Chapter 19 Pt. 2 Flashcards
The most common error associated with Doppler Ultrasound
Aliasing
High velocity flow in one direction that is incorrectly displayed as traveling in the opposite direction is?
Aliasing
The very top of the display is called?
Nyquist limit
Part of the spectrum appearing at the bottom
Aliasing
The highest Doppler frequency or velocity that can be measured without the appearance of aliasing
Nyquist frequency (limit)
Nyquist limit is ___________ of the pulse repetition frequency (PRF)?
half
Two ways to avoid aliasing are:
- raise the nyquist limit
2. reduce the Doppler shift
Higher frequency transducers create________ aliasing,
more
Higher frequency transducers create _________Doppler shifts and lower frequency transducers create ____ Doppler shifts
Higher, lower
5 techniques used to avoid aliasing
- Adjust the scale to its max
- Select a new ultrasonic view with a shallower sample volume
- Select a lower frequency transducer
- Use baseline shift
- Use continuous wave doppler
Color Doppler measures. . .
average or mean velocity
Spectral Doppler (continuous and pulsed) measures
peak velocity
In Velocity mode the colors above the black stripe indicate?
Blood cells moving towards the transducer, Positive Doppler shift
Colors below the black stripe indicate?
Blood cells moving away from the transducer, Negative Doppler shift
The black region in the middle of the color map indicates:
No Doppler shift
Variance mode distinguishes
laminar and turbulent flow
In variance mode, colors of the left side of the map indicate?
Laminar flow
In Variance mode, colors on the right side of the map indicate?
Turbulent flow
Multiple pulses used in color Doppler to accurately determine blood velocity
Packet or ensemble
Power mode is
Nondirectional Doppler
Power Doppler is also called
energy mode or color angio
On Spectral displays, low frequency Doppler shift artifacts are called
Clutter
With color Doppler low frequency Doppler shift artifacts are called?
Ghosting
Wall filters are used to eliminate what?
Clutter
a special form of “mirror” image artifact, that arises only with spectral Doppler
Crosstalk