Which organ receives the highest radiation dose when using Tc HMPAO tagged WBCs?

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

Answer: (C)

The organ that receives the highest radiation dose when using Technetium (Tc) HMPAO tagged white blood cells (WBCs) is the spleen. This is primarily due to the spleen's role in filtering blood and its relative uptake of the radiopharmaceutical. When WBCs are labeled with Tc HMPAO, they are often used for imaging infections and inflammatory processes, and the spleen plays a critical role in these processes.

After administration, the tagged WBCs preferentially localize in areas of active inflammation and infection, which include the spleen, where they accumulate significantly more than in other organs. The spleen not only harbors a large number of WBCs but also has a strong perfusion rate, contributing to a higher dose of radiation absorbed from the radiopharmaceutical during imaging.

While the bone marrow, liver, and lungs do receive some dose due to blood circulation and various biological processes, the unique characteristics of the spleen in relation to the behavior of labeled WBCs lead to it receiving the highest radiation dose in this context. Additionally, the biological and physical properties of Tc HMPAO promote greater accumulation in the spleen for imaging purposes.