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Sonography > Ch. 9 Physics: Sound Beams > Flashcards

Ch. 9 Physics: Sound Beams Flashcards

1
Q

As sound travels, the width of the beam______

A

changes

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2
Q

How does the beam change?

A

Begins the same diameter as the transducer (aperture)

Narrows progressively

Then expands again

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3
Q

What are the zones of the beam?

A

Near zone

focus

focal zone

far zone

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4
Q

What is another name for the near zone?

A

Fresnel zone

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5
Q

The region from the transducer to the focus.

A

near zone or fresnel zone

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6
Q

The sound beam is at its most narrow in this section of the beam?

A

Focus or focal point

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7
Q

Structures imaged at this point are the highest quality and most accurate.

A

Focus or focal point

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8
Q

How big is the focus of the original beam’s diameter?

A

one-half

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9
Q

What section of the beam has the highest spatial peak intensity?

A

Focus

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10
Q

Region from the focal point and beyond, also called the Fraunhofer zone.

A

Far zone

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11
Q

True or false
At depths more than two near zones lengths, the beam is still the same size as the active element

A

False
At depths more than two near zones lengths, the beam is wider than the active element

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12
Q

What happens to the beam after the focal point?

A

The beam diverges, or spreads out, after the focal point

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13
Q

Which region is the most important region in diagnostic imaging, where the most accurate images are created?

A

Focal zone

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14
Q

What is the exact center of the focal zone called?

A

Focus

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15
Q

Also known as focal depth or near zone length.

A

Focal length

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16
Q

The distance from the transducer to the focus, also is the length of the near zone.

A

Focal length

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17
Q

The diameter of the crystal at the transducer face is 12 mm. The near zone length measures 8 cm. The focal zone is 4 cm long.

What is the diameter of the sound beam as it exits the transducer?

What would the beam diameter measure at 8 cm?

What would the beam diameter measure at 16 cm?

What distance would mark the beginning of the focal zone?

When would the beams diameter be larger than 12 mm?

A
  • 12mm

-6mm

-12mm

-6 cm

-At a length greater than 16 cm, or after the second near zone length

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18
Q

What are the two factors that effect the depth on fixed focus?

A

Transducer diameter (aperture)

Frequency of the sound beam

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19
Q

Crystal diameter is _______ related to focal depth.

A

Directly

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20
Q

Frequency is ________ related to focal depth.

A

Directly

21
Q

A smaller crystal diameter has a ______ focal depth.

A

Shallow

22
Q

A bigger crystal diameter has a ______ focal depth.

A

Deeper

23
Q

Low frequency has a _______ focal depth

A

shallow

24
Q

Higher frequency has a ______ focal depth

A

deeper

25
Q

What describes the gradual spread of the sound beam in the far field?

A

Divergence

26
Q

Is it more or less divergence that has better resolution in deeper tissues?

A

Less divergence

26
Q

Is it more or less divergence that has better resolution in deeper tissues?

A

Less divergence

27
Q

Divergence of the sound beam is _________ related to:

Transducer diameter (aperture)

Frequency of the sound beam

A

Inversely

28
Q

Smaller element diameter =________ divergence in the far field

A

Greater

29
Q

Larger element diameter = _________ divergence in the far field (improves lateral resolution deeper)

A

Less

30
Q

Lower frequency = _______ divergence in the far field

A

Greater

31
Q

Higher frequency =
______ divergence in the far field

A

Less

32
Q

Aperture (Beam) Diameter & Frequency of Sound are BOTH _________ RELATED to Divergence

A

Inversely

33
Q

Aperture (Beam) Diameter & Frequency of Sound are BOTH _________ RELATED to Depth

A

Directly

34
Q

Which of the following probes would create the most divergence?

Small diameter, high frequency

Large diameter, low frequency

Large diameter, high frequency

Small diameter, low frequency

A

Small diameter, low frequency

35
Q

Two 12MHz transducers have apertures measuring 6 mm and 9 mm.
Which would have the best lateral resolution in the far field?

A

The 9 mm diameter – larger = less divergence

36
Q

Two 5 mm diameter crystals have frequencies of 4Mhz and 6MHz. Which will produce the most divergence?

A

4 MHz – lower = more divergence

37
Q

Which of the following probes would create the most divergence?

2 mm, 8 MHz

6 mm, 6 MHz

2 mm, 4 MHz

8 mm, 6 MHz

A

2 mm, 4 MHz

38
Q

True or False:
Lateral resolution is inversely related to beam diameter?

A

True

39
Q

true or False:
Larger diameter crystals have better lateral resolution than smaller crystals?

A

True

40
Q

Which of the following probes would create the shallowest focus?

3 MHz, 4 mm crystal diameter

3 MHz, 6 mm crystal diameter

6 MHz, 4 mm crystal diameter

6 MHz, 6 mm crystal diameter

A

3 MHz, 4 mm crystal diameter

41
Q

True or False:
Frequency is directly related to focal depth

A

True

42
Q

True or False:
Aperture diameter is directly related to focal depth

A

True

43
Q

True or False:
Lower frequency transducers diverge more

A

True

44
Q

True or False:
Smaller apertures diverge less

A

False

45
Q

Sound waves produced by very small sources (tiny pieces of PZT) and all diverge to form the shape of a V.

A

spherical waves

diffraction patterns

Huygen’s wavelets

46
Q

States that a large active element may be thought of as millions of tiny sound sources each producing its own V-shaped waves called wavelets.

A

Huygen’s principle

47
Q

Explains that the shape of an imaging transducer’s sound beam is based upon the idea that in-phase and out-phase wavelets are interfering with each other.

A

Huygen’s principle

Sonography (39 decks)

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