Biological Effects & Safety

Question 1

What are biological effects on ultrasound?

Answer 1

Potential adverse changes in biological tissues caused by US exposure

Question 2

What are 3 advantages of indices for biological safety?

Answer 2

1) standardisation of output info between manufacturers
2) visibility of output values relevant to potential bioeffects from US
3) availability of into the implement ALARA

Question 3

Describe thermal effects

Answer 3

the absorption of US caused by heating of tissues

Question 4

What are some factors that determine how much temperature rises?

Answer 4

-US intensity
-frequency
-absorption properties
-conduction properties
-blood perfusion of tissues

Question 5

What is the equation for TI?

Answer 5

TI=W/Wdeg
(W=current acoustic power output)
(Wdeg=power required to raise temp 1 degree)

Question 6

What is the mechanical index equation?

Answer 6

MI=Pr/f
(Pr=peak rarefractional pressure)
(f=frequency)

Question 7

List two types of cavitation

Answer 7

Stable and transient

Question 8

What is stable cavitation?

Answer 8

Creation of gas bubbles that oscillate with sound

Question 9

What is transient cavitation?

Answer 9

Oscillations grow strong that bubbles collapse causing disruption and interference of cell function

Question 10

List some factors influencing cavitation

Answer 10

-amplitude
-presence of gas bubbles
-transducer frequency
-exposure time
-PRF
-mode of operation

Question 11

What is ALARA?

Answer 11

as low as reasonably achievable

Question 12

List some ways to follow ALARA

Answer 12

-correct exam presets
-adjust power to lowest. setting
-monitor MI and TI
-lift transducer when stationary
-minimize overall scanning time