Spleen scintiphotography with technetium-99m sulfur colloid and the gamma ray scintillation camera.

Several radionuclides in a variety of chemical forms have been used for spleen scanning (1). None of these has as desirable physical properties as tech netium-99m, namely, the clean 140 keV gamma, absence of particulate radiation, and short physical half-life (2). As a result, it would be desirable to find a com pound of “9―Tc that could be used for spleen scanning. Technetium-99m sulfur colloid has been investigated with this use in mind. The preparation of this agent has been detailed elsewhere (4). Harper et al have shown that the sulfur colloid of technetium-99m is an ex cellent agent for visualizing the reticuloendothelial system (3, 4). Its rapid dis appearance from the blood stream (a half-life of 2-5 minutes) allows scanning to be initiated shortly after intravenous administration. In experimental animals, 80-90 per cent is found in the liver, 5-10 per cent in the spleen and virtually all of the remainder in the bone marrow. On a weight basis, however, the concen tration in the liver and spleen is equal. In other words, the distribution of radio activity in the liver, spleen and bone marrow is similar to that of other colloidal material. Assuming 90 per cent of the technetium-99m sulfur colloid to be local ized in the liver, 5 per cent in the spleen and 5 per cent in the bone marrow, the dose to the liver (using classical calculations) is 300 millirads, the dose to the spleen 150 millirads and the dose to the bone marrow 30 millirads. Because of the 100 per cent absorption of 140 keV gamma rays in a one-half inch sodium iodide crystal, technetium-99m gives extremely high count rates when used with the scintillation camera (5, 6).