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Ultrasound Physics

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Multiple waves together cause interference. Can be 'constructive' and/or 'destructive' ... Here the intensity of the beam is highest and the clearest picture obtained. ... – PowerPoint PPT presentation

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Title: Ultrasound Physics


1
Ultrasound Physics
2
Outline
  • Understand interference
  • Interference and beam formation
  • Resolution

3
Interference
  • Multiple waves together cause interference.
  • Can be constructive and/or destructive
  • Can be used to shape and direct beams

4
180 degrees out of phase
No output
5
Different wavelengths
6
Beam forming
Array of Transducers
Wavefronts
7
Directed Beams
If the elements are fired in order, the beam can
be directed
8
Optics of Ultrasound
Focal plane
By using beam forming techniques, a focal plane
can be produced. Here the intensity of the beam
is highest and the clearest picture obtained.
9
Beam characteristics
  • Beams are 3 dimensional usually the peak
    intensity is at the centre of the beam
  • There are side lobes, which are not on the axis
    of the beam
  • Beam focus can be changed.
  • There can be more than one focal plane
  • If there is more than 1 object in the beam at the
    same depth, they cannot be resolved

10
Resolution
  • Spatial (distance) and temporal (time).
  • Can be thought of as the point at which two
    objects just merge.
  • Axial resolution along the beam i.e. depth
  • Lateral resolution across the beam i.e. width.

11
Improving resolution
  • Best resolution is at the focus.
  • Higher frequencies and shorter pulse length give
    better axial resolution
  • Narrower beams give better lateral resolution
    focal point is best and it gets worse with depth.
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