Continuous Zoom Calibration by Tracking Salient Points in Endoscopic Video

Abstract

Abstract. Many image-based systems for aiding the surgeon during minimally invasive surgery require the endoscopic camera to be calibrated at all times. This article proposes a method for accomplishing this goal whenever the camera has optical zoom and the focal length changes during the procedure. Our solution for online calibration builds on recent developments in tracking salient points using differential image alignment, is well suited for continuous operation, and makes no assumptions about the camera motion or scene rigidity. Experimental validation using both a phantom model and in vivo data shows that the method enables accurate estimation of focal length when the zoom varies, avoiding the need to explicitly recalibrate during surgery. To the best of our knowledge this the first work proposing a practical solution for online zoom calibration in the operation room.

Stitching and Surface Reconstruction From Endoscopic Image Sequences: A Review of Applications and Methods

“…A practical problem of endoscopy calibration are frequent changes of focus or zoom settings, which make prior calibration invalid or at least imprecise. The problem of continuous re-calibration was addressed by Lourenco et al [93] (2014), who tracked salient points in the images to correct for a change of the focal length. Pratt et al [116] presented a solution for intraoperative re-calibration of a stereo camera setup by reducing the variable parameter space to one parameter (focus position).…”

The status of augmented reality in laparoscopic surgery as of 2016

“…However, this approach is applicable only to endoscopes that display such a circular outline (monocular) and also the zooming is restricted as most of this contour has to appear. In a similar manner, Lourenco et al propose to determine the zoom by tracking salient points in the image ( Lourenço et al, 2014 ). An issue with both approaches is that, while they seek to remove the need for camera calibration, they still require one lengthy pre-calibration process per endoscope model used.…”

Video-Based Computer Aided Arthroscopy for Patient Specific Reconstruction of the Anterior Cruciate Ligament

“…Marker detection and pose estimation: There are several publicly available libraries for augmented reality that implement the process of detection, identification and pose estimation of square markers. We opted for the ARAM library [2] and, for better accuracy, also used a photogeometric refinement step as described in [12] with the extension to accommodate radial distortion as in [8], making possible the accommodation of variable zoom in a future version.…”