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physics principles Flashcards

1
Q

what is sound

A

a mechanical, longitudinal wave.

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2
Q

what does longitudinal mean?

A

parallel from the sound source.

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3
Q

what does 1 complete cycle mean?

A

it means 1 compression & 1 rarefaction

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4
Q

λ

A

wavelength

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5
Q

c

A

propagation speed

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6
Q

f

A

frequency

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7
Q

what does wavelength depend on?

A

frequency & propagation speed

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8
Q

what is propagation speed determined by?

A

a medium

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9
Q

what is frequency determined by?

A

a sound source

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10
Q

mediums with fast propagation speed = ______

A

longer wavelength

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11
Q

mediums with slower propagation speed = ______

A

shorter wavelength

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12
Q

infrasound

A

<less than 20Hz

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13
Q

audible sound

A

20 - 20,000Hz

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14
Q

ultrasound

A

> greater than 20,000Hz

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15
Q

diagnostic ultrasound

A

2 - 20MHz

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16
Q

power

A

rate of flow of energy

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17
Q

intensity

A

power/area

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18
Q

amplitude

A

height of pressure wave

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19
Q

why do we use decibels?

A

to describe how much our intensity has changed

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20
Q

a reduction of 6dB means the intensity is reduced by how much?

A

1/4. 25%

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21
Q

adjusting overall gain from 25dB to 28dB will cause what affect to the intensity of the echoes?

A

there was an increase of 3dB which means the intensity was doubled.

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22
Q

in soft tissue..

A

1.54 mm/ms or 1540 m/s

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23
Q

bulk modulus

A

stiffness

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24
Q

is propagation speed affected by frequency or wavelength?

A

NO

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25
Q

impedance

A

obstruct or hinder

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26
Q

each medium has it’s own _______.

A

impedance

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27
Q

what is impedance dependent on?

A

the medium

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28
Q

Z

A

impedance

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29
Q

p

A

density

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30
Q

Z = pc means…

A

impedance = density & propagation speed

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31
Q

interface

A

tissue change

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32
Q

when sound encounters interface what can happen?

A

some sound can be reflected (bounce back) & the rest continues traveling or is transmitted.

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33
Q

attenuation

A

weakening of sound

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34
Q

what does attenuation depend on?

A

a medium

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35
Q

what is the average rate of attenuation in soft tissue?

A

1/2 dB/cm/MHz

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36
Q

decibels change in ..

A

intensity

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37
Q

frequency & attenuation are ______ related.

A

directly

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38
Q

increase in frequency = _____________

A

increase attenuation

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39
Q

how much is the frequency going to attenuate per cm?

A

half the frequency

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40
Q

4 MHz will attenuate ___

A

2 dB/cm

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41
Q

8 MHz will attenuate _______

A

4 dB/cm

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42
Q

What are Pulsed Ultrasound Parameters?

A

PRF, PRP, SPL, PD, DF

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43
Q

PRF

A

Pulsed Repetition Frequency

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44
Q

PRP

A

Pulsed Repetition Period

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45
Q

SPL

A

Spatial Pulse Length

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46
Q

PD

A

Pulse Duration

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47
Q

DF

A

Duty Factor

48
Q

what does Pulsed US Parameters do?

A

generate 2-3 cycles only

49
Q

what does PRF depend on

A

depends on depth since the machine as to wait for the echo before sends it to next pulse.

50
Q

if PRF is too high the machine will…

A

the machine will not know the location or depth.

51
Q

PRF is ______ related to depth.

A

inversely ↑Depth ↓PRF

52
Q

pulse repetition frequency =

A

number of uses in 1s

53
Q

pulse repetition period=

A

time between beginning of 1 pulse to beginning of next pulse

54
Q

PRP is _______ related to PRF

A

inversely ↑PRF ↓PRP

55
Q

PRP is _____ related to depth

A

directly ↑PRP ↑PRF

56
Q

spatial pulse length=

A

length of one pulse

57
Q

what does SPL depend on

58
Q

pulse duration=

A

time for one pulse to occur

59
Q

what does PD depend on?

60
Q

in diagnostic US, PRF is in ___

61
Q

what is DF?

A

the fraction or % of time that an imaging system is transmitting

62
Q

is DF used often?

A

no, only 0.1 - 1.0%

63
Q

what is resolution?

A

the machines ability to detect & display accurately

64
Q

what are the 2 main types of resolution?

A

spatial resolution & temporal resolution

65
Q

what is spatial resolution?

A

the machines ability to distinguish between 2 closely spaced objects & display them separately.

66
Q

what is spatial resolution measured in?

A

space or distance (mm)

67
Q

axial

68
Q

lateral

A

horizontal

69
Q

1/2 SPL is ____

70
Q

LARRD

A

longitudinal, axial, radial, range, depth

71
Q

what is the axial res from a SPL of 1.8mm

72
Q

how do you find the axial resolution of a SPL?

73
Q

the 2 objects have to be separated by ____ in order to be resolved.

74
Q

an SPL of 1.8mm = axial resolution of 0.9mm. Is it resolved?

75
Q

an SPL of 2.2mm = axial resolution of 1.1mm. Is it resolved?

A

no, its more than 1.0mm so they are blurred together vertically

76
Q

what is the goal of axial resolution?

A

shorten the pulse

77
Q

when you decrease frequency what happens?

A

decreases wavelength=decreases pulse

78
Q

what is damping/backing material do?

A

reduces ringing of crystal = shortens the pulse

79
Q

what does a wide bandwidth do?

A

shorter pulse (low Q-factor)

80
Q

what is a trade off?

A

when you gain something by giving something else up

81
Q

what has trade offs?

A

resolutions

82
Q

what is the main way to improve axial resolution?

A

increase frequency

83
Q

do you always chose the highest frequency you have?

A

no, because you will not be able to scan deeper

84
Q

what is axial resolution?

A

the ability to see the two structures that are side by side as separate and distinct when parallel to the beam.

85
Q

lateral = _______

A

beam width

86
Q

LATA

A

lateral, azimuthal, transverse, angular

87
Q

what is lateral resolution?

A

the image generated when the two structures lying side by side are perpendicular to the beam

88
Q

what does temporal mean?

89
Q

in order for the 2 objects to be seen what has to happen?

A

the 2 objects have to be hit by their own beam, then they will produce separate echoes & the machine will display both go them.

90
Q

what is the goal in lateral resolution?

A

narrow the beam

91
Q

what are some ways to narrow the beam?

A
  1. focusing:
    multiple focal zones=overall beam narrowing
  2. # scan lines/scan line intensitysea lines=beams. increase line density=smaller beam size
  3. sector angle
    decreasing sector size=increase line density
  4. transducer choice
    sector FOV(field of view)=lower line density in far field, lat res worsens
92
Q

temporal

A

frame rate

93
Q

what is frame rate determined by?

A

the amount of work the machine has to do or time it needs to produce the frame.

94
Q

what happens if you have poor frame rate?

A

the images will be blurred together giving it a slow motion effect

95
Q

what is frame rate?

A

it helps the machine keep up with whatever is going on in the body

96
Q

high PRF =

A

faster frame rate

97
Q

piezoelectric

A

pressure-electric

98
Q

PZT

A

lead ziconate titanate (man made ceramic crystal)

99
Q

what are the 2 crystal materials?

A

PZT & Quartz

100
Q

what is operating frequency determined by?

A

the thickness of the crystal (typically 0.2 - 1.0mm)

101
Q

crystal thickness = _____

A

1/2 wavelength

102
Q

crystal thickness & frequency are _____ related

103
Q

the thinner the crystal ________

A

the higher the frequency

104
Q

fixed

A

we cannot control

105
Q

what do the lens do?

A

focuses ultrasound beams on a target

106
Q

what is the impedance matching layer?

A

a layer at the transducer face that matches the impedances.

107
Q

why do you need to match the impedances?

A

so that most of the beam can be transmitted easily into the body

108
Q

what does the matching layer do?

A

reduces reflection. similar to gel

109
Q

what is backing/damping material do?

A

reduce the ringing of the crystal & shortens the pulse

110
Q

for pulsed US how many cycles do you want?

A

2-3 cycles only

111
Q

bandwidth

A

the range of frequencies

112
Q

what determines bandwidth

A

the size of the pulse

113
Q

short pulse = _____ bandwidth

114
Q

long pulse = ______ bandwidth

115
Q

do we want high Q transducers ?

A

no, high Q means narrow bandwidth which means long pulses which means poor axial resolution. we want lower Q Factor.

116
Q

Q-Factor

A

quality of frequency off the transducer

117
Q

what are the 3 beam characteristics?

A
  1. Fresnel Zone
  2. Fraunhofer Zone
    3.Focal zone/point

spi (1 decks)

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