Dye used in SPECT-
**Core Concept**
Technetium-99m (Tc-99m) is a radioactive isotope used as a tracer in Single Photon Emission Computed Tomography (SPECT) imaging, a type of nuclear medicine. Tc-99m has optimal properties for SPECT imaging, including a suitable half-life, gamma radiation energy, and chemical stability.
**Why the Correct Answer is Right**
Tc-99m is widely used in SPECT imaging due to its favorable characteristics. It has a half-life of 6 hours, which allows for sufficient time to perform imaging procedures without excessive radiation exposure. The gamma radiation energy of 140 keV is ideal for detection by SPECT cameras. Additionally, Tc-99m can be easily conjugated to various biomolecules, making it a versatile tracer for imaging a range of biological processes.
**Why Each Wrong Option is Incorrect**
**Option A:** Technetium-99m is not used in PET (Positron Emission Tomography) imaging due to its gamma radiation energy, which is not suitable for PET detectors.
**Option B:** Iodine-123 is used in SPECT imaging, but it has a shorter half-life (13 hours) compared to Tc-99m, making it less suitable for routine imaging procedures.
**Option C:** Gallium-67 is used in SPECT imaging, particularly for infection and inflammation imaging, but it is not as widely used as Tc-99m due to its higher radiation dose and lower gamma radiation energy.
**Option D:** Indium-111 is used in SPECT imaging, particularly for labeling white blood cells, but it has a longer half-life (67 hours) compared to Tc-99m, which can result in higher radiation exposure.
**Clinical Pearl / High-Yield Fact**
The most commonly used SPECT tracer, Technetium-99m, is often labeled with a variety of compounds, such as mebrofenin (for hepatobiliary imaging) or pertechnetate (for thyroid imaging).
**Correct Answer: D. Indium-111**