Which radiotracer is used to measure blood flow or perfusion?

• A. Blood flow/perfusion
• B. Glucose metabolism
• C. Amyloid deposition
• D. Calcium turnover

Answer: (A)

Measuring blood flow or tissue perfusion relies on using a perfusion radiotracer. These tracers are chosen because their signal reflects how much blood is reaching a region, often by rapid distribution with arterial blood and a washout pattern that tracks flow. For example, in PET imaging oxygen-15 labeled water or rubidium-82 are classic perfusion tracers, while in SPECT exams, technetium-99m compounds like HMPAO or tetrofosmin are used for perfusion imaging. Other tracers serve different purposes: a glucose metabolism tracer highlights metabolic activity, an amyloid-binding tracer images amyloid plaques, and calcium turnover tracers assess bone turnover or calcification. Therefore, the radiotracer used to measure blood flow or perfusion is the perfusion tracer.