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Physics 3 > M2: Bioeffects > Flashcards

M2: Bioeffects Flashcards

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1
Q

what is acoustic propagation

A

the effect of tissue on sound

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2
Q

does diagnostic US use a lower or higher intensity than therapeutic US

A

lower

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3
Q

3 ways to describe the strength of a wave

A

amplitude
power
intensity

these can also express the loudness or volume of a sound

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4
Q

formula for intensity

A

I = P/A or

I is inversely proportional to Amp^2

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5
Q

what happens if you double amplitude

A

you quadruple intensity

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6
Q

list the acoustic variables

A

press
density
particle motion
temperature

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7
Q

define amplitude

A

maximum variation of an acoustic variable…. also the particle displacement, velocity or acoustic pressure of a sound wave

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8
Q

what does amplitude indicate

A

the strength of the detected echo or the voltage generated in the crystal from a press wave

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9
Q

what determines the initial amplitude of a pulse

A

power output - determined by the pulser

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10
Q

as a sound wave travels though tissue, what is the reduction in power called

A

attenuation

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11
Q

5 mechanisms of attenuation

A 
absorption
reflection (z values)
refraction (diff velocities and non perpendicular insonation)
wavefront divergence
scatter
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12
Q

does the amplitude of an echo decrease as it returns to the probe

A

yes

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13
Q

define power

A

measure of total energy transmitted over the cross sectional area of the beam, per unit time

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14
Q

formula for power

A

P = I x A

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15
Q

absolute unit of power

A

watt (joules/s)

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16
Q

relative unit of power

A

decibel

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17
Q

how many dB is 100% power

A

0dB

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18
Q

a reduction of 3 dB drops the intensity by how much

A

1/2 the original intensity

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19
Q

a reduction of 10 dB drops the intensity by how much

A

0.1 of original intensity

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20
Q

what determines how much power is produced by the transducer

A

pulser

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21
Q

power output for PW

A

1140 mW/cm^2

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22
Q

absolute unit of intensity

A

W/cm^2 or mW/cm^2

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23
Q

relative unit of intensity

A

decibel

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24
Q

is intensity constant in time or space

A

no

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25
Q

which intensity do we use when considering bioeffects

A

SPTA

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26
Q

where is the spatial average found

A

probe face

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27
Q

where is the spatial peak found

A

focal point

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28
Q

how are SP and SA related?

Formula

A

BUR

BUR = SP/SA

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29
Q

What does the BUR compare

what does the it tell us about the focusing of the probe

A

The near and far field

gives us an idea of how much focusing there is in the beam

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30
Q

highly focused beams have what kind of BUR?

weakly focused?

A

high - high BUR

low - low BUR

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31
Q

the BUR will alwasy be greater than what value

why

A

1

peak is always higher than the avg

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32
Q

a perfectly uniform beam would have a BUR of what value

A

1

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33
Q

what kind of probe has a BUR of 1

A

old single disc mechanical probe w/ no natural or applied focusing

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34
Q

factors that effect the spatial intensities in a probe

A

SP will increase w/ an increase in power of focusing
and decrease with increasing depth (aperture must widen to maintain constant beam width at the focus so its less intense)

SA will increase w/ an increase in power
and decrease with increasing depth due to attenuation

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35
Q

what is temporal avg

A

includes both ringing and listening phase of the pulse

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36
Q

what is temporal peak

A

highest amplitude in a pulse at any given time

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37
Q

how are TP and TA related

formula

A

duty factor

DF = TA/TP
or
DF = PD/PRP x 100

38
Q

describe PD and PRP

A 
PD = time it takes for one pulse to occur (ringing time)
PRP = time from beginning of one pulse to the beginning of the next.... includes ringing and listening time (also go return time in range equation)
39
Q

why are TP and PA almost the same value

A

b/c the pulse is so short…. TP always a bit higher than TA

40
Q

in the simplified DF formula, TP should be more accurately replaced by which value

A

PA

DF = TA/PA

41
Q

another name for SPTP

A

instantaneous peak

42
Q

what is the PA

A

avg of all intensities found w/in a single pulse

43
Q

in a sine graph, where is the TP found

A

the first amplitude peak

44
Q

whats the intensity at the listening phase

A

0

45
Q

factors that effect temporal intensities

A

increase in power or duty factor

46
Q

what is DF

what factors increase it

A

% of time the crystal is ringing

increased PRF or PD

47
Q

how will an increase in depth effect the TA

A

reduces it because you are increasing the listening time

48
Q

why does CW have a higher SPTA than PW

A

its always ringing (DF will be 100%)

49
Q

another name for SPPA

A

maximum intensity or time averaged half maximum

50
Q

info we have on bioeffects come from what 3 sources

A

epidemiology
in vitro studies
in vivo or animal studies

51
Q

describe an epidemiological study

A

study conducted over a long period of time… there is a control grp and a group who have been exposed to US
….these grps are tracked over several years to look for cause and effect

52
Q

when was US power output regulated

A

1992

53
Q

conclusions of epidemiological studies for OB

A

…no evidence of low birth weight, delayed speech, dyslexia and non-right handedness @ the intensities we use today

54
Q

describe in vitro studies

do their findings have clinical significance

A

exposes cells in liquid to US

hard to say

55
Q

purpose of in vitro studies

A

give valuable info to set thresholds for in vivo studies

56
Q

have in vivo studies shown possible bioeffects

explain

A

yes….

shown fetal weight reduction, postpartum mortality, abnormalities, lesions, etc… but also shown good bioeffects like wound repair enhancement and tumor regression

57
Q

US intensity threshold for an unfocused probe that is considered safe

A

< 100 mW/cm^2

58
Q

US intensity threshold for a focused probe that is considered safe

A

< 1000 mW/cm^2 (1 W/cm^2)

59
Q

see table on pg 34

A

/

60
Q

2 main categories of bioeffects

A

thermal

non-thermal/mechanical

61
Q

which mechanism of attenuation accounts for the majority of this process

A

absorption (80%).. the conversion of sound into heat

62
Q

tissue must not be heats more than how many degrees in order to avoid bioeffects

A

> /=2 degrees

63
Q

an increase in temp of what value is considered significant

A

2 degrees

64
Q

what effect can an increase of 4 degrees have on a fetus

A

can kill it

65
Q

if tissue is heated b/w 2-6 degrees, what becomes an important consideration

A

exposure time

66
Q

a 6 degree increase in temp (for a fetus) will not cause any bioeffects if exposure time is under how many minutes

A

16 mins

67
Q

2 types of mechanical bioeffects

A

radiation forces

cavitation:

68
Q

describe radiation forces

A

the force exerted by sound on the medium which can deform and disrupt structures (think of debris in a cyst)…. this force can cause flow in absorbing fluids leading to tearing (shear forces)

69
Q

describe cavitation

2 types

A

production and behavior of bubbles in a liquid medium

2 types:
stable cavitation (we like this)
transient cavitation
70
Q

describe stable cavitation

A

the oscillation of the bubbles (resonating) in a liquid medium that can result in the streaming of liquid which can cause enough stress to tear the structure if theres too much stable cavitation

71
Q

describe transient cavitation

A

when a bubble in a liquid medium collapses and produces shock waves that can cause localized extremely high temp and can emit light in clear fluids (sonoluminescent)

72
Q

what year was the output display standard displayed (ODS) on the US screen

what is it

A

1992

give you info about the potential or bioeffects based on the power you’re using the scan

73
Q

2 ODS displayed

A 
Thermal index (TI)
Mechanical Index (MI)
74
Q

what is the TI

A

How much you are heating the tissue… TI of 1 means that you may increase the temp of the tissue by 1 degree

75
Q

are TI and MI assumed values

A

yes

76
Q

3 categories of TI

A

divided based on diff tissue scanned and their absorption rates (will have different density and compressibility)

TIS - soft tissue, most common
TIB - for bone near the focus, used for OB scanning
TIC - for bone near the surface, used for transcranial

77
Q

what is MI

when is it especially import to consider this number

A

number that represents the likelihood that cavitation will occur…. MI is proportional to the peak rarefractional press (highest amplitude) so if the press doubles so will the MI

contrast US

78
Q

how are frequency and MI related

A

inversely… but you would need a big change in frequency (quadruple) to see this effect

79
Q

how can we reduce MI

A

reduce the power

80
Q

when can MI and TI be underestimated

A

when scanning a large fluid collection…. but we can usually use less power in this situation

81
Q

what is the TI and MI max

A

TI: 6
MI: 1.9

82
Q

since PW doppler has an SPTA of 1140, what becomes an important consideration when using it

A

exposure time

83
Q

2 types of applications of US

A

scanned and non-scanned

84
Q

what are some non-scanned US application

A

CW, PW and M-mode

85
Q

why do non-scanned US applications have a higher risk for thermal effect?

A

since we are repeatedly insonating the sound beam in the same spot and its not swept across the face of the probe like 2D scanning… CW has the highest risk

86
Q

when might we see non-thermal bioeffects when scanning below our acceptable threshold of 1000mW/cm^2

what are some of these effects

A

when gas bodies are present in circulation (contrast US)

PVCs
micovascular leaks w/ petechiae
glomerular capillary hemorrhage
local cell killing

87
Q

MI must be below what value when doing contrast US

A

0.4

88
Q

how do we follow ALARA in US

A

only scanning when medically necessary, not for entertainment or other purposes (eg learning the sex of the fetus, pictures of the fetus, commercial purposes)

89
Q

what are the 4 restricted acts the US technicians perform

A

OB scans
EV
Contrast
IVs

90
Q

Another name for transient cavitation

A

Collapse cavitation

Physics 3 (5 decks)

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