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The Doppler shift is a change in frequency that occurs when sound (or light) is emitted from, or bounced off of, a moving object. When a moving target reflects a sound the frequency of the reflected sound wave is altered. The frequency is shifted up by an approaching target and shifted down by a receding target. This is illustrated in Fig. 3.1. The amount the frequency is shifted is proportional to the velocity of the moving object. Because the Doppler shift was originally described for energy in the visible light spectrum, an upward Doppler shift is referred to as a blue shift, (a shift to a higher visible light frequency) and a downward Doppler shift is referred to as a red shift.

Ultrasound utilization of the Doppler shift falls into three main categories. Analysis of the Doppler frequency spectrum allows for calculation of velocity, and is used in vascular studies. Color-flow Doppler and power Doppler superimpose a color image representing motion onto a B-mode image to illustrate location of motion (blood flow).

Keywords

Thyroid Nodule Doppler Imaging Parathyroid Adenoma Doppler Flow Malignant Lymph Node 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  • Robert A. Levine
    • 1
  1. 1.Thyroid Center of New HampshireNashuaUSA

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