Chapter 2 Ultrasound Terms

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1

Absorption

conversion of sound to heat

2

Acoustic

Having to do with sound

3

Acoustic Variable

Pressure, density, and particle vibration: sound wave quantities that vary in space and time.

4

Amplitude

Maximum variation of an acoustic variable or voltage

5

Attenuation

Decrease in amplitude and intensity with distance as a wave travels through a medium

6

Attenuation Coefficient

Attenuation per centimeter of wave travel

7

Backscatter

Sound scattered back in the direction from which it came

8

Bandwidth

Range of frequencies contained in an ultrasound pulse; range of frequencies within which a material, device, or system can operate.

9

Compression

Reduction in differences between small and large amplitude. Region of high density and pressure in a compressional wave

10

Constructive Interference

Combination of positive or negative pressures

11

Continuous Wave

CW

A wave in which cycles repeat indefinitely; not pulsed

12

Contrast Agent

A suspension of bubbles or particles introduced into circulation to enhance the contrast between anatomical structures, thereby improving their imaging

13

Coupling Medium

A gel used to provide a good sound path between echoes of slightly different intensities

14

Cycle

One complete variation of an acoustic variable

15

Decibel

Unit of power or intensity ratio; the number of decibels is 10 times the logarithm (to the 10 base) of the power or intensity ratio

16

Density

Mass divided by volume

17

Destructive Interference

Combination of positive and negative pressures

18

Duty Factor

Fraction of time that pulsed ultrasound is on

19

Echo

Reflection

20

Energy

capability to do work

21

Fractional Bandwidth

Bandwidth divided by operating frequency

22

Frequency

Number of cycles per second

23

Fundamental Frequency

The primary frequency in a collection of frequencies that can include odd and even harmonics and subharmonics

24

Harmonics

Frequencies that and odd multiples of another

sometimes called Fundamental or operating Frequency

25

Hertz

Hz

Unit of frequency, one cycle per second; units of pulse repetition frequency, one pulse per minute

26

Impedance

Density multiplied by the sound propagation speed

27

Incidence Angle

Angle between incident sound direction and a line perpendicular to the boundary of a medium

28

Intensity

Power divided by area

29

Intensity Reflection Coefficient

Reflected intensity divided by incident intensity; the fraction of incident intensity reflected

30

Intensity Transmission Coefficient

Transmitted intensity divided by incident intensity; the fraction of incident intensity transmitted into the second medium

31

Interference

Combination of positive and/or negative pressure

32

Kilohertz

kHz

One thousand hertz

33

Longitudinal Wave

Wave in which the particle motion is parallel to the direction of wave travel

34

Medium

material through which a wave travels

35

Megahertz

MHz

One million hertz

36

Nonlinear propagation

Sound propagation in which the propagation speed depends on pressure causing the wave shape to change and harmonics to be generated

37

Oblique Incidence

Sound direction that is not perpendicular to the media boundaries

38

Penetration

imaging depth

39

Period

time per cycle

40

Perpendicular

Geometrically related to 90 degrees

41

Perpendicular Incidence

Sound direction that is perpendicular to the boundary between media

42

Power

Rate at which work is done; rate ate which energy is transferred

43

Pressure

force divided by an area in a fluid

44

Propagation

progression or travel

45

Propagation Speed

Speed at which a wave moves through a medium

46

Pulse

A brief excursion of a quantity from it's normal value; a few cycles

47

Pulse Duration

Interval of time from beginning to end of a pulse

48

Pulse Repetition Frequency

PRF

Number of pulses per second; sometimes called pulse repetition rate

49

Pulse Repetition Period

Interval of time from the beginning of one pulse to the beginning of the next

50

Pulsed Ultrasound

Ultrasound produced in pulsed form by applying electric pulses or voltage of on or a few cycles to the transducer

51

Range Equation

relationship between round-trip pulse travel time, propagation speed, and distance to a reflector

52

Rarefaction

region of low density and pressure in a compressional wave

53

Rayl

unit of impedence

54

Reflection

portion of a sound returned from a media boundary; echo

55

Reflection Angle

Angle between the reflected sound direction and a line perpendicular to the media boundary

56

Reflector

Media boundary that produces a reflection; reflecting surface

57

Refraction

change of sound direction on passing from one media to another

58

Scatterer

AN object that scatters sound because of its small size or its surface roughness

59

Scattering

Diffusion or redirection of sound in several directions upon encountering a particle suspension or rough surface

60

Sound

traveling wave of acoustic variable

61

Spatial Pulse Length

length of space over which a pulse occurs

62

Speckle

The granular appearance of images and spectral displays that is caused by the interference of echos from the distribution of scatterers in tissue

63

Specular Reflection

Reflection from large (relative to wavelength), flat, smooth boundary

64

Stiffness

Property of a medium; applied pressure divided b the fractional volume change produced by the pressure

65

Strength

Non specific term referring to amplitude or intensity

66

Transmission Angle

Angle between the transmitted sound direction and a line perpendicular to the media

67

Ultrasound

A form of sound

Sound that has a higher frequency than the sound we can hear

Over 20 kHz

68

Wave

is a traveling variation in one or more quantities, such as Pressure

69

Wavelength

length of space over which a cycle occurs

70

Work

Force multiplied by displacement

71

A wave is a traveling variations in quantities called wave _________________.

A) length
B) variables
C) cycles
D) periods

B) variables

72

Sound is a traveling variations in quantities called _________________ variables.

A) wave
B) pressure
C) density
D) acoustic

D) acoustic

73

Ultrasound is a sound with a frequency greater than ____________ Hz.

A) 2
B) 15
C) 20,000
D) 1540

C) 20,000

74

Acoustic variables include __________________, ____________, and particle vibration.

A) stiffness, density
B) hardness, impedance
C) amplitude, intensity
D) pressure, density

D) pressure, density

75

Which of the following frequencies is in the ultrasound range?

A) 12 Hz
B) 15,0000 Hz
C) 15 kHz
D) .004 MHz

D) .004 MHz

76

Which of the following is not an acoustic variable?

A) Pressure
B) Propagation speed
C) Density
D) Particle Motion

B) Propagation speed

77

Frequency is the number of ______________ an acoustic variable goes through in a second.

A) cycles
B) amplitude
C) pulse lengths
D) duty factors

A) cycles

78

The unit of frequency is ________________, which is abbreviated _______________.

A) hertz, Hz
B) megahertz, mHz
C) kilohurts, khts
D) cycles, cps

A) hertz, Hz

79

Period is the _________that it takes for one cycle to occur.

A) length
B) amplitude
C) time
D) height

C) time

80

Period decreases as _____________ increases.

A) wavelength
B) pulse length
C) frequency
D) bandwidth

C) frequency

81

Wavelength is the length of ________________ over which one cycle occurs.

A) time
B) space
C) propagation
D) power

B) space

82

Propagation speed is the speed with which a(n) ___________ moves though a medium.

A) wave
B) particle
C) frequency
D) attenuation

A) wave

83

Wavelength is equal to _______________, ____________ divided by ___________.

A) propagation speed, frequency
B) media density, stiffness
C) pulse length, frequency
D) wave amplitude, period

A) propagation speed, frequency

84

The _______________ and _____________ of a medium determine propagation speed.

A) amplitude, intensity
B) wavelength, period
C) impedance, attenuation
D) density, stiffness

D) density, stiffness

85

Propagation speed increases if ____________ is increased.

A) amplitude
B) frequency
C) density
D) stiffness

D) stiffness

86

The average propagation speed in soft tissue ___________m/s or ______________ mm/μs.

A) 10, 3
B) 1540, 1.54
C) 3, 10
D) 1.54, 1540

B) 1540, 1.54

87

Propagation speed is determined by the ___________.

A) frequency
B) amplitude
C) wavelength
D) medium

D) medium

88

Place the following in order of increasing sound propagation speed:

A) gas, solid liquids
B) solid, liquid, gas
C) gas, liquid, solid
D) liquid, solid, gas

C) gas, liquid, solid

89

The wavelength of 7 MHz ultrasound in soft tissue is ___________________ mm.

A) 1.54
B) .54
C) .22
D) 33.33

C) .22

(λ=1.54/7)

90

Wavelength in soft tissue _________ as frequency increases.

A) is constant
B) decreases
C) increases
D) weakens

B) decreases

91

It takes _______ μs for ultrasound to travel 1.54 cm in soft tissue

A) 10
B) .77
C) 1.54
D) 100

A) 10

92

Propagation speed in bone is ____________ that in soft tissue.

A) lower than
B) equal to
C) higher than
D) 10 m/s greater than

C) higher than

93

Sound travels fastest in ________________.

A) air
B) helium
C) water
D) steel

D) steel

94

Solids have higher propagation speeds than liquids because they have greater ____________.

A) density
B) stiffness
C) attenuation
D) propagation speed

B) stiffness

95

Sound travels slowest in _______________.

A) gases
B) liquids
C) tissue
D) bone

A) gases

96

Sound is a ________ ________ wave.

mechanical, longitudinal

97

If propagation speed is doubled (a different medium) and frequency is held constant, the wave-length is _________________.

doubled

98

If frequency in soft tissue is doubled, propagation speed _________________.

unchanged

99

If wavelength becomes 2 mm and frequency is doubled the wavelength becomes _______________mm.

1

100

Waves can carry ____________ from one place to another.

information

101

From given values for propagation speed and frequency, which of the following can be calculated?

A) Amplitude
B) Impedance
C) Wavelength
D) A and B
E) B and C

C) Wavelength

102

True or False?

If two media have different stiffnesses, the one with the higher stiffness will have the higher propagation speed.

True

103

The second harmonic of 3 MHz is ________________.

6

104

The odd harmonics of 2 MHz are ________________.

A) 1, 3, 5
B) 2, 4, 6
C) 6, 9, 12
D) 6, 10, 14
E) 10, 12, 14

D) 6, 10, 14

105

The even harmonics of 2 MHz are ___________.

A) 1, 3, 5
B) 2, 4, 6
C) 4, 8, 12
D) 6, 10, 14
E) 10, 12, 14

C) 4, 8, 12

106

Nonlinear propagation means ________________.

A) the sound beam does not travel in a straight line
B) propagation speed depends on frequency
C) propagation speed depends on pressure
D) the waveform changes shape as it travels
E) more than one of the above

E) more than one of the above

C) propagation speed depends on pressure
D) the waveform changes shape as it travels

107

As a wave changes from sinusoidal form to sawtooth form, additional _____________ appear that are ______ and _________ multiples of the __________. They are called ________________.

Frequency, even , odd, fundamental, harmonics

108

If Density of a mediu is 1000 kg/m^3 and the propagation speed is 1540 m/s, the impedance is _________ rayls

1,540,000

109

True or False?

If two media have the same propagation speed but different densities, the one with the higher density will have the higher impedance.

True

110

If two media have the same density but different propagation speeds, the one with the higher propagation speed will have the higher impedance.

True

111

Impedance is _______________ multiplied by __________ ____________.

Density, propagation speed

112

The abbreviation CW stands for _______________.

Continuous wave

113

Pulse repetition frequency is the number of _________ occurring in 1 second.

Pulses

114

Pulse repetition _______________ is the time from the beginning of one pulse to the beginning of the next.

Period

115

Pulse repetition period _________________ as pulse repetition frequency increases.

Decreases

116

Pulse duration is the _________________ it takes for a pulse to occur.

time

117

Spatial pulse length is the ___________ of ___________ that a pulse occupies as it travels.

length, space

118

_________________ ________________ is the fraction of time that pulse ultrasound is actually on.

Duty factor

119

Pulse duration equals the number of cycles in the pulse multiplied by __________________.

Period

120

Spatial pulse length equals the number of cycles in the pulse multiplied by __________________.

wavelength

121

The duty factor of continuous wave sound is ______________.

1 (100%)

122

If the length is 2 mm, the spatial pulse length for a three-cycle pulse is ______________ mm.

6

3 cycles x 2 mm

123

The spatial pulse length in soft tissue for a two-cycle pulse of frequency 5 MHz is _____________ mm.

.616

(1.54 mm/μs x 2) / 5 MHz

124

The pulse duration in soft tissue for a two-cycle pulse of frequency 5 MHz is _______________ μs.

.4

2 / 5 MHz

125

For a 1-kHz pulse repetition frequency, the pulse repetition period is ________________ ms.

1

1 /1 kHz

126

The pulse duration in soft tissue for a two-cycle pulse of frequency 5 MHz is _______________ μs.

For a 1-kHz pulse repetition frequency, the pulse repetition period is ________________ ms.

The duty factor is ____________________.

.0004 (.04%)

.4 μs x .001 μs = .0004

127

How many cycles are there in a 1 second of continuous wave 5-MHz ultrasound.

A) 5
B) 500
C) 5000
D) 5,000,000
E) none of the above

D) 5,000,000

128

How many cycles are there in a 1 second of pulsed 5-MHz ultrasound with a duty factor of .01 (1%).

A) 5
B) 500
C) 5000
D) 5,000,000
E) none of the above

E) none of the above

5,000,000 x .01 = 50,000

129

How many cycles are there in a 1 second of pulsed 5-MHz ultrasound with a duty factor of .01 (1%).

How many cycles did pulsing eliminate?

A) 100%
B) 99.9%
C) 99%
D) 50%
E) 1%

C) 99%

130

For pulsed ultrasound, the duty factor is always ____________ __________________ one.

less than

131

_____________ is a typical duty factor for sonography.

A) .1
B) .5
C) .7
D) .9

A) .1

132

Amplitude is the maximum _________ that occurs in an acoustic variable.

variation

133

Intensity is the ________________ in a wave divided by ________________.

Power, area

134

The unit for intensity _____________.

W/cm^2

135

Intensity is proportional to _____________ squared.

amplitude

136

If power is doubled and area remains unchanged, intensity is _______________.

doubled

137

If area is doubled and power remains unchanged intensity is ________________.

halved

138

If both power and area are doubled, intensity is ___________.

unchanged

139

If amplitude is doubled, intensity is ______________.

quadrupled

140

If a sound beam has a power of 10 mW and a beam area of 2 cm^2, the spatial average intensity is __________________ mW/cm^2.

5 mW/cm^2

10mW/2cm2= 5

141

Attenuation is the reduction in _____________ and _______________ as a wave travels through a medium.

amplitude, intensity

142

Attenuation consists of _______________, ______________, and ______________.

absorption, reflection, scattering

143

The attenuation coefficient is attenuation per ____________ of sound travel.

centimeter

144

Attenuation and the attenuation coefficient are given in units of _____________ and _______________ respectively.

dB. dB/cm

145

For soft tissues, there is approximately ___________ dB of attenuation per centimeter for each megahertz of frequency.

.5 dB

3 MHz/.5dB

146

For soft tissue the attenuation coefficient at 3 MHz is approximately ________________.

1.5 dB/cm

147

The attenuation coefficient in soft tissue __________ as frequency increases

increases

148

For soft tissue, if frequency is doubled, attenuation is ________________. If path length is doubled attenuation is ________________. If both frequency and path length are doubled, attenuation is __________________.

doubled, doubled, quadrupled

149

If frequency is doubled and path length is halved attenuation is ________________.

unchanged

150

Absorption is the conversion _________ to _______________.

sound, heat

151

Can absorption be greater than attenuation in a given medium at a given frequency?

No

152

Is attenuation in bone higher or lower than in soft tissue?

higher

153

The imaging depth (penetration) ____________ as frequency increases.

decreases

154

If intensity of 4-MHz ultrasound entering soft tissue is 2 W/cm^2, the intensity at a depth of 4 cm is ______________W/cm^2

.32

(.5 * 4 MHz) * 4cm = 8 dB attenuation
intensity ratio is .16 * 2 W/cm2 = .32 W/cm2

155

If the intensity of 40-MHz ultrasound entering soft tissue is 2 W/cm^2, the intensity at a depth of 4 cm is ______________ W/cm^2

.000 000 02

(.5 *40 MHz) * 4 cm = 80 dB attenuation
.000 000 01 * 2 W/cm2 = .000 000 02 W/cm2

156

The depth at which half-intensity occurs in soft tissue at 7.5 MHz is _________________.

A) .6 cm
B) .7 cm
C) .8 cm
D) .9 cm
E) 1.0 cm

C) .8 cm

.5 * 7.5 MHz * .8 cm = 3 dB

157

When ultrasound encounters a boundary with perpendicular incidence, two ___________ of the tissue must be different to produce a reflection (echo).

impedances

158

With perpendicular incidence, two media _____________ and the incident ____________ must be known to calculate the reflected intensity.

impedances, intensity

159

with perpendicular incidence, two media ___________ must be known to calculate the intensity reflection coefficient.

impedances

160

For an incident intensity of 2 mW/cm^2 and impedances of 49 and 51 rayle, the reflected intensity is ____________ mW/cm^3

.0008, 1.9992

161

True or False

If the impedance of the media are equal, there is not reflection.

True

for perpendicular incidence

162

With perpendicular incidence, the reflected intensity depends on the _________________.

A) density difference
B) impedance difference
C) impedance sum
D) b and c
E) a and b

D) b and c

B) impedance difference
C) impedance sum

163

Refraction is a change in ______________ of sound when it crosses a boundary, Refreaction is caused by a change in __________ ____________ at the boundary.

Direction Propagation speed

164

Under what two conditions does refraction not occur?

Perpendicular incidence, equal media propagation speeds

165

The low speed of sound in fat is a source of image degradation because of refraction. If incidence angle at a boundary between fat (1.45 mm/μs) is 30 degrees, the transmission angle is ______________ degrees.

32

166

Redirection of sound in many directions as it encounters rough media junctions or particle suspensions (heterogeneous media) is called __________.

scattering

167

True or False?

Back scatter helps make echo reception less dependent on incident angle.

True

168

What must be known to calculate the distance to a reflector?

A) attenuation, speed, and density
B) attenuation and impedance
C) attenuation and absorption
D) travel time and speed
E) density and speed

D) travel time and speed

169

No reflection will occur with perpendicular incidence if the media ________________ are equal.

impedances

170

True or False?

Scattering occurs at smooth boundaries and within homogeneous media.

False