Parathyroid scanning in the human with selenomethionine-75Se

Abstract

The neck area was scanned in 8 patients at intervals for 10 to 90 min. following the intravenous injection of 200 [mu]Ci of selenomethionine-75Sec. Seven of the patients were subsequently explored and one or more enlarged parathyroids were found in all of them. The identification of active areas on the scans did not correspond well with the operation finding. The concentration of the isotope in the parathyroids was 3 to 4 times that in circulating blood, while in lymph nodes it was about twice that of blood. The concentration in the thyroid was not much above that of blood but despite this it is thought that the large bulk of the thyroid must make a considerable contribution to the background radioactivity in the neck. Apparent areas of concentration of selenomethionine-75Se were in the knee area 90 min. after injection. An in vitro study suggested that it would be impossible to detect small parathyroid tumors unless a concentration of 4-fold or more above blood level can be obtained.