Radioisotope determination of regional colonic transit in severe constipation: comparison with radio opaque markers.

Radio-opaque markers have a well established role in distinguishing between patients with normal and those with slow intestinal transit, but in the latter group their accuracy in defining the region of delay has not been established. To study regional colonic transit accurately the transit of a radioisotope labelled meal was determined and findings were compared with those of simultaneously ingested radio-opaque markers. Twelve healthy controls (mean age 33 years) and 12 severely constipated women (mean age 36 years, bowel frequency < once per week) were studied On day 1, a meal containing 10 MBq 111In bound to 0.7 mm resin microspheres was ingested. Subjects also ingested a set of radiologically distinguishable markers on three successive days. Abdominal scans were obtained three times daily for 7 days. Abdominal radiographs were obtained after 72 or 96 hours and again at 144 or 168 hours. Eight 'regions of interest' were created--one for the small bowel, six for the colon, and one for excreted stool. The constipated patients all showed colonic transit outside the normal range, with a variable site of delay demonstrated by time activity curves for each region. To provide a different measure of the effectiveness of colonic transport, the movement of the 'centre of mass' for the radioisotope and for the markers was then determined. The radioisotope and radiopaque marker methods gave similar results. At all times between 24 and 144 hours there was no significant difference for the position of the centre of mass between the radio-opaque and marker methods. At all times, however, the mean difference between the markers and the radioisotopes was positive, indicating that the center of mass of the markers was always head of that of the radioisotope. The mean difference between the methods was never greater than one region of interest, and ranged from 12 to 72% of one region of interest in the colon. The difference between these two methods could reach up to two colonic segments in certain patients at one time. Radioisotope ingestion provides accurate information about the transit through individual colonic regions because of the possibility of frequent observations and the clear delineation of the entire colon. Although these features were not obtained with radio-opaque markers, they are suitable as a screening test for the presence and pattern of colonic delay.