doppler Flashcards
3 common types
- colour
- pulsed wave
- power
what information does colour doppler give us
- information about presence of blood flow and it’s direction
- adding contrast in CT
red colour doppler
towards the probe
blue colour doppler
away from the probe
what information does pulsed wave doppler give us
direction and velocity of blood flow in vessel
what is pulsed wave doppler commonly used in
obstetrics to assess function of placenta
what is power doppler used for
- to assess blood flow
- not the direction of blood flow, only strength/ power of blood flow
what are the potential thermal effects of US
- as US passes through tissue some energy lost through absorption
- absorbed energy converted to heat - causing tissue temp to rise
- amount of energy absorbed depends on how attenuating tissue is
at what temperature does heat cause tissue damage
above 1.5 degrees
where is the highest effect in tissues
- bone/ bone interface
- where there is minimal blood circulation
what are the biochemical effects of US
- produces oscillating pressure wave through tissue
- can cause formation of microbubbles in tissues
what happens if microbubbles oscillate too much in size
they can collapse causing cavitation
- cavitation generates high pressure and increased temperatures in local tissues causing physical damage
how do we measures risks
- use of safety indices
- OUTPUT DISPLAY STANDARDS (ODS)
- for each exam, there is an on-screen display indicating risks
what is thermal index defined as
amount of power needed to raise tissue temp by 1 degree
what happens if you are near or over limit on thermal index
reduce scan time or adjust the settings
