reprojection error of < 1 pixel RMS is achieved using the proposed camera model on calibration data. Validation data is acquired in opposite rotation direction of the laparoscope compared to the calibration data. On the validation data the reprojection error increases to a maximum of 100 pixels RMS. The cause of this error is determined to be a movement of the camera’s image sensor within the laparoscope. As the image sensor’s pose cannot be tracked externally, it does not seem feasible to create a camera model for the specific type of laparoscope used during this study. As the proposed model performs well on calibration data, it should be evaluated on other laparoscopes to investigate if a different laparoscope allows implementation of AR and thereby expand SN to laparoscopic procedures.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:30 exact sciences in general, 31 mathematics, 33 physics, 44 medicine, 50 technical science in general, 54 computer science
Programme:Technical Medicine MSc (60033)
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