During a PET scan, the patient is injected with radioactive tracer molecules that emit positrons when they decay.

正电子断层扫描仪进行人体扫描的时候，病人被注入正电子放射性核素，然后推入检测环。

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The renal parenchymal ROI: drawing a closed curve excluding the renal pelvis detentioned the radioactive tracer.

肾实质ROI：沿肾皮质外缘亦勾画一个闭合的曲线，不包括有示踪剂滞留的肾盂。

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The researchers used a radioactive tracer to be sure that the slugs are actually producing the chlorophyll themselves, as opposed to just stealing the ready-made pigment from algae.

研究人员利用放射性示踪法确定，这种海蛞蝓确实能自己产生叶绿素，而不仅仅是从海藻那里偷取现成的色素。

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The researchers knew this because they had introduced a radioactive tracer that selectively binds to the same type of receptor in the brain, the mu-opioid variety, as the endorphins.

ECONOMIST: Pain perception

They combined conventional PET imaging, which requires a radioactive tracer to highlight the brain's metabolic activity, with other recent advances in the genetic engineering of brain cells that allows them to target specific brain circuits in lab animals.

WSJ: Brain Science: Mysterious Neural Circuitry Becomes Viewable