PET is a non-invasive imaging technique that uses radioactivity emitted from injected tracer chemicals to measure and image biological activity.

PET是一项非损伤的成像技术，它将示踪迹注入血液利用其放射性来检测生物活性并成像。

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This paper presents a determination method of specific activity for uranium isotope in rocks, soil, water and thorium isotope in rocks using 232u as a tracer isotope.

本文介绍了用(232u)作示踪同位素，测定岩石、土壤、水体中铀同位素及岩石中钍同位素比活度的方法。

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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