*bioeffects Flashcards
bioeffects categorized as (2)
thermal or mechanical
extent of thermal effects is determined by (5)
- output power
- frequency
- exposure time
- focal zone position
- decreased field of view (increased line density)
mechanical bioeffects include (2)
cavitation
radiation
cavitation bioeffect can be classified as (2)
stable or transient
TI means
sound increased tissue by 1 degree celcius
TI is most commonly associated with what variation in intensity (SPTP, SPPA, SPTA, SATP, SAPA, SATA)
SPTA
AIUM states no adverse effects have been observed for an UNfocused beam having a SPTA < ??
unfocused beam <100 mW/cm2
AIUM states no adverse effects have been observed for a FOCUSED beam having a SPTA < ??
<1 w/cm2
what is the typical output intensity of a beam?
<1 w/cm2
order of intensity graded from highest to lowest
SP TP SP PA SP TA SA TP SA PA SA TA
factors that cause changes in intensity (6)
- pulse length
- depth of focus (beam is narrower)
- multiple focal zones
- frame rate
- line density
- PRF (increase in duty factor)
AIUM standard for TI in soft tissue
TIS <2
AIUM standard for TI in bone
TIB <1.5 (higher attenuation in bone) - fetal bone at risk
stable vs transient cavitation
stable = oscillating bubbles create waves / shear forces on nearby cells transient = oscillating bubbles POP
mechanical index is proportionatal to
peak rarefractional pressure
mechanical index is inversely related to
frequency
a hydrophone measures
output of diagnostic US images (acoustic pressure)
Weakest to strongest intensity ultrasound (4)
- 2D ultrasound
- M mode
- colour doppler
- PW spectral / duplex pulsed
FDA ISPTA =
720 mW/cm2
AIUM standard for mechanical index < ?
<1.9
*Transient cavitation is most dependent on the
Ultrasound pulse
*Cavitation is the interaction of the sound wave with:
Microscopic gas bubbles found in tissues
*Which organization regulates US equipment
FDA
*Cavitation is the result of
Pressure changes in soft tissue causing the formation of gas bubbles
