Re-localisation of a biopsy site in endoscopic images and characterisation of its uncertainty.

Endoscopy guided probe-based optical biopsy is a new method for detecting sites for tissue biopsy and treatment. After detection, it can be useful to provide a visual aid in the endoscopic images to the endoscopist for example for guidance of forceps to the biopsy sites detected optically. A new method for re-localisation of these sites during the endoscopic examination is presented in this paper. It makes use of a sequence of endoscopic images, where the biopsy site location is known, in order to derive the same number of epipolar lines as images in the sequence projected onto a subsequent target image where the re-localised biopsy site needs to be computed. The location of the re-localised biopsy site is found by minimisation of the sum of squared distances to the epipolar lines. The method also determines analytically the uncertainty of the re-localised biopsy site. This provides the endoscopist with a confidence region around the re-localised biopsy site and a measure of the re-localisation precision. Simulations confirmed that the analytical uncertainty has the potential to be a good estimation of the experimental uncertainty. The method was tested on a physical phantom and on real data from four patients with eight sequences of images acquired during gastroscopy. The re-localisation precision and accuracy were estimated at 1 millimetre or better, which is sufficient for re-localisation of optical biopsy sites.