What is a microprobe?
small transducer that measures the characteristics of a sound beam
What is another name for a microprobe?
hydrophone
How is a hydrophone used?
it is placed in the sound beam and a voltage from the hydrophone relates to the sound beams pressure and is displayed on the oscilloscope
Does a hydrophone measure at specific locations?
yes
What is the benefit of using a hydrophone?
determines sound beams shape
can measure intensity and output from signal
What can a hydrophone measure?
period, PRP, PRF and pulse durationintensity
What can be measured with a calibrated hydrophone?
intensity
What is typically lowest when performing gray scale imaging?
transducer output
What is typically higher with pulsed doppler?
transducer outputt
What is radiation force?
a force created by the transducers sound beam
What is a feedback microbalance?
measured force of the beam relates to the power in the beam
What is a Schlieren?
a shadowing system that allows you to view the shape of a sound beam in a medium
What is acousto-optics?
interaction of sound and light that allows us to view the sound beam in the medium
What are three devices that measure absorption?
calorimeter
thermocouple
liquid crystal
What is absorption?
the conversion of sound energy to heat
What is a calorimeter?
measures the power of a sound beam through absorption
How does a calorimeter measure the sound beams power?
the temperature rise and time of heating
What is the difference between a thermocouple and calorimeter?
a thermocouple measures the beams power at a specific location, whereas the calorimeter measures the power of the entire beam
How do liquid crystals show beams power?
color change
What must be true about the risk of ultrasound?
that the benefit outweigh the risks
What is dosimetry?
the science of identifying and measuring the characteristics of an ultrasound beam that are relevant to its potential for producing biological effects
What is in vivo?
research performed within a living body
What is research performed within a living body?
in vivo
What is in vitro?
research performed outside a living body
What is research performed outside a living body?
in vitro
What can in vitro research indicate about intensities?
that the sound intensities are very high and can cause genetic damage and cell death
Is in vitro bioeffect research important?
yes
What are the two techniques used to study bioeffects?
mechanistic and empirical
What is a mechanistic approach?
searches for a relationship between cause and effect
What is an empirical approach?
searches for a relationship between exposure and response
Which approach - mechanistic or empirical is best with regard to studying bioeffects?
when they are in agreement
What are the two mechanisms of bioeffects?
thermal and cavitation
What is another term for cavitation?
nonthermal
What is the thermal mechanism of bioeffect?
proposes that bioeffects result from tissue temperature elevation
What is the thermal index?
a predictor of max temp increase under clinically relevant conditions
What are the 3 thermal indices
soft tissue index - TIS
bone thermal index - TIB
cranial bone thermal index - TIC
What type tissue elevation do thermal indices estimate?
in vivo
What is the empirical finding associated with thermal mechanism?
a combination of temperature and exposure time determine liklihood of harmful effects
What is the maximal heating combination?
SPTA
What is the nonthermal mechanism?
consist of cavitation and radiation force
What is cavitation?
interaction of sound waves with microscopic, stabilized gas bubbles in the tissues
What are the gas bubbles known as in cavitation?
gaseous nuclei
What is radiation force?
sheer stresses and streaming of fluids can distort biologic structures
What are the two forms of cavitation?
stable and transient
What is stable cavitation?
when gaseous nuclei expand and contract, but DO NOT burst
What is transient cavitation?
when the microbubbles burst
Why are the destructive effects of transient cavitation no considered clinically important?
because they are highly localized and only affect a few cells
What is a mechanical index?
a calculated number related to the liklihood of harmful bioeffects from cavitation
What are the characteristics of a higher MI?
more cavitation
more pressure
lower frequency
What are the characteristics of a lower MI?
less cavitation
less pressure
higher frequency
What is epidemiology?
branch of medicine associated with population studies
What type of study is epidemiology?
empirical
What are the limitations of epidemiologic studies?
retrospective
ambiguous
mulitple risk factors
What makes an epidemiologic study better?
prospective and randomized
What causes the greatest risk to electrical safety with ultrasound?
electrical shock from a cracked transducer housing
What does ALARA stand for?
As Low As Reasonably Achievable
What is cavitation?
the interaction between sound waves and small gas bubbles that exist in tissues
What are additional names for normal cavitation?
inertial and transient
What two mechanisms are likely to induce bioeffects?
thermal and mechanical