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。
2
The placebo group showed a slight increase of activity up to the 5th day. Only then radioactivity began to decline.
而安慰剂组直至试验的第五天放射活性仍有轻微的增加，从那以后放射活性才开始下降。
3
An activity metering unit (9) is operable to determine a level of radioactivity in a metering section (8) of the fluid delivery path downstream from the valve means (V1).