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1·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。

2·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。

3·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。

4·The multiple tracer approach addresses the complexities of transport at the site and differentiates various municipal, industrial and radioactive waste sources.

多重示踪方法可解决当地运移的复杂性，并可区分各种城市的、工业的和放射性的废物的来源。