来自《耶鲁大学开放课程：生物医学工程探索 第21集 第21集》

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  When positrons are emitted,
  当它发射出正电子时
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  they will move through tissue until they hit an electron.
  它们会穿过组织 直到遇见电子
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  Positrons don't have to move very far,
  正电子不能移动得很远
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  there's lots of electrons around in tissues.
  因为在组织中有很多电子
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  When a positron hits an electron,
  当正电子遇到电子时
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  they annihilate one another and they generate two gamma rays
  它们就湮灭了 产生两个伽马射线粒子
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  which move in opposite directions.
  向相反的方向运动
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  If I have a positron emitting substance in the brain,
  如果在脑部有能够发射正电子的物质
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  it will emit gamma rays which can be detected.
  它就会释放出伽马射线 从而被检测到
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  Because I'm detecting one here
  因为我能检测出这里有一条轨迹
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  and one here,
  这里有一条轨迹
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  I know exactly where the source came from.
  我就能知道它们的准确来源