Radio pharmaceutical used for phagocyte study scan:-
**Core Concept**
The question requires knowledge of radio-pharmaceuticals used for imaging specific cells or tissues, in this case, phagocytes. Phagocytes, including neutrophils and macrophages, play a crucial role in the immune response. A radio-pharmaceutical that selectively targets phagocytes would be useful for studying their function and distribution in the body.
**Why the Correct Answer is Right**
Technetium-99m hexamethylpropylene amine oxime (Tc-99m HMPAO) is a lipophilic complex that crosses the cell membrane and is taken up by phagocytic cells, including neutrophils and macrophages, through an unknown mechanism. Once inside the cell, the complex is converted to a more hydrophilic form, which becomes trapped within the cell. This results in a high concentration of the radioactive tracer within phagocytic cells, allowing for imaging of these cells using gamma camera technology.
**Why Each Wrong Option is Incorrect**
**Option A:** Technetium-99m sulfur colloid is primarily taken up by the reticuloendothelial system, including the liver, spleen, and bone marrow, but it is not specifically targeted to phagocytes.
**Option B:** Indium-111 oxine is a radio-pharmaceutical used for labeling lymphocytes, but it is not the preferred choice for imaging phagocytes.
**Option C:** Gallium-67 citrate is a radio-pharmaceutical used for imaging inflammatory lesions and certain types of tumors, but it is not specifically targeted to phagocytes.
**Clinical Pearl / High-Yield Fact**
When using Tc-99m HMPAO for imaging phagocytes, it is essential to note that the test is typically performed after an inflammatory stimulus, such as an injection of endotoxin, to ensure that the phagocytic cells are actively engaged.
**Correct Answer: D. Technetium-99m hexamethylpropylene amine oxime (Tc-99m HMPAO)**