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ultrasound physics > exam 1 review > Flashcards

exam 1 review Flashcards

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1
Q

Attenuation coefficient in blood

A

0.125 dB/cm*MHz

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2
Q

Attenuation coefficient in soft tissue

A

0.5 dB/cm*MHz

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3
Q

Attenuation coefficient in muscle

A

1.0 dB/cm*MHz

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4
Q

Attenuation coefficient in bone

A

20.0 dB/cm*MHz

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5
Q

Speed of sound in soft tissue

A

1540 m/s or 1.54 mm/microsecond

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6
Q

Reflection percentage in soft tissue-soft tissue

A

< 1%

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7
Q

Reflection percentage in soft tissue-bone

A

10-60%

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8
Q

Reflection percentage in soft tissue-air

A

> 99%

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9
Q

Round trip time for sound to travel 1 cm

A

13 microseconds/cm

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10
Q

wavelength equation

A

wavelength= propagation velocity (c)/frequency (f)

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11
Q

distance equation

A

distance= speed * time

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12
Q

density equation

A

density= mass/volume

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13
Q

frequency equation

A

frequency * period= 1 (reciprocal)

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14
Q

amplitude equation

A

crest-baseline or trough-baseline

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15
Q

power equation

A

energy/s

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16
Q

intensity equation

A

power/area

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17
Q

total attenuation equation

A

TA= attenuation coefficient * MHz * image depth (cm)

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18
Q

impedance equation

A

density * velocity

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19
Q

half intensity depth (HID) equation (for soft tissue only)

A

6/frequency

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20
Q

attenuation coefficient equation (for soft tissue only)

A

frequency/2

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21
Q

Waves carry ___?

A

Waves carry energy

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22
Q

What kind of wave is sound?

A

Sound is a mechanical, longitudinal wave

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23
Q

Wave classification

A

Mechanical (needs a medium) vs. electromagnetic (will work in a medium or vacuum)

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24
Q

Transverse wave propagation

A

Transverse waves propagate perpendicular to the wave direction

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25
Q

Longitudinal wave propagation

A

Consist of compressions and rarefactions, propagates in the same direction

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26
Q

Acoustic variables

A

Measures sound (determined entirely by the medium).

  1. pressure
  2. density
  3. temperature
  4. particle motion (distance)
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27
Q

Most common unit for pressure

A

Pascals

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28
Q

In human tissue, if density increases, stiffness will ___?

A

increase

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29
Q

If the intensity/power doubles, what is the decibel value?

A

+ 3dB

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30
Q

If the amplitude doubles, what is the decibel value?

A

+ 6dB

31
Q

If the intensity/power increases 10X, what is the decibel value?

A

+ 10dB

32
Q

If the amplitude increases by 10X, what is the decibel value?

A

+ 20dB

33
Q

If the intensity/power halves, what is the decibel value?

A
  • 3dB
34
Q

If the amplitude halves, what is the decibel value?

A
  • 6dB
35
Q

If the intensity/power decreases by 1/10, what is the decibel value?

A
  • 10dB
36
Q

If the amplitude decreases by 1/10, what is the decibel value?

A
  • 20dB
37
Q

What is attenuation?

A

A decrease in wave intensity

38
Q

What are the 3 things attenuation is caused by?

A
  1. Absorption
  2. Reflection
  3. Refraction
39
Q

What is the most dominant form of attenuation in ultrasound?

A

Absorption

40
Q

What 2 things measure attenuation?

A

Attenuation coefficient and Half value layer/half intensity depth

41
Q

Reflection is caused by ____?

A

Impedance (z)

42
Q

Refraction is caused by ___?

A

Speed of sounds

43
Q

Specular reflection

A
  • smooth, angle dependent, strong echoes
  • not proportional to frequency
  • ex: diaphragm, liver capsule, pericardium
  • think of a mirror*
44
Q

non-specular reflection

A

diffuse, scattering and Rayleigh

45
Q

diffuse reflection

A
  • rough, irregular, not angle dependent, weak echoes
  • not proportional to frequency
  • reflections scatter in random, chaotic directions
46
Q

scattering

A
  • small objects, not angle dependent, weaker echoes
  • proportional to frequency
  • reflections scatter in random, chaotic directions
47
Q

Rayleigh

A
  • very, very small objects (red blood cells), not angle dependent, weakest echoes
  • proportional to frequency(4)
  • reflections scatter equally in all directions
48
Q

The greater the mismatch of impedance, the ____ the reflection

A

greater. There needs to be a mismatch of impedance for reflection to occur.

49
Q

Z1=Z2

A

no reflection, 100% transmitted

50
Q

Z1&raquo_space; Z2

A

100% reflected, 0% transmitted

51
Q

Z2&raquo_space; Z1

A

100% reflected, 0% transmitted

52
Q

Refraction

A

-Bending of a wave at the interface between two media with different speeds of sound

53
Q

What two things need to occur for refraction to happen?

A
  1. A change in propagation speeds

2. an incident angle that is NOT perpendicular to the interface (boundary)

54
Q

Snell’s law measures ___?

A

Refraction

55
Q

What happens if the incident angle reaches the critical angle?

A

The result is a loss of transmission and 100% reflected

56
Q

Fast to Slow bends _____ the normal

A

Fast to Slow bends Towards the normal (FST)

57
Q

Slow to Fast bends ____ the normal

A

Slow to Fast bends Away from the normal (SFA)

58
Q

Amplitude is measured in ___?

A

Volts

59
Q

What determines the speed of sound through a particular medium?

A

Stiffness and density

60
Q

Unit of measurement for attenuation coefficient

A

dB/cm*MHz

61
Q

Unit of measurement for HVL or HID

A

usually cm but can be any length measurement

62
Q

Characteristics of Absorption

A
  • caused by friction
  • directly exponentially proportional to frequency
  • directly proportional to viscosity
  • there is less absorption in body fluids than soft tissue*
63
Q

Cycle, wavelength, period and frequency are all determined entirely by the ____.

A

Transducer

64
Q

Is the speed of sound faster in air or bone?

A

air= 347 m/s
bone= 4080 m/s
Speed of sound is faster in bone

65
Q

Attenuation in air is low, extremely low or extremely high?

A

Attenuation in air is extremely high

66
Q

Attenuation in water is high, extremely low or intermediate?

A

Attenuation in water is extremely low

67
Q

sound wave frequencies (infrasound, audible, and ultrasound)

A

infrasound: < 20Hz
audible sound: 20 Hz-20 kHz
ultrasound: >20kHz
diagnostic ultrasound: 2 MHz-20 MHz

68
Q

If the frequency increases, the wavelength will ____.

A

The wavelength halves

69
Q

What causes a wave?

A

Vibrations cause waves

70
Q

What parameter(s) are determined by both the sound source and the medium?

A

Wavelength

71
Q

What parameter(s) are determined by the sound source only?

A

Period, frequency, amplitude, power and intensity

72
Q

What parameter(s) are determined by the medium only?

A

Speed

73
Q

Unit for impedance

A

Rayls

ultrasound physics (3 decks)

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