209 quiz (wk9) Flashcards
Color Doppler superimposes Doppler shift information onto a 2D image with color. The color represents ____ of flow.
direction
color Doppler reports
average/mean velocity
color Doppler imaging is a pulsed-wave device, and is therefore bounded by the same limitations such as _____
aliasing
What are 3 components of color?
hue: the perceived color, lowest (red) yo highest (violet)
saturation: shade of the original color, “saturated” = pure hue & white = less hue i.e. red = very saturated, and pink = less saturated
brightness (luminance/intensity): from dull to brilliant
color information obtained at many points on the scan lines within the gate. what is this called?
ensemble length
or
packet size
the greater the ensemble length, the better to detect slow flow and the more accurate the mean velocity. what is the effect on frame rate?
color Doppler with large gates cause a significant decrease in the frame rate (frame rate killer!)
When ensemble length increases…
flow sensitivity _____ & frame rate _____
increases, decreases
*ensemble length = pocket size = the number of pulses per scan line
What is color persistence?
also called: smoothing
It averages frames of color information (let color linger longer to fill the color in the vessel)
*good for slow flow and poor color filling
*for echo, color persistence should be 0 due to rapid movement/flow of blood
color Doppler instruments use ______ to process signal information
auto-correlation
what are the characteristics of autocorrelation?
- faster technique than FFT but not as accurate as FFT
- not as detailed
- no information on peak velocities
what information does autocorrelation provide?
- mean velocities
- direction of flow (positive or negative shift)
- variance
what does power Doppler do?
identifies amplitude of Doppler shift (*NOT speed or direction)
power Doppler also known as:
- CDE (color Doppler energy)
- power angio
- amplitude Doppler
what are the pros of power Doppler?
- very sensitive: good to detect slow flow & small vessels
- nearly independent of beam angle
what are the cons of power Doppler?
due to its sensitivity, adversely affected by motion = flash artifact
what does affect power Doppler signal?
the density/concentration of RBCs determines the amplitude
more RBCs = increased amplitude = brighter the image
Power Doppler does not detect _____
It detects only ________
- velocity or flow direction
- presence and strength of the shift
what is FFT?
fast fourier transform
what does FFT do?
a mathematical process to display various velocities of RBCs traveling through vessels as a graph of velocities over time. spectral analysis allow us to identify the individual components that make up the returned signal, and FFT rapidly transforms a function into components we can identify
Doppler Artifacts - noise resulting from wall or organ motion - eliminated by wall filters (high pass filter) what is it?
clutter
which direction does the blood flow?
right to left
what does this image indicate?
stenosis
color Doppler aliases when Doppler shift exceeds _____ *same as spectral Doppler
1/2 PRF
*color aliasing at high PRF settings can be used to pinpoint potential areas of stenosis
what is wrong with this image?
improper color box steering
