What mechanism of localization is primarily responsible for the uptake of Tc sulfur colloid in liver and spleen scans?

• A. Diffusion through membranes
• B. Phagocytosis by the RES
• C. Chemotaxis of leukocytes
• D. Active transport

Answer: (B)

The uptake of Technetium (Tc) sulfur colloid in liver and spleen scans is primarily due to phagocytosis by the reticuloendothelial system (RES). This mechanism is particularly relevant because sulfur colloid particles are small enough to be recognized and engulfed by the macrophages in the liver and spleen.

In these organs, the RES plays a crucial role in filtering the blood and clearing foreign substances, including radiopharmaceuticals such as sulfur colloid. The macrophages readily ingest the colloid particles, which results in the concentration of the radiotracer in the liver and spleen, making it possible to visualize these organs during imaging studies.

Understanding this mechanism is critical for interpreting liver and spleen scans, as the successful uptake and accumulation of the colloid is directly related to the function of the RES in capturing and processing these particles.