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Ultrasound Physics > Quiz #2 > Flashcards

Quiz #2 Flashcards

1
Q

What is attenuation?

A

It is a loss of energy.

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2
Q

What happens when sound waves travel through a tissue?

A

It weakens.

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3
Q

What does a wave lose the deeper it propagates?

A

A wave loses amplitude, power and intensity (energy.)

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4
Q

What does attenuation depend on?

A

It depends on frequency, distance and tissue.

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5
Q

What is the relationship between frequency, distance and attenuation?

A

They are directly related.

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6
Q

What is attenuation always measured in?

A

dB

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7
Q

What are the 3 sources of attenuation?

A
  • Reflection
  • Scattering
  • Absorption
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8
Q

What is the most important source of attenuation?

A

Absorption, which is in the form of heat.

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9
Q

Will you have more or less attenuation with longer distances?

A

More attenuation.

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10
Q

Will you have more or less attenuation with shorter distances?

A

Less attenuation.

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11
Q

Will you have more or less attenuation with higher frequencies?

A

More attenuation.

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12
Q

Will you have more or less attenuation with lower frequencies?

A

Less attenuation.

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13
Q

Echo amplitude lost by:

A

dB/cm

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14
Q

For most soft tissues, the attenuation coefficient is?

A

.5-1 dB/cm for a 1 MHz probe.

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15
Q

What is the attenuation coefficient for water?

A

.0002

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16
Q

What is the attenuation coefficient for blood?

A

0.18

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17
Q

What is the attenuation coefficient for the liver?

A

0.5

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18
Q

What is the attenuation coefficient for the muscle?

A

1.2

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19
Q

What is attenuation highly dependent on?

A

It is highly dependent on probe frequency.

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20
Q

What happens to attenuation coefficient for a tissue at 1MHz when using a 2MHz probe?

A

It doubles.

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21
Q

What happens to attenuation coefficient for a tissue at 1 MHZ when using a 4MHz probe?

A

It quadruples.

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22
Q

How do you calculate attenuation?

A

dB=(Tissue attenuation coefficient)x(distance)x(frequency of probe)

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23
Q

What is the term used to describe the brighter echoes deep to a liquid mass compared to adjacent tissues?

A

Enhancement.

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24
Q

What is penetration?

A

depth.

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25
Q

What improves penetration?

A

Penetration improves with a lower frequency probe (less attenuation).

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26
Q

What is resolution?

A

Clarity.

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27
Q

What improves the resolution?

A

Resolution improves with a high frequency probe (decreased wavelength).

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28
Q

What is another way to describe attenuation?

A

Half value attenuation.

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29
Q

What does half value thickness equal?

A

It equals the distance sound must travel to reduce the intensity to 1/2 its original value.

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30
Q

Describe THIN HALF VALUE

A

It can’t go very deep without losing half its energy.

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31
Q

What are the characterisitics of THIN HALF VALUE?

A
  • High attenuation
  • High frequency
  • Tissue with high impedance
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32
Q

Describe THICK HALF VALUE

A

It can go very deep before losing half its energy.

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33
Q

What are the characteristics of THICK HALF VALUE?

A
  • Lower attenuation
  • Low frequency
  • Tissue with low impedance.
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34
Q

What is the most important cause of attenuation?

A

Absorption.

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35
Q 
Which of the following transducers would be the best choice for scanning the greater saphenous vein?
A. 2 MHz
B. 5 MHz
C. 7 MHz
D. 10 MHz
A

D. 10 MHz

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36
Q 
Which of the following transducers would be the best choice for scanning the renal arteries?
A. 2 MHz
B. 5 MHz
C. 7 MHz
D. 10 MHz
A

A. 2 MHz

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37
Q

What is the term used to describe the brighter echoes deep to a liquid mass compared to adjacent tissues?

A

Enhancement

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38
Q

Why are the echoes deep to a fluid filled structure brighter?

A

The fluid has less attenuation than adjacent tissues.

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39
Q

How does the sound beams interact with the tissues?

A
  • Some energy is reflected (as echoes)
  • Some energy is transmitted (travels deeper)
  • Some energy is changed (absorbed as heat)
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40
Q

What are B-mode images created from?

A

B-mode images are created from echoes while some energy is transmitted deeper.

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41
Q

What does it mean when energy remains constant?

A

It is not lost, only changed (conservation of energy)

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42
Q

How is ultrasound energy changed?

A

It is reflected, transmitted or changed into heat.

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43
Q

What are the 3 main reflectors?

A
  1. Specular; which can be prependicular or non perpendicular
  2. Diffuse or non-specular
  3. Scatterer; Rayleigh scatter.
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44
Q

What are specular reflectors?

A

It is the bouncing of light from the surface of a mirror, or something similarly shiny and smooth, where parallel rays of light all bounce off at the same angle.

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45
Q

What are the two types of specular reflectors?

A
  • Perpendicular

- Non-perpendicular

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46
Q

What is “incidence”?

A

It refers to the angle the soundbeam came in to hit the flat surface specular reflector.

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47
Q

Incidence and transmitted beams are at the same angle as long as what?

A

Tissue 1 and tissue 2 have similar speed of sound.

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48
Q

On an ultrasound b-mode image, how can you tell what is a perpendicular or non-perpendicular image?

A
  • Perpendicular image: Detail is visible (double lines in the vessel wall)
  • Non-perpendicular: double line is not visible
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49
Q

When scanning a specular reflector, a 90° angle of incidence yields what quality of picture?

A

It yields a clearer image.

50
Q

How can a sonographer obtain a perpendicular image with their probe?

A

The heel and toe method.

51
Q

At a specular reflector with perpendicular incidence, how much energy is reflected?

A

It depends on the difference of the tissues at the interface.

52
Q

What does the amplitude or strength of the reflected wave (echo) depend on?

A

It depends on the difference in acoustic impedance of the tissues at interface.

53
Q

The bigger the difference in acoustic impedance….

A

The greater the percentage of energy is reflected.

54
Q

What is an interface?

A
  • Boundary
  • Border
  • Crossing point
  • Edge
55
Q

What are some examples of interfaces encountered by the ultrasound beam?

A
  • air to muscle
  • muscle to blood
  • blood to fat
  • muscle to bone
56
Q

What is the symbol for acoustic impedance?

57
Q

What is acoustic impedance?

A

It is a characteristic of the tissue that affects the amplitude of an echo.

58
Q

What is the equation for acoustic impedance?

A

Z= ρ x C

ρ= density
c=speed of particle vibrations.

59
Q

What is the unit for acoustic impedance?

60
Q

What is the acoustic impedance for lungs?

61
Q

What is the acoustic impedance for fat?

62
Q

What is the acoustic impedance for kidney?

63
Q

What is the acoustic impedance for blood AND liver?

64
Q

What is the acoustic impedance for muscle?

65
Q

What is the acoustic impedance for skull bone?

66
Q

What is the reflection coefficient?

A

It is the % of strength of wave that is reflected at an interface.

67
Q

What does the reflection coefficient depend on?

A

It depends on Z and C (acoustic impedance and speed of particle vibration)

68
Q

what are the two types of reflection coefficient?

A
  • amplitude reflection coefficient

- Intensity reflection coefficient

69
Q

What is amplitude?

A

Strength and acoustic pressure.

70
Q

What is AMPLITUDE REFLECTION COEFFICIENT? (aka ARC)

A

it is the percentage of the strength of the wave that is reflected at an interface.

ARC= P(reflected)/P(Incident)

P=amplitude or acoustic pressure.

71
Q

What is the equation for ARC?

A

ARC%=Pr/Pi=(Z2-Z1)/(Z2+Z1)

*the answer should always be a percentage.

72
Q

When does reflection occur?

A

It occurs when adjacent tissues have different acoustic impedances.

73
Q

When do interfaces reflect more?

A

When there are large differences in their impedance.

74
Q

For soft tissue interfaces, the reflection coefficient is?

A

Less than .1

75
Q

air and bone offer large impedance mismatches to issue, which causes?

A

Very little ultrasound to transmit past these medias.

76
Q

Why do we use gel between the transducer and the skin?

A

It has similar impedance to soft tissue.

77
Q

What is a diffuse reflection?

A

Light bounces off all kinds of random angles due to the imperfections in the surface.

78
Q

Most interfaces in the body are regular or irregular?

A

irregular.

79
Q

Which reflection produces weaker echoes?

A

Diffuse reflection.

80
Q

What is another name for diffuse reflection?

A

Backscatter.

81
Q

What is the most important source of echoes in the body?

A

Acoustic scattering.

82
Q

What are the size of scatters?

A

It is the size of the wavelength or smaller.

83
Q

Where do scatters reflect beams?

A

In all directions, in a disorganized and chaotic fashion..

84
Q

What are rayleigh scatters?

85
Q

What is the rayleigh scatters reflector size in comparison to the wavelength?

A

It is MUCH less than the wavelength.

86
Q

Since rayleigh scatters have very weak echoes, what happens to the screen?

A

The screen is black.

87
Q

When does rayleigh scattering increase?

A

Rayleigh scattering increases greatly as frequency increases.

88
Q

What is hyperechoic?

A

Areas of increased level of scattering compared to surrounding tissue. (brighter)

89
Q

What is hypoechoic?

A

Areas of decreased level of scattering compared to surrounding tissue. (darker)

90
Q

What does echogenic mean?

A

Echoes present.

91
Q

What does echolucent mean?

A

No echoes.

92
Q

What does homogenous mean?

A

Similar strength echoes.

93
Q

What does heterogenous mean?

A

Bright and dark.

94
Q

What is refraction?

A

Reffraction is when an ultrasound beam meets an interface of tissues with different propagation speeds at a non-perpendicular angle, refraction may occur.

95
Q

Refraction can cause what?

A

It can cause an artifact whereby s dtructure may appear on the image in a different location than it is.

96
Q

What does Snell’s law predict?

A

It predicts the amount of refraction.

97
Q

What must you have for an artifact to occur?

A

A non-perpendicular angle.

98
Q

Slow to fast C yields what?

A

A higher angle of transmission.

99
Q

Fast to slow C yields what?

A

A lower angle of transmission.

100
Q

For refraction to occur there must be these two criteria:

A
  • Sound beam must approach a specular reflector at a non-perpendicular angle.
  • C must be different on each side of the specular reflector.
101
Q

What is the equation for Snell’s law?

A

SINt=(C2xSINi)/C1

102
Q

What is the speed of sound for fat?

103
Q

What is the speed of sound for the liver?

104
Q

What is the speed of sound for soft tissue?

105
Q

What is the speed of sound for blood?

106
Q

What is the speed of sound for muscle?

107
Q

What is the speed of sound for bone?

108
Q

There is a critical incident angle whereby no energy travels past the interface, and all the energy is reflected. What is it called?

A

Total internal reflection.

109
Q

The acoustic impedance is a characteristic of the _______

A. Tissue
B. Soundwave
C. Ultrasound Wave
D. Pressure

110
Q

The acoustic impedance is a calculation based on which two measurements?
A. Frequency and amplitude
B. Propagation speed and density
C. Attenuation coefficient and wavelength
D. Pressure and frequency

A

B. Propagation speed and density

111
Q 
Acoustic impedance affects which of the following?
A. Rarefraction
B. Reflection
C. Frequency
D. Period
A

B. Reflection

112
Q 
Acoustic impedance is measured in which of he following units?
A. Hz
B. Cm/sec
C. mmHg
D. Rayls
113
Q

What abbreviation is used for acoustic impedance?

114
Q 
The amplitude reflection coefficient (ARC) of a boundary indicates the percentage amount of the sound that will be?
A. Reflected
B. Transmitted
C. Refracted
D. Attenuated
A

A. Reflected

115
Q

If a sound wave hits a boundary with two very different acoustic impedance most of the soundwave energy will be_________

A

Reflected with little transmission, if any.

116
Q

If a soundwave hits a boundary with two similar acoustic impedance’s most of the soundwave energy will________

A

Be transmitted deeper into the tissue .

117
Q

If an ultrasound beam leaves the transducer and hits air in its path along the way, what will happen to the image and why?

A

When the ultrasound beam hits air, most of the energy will be reflected due to the large mismatch in acoustic impedances of the air/tissue boundary. Since nearly 100% of the energy is reflected, basically no energy is transmitted to be reflected from the tissue below the air. Instead, there is a dark area which appears below the air which is called an acoustic “shadow”.

118
Q

Which of the following conditions must be present for refraction to occur?
A. Perpendicular angle to a specular reflector.
B. Non-perpendicular angle to a tissue interface with similar impedances
C. Perpendicular angle to a diffuse reflector.
D. Angle less than 90° crossing tissues with different propagation speeds.

A

D. Angle less than 90° crosing tissues with differing propagation speeds.

119
Q

Which type of reflector may result in refraction of the ultrasound beam?

A

A non-perpendicular beam on a specular reflector.

120
Q 
Refraction is important because it may result in which of the following?
A. An accurate image
B. An artifact
C. Increased frequencies
D. Visualizations of blood flow
A

B. An artifact

121
Q

Snell’s law predicts _____ when refraction occurs.

A

The angle difference of a transmitted beam and an incident beam.

Ultrasound Physics (12 decks)

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