In a Tc sulfur colloid liver-spleen scan, which organ receives the highest dose?

• A. Spleen
• B. Liver
• C. Bone marrow
• D. Stomach

Answer: (B)

In a Tc sulfur colloid liver-spleen scan, the liver receives the highest dose primarily due to the distribution and liver uptake characteristics of the radiopharmaceutical. Technetium-99m sulfur colloid is designed to localize in the reticuloendothelial system, which is prominently present in the liver and spleen.

During the scan, after administration, the sulfur colloid is predominantly phagocytized by the Kupffer cells in the liver, leading to a higher concentration of the radioactive material in that organ. The liver has a significant role in filtering and processing the colloid particles, resulting in increased radiation exposure compared to other organs.

The spleen also takes up some amount of the sulfur colloid as part of the reticuloendothelial system, but not nearly to the extent that the liver does. Consequently, while both organs are involved in the scan, the liver's extensive uptake results in it receiving the highest radiation dose.

Other organs such as the bone marrow and stomach, while they may receive some exposure, are far less involved in metabolizing or concentrating the radiopharmaceutical, thus resulting in lower doses relative to the liver.