20 Bioeffects

Question 1

What is a hydrophone?

Answer 1

A small needle with a piezoelectric crystal at its end that can quantitate amplitude, period, pulse duration and pulse repetition period

Question 2

What is a calorimeter?

Answer 2

A transducer which turns acoustic energy into heat

Measure total heat gain and the time that it took to obtain the heat, the total power of the US beam can be calculated

Question 3

What is a thermocouple?

Answer 3

A small device embedded in absorbing material that measures the temp change from US energy being converted into heat
The intensity at specific locations are measured

Question 4

What is dosimetry?

Answer 4

Science of identifying and measuring those characteristics of an US field which are especially relevant to its potential for producing biological effects

Question 5

What are the bioeffects intensity limit?

Answer 5

SPTA
100mW/cm^2 unfocused
1W/cm^2 or 1000mW/cm^2 focused

Question 6

What has the greatest effect on patient exposure?

Answer 6

Exam duration

Question 7

What are ouput intensities used with?

Answer 7

Highest - pulsed Doppler

Lowest - gray scale imaging

Question 8

What is the mechanistic approach for study techniques?

Answer 8

Propose a specific physical mechanism that could produce bioeffects
Theoretical analysis to estimate scope of bioeffects at various exposures
Identify “cause-effect” relationship

Question 9

What is the empirical approach for sturdy techniques?

Answer 9

Acquire/review data from pts or animals
Correlate exposure and effects
Identify “exposure-response” relationship

Question 10

What is thermal mechanism?

Answer 10

Temp elevation via absorption resulting from interaction of biologic tissue and US

Question 11

Which tissue is an absorber?

Answer 11

Bone

Question 12

Which tissue is considered potentially at greater harm than in adults?

Answer 12

Fetal soft tissues, especially adjacent to bone

Question 13

Which intensity is related to tissue heating?

Answer 13

SPTA (spatial peak, temporal average)

Question 14

At what temperature is considered potentially harmful to a fetus?

Answer 14

> 41 C

Question 15

What is the thermal index?

Answer 15

Number related to tissue heating

TI of 2 = elevation of 2 degrees C may occur

Question 16

What is TIS?

Answer 16

Thermal index calculated for sound beam travel in soft tissue

Question 17

What is TIB?

Answer 17

Thermal index calculated for a sound beam with it’s focus in bone

Question 18

What is TIC?

Answer 18

Thermal index calculated for a sound beam in cranial bone

Question 19

What is gaseous nuclei?

Answer 19

Microbubbles may be excited by US - shrinks and expands the bubble

Question 20

What is the mechanical index?

Answer 20

Number related to cavitation

MI = peak rarefaction pressure/square root frequency

Question 21

What can cause a higher mechanical index?

Answer 21

Peak rarefaction pressure

Lower frequency sound

Question 22

What creates a cavitation?

Answer 22

Microbubbles that get bigger during rarefactions that shears bubbles apart

Question 23

Where is cavitation most likely to occur?

Answer 23

Lung

Question 24

What is a stable cavitation?

Answer 24

Bubbles do not burst when exposed to acoustic waves of small amplitude

Question 25

What are the effects of a stable cavitation?

Answer 25

Shear stresses and micro streaming in surrounding fluid

Question 26

What is a transient cavitation?

Answer 26

Bubbles that expand during rarefactions and burst

Question 27

What are the effects of a transient cavitation?

Answer 27

Highly localize violent effects:
Enormous pressures
Colossal temps

Question 28

What are epidemiological studies?

Answer 28

Population studies

Question 29

What is the best study type?

Answer 29

Prospective and randomized

Question 30

What are limitations to epidemiologic studies?

Answer 30

Often retrospective
Ambiguities
Other risk factors