Radionuclide Imaging



Improvements in radiopharmaceuticals and im­aging devices have resulted in new techniques that are of value in selected circumstances. The traditional liver-spleen scan, using 99mTc-sulfur colloid that undergoes phagocytosis by reticu­loendothelial cells, has largely been supplanted by US or CT but is still useful in the evaluation of benign hepatic neoplasms (see Chapter 48) and, when combined with a lung scan, subphrenic ab­scesses. Newer agents, such as 99mTc-HIDA, which are taken up by hepatic parenchymal cells and excreted in bile, outline the shape of the liver and are useful in the evaluation of acute chole­cystitis (see Chapter 49] or of biliary atresia in infants. In general, they are not useful in other biliary tract disorders, as anatomical definition is poor. The affinity of 99mTc-pertechnetate for gas­tric mucosa makes this agent useful for the de­tection of Meckel’s diverticula, 85 per cent of which contain ectopic gastric mucosa. Finally, 99mTc-labeled red blood cells have been used in some centers to detect the site of bleeding in pa­tients with slow and/or intermittent gastrointes­tinal hemorrhage.