Which radioactive tracer is injected intravenously to show perfusion of heart muscle and is not taken up in areas of ischemia?

• A. Thoracoscopy
• B. Sigmoidoscopy
• C. Skin Biopsy
• D. Technetium Tc-99m

Answer: (D)

In myocardial perfusion imaging, a radioactive tracer is injected into a vein and travels with the blood to the heart. Tracers labeled with technetium-99m (such as Tc-99m compounds) emit gamma rays that a camera detects, allowing visualization of blood flow to the heart muscle. Normal perfused tissue takes up the tracer; areas with reduced blood flow from ischemia take up less tracer, appearing as defects on the image. Other options listed are invasive procedures or tissue sampling and do not involve a radioactive tracer for perfusion imaging. So, the tracer used intravenously to show heart muscle perfusion and to highlight regions of ischemia is Technetium Tc-99m.