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SPI > Ch 6 Sound in Media > Flashcards

Ch 6 Sound in Media Flashcards

1
Q

What two things do sound waves do when traveling?

A

Some reflect at the boundaries of 2 different media, remainder travels deeper to next medium boundary

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2
Q

Sound ______ as it travels.

A

weakens

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3
Q

Propagation

A

sound traveling through tissue

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4
Q

Reflection

A

portion of sound that bounces off medium boundaries

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5
Q

Receive

A

reflected wave traveling back to transducer

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6
Q

Attenuate

A

sound wave weakening while traveling
absorption

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7
Q

Amplified

A

US system strengthens reflected waves received by transducer

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8
Q

What are the 6 steps to signals traveling?

A
  1. Sound waves created & transmitted into body by US system & transducer
  2. Sound waves attenuate as they propagate
  3. Waves are reflected at boundary of 2 media
  4. Reflections received by transducer
  5. Waves converted to electrical signal
  6. Signal sent to US system to be amplified
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9
Q

What do decibels measure?

A
  • strength of sound beams as they are created and propagate
  • strength and brightness of images created by electrical signals
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10
Q

What is decibel notation?

A
  • uses logarithms
  • does not use absolute numbers
  • reports relative change
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11
Q

Decibel notation is: (4 things)

A
  • relative measurement
  • a comparison
  • a ratio
  • logarithmic
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12
Q

Positive decibels report signals that are what?

A

Increasing in strength or getting larger

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13
Q

When intensity doubles, the relative change is ______?

A

3 dB

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14
Q

Negative decibels report what kind of signals?

A
  • signals that are decreasing or getting smaller
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15
Q

When intensity is reduced to half the original value, the relative change is _____?

A

-3 dB

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16
Q

What is a logarithm?

A
  • method of rating numbers
  • represents the number of 10s multiplied to create the original number
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17
Q

If a log increases by 1, the number increases _____

A

10 fold

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18
Q

What is the log of 1000? 10000?

A

3, 4

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19
Q

Attenuation is a decrease in what 3 parameters as sound propagates?

A

Power, intensity, amplitude

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20
Q

What two factors is attenuation determined by?

A

Path length and frequency of sound

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21
Q

How does path length affect attenuation?

A
  • directly affects it
  • increased distance = increased attenuation
  • increased distance = decreased strength
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22
Q

How does frequency affect attenuation?

A
  • directly affects
  • increased frequency = increased attenuation
  • increased frequency = decreased strength
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23
Q

What 3 processes contribute to attenuation?

A

Reflection, scattering, absorption

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24
Q

What does reflection do to part of the wave that keeps traveling?

A

Weakens it

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25
Q

What are the two types of reflection in soft tissue?

A

Specular, diffuse

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26
Q

What is specular reflection?

A
  • smooth boundary
  • reflected sound travels in one direction
  • travels in an organized manner
  • if wave is off-axis reflection doesn’t return to sound source
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27
Q

What is an example of specular reflection?

A

Mirror

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28
Q

What is diffuse reflection?

A
  • most boundaries not smooth
  • reflected sound travels in more than one direction
  • interfaces at variable angles w sound source will still produce reflections that will travel back to sound source
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29
Q

“Backscattered” reflections have _______ strength than specular reflections

A

Weaker

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30
Q

What is scattering?

A
  • random redirection of sound in diff directions
  • sound scatters when tissue interface is small
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31
Q

Higher frequency sound scatters ____ than lower frequency.

A

More

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32
Q

How is scattering related to frequency?

A

Directly

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33
Q

What is Rayleigh scattering?

A
  • organized form of scattering
  • occurs when structure dimensions are smaller than beam’s wavelength
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34
Q

What kind of structures could cause Rayleigh scattering?

A

RBCs, tissue cells

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35
Q

How does Rayleigh scattering change with increased frequency?

A

Drastically increases, it is proportional to frequency^4

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36
Q

When frequency doubles Rayleigh scattering is how much greater?

A

16 times

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37
Q

What is absorption?

A

It occurs when sound energy is converted into heat and radiates away

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38
Q

How is absorption related to frequency?

A

Directly, increased freq = increased absorp

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39
Q

What is attenuation coefficient?

A

Process where sound energy is extracted from a wave by absorption, scattering and reflection

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40
Q

How is attenuation coefficient measured?

A

Number of decibels of attenuation that occurs when sound travels one cm
dB/cm

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41
Q

What does total attenuation depend on?

A
  • Frequency of sound wave
  • distance wave traveled
  • tissue wave traveled through
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42
Q

How is total attenuation calculated?

A

Attenuation coefficient (dB) x distance (cm)

43
Q

How are attenuation coefficient and frequency related in soft tissue?

44
Q

AC is equal to

A

1/2 frequency, frequency/2

45
Q

Do higher or lower frequency waves lose more energy per cm?

46
Q

What is half-value layer thickness?

A
  • distance sound travels in a tissue that reduces the intensity of sound to 1/2 it’s original value
  • can also be described as the depth of tissue that results in 3 dB of attenuation to the intensity
47
Q

How is half-value layer thickness measured? Range?

A

Any length, cm
0.25-1.0 cm

48
Q

What does half-value layer thickness depend on?

A

Medium and frequency

49
Q

Thin half value is characterized by

A

High frequency, media with high attenuation rate (muscle, fibrous, bone)

50
Q

Thick half value is characterized by

A

Low freq wave, media with low attenuation rate (fluid, fat)

51
Q

What is impedance?

A

Acoustic resistance to sound traveling in a medium

52
Q

How is impedance calculated?

A

Density of a medium x speed that sound travels in the medium
Impedance (rayls) = density (kg/m^3) x propagation speed (m/s)

53
Q

What letter represents impedance?

54
Q

What is impedance determined by?

A

Medium only

55
Q

How does impedance affect reflections?

A

Reflection depends on the difference in impedance of the two media at the boundary

56
Q

What is incidence?

A

A pulsed sound wave strikes many tissue interfaces as it propagates through the body
The angle the wave hits the boundary determines the behavior of rest of pulse & reflection angles

57
Q

What is normal incidence?

A

Angulation of sound wave hitting boundary is 90 degrees

58
Q

What is oblique incidence?

A

Angulation of sound wave hitting boundary is anything other than 90 degrees

59
Q

What is incident intensity?

A

Sound wave’s intensity immediately before reaching a boundary

60
Q

What is reflected intensity?

A

Intensity of the portion of the incident sound beam that returns to the sound source after hitting a boundary

61
Q

What is transmitted intensity?

A

Intensity of the portion of the incident sound beam that continues traveling forward after hitting a boundary

62
Q

What is intensity reflection coefficient (IRC)?

A
  • percentage of intensity that bounces back when a sound beam hits a boundary between 2 media
63
Q

How much of a sound wave’s intensity is reflected at a boundary between 2 soft tissues?

A

Less than 1%

64
Q

A _______ % of a sound wave’s intensity is reflected between larger impedance differences

65
Q

What is intensity transmission coefficient (ITC)?

A
  • percentage of intensity that continues traveling forward when a sound beam hits a boundary between 2 media
66
Q

How much of a sound wave’s intensity is transmitted at a boundary between 2 soft tissues?

A

99% or more

67
Q

A ______ % of a sound wave’s intensity is transmitted between larger impedance differences

68
Q

When a pulsed sound wave hits a boundary at 90 degrees, reflection only occurs if

A

Media on either side of the boundary have different impedances

69
Q

The percentage of the incident beam that is reflected is related to

A

The difference in tissue impedances

70
Q

If a sound wave hits a boundary at 90 degrees and the two tissue have the same impedances, how much of the sound wave is reflected?

71
Q

If a sound wave hits a boundary at 90 degrees and the 2 tissues have different but close impedances, how much reflection will occur?

A

A small reflection

72
Q

If a sound wave hits a boundary at 90 degrees and the tissues have significantly different impedances, how much reflection will occur?

A

Large reflection

73
Q

With normal incidence, all sound is transmitted when

A

The tissues have the same impedances

74
Q

When a sound beam hits a boundary at an oblique angle, what happens with reflection?

A

It may or may not occur depending on the degree of angulation at the boundary

75
Q

The reflection angle is the same as

A

Incident angle

76
Q

When a sound wave hits a boundary at an oblique angle, what happens with transmission?

A

It may or may not occur depending on the degree of angulation at the boundary

77
Q

If transmission occurs with oblique incidence, how will the sound beam travel?

A

Straight or bend/change direction

78
Q

Bending of a wave is

A

Refraction

79
Q

What is conservation of energy?

A

Sum of reflected sound and transmitted sound = 100%

80
Q

Incident intensity (w/cm^3) =

A

Reflected intensity + transmitted intensity

81
Q

The angle of incidence equals

A

The angle of reflection

82
Q

The direction of reflected sound is equal and opposite to

A

The direction of incident beam

83
Q

What is refraction?

A

Change in direction of wave propagation when traveling from one medium to another

84
Q

Refraction only occurs with

A
  • oblique incidence
  • different propagation speeds of 2 media
85
Q

If transmission occurs and there is oblique incidence and different propagation speeds of the 2 media, how will the wave travel?

A

It will bend, never travel straight

86
Q

There is a _____ degree of bending in similar propagation speeds

87
Q

What does Snell’s law do?

A

Quantifies the physics of retraction

88
Q

Snell’s law equation

A

Sin(transmission angle)/sin(incident angle) = speed (med 2)/speed (med 1)

89
Q

What is sine?

A

A unitless number with a value of 0-1

90
Q

What is medium 1 in Snell’s law?

A

The medium in which sound is currently traveling

91
Q

What is medium 2 in Snell’s law?

A

Medium in which sound will be entering

92
Q

Decibels require _____ intensities

93
Q

A wave’s intensity is 2 mW/cm^2. There is a change of 9 dB. What is the final intensity?

A

16 mW/cm^2

94
Q

Reflection is likely to occur when the dimension of the boundary is _____

95
Q

How does sound attenuate in muscle?

A

Sound attenuates twice as much when traveling across the fibers compared to when traveling along the length of the fibers

96
Q

The half-value layer is _____ for lung and bone.

97
Q

Typical values for impedance range from

A

1.25-1.75 Mrayls

98
Q

T or F. In a given medium, attenuation is unrelated to the speed of sound.

99
Q

What is normal incidence?

A

The sound beam strikes the boundary at exactly 90 degrees

100
Q

Normal incidence is also known as

A
  • perpendicular
  • orthogonal
  • right angle/90 deg
101
Q

When will the transmission angle equal the incident angle?

A

When the speeds of the two media are identical both angles with be equal and the beam will travel straight ahead

102
Q

When will the transmission angle be greater than the incident angle?

A

When the speed of medium 2 is greater than the speed of medium 1

103
Q

When will the transmission angle be less than the incident angle?

A

When the speed of medium 2 is less than medium 1

SPI (9 decks)

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