Ch. 24 Bioeffects Flashcards
amount of acoustic energy the patient receives
acoustic exposure
Lowest to highest intensities for various imaging modalities
gray scale, m-mode, color doppler, pulsed wave doppler
measures period, PRP, PRF and pulse duration, amplitude and beam shape
hydrophone
What devices measure output of ultrasound trdx by absorption
calorimeter, thermocouple, liquid crystal
uses absorption, the sound beams total power is calculated by measuring the temperature rise and time of heating
calorimeter
uses a tiny electric thermometer, temperature rise is related to the power of the sound beam at the particular location where the device is positioned
themocouple
change color based on temp, provides insight into the shape and strength of the sound beam
liquid crystal
the ______ must outweigh the _______
benefit, risk
what are standard intensities
50-500 W/cm2
Science of identifying and measuring the characteristics of an ultrasound beam that are relevant to its potential for producing biological effects
dosimetry
research that is preformed with in the living body of an an animal or plant
in vivo
research that is preformed outside the living body and in an artificial evironment, indicate high ultrasound intensities can cause genetic damage and cell death
in vitro
something has the potential to produce bioeffects, searches for a relationship between cause and effect
mechanistic approach
based on acquisition and review of information from patients or animals exposed to ultrasound, seeks a relationship between the exposure and response
empirical approach
bioeffects that result from temperature elevation
thermal
interaction of the sound waves with microscopic, stabilized, gas bubbles in the tissues
cavatation
two forms of cavatation
stable, transient
useful predictor of maximum temp increase under most clinical relevant conditions, combination of temp and exposure time, related to output power and properties of the tissue
thermal index
thermal index three forms
TIS, TIB, TIC (soft tissue, bone, calvarium-head).
TIS-, or soft tissue thermal index, assumes that sound is traveling in soft tissue
TIB-or bone thermal index, assumes that bone is at or near the focus of the sound beam (think fetal exams)
TIC-or cranial bone thermal index, assumes that cranial bone is in the sound beam’s near field
maximal heating is related to the beams ______ intensity
SPTA
Current FDA regulation for max intensity is
720 mW/cm2
A temp increase of up to ______C has not shown any bioeffects
A ___to___C rise in testicular temp can cause infertility
No fetal defects have been observed at temperatures less than
2
2 to 4
39C
pressure changes that cause the formation of bubbles, can produce severe tissue damage
cavitation
gaseous nuclei already present, expand and collapse with pressure, bubbles can absorb a large amount of acoustic energy
the fluids surrounding the cells undergo____and the cells are exposed to _____
stable cavitation
will stable cavitation bubbles bust
no, low MI
dependent on the pressure of the ultrasound pulse, produces highly localized violent effects (shock waves and high temp)
AkAs: inertial or normal cavitation
transient cavitation
will transient cavitation bubbles burst
yes
a calculated number related to the likelihood of harmful bioeffects from cavitation
mechanical index
Lower MI:
_______ cavitation
_______ pressure
_______ frequency
less, less, higher
Higher MI:
_______ cavitation
_______ pressure
_______ frequency
more, more, lower
indicator of cavitation, equal to the peak rarefractional pressure divided by the square root of the frequency
MI
ratio of acoustic power produced by the trdx and the power required to raise the temp of tissue 1 degree C, relates to attenuation (heat) and SPTA
TI
Preventing Bioeffects:
_______ the machine you use
Keep the exam as ____ as possible
Always start with lowest possible ______
Follow _______ principles
Use ________ _____ to optimize image
Keep track of ______ and ____ values on screen
Be extremely cautious when using doppler in ______ trimester of pregnancies
know, short, power, alara, receiver gain, mi, ti, first
Keep TI values below
1
Keep MI values below
1
branch of medicine associated with population studies, it is an empirical survey method,
epidemiology
