What mechanism does Tc MAA use for localization in the body?

• A. Capillary blockage
• B. Fluid diffusion
• C. Cellular uptake
• D. Active transport

Answer: (A)

Technetium-99m macroaggregated albumin (Tc MAA) uses capillary blockage as its mechanism for localization within the body. When injected, Tc MAA particles are too large to pass through the capillaries of normal tissues and are thus trapped in the capillary beds of the lungs or wherever the injection is directed. This results in localization specifically in the pulmonary circulation during imaging procedures, such as lung perfusion scans.

This mechanism is particularly useful in assessing vascular supply and function in various organs, as the areas where the particles collect indicate regions of adequate or inadequate perfusion based on blood flow. The size of the particles ensures they do not enter smaller capillary networks, making capillary blockage the predominant accumulation method for diagnostic imaging in this context. This is why capillary blockage is regarded as the correct answer for how Tc MAA localizes in the body.