Figure 12a. Meckel diverticulum diagnosed with Tc-99m pertechnetate scintigraphy. (a) Tc-99m pertechnetate scans of a 17-year-old boy with painless rectal bleeding show a small focus of uptake in the right lower quadrant within minutes of radiopharmaceutical injection. The activity changes shape and position during the study (arrows), which is indicative of active hemorrhage and extravasation of radioactivity into the intestinal lumen. (b) Tc-99m pertechnetate scans of a 4-year-old boy who had multiple episodes of bright red bleeding from the rectum show a persistent focus of uptake in the right lower quadrant, a finding consistent with a Meckel diverticulum. There is delayed appearance of proximal small intestinal activity (arrow), most likely secondary to transit of activity from the stomach.