20 Bioeffects Flashcards
What is a hydrophone?
A small needle with a piezoelectric crystal at its end that can quantitate amplitude, period, pulse duration and pulse repetition period
What is a calorimeter?
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
What is a thermocouple?
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
What is dosimetry?
Science of identifying and measuring those characteristics of an US field which are especially relevant to its potential for producing biological effects
What are the bioeffects intensity limit?
SPTA
100mW/cm^2 unfocused
1W/cm^2 or 1000mW/cm^2 focused
What has the greatest effect on patient exposure?
Exam duration
What are ouput intensities used with?
Highest - pulsed Doppler
Lowest - gray scale imaging
What is the mechanistic approach for study techniques?
Propose a specific physical mechanism that could produce bioeffects
Theoretical analysis to estimate scope of bioeffects at various exposures
Identify “cause-effect” relationship
What is the empirical approach for sturdy techniques?
Acquire/review data from pts or animals
Correlate exposure and effects
Identify “exposure-response” relationship
What is thermal mechanism?
Temp elevation via absorption resulting from interaction of biologic tissue and US
Which tissue is an absorber?
Bone
Which tissue is considered potentially at greater harm than in adults?
Fetal soft tissues, especially adjacent to bone
Which intensity is related to tissue heating?
SPTA (spatial peak, temporal average)
At what temperature is considered potentially harmful to a fetus?
> 41 C
What is the thermal index?
Number related to tissue heating
TI of 2 = elevation of 2 degrees C may occur
What is TIS?
Thermal index calculated for sound beam travel in soft tissue
What is TIB?
Thermal index calculated for a sound beam with it’s focus in bone
What is TIC?
Thermal index calculated for a sound beam in cranial bone
What is gaseous nuclei?
Microbubbles may be excited by US - shrinks and expands the bubble
What is the mechanical index?
Number related to cavitation
MI = peak rarefaction pressure/square root frequency
What can cause a higher mechanical index?
Peak rarefaction pressure
Lower frequency sound
What creates a cavitation?
Microbubbles that get bigger during rarefactions that shears bubbles apart
Where is cavitation most likely to occur?
Lung
What is a stable cavitation?
Bubbles do not burst when exposed to acoustic waves of small amplitude
What are the effects of a stable cavitation?
Shear stresses and micro streaming in surrounding fluid
What is a transient cavitation?
Bubbles that expand during rarefactions and burst
What are the effects of a transient cavitation?
Highly localize violent effects:
Enormous pressures
Colossal temps
What are epidemiological studies?
Population studies
What is the best study type?
Prospective and randomized
What are limitations to epidemiologic studies?
Often retrospective
Ambiguities
Other risk factors
