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Ultrasound Physics > Ch 5, 6, 7 > Flashcards

Ch 5, 6, 7 Flashcards

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1
Q

How long does it take for sound to make a round trip to and from the skin’s surface to a reflector depth of 1 cm in soft tissue?

A

13 us

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2
Q

In soft tissue, sound travels to a reflector and back to the transducer in 39 us. How deep is the reflector?

A

39/13 = 3cm

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3
Q

In soft tissue, sound travels to a reflector and back to the Tx in 39us. What is the total distance that the pulse traveled?

A

39/13= 3cm (x2) = 6cm

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4
Q

One reflector is 5 times deeper than another. The time of flight of sound to the deeper structure is _____ the time of flight of the shallower reflector.

A

5 times greater than

Time of flight is directly related to depth of reflector.

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5
Q

True or False?

We need one intensity to calculate decibels?

A

False- decibels measure relative changes, comparison/ratio

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6
Q

-10dB means that the intensity is reduced to ____ of its original value.

A

One-tenth

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7
Q

What is the log is 10,000?

A

4

10x10x10x10

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8
Q

Every 3 dB means that the intensity will ____.

A

Double

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9
Q

A drop in intensity to one-quarter of its original value is ___dB.

A

-6

If -3dB is half, then -6 dB is one quarter

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10
Q

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

A

Bc it’s +9dB -every 3 decibels doubles so it would be

2(2)=4(2)=8(2)= 16

break it down

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11
Q

What combination of the following is related to greater attenuation?

Long or short distance

AND

Low or high frequency

A

Long distance

High frequency

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12
Q

What combination of the following results in the wave with the highest intensity?

Long or short distance

AND

Low or high frequency

A

Short Distance

Low frequency

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13
Q

Which of the following results in the least attenuation?

A) 4MHz sound, path length 2 cm
B) 4 MHz sound, path length 8 cm
C) 6 MHz sound, path length 8 cm
D) 6 MHz sound, path length 4 cm

A

4 MHz sound, path length 2 cm

High frequency, short distance

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14
Q

Which of the components of attenuation is the dominant contributor?

A

Absorption

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15
Q

Rayleigh scattering is proportional to _____.

A

Frequency^4

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16
Q

Attenuation is measured in ___.

A

Decibels

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17
Q

____ is an extremely low attenuater.

A

Water

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18
Q

____ has the highest attenuation.

A

Air

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19
Q

Bone and lungs have a _____ attenuation.

A

High

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20
Q

What is the relationship btw propagation speed and attenuation coefficient in soft tissue?

A

They are unrelated

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21
Q

In soft tissue, attenuation coefficient is directly related to ____.

A

Frequency

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22
Q

As path length increases, the attenuation coefficient of ultrasound in soft tissue _____.

A

Remains the same

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23
Q

A sound wave, with an intensity of 50W/cm^2, strikes a boundary and is totally reflected.

What is the IRC?

A

100%

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24
Q

A sound wave, with an intensity of 50W/cm^2, strikes a boundary and is totally reflected.

What is the reflected intensity?

A

50W/cm^2

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25
Q

The ITC of sound is 99.9%. What percent of sound is reflected back to the transducer?

A

0.1%

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26
Q

What is this formula for?

(Z2-Z1 / Z2+Z1) x100

A

IRC%

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27
Q

ITC% =

A

(Transmitted intensity/ incident intensity) x 100

Or

ITC%= 1-IRC

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28
Q

What is Snell’s Law?

A

Quantifies the physics of refraction

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

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29
Q

The angle btw an ultrasound pulse and the boundary btw two media is 56 degrees. This is called _____.

A

Oblique incidence

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30
Q

With normal incidence, what factors affect refraction?

A

None

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31
Q

True or false?

Right angle incidence reflections are always generated at a boundary if the propagation speeds of the media are different.

A

False

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32
Q

What is most likely to create Rayleigh scattering?

A

Red blood cells

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33
Q

Snell’s law describes physics of ____.

A

Refraction

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34
Q

The most likely amount of reflection at a boundary btw soft tissue is ____.

A

1%

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35
Q

Sound is traveling from medium 1 to medium 2. Propagation speeds of M1 and M2 1600 m/s and 1500 m/s respectively. There is normal incidence.

A) incident angle > reflection angle
B) incident angle = reflection angle
C) incident angle < reflection angle

A

Incident angle = reflection angle

36
Q

Intensities may be reported in various ways with respect to ___

A

Time and space

37
Q

____ measurements are important in the study of ____

A

Intensity

Bioeffects

38
Q

What is the measurement for all intensities?

A

W/cm2

39
Q

____ is the most relevant intensity with respect to tissue heating

A

SPTA

Spatial peak temporal average

40
Q

Bc peak measurements are larger than avg measurements, ____ intensity has the highest value while ____ has the lowest value.

A

SPTP (spatial peak temporal peak)

SATA (spatial avg temporal avg)

41
Q

____ is always higher than Spatial avg intensity.

A

Spatial peak intensity

42
Q

A number called _____ describes the spread of a beam in space.

A

Beam uniformity coefficient
- also called SP/SA factor

SP/SA factor is unitless with a value of 1 or greater

43
Q

____ describes the relationship of the beam intensities with time. A unitless number with a value btw 0 & 1

A

Duty factor

44
Q

For a ____ ultrasound, the beam is always “on” and the pulse avg and temporal avg intensities are the same.

Thus, ___ = ____ and ___=____

A

Continuous wave

SPTA=SPPA

SATA=SAPA

45
Q

When pulsed and continuous wave sound beams have the same ____ intensities, the continuous wave beam has the higher SPTA intensity.

A

SPTP

46
Q

When pulsed and continuous wave sound beams have the same SATP intensities, the continuous wave beam has the higher _____ intensity.

A

SATA

47
Q

Itp is the maximum intensity in ____

A

Time

48
Q

Im intensity is averaged over the most intense ___

A

Half-cycle

49
Q

Ipa is averaged only during the pulse duration ____ time only.

A

“On”

50
Q

Ita is averaged during the ___

A

PRP

both “on” and “off” times

51
Q

Rank intensity from largest to smallest

A 
SPTP
Im 
SPPA
SPTA
SATA
52
Q

Isp is the maximum in ____

A

Space

53
Q

Isa is averaged over the _____ of the beam

A

Cross sectional area

54
Q

Attenuation is measured in ____ and reported as a ____ change.

A

Decibels

Relative

55
Q

10 dB of attenuation means

A

A decrease in 10dB

-10dB

56
Q

___ is likely to occur when the dimension of a boundary is large

A

Reflection

57
Q

2 types of reflection

A

Specular

Diffuse (backscatter)

58
Q

Sound scatters when tissue _____

A

Interface is small

59
Q

Scattering is directly related to ____

A

Frequency

60
Q

Lung tissue ____ bc aveoli are filled with air.

A

Scatters

61
Q

One example of Rayleigh scattering is when there is interaction of ultrasound and ____

A

RBC

62
Q

____ is the largest component of attenuation

A

Absorption- when ultrasound energy is converted to another energy (heat)

63
Q

Due to ____, high frequency waves attenuate more than lower frequency waves.

A

Absorption

64
Q

A tissue’s impedance is ____ not ____.

A

Calculated not measured for

65
Q

Sound not reflected must be ____.

A

Transmitted

66
Q

With normal incidence, what factors affect refraction?

A

None

67
Q

Incidence angle ALWAYS equals ____

A

Reflection angle

68
Q

2 physical principles ALWAYS apply to reflection with oblique incidence:

A

Conservation of energy

Reflection angle = incident angle

69
Q

Refraction ONLY occurs with ___ and ____

A

Oblique incidence and different propagation speeds

70
Q

Whichever medium has the higher speed has the ____ angle.

A

Greatest

71
Q

Time of flight is ____ for shallow and ___ for deep reflectors.

A

Shorter

Longer

72
Q

Time of flight (go return time/round trip time) is directly related to

A

Depth of reflector

73
Q

Time of flight is calculated using

A

Speed of sound in soft tissue (1.54mm/us) and go return time

74
Q

A pulse’s time of flight will be twice as long for a reflector that is ____ the depth of another.

A

Twice

75
Q

13 microsecond always applies when

A

Sound travels through soft tissue

76
Q

Total distance is always ___ the depth.

A

Twice

77
Q

____ is the go return time of a sound pulse btw the transducer and the bottom of the image.

A

PRP

78
Q

PRP =

A

imaging depth (cm) x 13 us/cm

79
Q

If the imaging depth is 10 cm, what is the PRP?

A

Depth x 13 us/cm

10x13 = 130 us

80
Q

If there is a depth of 5 cm, what is the PRP?

A

5cm x 13us/cm = 65us

81
Q

In one second, sound can travel into tissue AND return from a depth of ____.

A

77,000 cm (nearly half a mile)

82
Q

In 1 one second, sound can travel to and from 77 cm a total of ___ times

A

1,000

83
Q

In 1 one second, sound can travel to and from 7.7 cm a total of ___ times

A

10,000

84
Q

Shallow depth of view = ___ PRF

A

High (more cycles per second)

85
Q

Deep depth of view =

A

Low PRF (less cycles per second)

86
Q

PRF (Hz) =

A

77,000 cm/s / imaging depth(cm)

87
Q

If the depth is 7.7 cm, what is the PRF?

A

77,000 / 7.7 = 10,000 Hz

*remember PRF is measured in Hz

Ultrasound Physics (6 decks)

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