**Question:** Isotope used in myocardial perfusion scan is – a) Technetium, b) Thallium, c) Stannous pyrophosphate, d) Gallium

**Core Concept:** Myocardial perfusion scans are diagnostic imaging tests used to evaluate the blood flow to the heart muscle (cardiac perfusion). They involve injecting a radioactive tracer into the bloodstream, which accumulates in the heart tissue based on blood flow.

**Why the Correct Answer is Right:** The correct answer, **c) Stannous pyrophosphate**, is used in myocardial perfusion scans due to its ability to selectively accumulate in areas of reduced blood flow or ischemia. Stannous pyrophosphate is a chelate compound, which binds to the enantiomer of adenosine triphosphate (ATP) present in ischemic heart tissue. This binding results in increased accumulation of the tracer in these areas, allowing for visualization of reduced blood flow and identification of coronary artery disease.

**Why Each Wrong Option is Incorrect:**

a) Technetium (option A) is used in other types of nuclear medicine scans, such as bone scans, but is not specifically targeted for myocardial perfusion.

b) Thallium (option B) is also used in myocardial perfusion scans but has been surpassed by newer tracers due to its poor tissue penetration and limited differentiation between reversible and irreversible ischemia.

d) Gallium (option D) is primarily used in oncology and infection imaging, not specifically for myocardial perfusion.

**Clinical Pearl:** Myocardial perfusion scans play a crucial role in diagnosing coronary artery disease, evaluating myocardial ischemia, and assessing the severity and extent of myocardial infarction. This information is essential for accurate diagnosis, treatment planning, and monitoring patient outcomes.

**Correct Answer:** c) Stannous pyrophosphate