Chapter 9 Sound Beams Flashcards

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
Higher frequency of sound results in?
deeper focus
26
What is the relationship between diameter and near zone length?
directly related
27
What is the relationship between frequency and near zone length?
directly related
28
What is the relationship between wavelength and near zone length?
inversely related
29
(Smaller|Larger) Crystals produce beams that spread out (more|less) in the far field
Small|more | Larger|less
30
Since larger diameter crystals create sound beams that diverge less in the far field, what would be improved in the far field?
Lateral resolution
31
What is the relationship between frequency and beam divergence?
Inversely related
32
Since high frequency sound beams diverge less in the far field, what would be improved in the far field?
Lateral resolution
33
Less divergence involves what two characteristics?
1. Larger diameter (PZT) | 2. Higher frequency
34
More divergence involves what two characteristics?
1. Smaller Diameter (PZT) | 2. Lower Frequency
35
Shallow focus involves what two factors?
1. Smaller Diameter (PZT) | 2. Lower Frequency
36
Deep focus involves what two characteristics?
1. Larger Diameter (PZT) | 2. Higher Frequency
37
Very small pieces of PZT are called what?
Huygen's Sources
38
Very small pieces of PZT create sound waves in the shape of a "V" called what?
Spherical Waves Diffraction Patterns Huygens' Wavelets
39
This explains the shape of an imaging transducer's beam based upon in-phase and out-of-phase wavelets interfering with each other.
Huygens' Principle