LECTURE 17 Flashcards
PRESENTATION OF FLOW INFORMATION IN COLOR, SUPERIMPOSED ON A 2D GREY SCALE IMAGE.
COLOR DOPPLER
- FORM OF PULSED DOPPLER
- MULTIPLE PULSES DOWN SCAN LINE
- INFO TAKEN FROM LOCATIONS ALONG EACH LINE
- INFO COMPOSITED TO YIELD IMAGE OF AREA OF INTEREST
HOW COLOR DOPPLER IS ACHIEVED.
NUMBER OF US PULSES PER LINE OF COLOR
PACKET SIZE
TYPICAL SIZE: 8-30
LARGER PACKET SIZES:
- BETTER VELOCITY MEASUREMENTS
- BETTER COLOR SENSITIVITY
- WORSE TEMPORAL RES. (DECREASED FRAME RATE)
SMALLER PACKET SIZES:
- WORSE VELOCITY MEASUREMENTS
- WORSE COLOR SENSITIVITY
- BETTER TEMPORAL RES.
INFORMATION YIELDED FROM COLOR DOPPLER:
- PRESENCE OF FLOW
- FLOW DIRECTION
- REFLECTOR VELOCITY (QUALITATIVE)
- REFLECTOR VARIANCE
ADVANTAGES OF COLOR DOPPLER:
- 2D INFO
- FACILITATES EXAM.
- PROVIDES: DIRECTION, CHARACTER, RELATIVE VELOCITIES, AMPLITUDE OF FLOW
DISADVANTAGES OF COLOR DOPPLER:
- POORER TEMPORAL RES.
- ALIASING
- CANNOT MEASURE EXACT VELOCITIES
REASONS FOR COLOR ALIASING:
- HIGH VELOCITIES
- COLOR SCALE SETTING TOO LOW
METHODS OF DISPLAYING COLORS IN RELATION TO VELOCITY INFO.
COLOR ASSIGNMENT MAPS
VELOCITY AND VARIANCE
- DARKER, DULLER COLORS = SLOWER VELOCITIES.
- BRIGHTER, LIGHTER COLORS = FASTER VELOCITIES.
VELOCITY MAP
- EXTRA COLOR ADDED (USUALLY GREEN)
- INCREASE OF VARIANCE = BRIGHTNESS OF GREEN INCREASES
- GREEN = DISTURBED, TURBULENT FLOW
- USED IN CARDIAC IMAGING
VARIANCE MAP
- USED FOR COLOR DOPPLER
- CALCULATES AVERAGE SHIFT OF ECHOS FROM SAME PACKET.
- SIMILAR TO FFT (NOT AS ACCURATE BUT FASTER)
- QUALITATIVE INFO.
AUTOCORRELATION!!!
AKA PHASE SHIFT AUTOCORRELATION.
- NEWER METHOD OF DOPPLER SHIFT ANALYSIS
- FASTER THAN FFT
- CAN PINPOINT SPECIFIC ECHO OUT OF MANY IN TIME
TIME DOMAIN PROCESSING
COLOR POWER DOPPLER AKA
COLOR DOPPLER ENERGY
ULTRASOUND ANGIO
COLOR POWER ANGIO
DIFFERENCES BETWEEN COLOR DOPPLER AND POWER DOPPLER:
POWER DOPPLER:
- ESTIMATES POWER OF DS WITHIN SPECIFIC REGION
- POWER OF SHIFT RELATES TO CONCENTRATION OF RBCs (REFLECTOR)
- INFO BASED ON STRENGTH OR POWER OF REFLECTORS, NOT VELOCITY
ADVANTAGES OF POWER DOPPLER:
- NOT ANGLE DEPENDANT
- NOT SUBJECT TO ALIASING.
- GREATER SENSITIVITY TO FLOW.
DISADVANTAGES OF POWER DOPPLER:
- NOT DIRECTION SENSITIVE
- CANNOT DETECT VELOCITY
- CANNOT DEPICT FLOW CHARACTERISTICS
- MORE TIME
- FLASH ARTIFACTS
