Lecture 22 Part 2 Flashcards
Aliasing depends
Nyguist limit
Nyquist limit is =
Half the PFR
Higher velocities are ________ alias
More likely to alias
Aliasing will often show within a ______ is PRF is set too _____
stenosis
low
Areas will show aliasing highlights areas
Of highest velocity
This is using it for good
Gain
Just like 2D we can amplify the returning echo voltages e
We want wall to wall filling
Priority aka
Echo write priorite
Priority is
The gray scale vs colour threshol
Echoes ______ cut off amplitude will show as colour
Below
Stronger echoes show as grayscale
Any movements in the tissue will produce
Doppler shifted colour
(Tissue vibration, vessel movement)
Aka clutter
Clutter has ______ velocities
Lower
____ will eliminate clutter, as it sets a _______
Wall filter
Cut off point
What does wall filter do
Filters out noise -> non useful info
Keeps the useful signal
Arterial speed tend to be _______ than venous speeds
Higher
If you increase PRF too much it can result in
Echo misplacement
Can increase the PRF to help with
Aliasing
Tortuous vessels may look like
Flow reversal
Aliasing
Higher freq are used for doppler leading to higher ______
Attenuation
A _____ patient may be difficult to get a good signal on
Larger
Power doppler
Determined by concentration of moving RBCs
We can display just power but shows only _____ of flow
Doesnt show _____
Presence
Velocity, direction, flow character info
Pros of power doppler
Increased sensitivity by small flow and small or deep vessles
Angle dependent
No aliasing
Cons of power doppler
No speed/ cannot quantify
No direction
No flow character to assess stenosis
Duplex scanning
We update between doppler and gray scale -
Transducer does one at a time but is simultaneous in the way it rapidly switched between the two
