What is the mechanism of localization for Tc sestamibi?

• A. Active transport
• B. Passive diffusion
• C. Antigen-antibody binding
• D. Receptor-mediated endocytosis

Answer: (B)

Tc sestamibi localizes in tissues primarily through passive diffusion rather than active transport or other mechanisms. When Tc sestamibi is administered, it is taken up by cells in the myocardium as it crosses cell membranes based on concentration gradients. This characteristic of passive diffusion allows Tc sestamibi to accumulate in regions of viable myocardial tissue, which is essential for imaging and assessing cardiac perfusion.

In the case of myocardial cells, the uptake of Tc sestamibi is significantly influenced by their metabolic activity and membrane characteristics, which facilitate the compound's passive movement into the cells. As a lipophilic compound, Tc sestamibi readily moves through cellular membranes without requiring energy or specific transport proteins, making passive diffusion the most accurate description of its mechanism of localization in tissues. This feature is particularly useful in nuclear medicine for assessing heart conditions, as it provides critical information about blood flow and tissue viability.