New large bowel segmentation on plain abdominal radiography in comparison with the conventional method.

Plain abdominal radiography is a very basic examination and plays an important role in primary care. The objectives of this study were to clarify colon distributions on plain abdominal radiographs. Forty-three healthy volunteers underwent gastric fluoroscopy, and 2 hours later, plain abdominal radiography in the supine position. A region of interest (ROI) was defined uniformly on each X-ray image to divide the image into 600 zones. The area corresponding to the large bowel within the ROI was divided into 4 segments (ascending colon, transverse colon, descending colon, and sigmoid colon + rectum). The percentage of barium in each segment relative to the total volume of barium used was calculated to evaluate the percent ROI occupancy. The large bowel covered 76.7% of the entire ROI, with the percent duplication being 55%. The duplicated area corresponded to the transverse colon region. When the method proposed by Arhan et al. was used, the percentage of the colon actually present in each segment relative to that determined theoretically was 99.6% for the right colon segment, 92.2& for the left colon segment, and 92.2% for the sigmoid/rectal segment. However, in cases in which the transverse colon descended partially from the fifth lumbar vertebra, the percentage occupied by the sigmoid colon + rectum decreased to 57.2%. We applied a new large bowel segmentation method especially for patients with ptosis, by devising a line joining the lateral side of the right lesser pelvis and the lower ends of both sacroiliac joints.