Which imaging test involves injecting a radioactive substance that travels to tissues and yields a cross-sectional image showing hot spots?

• A. PKU test
• B. PET scan
• C. Prothrombin Time
• D. Proctosigmoidoscopy

Answer: (B)

The imaging test described is PET scanning. In a PET scan, a small amount of radioactive tracer is injected and travels through the body, accumulating in tissues according to their metabolic activity. The scanner detects the radiation and, with computer processing, creates cross-sectional images of the body. Areas with high tracer uptake show up as hot spots, reflecting increased metabolic activity that can indicate cancer, infection, or inflammation. PET is often combined with CT (PET/CT) to localize these metabolic signals precisely.

The other options aren’t imaging tests that use a radioactive tracer to produce cross-sectional metabolic images. The PKU test screens for metabolic disorders using a blood sample. Prothrombin Time assesses blood clotting. Proctosigmoidoscopy is an endoscopic examination of the lower colon.