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Ultrasound Physics > Chapter 9 Sound Beams > Flashcards

Chapter 9 Sound Beams Flashcards

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1
Q

At the starting point, how wide is the sound beam width?

A

The sound beam’s width is the same as the transducer diameter.

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2
Q

As the sound beam gets further from the transducer, what happens to it?

A

The sound beam narrows (converges), like a funnel.

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3
Q

After the sound beam narrows, what happens to it’s shape?

A

The sound beam expands (diverges)

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4
Q

What is the location where the beam diameter is the narrowest called?

A

Focus or Focal Point

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5
Q

What is the region from the transducer to the focus called?

A

Near Zone

aka Fresnel Zone, or Near Field

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6
Q

At the far end of he near zone, what is the diameter of the near zone?

A

1/2 the width of the active element

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7
Q

The distance from the transducer to the focus is called what?

A

Focal Length

aka Focal depth or Near Zone length

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8
Q

The region starting at the focus and extending deeper is called what?

A

Far Zone

aka Fraunhofer Zone

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9
Q

What is the width of the sound beam at the focus?

A

1/2 of transducer diameter

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10
Q

At the beginning of the far zone what is the beams width?

A

1/2 as wide as it is at the transducer

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11
Q

When the beam is two near zone lengths from the transducer, how wide is it?

A

The beam is as wide as the active element again

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12
Q

What happens to the sound beam width beyond two near zone lengths from the transducer?

A

The beam widens beyond the width of the active element, and continues expanding.

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13
Q

The region around the focus where the beam is relatively narrow is called what?

A

Focal Zone

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14
Q

Why is the focal zone important to sonographers?

A

Reflections arising from the focal zone create images of superior detail, compared to other depths.

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15
Q

What marks the end of the near zone?

A

Focus

aka focal point

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16
Q

At what point does the sound beam first begin to widen?

A

Focus

aka focal point

17
Q

The focal zone is found where?

A

Half in the near zone

Half in the far zone

18
Q

What is the beams width at the end of the near zone?

A

1/2 the transducer diameter

19
Q

What is the beams width at 2 near zone lengths?

A

beam diameter equals transducer diameter

20
Q

Is focal depth adjustable by sonographers on most modern ultrasound systems? If so, what is this called?

A

Yes. Adjustable focus systems are called Phased Array

21
Q

For a fixed-focus transducer, what two characteristics determine the focal depth?

A
  1. Transducer Diameter

2. Sound Frequency

22
Q

What is the relationship between transducer diameter and focal depth?

A

Directly related

23
Q

What is the relationship between frequency and focal depth?

A

Directly related

24
Q

A larger diameter results in?

A

a deeper focus

25
Q

Higher frequency of sound results in?

A

deeper focus

26
Q

What is the relationship between diameter and near zone length?

A

directly related

27
Q

What is the relationship between frequency and near zone length?

A

directly related

28
Q

What is the relationship between wavelength and near zone length?

A

inversely related

29
Q

(Smaller|Larger) Crystals produce beams that spread out (more|less) in the far field

A

Small|more

Larger|less

30
Q

Since larger diameter crystals create sound beams that diverge less in the far field, what would be improved in the far field?

A

Lateral resolution

31
Q

What is the relationship between frequency and beam divergence?

A

Inversely related

32
Q

Since high frequency sound beams diverge less in the far field, what would be improved in the far field?

A

Lateral resolution

33
Q

Less divergence involves what two characteristics?

A
  1. Larger diameter (PZT)

2. Higher frequency

34
Q

More divergence involves what two characteristics?

A
  1. Smaller Diameter (PZT)

2. Lower Frequency

35
Q

Shallow focus involves what two factors?

A
  1. Smaller Diameter (PZT)

2. Lower Frequency

36
Q

Deep focus involves what two characteristics?

A
  1. Larger Diameter (PZT)

2. Higher Frequency

37
Q

Very small pieces of PZT are called what?

A

Huygen’s Sources

38
Q

Very small pieces of PZT create sound waves in the shape of a “V” called what?

A

Spherical Waves
Diffraction Patterns
Huygens’ Wavelets

39
Q

This explains the shape of an imaging transducer’s beam based upon in-phase and out-of-phase wavelets interfering with each other.

A

Huygens’ Principle

Ultrasound Physics (7 decks)

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