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Sonographic Topics > Chapter 1: Physical Principles > Flashcards

Chapter 1: Physical Principles Flashcards

1
Q

Sound is a pressure wave, created by a mechanical action, and is therefore called a ________

A

mechanical wave

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2
Q

produced when a vibrating source causes the molecules of a medium to move back and forth

A

sound wave

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3
Q

any form of matter: solid, liquid, or gas

A

medium

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4
Q

Sound requires a _____ to propagate; therefore it cannot travel in a vacuum

A

medium

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5
Q

When sound energy propagates through a medium, it does so in _____ waves, meaning that the molecules of the medium vibrate back and forth in the same direction that the wave is traveling.

A

longitudinal

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6
Q

Sound is a _______, _______ wave.

A

mechanical
longitudinal

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7
Q

molecules in a medium vibrate at 90 degrees to the direction of the traveling wave

A

transverse waves

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8
Q

changes that occur within a medium as a result of sound traveling through that medium

A

acoustic variables

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9
Q

The three primary acoustic variables are _____, ______, and ______.

A

pressure
density
particle motion

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10
Q

Each back and forth movement of molecules completes one _____ or one cycle of movement

A

wave

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11
Q

Each cycle consists of two parts: _______ and ______

A

compression
rarefaction

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12
Q

molecules are pushed closer together

A

compression

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13
Q

molecules are spread wider apart

A

rarefaction

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14
Q

mass per unit of volume

A

density

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15
Q

the back and forth motion of the molecules in the medium, and its units are that of distance

A

particle motion

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16
Q

how far apart objects are, and it is the measurement of particle motion

A

distance

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17
Q

may also be referred to as vibration or displacement

A

distance

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18
Q

if one variable increases the other increases

A

directly related

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19
Q

if one variable increases the other decreases

A

indirectly related

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20
Q

Parameters of sound

A

period
frequency
amplitude
power
intensity
propagation speed wavelength

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21
Q

the time it takes for one cycle to occur

A

Period

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22
Q

units of Period

A

us

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23
Q

the number of cycles per seond

A

frequency

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24
Q

Frequency units

A

Hs, kHz, MHz

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25
Q

Frequency and period are _____ related

A

inversely

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26
Q

When two reciprocals are multiplied together the result is

A

1

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27
Q

the speed at which a sound wave travels through a medium

A

propagation speed

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28
Q

Propagation speed is faster in _____

A

solids

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29
Q

Units for propagation speed

A

m/s or mm/us

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30
Q

average speed of sound in all soft tissue

A

1540 m/s
1.54 mm/us

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31
Q

Propagation speed is influenced by two properties

A

stiffness
density

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32
Q

the ability of an object to resist compression and related to hardness of the medium

A

stiffness

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33
Q

Stiffness and propagation speed are _____ related

A

directly

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34
Q

Density is _____ related to propagation speed

A

inversely

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35
Q

the length of a single cycle of sound

A

wavelength

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36
Q

distance from the beginning of a cycle to the end of that cycle

A

wavelength

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37
Q

In clinical imaging, the wavelengths measures between ___ and __ mm

A

0.1
0.8

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38
Q

Wavelength and frequency are _____ related

A

inversely

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39
Q

propagation speed divided by the frequency

A

wavelength

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40
Q

____, _____, and _____ all relate to size of strength of a sound wave.

A

amplitude
power
intensity

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41
Q

maximum or minimum deviation of an acoustic variable from the average value of that variable

A

amplitude

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42
Q

Ultrasound physics = _______ amplitude

A

pressure

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43
Q

units of amplitude

A

pascals

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44
Q

defined as the rate at which work is performed or energy is transmitted

A

Power

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45
Q

units of power

A

Watts or milliwatts

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46
Q

Power is proportional to ______

A

amplitude squared

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47
Q

If the amplitude doubles, the power ______

A

quadruples

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48
Q

defined as the power of the wave divided by the area over which it is spread, or the energy per unit area

A

intensity

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49
Q

_______ is proportional to both power and to amplitude squared

A

intensity

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50
Q

Intensity range in diagnostic ultrasound

A

0.01 to 100 mW/cm^2

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51
Q

Resistance to the propagation of sound through a medium

A

impedance

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52
Q

The amount of ______ depends on the density and the propagation speed of the medium

A

impedance

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53
Q

______ and ______ are controlling factors of propagation speed

A

density
stiffness

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54
Q

impedance units

A

Rayls

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55
Q

the product of the density of the medium and the propagation speed of sound in the medium

A

impedance

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56
Q

average speed of sound in soft tissue

A

1540 m/s

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57
Q

Assuming the beam strikes the interface at a 90 degree angle and there exists a large impedance difference between two tissues, there will be a _______

A

strong reflection

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58
Q

If the impedance between two tissues is the same there will be ______ reflection.

A

no

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59
Q

sound that is continuously transmitted

A

continuous wave ultrasound

60
Q

material within transducers that when electronically stimulate, produce ultrasound waves

A

piezoelectric materials

61
Q

pressure is created when voltage is applied to the material and electricity is created when a pressure is applied to the material

A

principle of piezoelectricity

62
Q

Parameters of pulsed sound

A

PRF
PRP
PD
DF
SPL

63
Q

number of pulses of sound produced in 1 second

A

PRF

64
Q

Diagnostic imaging typical values PRF

A

1-10 kHz

65
Q

The PRF changes when the sonographer changes the ______ control.

A

depth

66
Q

If imaging depth increases, PRF ______

A

decreases

67
Q

The time taken for a pulse to occur

A

PRP

68
Q

the time from the start of one pulse to the start of the next pulse, and therefore, it includes the “on” and “off” times.

A

PRP

69
Q

If PRP increases, PRF ______

A

decreases

70
Q

the time during which the sound is actually being transmitted, the “on” time

A

Pulse Duration

71
Q

The duration of “on” time depends on:

A

how many cycles there are in each pulse
period of each cycle

72
Q

equal to the number of cycles in the pulse multiple by how long each cycle lasts

A

pulse duration

73
Q

A ____ PD is preferred for imaging

A

short

74
Q

The _____ or _____ layer reduces the long “ring” of a vibrating crystal to two or three cycles per pulse.

A

backing
damping

75
Q

The backing layer helps improve _____ resolution.

A

axial

76
Q

the percentage of time that sound is actually being produced

A

duty factor

77
Q

PD/PRP =

A

duty factor

78
Q

If the PRP is short, the DF will be _____

A

greater

79
Q

In continuous wave, the DF is:

A

100%

80
Q

In clinical imaging with pulsed wave, the DF will be:

A

1% or less

81
Q

the length of a pulse

A

spatial pulse length

82
Q

depends on the wavelength of each cycle and the number of cycles in each pulse

A

SPL

83
Q

equals the number of cycles in the pulse multiplied by the wavelength

A

SPL

84
Q

If the wavelength increases, the SPL ______

A

increases

85
Q

If the number of cycles in the pulse increases, then SPL ______

A

increases

86
Q

Shorter SPLS mean ______ pulse durations

A

shorter

87
Q

Parameters determined by the sound source

A

period
frequency
amplitude
power
intensity
pulse duration
duty factor
pulse repetition period
pulse repetition frequency

88
Q

Parameters determined by the medium

A

propagation speed
impedance

89
Q

Parameters determined by the sound source and the medium

A

wavelength
spatial pulse length

90
Q

decrease in the amplitude, power, and intensity of the sound beam as sound travels through tissue

A

attenuation

91
Q

3 mechanisms of attenuation

A

absorption
reflection
scattering

92
Q

used when evaluating two intensities, such as powers or amplitudes

A

decibels

93
Q

If intensity or power doubles = change by ___ dB

A

3

94
Q

If intensity or power decreases by half = change by ___ dB

A

-3

95
Q

conversion of sound energy to heat

A

absorption

96
Q

greatest contributor to attenation

A

absorption

97
Q

The amount of attenuation that occurs as sound travels is related to the ____ of the beam

A

frequency

98
Q

rate at which sound is attenuated per unit depth

A

attenuation coefficient

99
Q

equal to 1/2 of the frequency in soft tissue

A

attenuation coefficient

100
Q

total amount of sound in dB that has been attenuated at a given depth

A

total attenuation

101
Q

If length increases, attenuation ____

A

increases

102
Q

Average rate of attenuation in soft tissue is

A

0.7 dB/cm/Mhz

103
Q

describes the depth at which sound has lost half, or -3dB of its intensity

A

half-intensity depth

104
Q

Soft tissue half intensity depth is equal to:

A

6/f

105
Q

dividing line between two different media

A

interface

106
Q

occur when sound impinges upon a large, smooth reflector at a 90 degree angle

A

specular reflections

107
Q

one in which the size of the reflector is larger than the wavelength of the incident beam

A

large specular reflector

108
Q

Which reflectors are highly angle dependent?

A

specular reflectors

109
Q

If the sound strikes the transducer at an _____ angle, the reflection will not return to the transducer.

A

oblique

110
Q

one in which their size is smaller than the wavelength of the incident beam

A

nonspecular reflector

111
Q

scattered sound in many different directions

A

backscatter

112
Q

_______ reflectors are not angle dependent

A

nonspecular

113
Q

constructive and destructive interactions

A

acoustic speckle

114
Q

Higher frequency transducers = ______ intensity of scatter

A

intensity

115
Q

very small reflectors; scatter sound equally in all directions

A

Rayleigh scatterers

116
Q

As the frequency increases, intensity of the scatter increases proportional to:

A

the fourth power of frequency

117
Q

When is reflection formed?

A

normal incidence
two media have two different impedances

118
Q

synonyms for normal incidence

A

orthogonal
right angle
perpendicular
90 degrees

119
Q

No change in impedance =

A

no reflection

120
Q

Angle of reflection =

A

angle of incidence

121
Q

Two types of oblique angles

A

obtuse
acute

122
Q

percentage of sound transmitted at an interface

A

intensity transmission coefficient

123
Q

equal to 1 minus the IRC

A

intensity transmission coefficient

124
Q

the percentage of sound reflected at an interface

A

intensity reflection coefficient (IRC)

125
Q

IRC + ITC

A

1

126
Q

If impedances are the same, then there is no reflection, and ITC =

A

100%

127
Q

The transmitted beam angle is equal to ______

A

incident angle

128
Q

When sound strikes an interface with an oblique angle of incidence, the transmitted beam angle will equal the incident angle only if the ______ are identical

A

propagation speeds

129
Q

If there is oblique incidence and a propagation speed mismatch, the transmitted angle will be different from the _____ angle

A

incident

130
Q

If the propagation speed of medium 2 is less than the propagation speed of medium 1, then the angle of transmission will be ____ than the angle of incidence

A

less

131
Q

describes the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media

A

Snells law

132
Q

______ and _____ refer to where the beam was measured.

A

Spatial average
Spatial peak

133
Q

SP intensity is measured where?

A

at the center of the beam

134
Q

SA intensity is average intensity across ______

A

face of entire beam

135
Q

SP/SA factor

A

beam uniformity ratio

136
Q

ratio of center intensity to average spatial intensity

A

Beam Uniformity Ratio

137
Q

intensity measured at the highest intensity, or peak, of the pulse

A

Temporal peak

138
Q

highest of all temporal intensities

A

Temporal peak

139
Q

average of all of the intensities during both transmission and the listening period

A

Temporal average

140
Q

lowest of all temporal intensities

A

Temporal average

141
Q

measured only during beam transmission

A

Pulse average

142
Q

PA x DF

A

TA

143
Q

lowest of intensities

A

SATA

144
Q

highest of intensities

A

SPTP

145
Q

used to measure output intensity

A

hydrophone, or microprobe

146
Q
A

Sonographic Topics (35 decks)

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