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Ultrasound Physics > Week 8 Sound Beams > Flashcards

Week 8 Sound Beams Flashcards

Sound Beams

1
Q

What is the anatomy of a sound beam?

A

1.Focus
2. Near zone
3. Focal Length/ Near zone Length
4. Far zone
5. Focal Zone

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2
Q

Where is the focus located?

A

at the narrowest part of the beam.

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3
Q

What shape are sound beams?

A

Bowtie shape

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4
Q

Where is the near zone located?

A

It is the region from the transducer to the focus.

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5
Q

What are other names for the near zone?

A
  1. Near field
  2. Fresnel zone
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6
Q

What are other names for the Focal Length?

A

focal depth or near zone length.

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7
Q

What is focal length?

A

is the distance from the transducer to the focus.

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8
Q

What are other names for Far zone

A
  1. Far Field
  2. Fraunhofer zone
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9
Q

What is the Far zone?

A

Is the region that starts at the focus and extends deeper.

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10
Q

What happens within the far zone?

A

the beam diverges and spreads out.

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11
Q

What is the focal zone?

A

region around the focus where the beam is relatively narrow.

Half of the focal zone is located in the near field and the other half is located in the far field.

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12
Q

Where does superior image detail occur?

A

The Focal zone.

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13
Q

What is another name for the area directly after the transducer?

A

Aperature

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14
Q

At the transducer…..

A

Beam diameter equals the transducer diameter.

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15
Q

At the focus……

A

beam diameter is 1/2 the transducer diameter.

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16
Q

At 2 near zone lengths….

A

beam diameter equals transducer diameter.

17
Q

Deeper than 2 near zone lengths….

A

beam diameter is wider than the transducer diameter.

18
Q

If a transducer has a diameter of 12 mm, what is the diameter of the sound beam at depth of 8cm?

A

6 cm

The beam diameter is 1/2 the transducer diameter.

19
Q

What characteristics determine the focal depth?

A
  1. transducer diameter
  2. Frequency of sound
20
Q

How are transducer diameter and focal depth related?

A

They are DIRECTLY related.

21
Q

How are frequency and focal depth related?

A

They are DIRECTLY related.

22
Q

Characteristics of shallow focus

A
  1. smaller diameter PZT
  2. Lower frequency
23
Q

Characteristics of deeper focus

A
  1. Larger diameter PZT
  2. Higher Frequency
24
Q

Can a sonographer change the focal depth?

A

No, it is set by the ultrasound system.

25
Q

How are wavelength and focal depth related?

A

They are INVERSELY related.

26
Q

What are 2 characteristics that determine beam divergence?

A
  1. Transducer diameter
  2. frequency of the sound
27
Q

How are crystal diameter and beam divergence related?

A

They are INVERSELY related.

28
Q

A smaller diameter transducer will diverge more or less in the far field?

A

It will diverge MORE in the far field.

29
Q

A larger diameter transducer will diverge more or less in the far field?

A

It will diverge LESS in the far field.

30
Q

Larger diameter crystals create what?

A

better lateral resolution in the far field.

31
Q

How are frequency and beam divergence related?

A

They are INVERSELY related.

32
Q

High frequency sound beams create what in the far field?

A

They create improved lateral resolution.

33
Q

Characteristics of beams that create less divergence.

A
  1. Large diameter
  2. Higher frequency
34
Q

Characteristics of beams that create more divergence.

A
  1. smaller diameter
  2. Lower frequency
35
Q

A pair of 6 MHz probes are identical except for the active element diameters which are 6mm and 10mm. Which beam will be more compact in the far field?

A

The probe with 10mm active element.

36
Q

A pair of 9mm diameter probes are identical except for frequencies which are 3MHz and 6 MHz. Which sound beam will spread out more in the far field?

A

The 3MHz probe is more divergent in the far field.

37
Q

Which of the following probes creates a beam with the least divergence?

A. 4mm, 4MHz
B. 6mm, 8MHz
C. 6mm, 2MHz
D. 5mm, 8MHz

A

B. 6mm, 8MHz probe will be best.

Least divergence = large diameter high frequency

38
Q

Which of the following probes creates a beam with the most divergence?

A. 4mm, 4MHz
B. 6mm, 8 MHz
C. 4mm, 2MHz
D. 5mm, 8MHz

A

C .4mm, 2MHz

More divergence is created with small diameter and low frequency.

Ultrasound Physics (10 decks)

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