A New Solution for Camera Calibration and Real-Time Image Distortion Correction in Medical Endoscopy–Initial Technical Evaluation

Abstract

Medical endoscopy is used in a wide variety of diagnostic and surgical procedures. These procedures are renowned for the difficulty of orienting the camera and instruments inside the human body cavities. The small size of the lens causes radial distortion of the image, which hinders the navigation process and leads to errors in depth perception and object morphology. This article presents a complete software-based system to calibrate and correct the radial distortion in clinical endoscopy in real time. Our system can be used with any type of medical endoscopic technology, including oblique-viewing endoscopes and HD image acquisition. The initial camera calibration is performed in an unsupervised manner from a single checkerboard pattern image. For oblique-viewing endoscopes the changes in calibration during operation are handled by a new adaptive camera projection model and an algorithm that infer the rotation of the probe lens using only image information. The workload is distributed across the CPU and GPU through an optimized CPU+GPU hybrid solution. This enables real-time performance, even for HD video inputs. The system is evaluated for different technical aspects, including accuracy of modeling and calibration, overall robustness, and runtime profile. The contributions are highly relevant for applications in computer-aided surgery and image-guided intervention such as improved visualization by image warping, 3-D modeling, and visual SLAM.

Benefits of radial distortion correction in arthroscopic surgery: a first experimental study on a knee model

“…This endoscope calibration is performed at the beginning of each procedure and requires the surgeon to take a picture of a calibration target (Figure 1). The camera parameters are then automatically computed in a few seconds without the need for any user intervention (27).…”

“…2. The image warping necessary for correcting the radial distortion is carried in the heterogeneous architecture of the RDFixer™ system, using GPGPU techniques (GeneralPurpose Computing on Graphics Processing Units) (27). This enables the system to process HD video streams at high frame rates (such as 1080p@60Hz)…”

“…In this article, we use a prototype of the RDFixer™ that has been kindly provided by Perceive3D, S.A. to conduct the experiments. RDFixer™ is a softwarebased system that calibrates the endoscopic camera and performs on-the-fly corrections of image radial distortion (27). It can be used with any type of medical endoscopic technology, including oblique-viewing endoscopes and high-definition (HD) image acquisition.…”

Description and Classification of Confocal Endomicroscopic Images for the Automatic Diagnosis of Inflammatory Bowel Disease

“…This is done by searching for boundary points around the center of the crypt and then fit a conic to them. The algorithm herein described was inspired and adapted from [28].…”

“…we use a polar mapping, as proposed in [28], by changing from Cartesian coordinates x = (x, y) to polar coordinates χ = (ρ, θ).…”