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Physics 3 > Module 2 : Bioeffects > Flashcards

Module 2 : Bioeffects Flashcards

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1
Q

what are the three waves we can describe the strength of a wave

A
  • amplitude
  • power
  • intensity
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2
Q

other than strength what else can amplitude, power, and intensity express

A
  • loudness/ volume of sound
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3
Q

what are the 4 definitions of amplitude

A
  • particle displacement
  • particle velocity
  • acoustic pressure of a sound wave
  • maximum variation of an acoustic variable
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4
Q

what does amplitude indicate about an echo

A
  • indicates the strength of the echo or voltage induced in a crystal by a pressure wave
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5
Q

what are the 4 acoustic variables

A
  • pressure
  • density
  • particle motion
  • temperature
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6
Q

what 4 questions should you ask yourself about amplitude

A
  • what determines the initial amplitude of a pulse
  • as the pulse travels through the medium what is the reduction in amplitude called
  • what are the 5 mechanisms that cause attenuation
  • does the amplitude of the echo decrease as the echo returns to the transducer
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7
Q

what determines the initial amplitude of a pulse

A
  • the pulser (output power)
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8
Q

as the pulse travels through the medium what is the reduction in amplitude called

A
  • attenuation
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9
Q

what are the 5 mechanisms that cause attenuation

A
  • ABSORPTION
  • reflection
  • refraction
  • wave front divergence
  • scatter
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10
Q

does the amplitude of the echo decrease as the echo returns to the transducer

A
  • yes
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11
Q

what is the definition of power

A
  • measure of the total energy transmitted summed over the cross sectional area fo the beam per unit time
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12
Q

power equation

A

power = intensity x area

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13
Q

what is the absolute unit of power

A
  • the watt (joules)
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14
Q

what is the relative unit of power and intensity

A
  • the decibel (db)
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15
Q

what is a decibel in relation to a bel

A
  • it is 1/10 of a bel
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16
Q

what does 0dB equate too

A
  • 100% power
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17
Q

what does a 3dB loss equate to

A
  • 1/2 the original power
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18
Q

what is power determined by

A
  • the pulser
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19
Q

what is the definition of intensity

A
  • measure of the strength of a sound wave

- equal to the power per unit area

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20
Q

what is the intensity equation

A

intensity = power / area

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21
Q

what is the absolute unit of intensity

A

mW/cm^2 or W/cm^2

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22
Q

how would you describe the relationship between intensity and power

A
  • it is proportional
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23
Q

if there is an increase in power then what happens to the intensity

A

the intensity increases

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24
Q

how would you describe the relationship between area and intensity

A
  • it is inversely proportional
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25
Q

if the area decreases what happens to the intensity

A
  • it increases
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26
Q

how is intensity related to amplitude

A
  • it is proportional to the square of the pressure amplitude
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27
Q

a small change in amplitude will do what to the intensity

A
  • result in a very very large change in intensity due to the square exponent
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28
Q

if the amplitude is doubled what happens to the intensity

A
  • it is quadrupled
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29
Q

is intensity constant in space and time

A
  • no
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30
Q

what are the four different expression of intensity

A
  • spatial average (SA)
  • spatial peak (SP)
  • temporal average (TA)
  • temporal peak (TP)
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31
Q

where is the spatial average found

A
  • at the transducer face
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32
Q

where is the spatial peak found

A
  • found at a the focal point where the beam area is the smallest
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33
Q

how are spatial peak and spatial average related

A
  • by the Beam Uniformity Ratio BUR
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34
Q

what is the Beam Uniformity Ratio equation

A
  • BUR = SP / SA
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35
Q

what does the BUR tell us about the beam

A
  • tells us the amount of focusing there is
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36
Q

highly focused beams have a high or low BUR

A
  • high
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37
Q

weakly focused beams have a high or low BUR

A
  • low
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38
Q

what number will the BUR always be over and why

A
  • the BUR will always be over 1

- the spatial peak will always be higher than the averages

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39
Q

what would the BUR be in a perfectly uniform beam

A
  • 1
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40
Q

what are the two factors that effect the spatial intensities

A
  • spatial peak will increase with an increase in power or focusing
  • spatial average will increase with an increase in power
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41
Q

what is the temporal average

A
  • over the time the pulse is generated it includes both the ringing and listens phase of the pulse
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42
Q

what is the temporal peak

A
  • the highest amplitude in the pulse at any given time

- instantaneous peak

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43
Q

how are the temporal average and temporal peak related

A
  • related by the Duty Factor DF
44
Q

what is the Duty Factor DF equation for TP and TA

A
  • DF = TA / TP
45
Q

what is the Duty Factor

A
  • it is the percent of time the sound is on / the probe is ringing
46
Q

Duty Factor Equation

A

DF = PD/PRP x 100

47
Q

what should the temporal peak be replaced by and why

A
  • the pulse average PA

- the pulse is so short that the TP almost equals the PA

48
Q

what is the duty factor equation for TA and PA

A
  • DF = TA / PA
49
Q

what is the pulse average

A
  • pulse average intensity is Thea average of all intensities found within a single pulse
50
Q

what are the two factors that effect temporal intensities

A
  • increase in power

- increase in duty factor

51
Q

when is the duty factor increase

A
  • if the PRF or PD is increased
52
Q

what is the duty factor for continuous wave CW

A
  • 100% because the crystal is always ringing

- usually has a higher SPTA than PW

53
Q

combined intensities from highest to lowest

A
  • SPTP
  • SPPA
  • SPTA
  • SATP
  • SAPA
  • SATA
54
Q

why don’t we use SPTP for bioconsiderations

A
  • not fair to use this because it is such a short part of the pulse its very fast
55
Q

what combined intensity do we use for bioconsiderations

A
  • SPTA
56
Q

what is the SPTP intensity also known as

A
  • instantaneous peak
57
Q

what are the three sources that we use for information on effects of ultrasound

A
  • epidemiology
  • in vitro cell studies
  • animal studies (invivo)
58
Q

what is an epidemiological study and what is the time line of it

A
  • people are monitored over the course of several years that were exposed to ultrasound in utero
  • conducted over a long term
59
Q

what is the purpose of an epidemiological study

A
  • look for cause and effect
60
Q

what is an in vitro study

A
  • exposes macromolecules, membran transport systems, cells, or clumps of cells suspended in liquid to ultrasound
  • it is difficult to say that an effect on cells will have a direct clinical significance
  • the results of in vitro studies can give valuable information to set thresholds for in vivo studies
61
Q

what have in vivo studies shown

A
  • potential for bio effects exists
62
Q

what 6 adverse effects have in vivo studies shown

A
  • fetal weight reduction
  • postpartum mortality
  • fetal abnormalities
  • tissue lesions
  • hind limb paralysis
  • blood flow stasis
63
Q

what two more positive effects have been reported from in vivo studies

A
  • wound repair enhancement

- tumor regression

64
Q

what does the official AIUM statement say about bio effects

A
  • there are no adverse effects observed if the intensities are kept below a certain threshold
65
Q

what is the highest safe intensity level for an unfocused probe

A
  • 100 mW/cm^2
66
Q

what is the highest safe intensity level for a focused probe

A
  • 1000 mW/cm^2 (1W/cm^2)
67
Q

what are the two main categories of bio effects

A
  • thermal

- non thermal (mechanical)

68
Q

what is an important thing to remember about thermal bioeffects

A
  • attenuation is primarily due to absorption which is the conversion of sound to heat
69
Q

do adult of fetal tissues handle temperature increases better

A
  • adult tissues
70
Q

no adverse effects occur when the temp increases is less than what number

A
  • 2ºC
71
Q

what other temperature range is considered safe as long as exposure time is reasonable

A
  • between 2-6ºC
72
Q

the higher the exposure time leads to what

A
  • more chance of adverse effects at higher temperatures

- 6ºC increase in temp will not produce effects if exposure time is under 16 minutes

73
Q

what two categories are included in mechanical effects

A
  • radiation force

- cavitation

74
Q

what is radiation force

A
  • force exerted by the sound on the medium which can deform and disrupt structures
75
Q

what can radiation force cause

A
  • can cause flow in absorbing fluids resulting in shear forces
76
Q

what is cavitation

A
  • production and behaviour of bubbles in a liquid medium
77
Q

what are the to divisions of cavitation

A
  • stable and transient
78
Q

what is stable cavitation

A
  • simple oscillation of the bubbles that can result int eh streaming of liquid resulting in shear stresses
79
Q

what is transient cavitation

A
  • when the bubble actually collapses producing shock waves

- the shock waves can result in localized extremely high temperatures and has even emitted light in clear fluids

80
Q

what is the standard set in 1992 for real time scanning called

A
  • the Output Display Standard (ODS)
81
Q

what 2 quantities are displayed by the ODS

A
  • thermal index TI

- mechanical index MI

82
Q

what is the thermal index

A
  • ratio of acoustic power produced by the transducer to the power required to raise the temperature in tissue 1ºC
  • assumed value
83
Q

what are the three other TI categories

A
  • TIS
  • TIB
  • TIC
84
Q

TIS

A
  • TI for soft tissue and is the MOST COMMON
85
Q

TIB

A
  • TI for bone near the focus and is used for OB
86
Q

TIC

A
  • TI for bone near the surface as in the case of a transcranial study
87
Q

what does the mechanical index represent

A
  • likelihood that the energy used will lead to cavitation
88
Q

what is the MI proportional to

A
  • peak rarefaction pressure so if the pressure doubles the MI doubles as well
89
Q

what is the MI inversely proportional to

A
  • proportional to the square root of the frequency so the frequency would have to quadruple for the MI to halve
90
Q

is there a chance for MI and TI to be underestimated and if yes then in what circumstance

A
  • yes it can be

- in presence of a large fluid collection but these situations usually allow for less power

91
Q

what is the max TI

A

6ºC

92
Q

what is the max MI

A

1.9

93
Q

cardiac SPTA limit

A

430 mW/cm^2

94
Q

peripheral vascular SPTA limit

A

20 mW/cm^2

95
Q

ophthalmic SPTA limit

A

17 mW/cm ^2

96
Q

fetal and other (abd, peds, SS, neonatal, brain) SPTA limit

A

94 mW/cm^2

97
Q

typical output intensity SPTA for b scan

A

18.7 mW/cm^2

98
Q

typical output intensity SPTA for m mode

A

73 mW/cm^2

99
Q

typical output intensity for SPTA for PW

A

1140 mW/cm^2

100
Q

typical output intensity SPTA for color

A

234 mW/cm^2

101
Q

what are the two different applications of ultrasound

A
  • scanned

- non scanned

102
Q

what are the 3 non scanned applications of ultrasound

A
  • CW
  • PW
  • m mode
103
Q

what do the non scanned applications of ultrasound pose risk of

A
  • highest risk of thermal effects with W having the most potential due to the fact they transmit repeatedly in a straight line
104
Q

what other non thermal adverse effects can occur

A
  • when gas bodies are present in the circulation contrast agents in the blood stream pose a concern since these findings were confirmed at intensities below the accepted threshold
  • when MI is below 0.4 there is little apparent risk
105
Q

what 4 adverse effects have been found from scanning the gas bodies

A
  • induction of premature ventricular contractions
  • microvascular leakage with petechiae (micro bleeds)
  • glomerular capillary hemorrhage
  • local cell killing
106
Q

ALARA

A
  • balancing between benefit and risk

- As Low As Reasonable Achievable

Physics 3 (5 decks)

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