**Question:** Isotope used in myocardial perfusion scan is -

A. Technetium-99m
B. Thallium-201
C. Gallium-67
D. Rubidium-82

**Correct Answer: D. Rubidium-82**

**Core Concept:**

Myocardial perfusion scan is a nuclear imaging technique used to assess the blood flow and oxygenation supply to the heart muscle. It helps in diagnosing coronary artery disease by evaluating the balance between myocardial oxygen demand and supply. The scan utilizes different radioactive isotopes that have unique properties to depict the blood flow in the heart muscle.

**Why the Correct Answer is Right:**

Rubidium-82 (Rb-82) is a positron emitter used in myocardial perfusion imaging. It is chosen due to its favorable properties for cardiac imaging:
1. Fast clearance from blood, ensuring short-lived radioactive isotope.
2. Good myocardial penetration, providing sufficient signal intensity.
3. Low radiation dose, making it safe for repeated scans.

**Why Each Wrong Option is Incorrect:**

A. Technetium-99m (Tc-99m) is a gamma emitter and has longer half-life (6 hours) compared to Rb-82 (1.1 seconds). This poses concerns regarding radiation exposure, especially for repeated scans.

B. Thallium-201 (Tl-201) is a gamma emitter with a longer half-life (11 hours). Similar to Tc-99m, it poses a higher radiation risk and is not a suitable choice for myocardial perfusion imaging.

C. Gallium-67 (Ga-67) is an alpha emitter, which is not suitable for cardiac imaging due to its ionizing radiation and low penetration depth.

**Clinical Pearl:**

Rubidium-82 is a valuable choice for myocardial perfusion imaging as it provides accurate and sensitive detection of coronary artery disease while minimizing radiation exposure. This makes it suitable for assessing the severity and extent of myocardial ischemia and estimating the left ventricular ejection fraction.

Avoiding other incorrect options (Tc-99m, Tl-201, Ga-67) is crucial to ensure safe and accurate cardiac imaging.