Vascular (doppler) Flashcards
Which parameter would profoundly affect the doppler equation?
-velocity of blood flow
Types of Doppler
- CW
- spectral (duplex)
- spectral and colour (triplex)
- power
What should angle correct be at?
60 degrees
What can we do to improve our doppler angle?
- heel/toe
- angle correct (60 degrees)
- change colour box angle
- change window of insonation
Where should the spectral baseline be positioned?
-1/3 from the bottom of spectrum (so we do not cut off diastolic flow)
What is the direction of flow that is above the baseline?
-toward transducer
What will a lg sample volume depict?
- unclean signal
- lots of velocities
What will a sm sample volume depict?
-clean signal
How does angle correct affect the signal?
Consistency Within:
- entire exam
- recheck exams
- patient to patient
How much of the display should the spectral trace show?
-2/3rds
What adjusts the scale?
PRF
What happens if spectral wall filter is too low?
-wall thump from arterial systole
What happens if spectral wall filter is too high?
-eliminates echoes within waveform
What causes aliasing?
- PRF too low
- increase the velocity scale
Where should the colour bar be set at for colour map? What will happen if you raise or lower the bar?
- in the middle
- inadequate colour representation
What happens if the colour baseline is too low?
-only higher velocity flow will be shown
What happens if the colour baseline is too high?
-only lower velocity flow will be shown
What does red flow indicate?
-flow toward transducer
What does blue flow indicate?
-flow away from transducer
What happens if your colour box is too big?
- decreased frame rate
- poor resolution of colour
What happens if your colour box is reduced to the vessel?
- increased frame rate
- improved image quality
How should you steer the colour box?
-parallel to flow (0 or 180 degrees)
What may you have to do with the colour box at a bifurcation?
-angle the colour box twice to show each branch (vessels are usually not parallel at bif)
What will happen if a venous setting is used to visualize arterial flow?
-aliasing
What happens if colour gain is set too low?
-no flow
what happens if colour gain is set too high?
- flaring
- bleeding outside vessel (false echoes)
Advantages of Power Doppler
- no aliasing
- angle independant
- increased sensitivity (detects low flows)
- useful for tortuous vessels
- increased accuracy for grading a stenosis
Disadvantages of Power Doppler
- no velocity
- no direction
- poor temporal resolution (because it is so sensitive)
