On-demand calibration and evaluation for electromagnetically tracked laparoscope in augmented reality visualization

Abstract

Purpose Common camera calibration methods employed in current laparoscopic augmented reality systems require the acquisition of multiple images of an entire checkerboard pattern from various poses. This lengthy procedure prevents performing laparoscope calibration in the operating room (OR). The purpose of this work was to develop a fast calibration method for electromagnetically (EM) tracked laparoscopes, such that calibration can be performed in the OR on demand. Methods We designed a mechanical tracking mount to uniquely and snugly position an EM sensor to an appropriate location on a conventional laparoscope. A tool named fCalib was developed to calibrate intrinsic camera parameters, distortion coefficients, and extrinsic parameters (transformation between the scope lens coordinate system and the EM sensor coordinate system) using a single image that shows an arbitrary portion of a special target pattern. For quick evaluation of calibration result in the OR, we integrated a tube phantom with fCalib and overlaid a virtual representation of the tube on the live video scene. Results We compared spatial target registration error between the common OpenCV method and the fCalib method in a laboratory setting. In addition, we compared the calibration re-projection error between the EM tracking-based fCalib and the optical tracking-based fCalib in a clinical setting. Our results suggested that the proposed method is comparable to the OpenCV method. However, changing the environment, e.g., inserting or removing surgical tools, would affect re-projection accuracy for the EM tracking-based approach. Computational time of the fCalib method averaged 14.0 s (range 3.5 s – 22.7 s). Conclusions We developed and validated a prototype for fast calibration and evaluation of EM tracked conventional (forward viewing) laparoscopes. The calibration method achieved acceptable accuracy and was relatively fast and easy to be performed in the OR on demand.

Laparoscopic stereoscopic augmented reality: toward a clinically viable electromagnetic tracking solution

“…A possible solution could be a fast and easy camera calibration method that can be performed during the procedure, and we have begun examining the accuracy of such a single-image calibration method. 33 To extend the EM-AR system for human use, a sterile Laparoscopic Cover (Civco Medical Solutions, Kalona, Iowa) marketed specifically for the exact LUS transducer can be used.…”

Laparoscopic Liver Resection with Augmented Reality: A Preclinical Experience

“…In addition, using a fast calibration method developed by our team, a second process known as laparoscope calibration was performed immediately before the surgery started. 8 Briefly, this process determines the laparoscope camera intrinsic parameters and the coordinate transformation from camera lens coordinates to that of the EM sensor. The AR system then maps the three-dimensional spatial coordinates to the twodimensional coordinates of the image captured by the laparoscope, thus correctly fusing the ultrasound image to the laparoscope image.…”

Electromagnetic tracking in image‐guided laparoscopic surgery: Comparison with optical tracking and feasibility study of a combined laparoscope and laparoscopic ultrasound system

“…Both optical and EM‐tracking systems exist for laparoscopy . The group at Children's National Medical Center in Washington moved from an optically tracked to an EM‐tracked system to reduce line‐of‐sight issues and ultimately to combine a laparoscope with a flexible LUS probe which necessitates EM tracking.…”

“…Both optical and EM‐tracking systems exist for laparoscopy . The group at Children's National Medical Center in Washington moved from an optically tracked to an EM‐tracked system to reduce line‐of‐sight issues and ultimately to combine a laparoscope with a flexible LUS probe which necessitates EM tracking. However, in that work, the EM sensor was placed on the distal end of the laparoscope, which must compound the poorer intrinsic level of accuracy of the EM tracker with the lever‐arm effect, leading to suboptimal localization of the camera.…”