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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  millions of Hertz range,
  或者百万赫兹的水平
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  so it's higher frequency sounds than you can hear.
  这个频率太高了 你们听不到的
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  Some have very short--
  超声具有很短的
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  of these high frequency sound waves have very short wavelengths.
  这种高频声波的波长都很短
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  They can penetrate through tissues.
  它们能够穿过组织
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  Ultrasound allows for good imaging of anatomical structure.
  超声成像能够清晰地显示解剖结构
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  It's also a fast imaging method,
  成像速度也很快
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  and so it can allow you to look at motion in ways
  所以你能用它来观察运动
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  that are difficult to do using some of these other techniques,
  比用其它方法都要简便
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  and I'll tell you about that.
  我要给你们讲讲这方面内容
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  The way that ultrasound works is you have to
  要想进行超声成像
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  get sound waves propagated into the body
  你必须得让声波进入人体