**6. Experimental phase**

The WCE images used in this study for the development and assessment of the proposed approach were drawn from six patients with ulcerous diseases, such as unexplained ulceration, ulceration from NSAID, ulcerative colitis and Crohn's diseases, who have undertaken a WCE examination in NIMTS Gastroenterology Clinic in Athens, Greece. The examinations were conducted with Pillcam SB (Given Imaging) WCE system. Rapid Reader 6.0 software (Given Imaging) was employed to export the images from the video sequence.

The dataset collected consists of 87 ulcer and 87 normal images. An example of the two categories is given in Fig. 11. The images were obtained by manual segmentation of the initial, complete WCE images. Two gastroenterologists reviewed the endoscopic video and manually isolated regions of interest (ROI), as the ones shown in Fig. 11, according to their expertise and upon agreement. It must be highlighted that the 87 ulcer images were obtained from 87 different events (ulcer regions) to achieve the lowest possible similarity. Furthermore, the normal images include both simple and confusing healthy tissue (folds, villus, bubbles etc.) in order to hamper the discrimination process. The ROI for the normal images varies from 110x110 to 220x220 pixels whereas the crop area of the ulcer images depends on the size, shape and position of the ulcer. The variety in ROI sizes does not affect the tissue discrimination procedure, since the feature vectors extracted from the images are utilized as the basis for comparison instead of the images themselves.

Fig. 11. An example of ulcerous (left) and normal (right) region of interest.
