module 2: bioeffects, safety & power

Question 1

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

Answer 1

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

Question 2

whats the absolute unit of power?

Answer 2

watt(joule)

Question 3

whats the relative unit of power

Answer 3

decibels

Question 4

whats power determined by

Answer 4

the pulser

Question 5

what does power default to?

Answer 5

100% or zero dB

Question 6

output value for PW

Answer 6

1140mW/cm

Question 7

define amplitude

Answer 7

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

Question 8

intensity

Answer 8

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

Question 9

whats the relationship between intensity and power?

Answer 9

proportional

Question 10

intensity formula

Answer 10

i=p/a

Question 11

if area decreases what happens to intensity?

Answer 11

increases

Question 12

if area is halved wat happens to intensity?

Answer 12

doubles

Question 13

whats the relationship between intensity and amplitude?

Answer 13

I is proportional to amp^2

Question 14

if u double amplitude what happens to intensity

Answer 14

quadrupled

Question 15

whats the BUR

Answer 15

BUR=SP/SA

Question 16

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

Answer 16

high

Question 17

what does spacial peak increase with?

Answer 17

power or focusing

Question 18

what will cause spatial avg to increase?

Answer 18

increase in power

Question 19

whats the duty factor

Answer 19

df=ta/pa

Question 20

whats the pulse avg intensity

Answer 20

the avg of all intensities found within a single pulse

Question 21

what factors effect temporal intensities?

Answer 21

an increase in power or duty factor

Question 22

whats prf limited by?

Answer 22

depth

Question 23

whats the DF for CW

Answer 23

100%

Question 24

does CW have a lower or higher SPTA than PW applications

Answer 24

higher

Question 25

whats SPTP intensity also known as

Answer 25

instantaneous peak

Question 26

SPPA intensity is also known as....

Answer 26

max intensity or time averaged half maximum

Question 27

what sources do we get info from about bioeffects

Answer 27

- epidemiology - in vitro cell studies - animal

Question 28

whats the extensive resource for bioeffects info

Answer 28

the american institute of ultrasound in medicine (AIUM)

Question 29

what happens in an epidemiologic study

Answer 29

- 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

Question 30

animal studies

Answer 30

- no adverse effects observed if intensities are kept below 100mW/cm^2 for UNFOCUSED - below 1000 mW/cm^2 for FOCUSED

Question 31

two main categories for bioeffects

Answer 31

- thermal | - non thermal (mechanical_

Question 32

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

Answer 32

2 degrees

Question 33

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

Answer 33

16 mins

Question 34

what do mechanical effects include

Answer 34

radiation force and cavitation

Question 35

whats radiation force

Answer 35

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

Question 36

whats cavitation

Answer 36

production & behavior of bubbles in a liquid medium

Question 37

what can cavitation be divided into

Answer 37

stabe and transient

Question 38

whats stable cavitation

Answer 38

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

Question 39

ODS

Answer 39

output display standard

Question 40

quantities displayed with ods

Answer 40

thermal index | mechanical index

Question 41

define TI

Answer 41

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

Question 42

ti is divided into 3 categories

Answer 42

- TIS soft tissue - TIB bone near focus - TIC bone near surface for transcranial study

Question 43

mechanical index

Answer 43

likelihood that energy used will lead to cavitation

Question 44

relationship between MI and peak rarefactional pressure

Answer 44

proportional

Question 45

what happens to MI if frequency goes up

Answer 45

goes down

Question 46

TI & MI max exposure time

Answer 46

6 & 1.9

Question 47

pulsed doppler output intensity

Answer 47

1140

Question 48

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

Answer 48

non scanned MMODE CW PW

Question 49

what MI value has little risk

Answer 49

below 0.4

Question 50

ALARA

Answer 50

as low as reasonably achievable | keep ultrasound exposure minimized while optimizing diagnostic info