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Physics3 > module 2: bioeffects, safety & power > Flashcards

module 2: bioeffects, safety & power Flashcards

1
Q

what are 3 ways in which we can describe the strength of a wave?

A
  • amp (max variation of acoustic variable)
  • power (P=IntensityXarea)
  • intensity (amp squared)
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2
Q

whats the absolute unit of power?

A

watt(joule)

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3
Q

whats the relative unit of power

A

decibels

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4
Q

whats power determined by

A

the pulser

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5
Q

what does power default to?

A

100% or zero dB

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6
Q

output value for PW

A

1140mW/cm

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7
Q

define amplitude

A

the particle displacement, particle velocity or acoustic pressure of a sound wave
- maximum displacement of an acoustic variabe

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8
Q

intensity

A

a measure of the strength of a sound wave and is equal to the power unit area

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9
Q

whats the relationship between intensity and power?

A

proportional

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10
Q

intensity formula

A

i=p/a

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11
Q

if area decreases what happens to intensity?

A

increases

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12
Q

if area is halved wat happens to intensity?

A

doubles

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13
Q

whats the relationship between intensity and amplitude?

A

I is proportional to amp^2

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14
Q

if u double amplitude what happens to intensity

A

quadrupled

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15
Q

whats the BUR

A

BUR=SP/SA

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16
Q

do highly focused beams . have a high or low BUR?

A

high

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17
Q

what does spacial peak increase with?

A

power or focusing

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18
Q

what will cause spatial avg to increase?

A

increase in power

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19
Q

whats the duty factor

A

df=ta/pa

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20
Q

whats the pulse avg intensity

A

the avg of all intensities found within a single pulse

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21
Q

what factors effect temporal intensities?

A

an increase in power or duty factor

22
Q

whats prf limited by?

A

depth

23
Q

whats the DF for CW

A

100%

24
Q

does CW have a lower or higher SPTA than PW applications

A

higher

25
Q

whats SPTP intensity also known as

A

instantaneous peak

26
Q

SPPA intensity is also known as….

A

max intensity or time averaged half maximum

27
Q

what sources do we get info from about bioeffects

A
  • epidemiology
  • in vitro cell studies
  • animal
28
Q

whats the extensive resource for bioeffects info

A

the american institute of ultrasound in medicine (AIUM)

29
Q

what happens in an epidemiologic study

A
  • conducted over a long period
  • ppl monitored that were exposed in utero
  • purpose to look for cause n effect
  • there is no evidence of insufficient low birth weight, delayed speech, dyslexia and non right handedness
30
Q

animal studies

A
  • no adverse effects observed if intensities are kept below 100mW/cm^2 for UNFOCUSED
  • below 1000 mW/cm^2 for FOCUSED
31
Q

two main categories for bioeffects

A
  • thermal

- non thermal (mechanical_

32
Q

there are no adverse effects when the temperature is less than….

A

2 degrees

33
Q

how long can you scan at 6 degrees before producing potential side effects

A

16 mins

34
Q

what do mechanical effects include

A

radiation force and cavitation

35
Q

whats radiation force

A

force exerted by sound on the medium which can deform and disrupt structures

36
Q

whats cavitation

A

production & behavior of bubbles in a liquid medium

37
Q

what can cavitation be divided into

A

stabe and transient

38
Q

whats stable cavitation

A

simple oscillation of bubbles that can result in streaming of liquid resulting in shear stress

39
Q

ODS

A

output display standard

40
Q

quantities displayed with ods

A

thermal index

mechanical index

41
Q

define TI

A

ratio of acoustical poer produced by the transducer to the power required to raise the temp in tissue 1 degree

42
Q

ti is divided into 3 categories

A
  • TIS soft tissue
  • TIB bone near focus
  • TIC bone near surface for transcranial study
43
Q

mechanical index

A

likelihood that energy used will lead to cavitation

44
Q

relationship between MI and peak rarefactional pressure

A

proportional

45
Q

what happens to MI if frequency goes up

A

goes down

46
Q

TI & MI max exposure time

A

6 & 1.9

47
Q

pulsed doppler output intensity

A

1140

48
Q

what poses a higher risk for thermal effects, scanned or non scanned

A

non scanned
MMODE
CW
PW

49
Q

what MI value has little risk

A

below 0.4

50
Q

ALARA

A

as low as reasonably achievable

keep ultrasound exposure minimized while optimizing diagnostic info

Physics3 (4 decks)

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