Presentation of flow information in color, superimposed on two dimensional grey scale image.
COLOR DOPPLER
Color doppler is formed of:
PULSED DOPPLER
Number of ultrasound pulses per line of color.
PACKET SIZE
- Better velocity measurements.
- Better color sensitivity.
- Worse temporal resolution (decreased frame rate)
LARGER PACKET SIZES
INFORMATION YIELDED:
- Pressure of flow.
- Flow direction.
- Reflector velocity. (qualitive)
- Reflector variance.
ADVANTAGES:
- Provides two dimensional information.
- Facilitates examination
- Provides info. - direction, character, relative velocities, amplitude of flow
DISADVANTAGES:
- Poorer temporal resolution.
- Subject to aliasing.
- Cannot measure exact velocities.
COLOR ALIASING DUE TO HIGH VELOCITIES OR COLOR SCALE SETTING TOO LOW.
- Colors wrap around color bar.
- Shows positive as negative.
Methods of displaying colors in relation to velocity.
COLOR ASSIGNMENT MAPS
- Darker, duller color represent slower velocities .
- Brighter, lighter colors represent faster velocities,
VELOCITY MAP
- Another color is added (usually green)
- With increase in variance, brightness of green increases.
- Color green signifies disturbed, turbulent flow-Used in cardiac imaging.
VARIANCE MAP
COLOR COMPONENTS
HUE- COLOR
SATURATION - DILUTED W/WHITE
LUMINANCE - BRIGHTNESS OF HUE AND SATURATION
AUTOCORRELATION
PHASE SHIFT AUTOCORRELATION
- Used for color doppler.
- Calculates AVERAGE shift of echos from same packet.
- Similar, but faster than FFT.
- QUALITATIVE INFO.
- Newer method of Doppler shift analysis.
- Faster than FFT.
- Can pinpoint specific echo out of many in time.
TIME DOMAIN PROCESSING
COLOR POWER DOPPLER
COLOR DOPPLER ENERGY, ULTRASOUND ANGIO, COLOR POWER ANGIO
- Estimates power of doppler shift in specific region.
- Power of shift relates to concentration of reflector.
- Info based on strength or power of reflectors.
ADVANTAGES OF POWER DOPPLER
- Not angle dependent.
- Not subject to aliasing.
- Greater sensitivity to flow.
DISADVANTAGES OF POWER DOPPLER
- Not direction sensitive.
- Cannot detect velocity.
- Cannot depict flow characteristics.
- Takes more time.
- May have more trouble with flash artifacts.
