Radioactive Iodinated Human Serum Albumin as Tracer Agent for Diagnosing and Localizing Intracranial Lesions ∗

Various isotopes have been used to diagnose and localize intracranial lesions by the isotope- encephalometric technic described by Moore( 2 , 3 , 4 ). So far, diiodofluorescein has given the most satisfactory results and therefore gained the widest acceptance. However, at this clinic radioactive-iodinated-human-serum albumin has been used and appears to be as satisfactory, if not superior, to diiodofluores-cein. The iodination of human serum albumin (RIHSA‡) is carried out with ele-mental iodine in an essentially neutral buffer. One cc of RISHA contains 5 mg of human serum albumin with a salt concentration of approximately 2 mg( 6 ). Metabolic studies in both animals and humans have shown that RIHSA given intravenously remains in the blood stream for a long period of time. It is apparently gradually metabolised by the body and free iodine liberated. Although most of the radioactive iodine is excreted through the urine, about 5%percnt; of it is taken up by the thyroid gland by the end of 24 hours( 5 ). A small amount of RIHSA, which is not readily metabolized, diffuses out into the tissue and into lymphatics unchanged. About 1-2%percnt; of the tagged albumin can be obtained from the thoracic duct by the end of one hour. The liver, however, apparently does not participate in the excretion of RIHSA. It has been shown in experimental animals that only a neglibgible amount of RIHSA can be recovered in the bile( 5 ).