Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Ultrasound Physics > Ch 6: Sound and Media > Flashcards

Ch 6: Sound and Media Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

What is it called when sound waves weaken as they travel in the body?

A

attenuation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is it called when the u/s system strengthens the electrical signal?

A

amplification

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Define ‘decibel notation’.

A

A standard measurement tool to report changes in the degree of attenuation or the extent of amplification.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Logarithms are…

A

the mathematical construct on which decibels are based; a novel method of rating numbers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the log of 1,000?

A
  1. (10 x 10 x10)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the log of 10,000?

A
  1. (10 x 10 x 10 x 10)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is an everyday example of a logarithmic scale?

A

The Richter scale, which measures the strength of earthquakes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Decibel notation does not measure absolute numbers; rather decibels report…

A

relative changes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the two intensities that decibels require?

A

a starting level and an actual (ending) level

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

In decibels, the measured level is divided by the starting level, which means that decibels are a…

A

ratio.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a relative measurement, a comparison, a ratio, and logarithmic?

A

decibel notation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Positive decibels report signals that are…

A

increasing in strength.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Negative decibels report signals that are…

A

decreasing in strenth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Attenuation is determined by which two factors?

A

path length and frequency of sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Distance and attenuation are ___ related.

A

directly. The farther sound travels, the more it attenuates.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Frequency and attenuation are ___ related.

A

directly. The higher the frequency, the more it attenuates.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What three processes contribute to attenuation?

A

reflection
scattering
absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is it called when a portion of the wave’s energy is redirected after striking a boundary?

A

reflection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What two forms of reflection are created in soft tissue?

A

specular and diffuse/backscatter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Define ‘specular reflection’.

A

Sound that is reflected in only one direction in an organized manner, as when a boundary is smooth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Define ‘diffuse/backscatter reflection’.

A

Sound that is reflected in more than one direction in a disorganized manner, as when a boundary is irregular.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

An advantage of diffuse reflections is that…

A

interfaces at suboptimal angles can still produce reflections that will return to the transducer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

A disadvantage of diffuse reflections is that…

A

backscattered signals have a lower strength than specular reflections.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is it called when u/s signals are redirected in many directions?

A

scattering

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Scattering and frequency are ___ related.

A

directly. The higher the frequency, the more the signal will scatter.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Sound scatters when the tissure interface is ___ the wavelength of the sound beam.

A

smaller than

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

This special form of scattering occurs when the structure’s dimensions are much smaller than the beam’s wavelength.

A

Rayleigh scattering

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Rayleigh scattering redirects the sound wave equally in ___ directions.

A

all

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Mathematically, scattering is related frequency raised to the ___ power.

A

fourth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

When frequency doubles, Rayleigh scattering is ___ times greater.

A
  1. (2 x 2 x 2 x 2)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is the significance of attenuation in diagnostic sonography?

A

More attenuation means less accurate images.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What occurs when u/s energy is converted into another energy form?

A

absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Absorption and frequency are ___ related.

A

directly. The higher the frequency, the more it absorbs.

34
Q

This is the number of decibels at attenuation that occurs when sound travels one centimeter.

A

attenuation coefficient

35
Q

Attenuation coefficient is reported in units of…

A

dB/cm.

36
Q

The value of the attenuation coefficient remains ___ regardless of how far the sound travels.

A

constant

37
Q

In soft tissue, the attenuation coefficient (dB/cm) and the frequency (MHz) are ___ related.

A

directly. As one increases, so does the other.

38
Q

The attenuation coefficient is ___ the frequency.

A

one half. dB/cm = MHz/2

39
Q

T/F? In air, sound waves attenuate due to absorption.

A

true

40
Q

T/F? In the lungs, sound waves attenuate due to absorption and scattering.

A

true

41
Q

T/F? In bone, sound waves attenuate due to scattering.

A

false; *due to absorption

42
Q

T/F? In biologic fluids (blood, urine, amniotic fluid), sound waves attenuate far more than in soft tissue.

A

false; *far less

43
Q

T/F? In water, there is no noticable attenuation with frequencies less than 10 MHz.

A

true

44
Q

T/F? In muscle, the attenuation properties vary.

A

true

45
Q

What is the distance sound travels that reduces the intensity of sound to one half its orginal value?

A

half-value layer thickness

46
Q

Half-value layer thickness is reported in units of…

A

cm.

47
Q

In clinical imaging, typical ranges of half-value layer thickness are…

A

.25 to 1 cm.

48
Q

Half-value layer thickness is also known as…

A

penetration depth, depth of penetration, half-boundary layer.

49
Q

Half-value layer thickness depends on what two factors?

A

the medium and the frequency of sound

50
Q

The half-value layer is ___ for tissues that attenuate sound a great deal, such as ___.

A

thin, lung or bone

51
Q

The half-value layer is ___ for tissues that attenuate sound just a little, such as ___.

A

thicker, fluids

52
Q

Higher frequencies result in a ___ half-value layer.

A

thin

53
Q

Lower frequencies result in a ___ thick half-value layer.

A

thick

54
Q

What is the acoustic resistance to sound traveling in a medium?

A

impedence

55
Q

Impedence is calculated by multiplying the ___ of a medium by the ___ at which sound travels in the medium.

A

density, speed.

Impedence (rayls) = density (kg/m^3) x speed (m/s)

56
Q

Impedence is reported in units of…

A

rayls (Z)

57
Q

In biologic media, typical values for impedence range from…

A

1.25 to 1.75 Mrayls

58
Q

Impedence is determined by the…

A

medium.

59
Q

___ depends upon the difference in impedences of the two media at a boundary.

A

Reflections

60
Q

What are the three types of angles?

A

acute - less than 90
right - exactly 90
obtuse - greater than 90

61
Q

Angles with a measure other than 90 are also called…

A

oblique angles, whether they’re acute or obtuse.

62
Q

Normal incidence means that the beam strikes the boundary at…

A

exactly 90 degrees.

63
Q

Normal incidence is also called…

A

perpendicular
orthogonal
right angle
90 degrees

64
Q

___ is the sound wave’s intensity immediately before it strikes a boundary.

A

Incident intensity

65
Q

___ is the intensity of the portion of the beam that returns back after striking the boundary.

A

Reflected intensity

66
Q

___ is the intensity of the portion of the beam that continues forward after striking the boundary.

A

Transmitted intensity

67
Q

Since there is a conservation of energy, the incident intensity equals the ___ plus the ___.

A

reflected intensity, transmitted intensity

68
Q

What is the percentage of the intensity that bounces back when a sound beam strikes the boundary called?

A

intensity reflection coefficient (IRC)

69
Q

In clinical imaging, ___ of a sound wave’s intensity is reflected back.

A

very little (1% or less)

70
Q

What is the percentage of intensity that passes forward when a sound beam strikes the boundary called?

A

intensity transmission coefficient (ITC)

71
Q

In clinical imaging, ___ of a sound wave’s intensity transmits forward.

A

most (99% or more)

72
Q

Since there is a conservation of energy, the ITC and the IRC equal ___.

A

100%

73
Q

At normal incidence, how much reflection will occur if the two media identical impedences?

A

none

74
Q

At normal incidence, how much reflection will occur if the two media have slightly different impedences?

A

a little

75
Q

At normal incidence, how much reflection will occur if the two media have substantially different impedences?

A

a large

76
Q

What two physical principles always apply to reflection with oblique incidence?

A

conservation of energy

reflection angle = incidenct angle

77
Q

At oblique incidence, the directionof the reflected echo is ___ and ___ to the direction of the incident beam.

A

equal and opposite

78
Q

Define ‘refraction’.

A

a change in direction of wave propagation when traveling from one medium to another; the bending of the sound beam

79
Q

Refraction only occurs if what two conditions are satisfied?

A
  • oblique incidence

* different propagation speeds of the two media

80
Q

Under what conditions will the transmission angle equal the incident angle?

A

When the speed of the two media are equal.

81
Q

Under what conditions will the transmission angle be greater than the incident angle?

A

When the speed of the second medium is greater than the speed of the first medium.

82
Q

Under what conditions will the transmission angle be less than the incident angle?

A

When the speed of the second medium in less than the speed of the first medium.

Ultrasound Physics (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions