Chapter 9 Flashcards
Sound beams
T or F Narrow beams create better images
true
T or F As sound travels the width of beam changes
True
The location where the beam reaches its minimum diameter
Focus or Facal point
Distance from the transducer to focus
Focal depth
Area between focus and transducer
Near zone
Another name for near zone
Fresnel zone
Area after focus, beyond the near zone
Far zone
Another name for far zone
Fraunhofer zone
The focus is located at the end of what
Near zone
Starts at the focus and extends deeper
Far zone
At the end of the near zone and beginning of the far zone the width of the beam is
One half as wide as at the transducer
Best quality image at this depth
Focal zone
Distance from the transducer to the focal point.
Focal depth, focal length, near zone length
What determines the depth
Transducer diameter
Frequency of ultrasound
Transducer diameter and focal depth are
directly related
Larger diameter crystal
deeper focus
Higher frequency and focal depth
directly related, deeper focus
Sound beam divergence
Larger diameter crystal, higher frequency sound produces
less diverge in far field
Sound beam divergence
smaller diameter crystal, lower frequency sound produces
diverge more in far field
The principle explains the hourglass shape of an imaging transducer’s sound beam
Huygens’s principle
