Loyola University Medical Education Network


Phagocytosis involves the physical entrapment of colloidal particles by Kupffer cells in the reticulothelial system following an intravenous injection. Colloidal suspensions contain particles in the range of approximately 0.05 to 4 µm (see Figure 5) and may include things as diverse as Tc-SC and cigarette smoke in air. The most commonly used phagocytic agents, Tc-sulfur colloid and Tc-microaggregated albumin, typically have particle sizes ranging from approximately 0.1-2.0 µm. The smaller the particles, the greater the bone marrow uptake; larger particles tend to localize in the liver and spleen. Due to the small size of the colloid compared to the diameter of the average capillary, which is 7 µm, capillary blockade does not occur. Distribution in the RES is typically 85% in the liver, 10% in the spleen, and 5% in marrow. In severely diseased livers, the ratio may change significantly with increased uptake in the spleen. The tbiol of Tc-sulfur colloid in the liver is infinitely long; by comparison, tbiol of microaggregated albumin is 6-12 hr. The t½ of clearance from the blood for these agents is approximately 2.5 min, so in 10 min only approximately 6% remains in the blood stream. Imaging may therefore begin as early as 5-10 min post injection.


Stephen Karesh, PhD.

Last Updated: August 14, 1996
Created: March 1, 1996