A radiotracer is a radioactive compound that is safe to inject into patients and shows up clearly on a scan.

这种放射示踪剂是一种具有放射活性的复合物，具有注射安全且扫描显示清晰的优点。

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At the same time, their brains were scanned with positron emission technology (PET), using a radioactive compound that allowed the researchers to visualize where caffeine was going once it arrived in the brain.

FORBES: A Snapshot of Caffeine's Fascinating Effects On The Brain