In which organs is the normal biodistribution of Tc RBCs primarily observed?

• A. Brain and lungs
• B. Blood, heart, liver, spleen
• C. Kidneys and bladder
• D. Stomach and intestine

Answer: (B)

The normal biodistribution of technetium-labeled red blood cells (Tc RBCs) reflects their behavior in the circulatory system. Technetium-99m (Tc-99m) is commonly used in nuclear medicine to label red blood cells for imaging studies. After injection, Tc RBCs circulate through the bloodstream and are primarily observed in the organs where blood flow is prominent.

The blood, heart, liver, and spleen are the main organs involved in this distribution. The heart receives the red blood cells directly as they flow from the arteries, and due to the high vascularization, the liver and spleen are also significant in terms of blood content and filtration processes. The liver contributes to the clearance and processing of many substances in the blood, and the spleen plays a role in filtering out aged or damaged red blood cells.

This biodistribution aids in diagnosing various cardiovascular and hematologic conditions, as the imaging can help visualize blood flow and the functional status of these organs. Understanding this biodistribution is crucial for interpreting imaging results accurately in clinical practice.