Fig. 2.
Ray search technique for segmentation of the region of interest (ROI). The points P1 and P2 are clicked to identify the approximate longest diameter of the ROI from which the foci (F1 and F2) are generated at 20% distance from the clicked points along the diameter. The black triangles show the edge points (Ei) detected by ray search. Along any particular ray (white lines), if there is no black triangle, it indicates that the edge of the ROI (i.e., stomach) was not detected. The location of each ray also shows the dynamic update of the ray position based on the previous position of the ROI (i.e., detected edge of the stomach wall). In the absence of this update procedure, the rays form an oblong shape as shown in the inset. R indicates the ray vectors cast and subscript i is the number of rays cast for a particular ROI. A 3 × 3 Gaussian filter was then applied that removed noise from the MR image but renders other abdominal contents slightly blurry. The black squares within the stomach show points clicked to identify a balloon-tipped catheter in the stomach, which is enclosed by the thin black line, the edge points within which are ignored by the algorithm.