Module 3 : Doppler Principles Flashcards
doppler principle
change in frequency of sound, light, or other waves caused by the motion of the source or the observer
Doppler effect - ultrasound
- change in frequency of sound caused by the motion of red blood cell (relative to transducer)
- difference between transmitted frequency (transducer frequency) and received frequency (reflected or echo frequency)
movement toward transducer
- echo frequency larger than transducer frequency
- ANTEGRADE FLOW
movement away transducer
- echo frequency will be smaller than transducer frequency
- RETROGRADE FLOW
methods used to detect and analyze doppler shifts
- color flow
- spectral waveforms
- audible sounds
doppler shift basic equation
Fd = Fr - Fo
doppler shift dependent factors
- transmitted (sent) frequency
- velocity of the moving blood
- angle between the moving blood and the sound beam
complex doppler shift equation
Fd = 2 x Fo x V x cos0 / c
angle of insonation
- MOST IMPORTANT FACTOR that influences calculation of the DOPPLER SHIFT
- ideal orientation would be at an angle 0 (largest doppler shift) cos 0 = 1 THIS IS VIRTUALLY IMPOSSIBLE TO ATTAIN EXCEPT IN HEART
- when the blood flow is at an angle of 90 (cos 0 = 0) there is NO SHIFT DETECTED so NO MEASURABLE RETURNING FREQUENCY
correct doppler angle
30 - 60 to the blood vessel
- REDUCE MARGIN OF ERROR, REPRODUCIBLE
doppler angle greater than 60
- doppler shifts difficult to quantify due to large margin of error
- lead to errors in estimates of peak frequency
venous flow assessment
- angle is not important
- velocities are not used
- angle correct is set to zero
continuous wave doppler (CW)
- continuously excited
- contains two piezoelectric elements
+ one transmitting, one receiving - no image produced
- impossible to select a specific depth and region to sample
- knowledge of the anatomy
- advantage : sample high velocity with no aliasing
pulsed wave doppler
- sound pulses produced by the transducer at regular intervals
- isolate signals from a desired depth
- PRF limits measurement of high velocities by producing aliasing
- pulsed doppler instruments combined with real time B Mode
- B mode allows visualization of structure
nyquist limit
- doppler shift exceeds 1/2 the PRF
- occurs when insufficient amount of time to collect the returning signal information before next pulse is sent
spectral display
- doppler shift frequencies are separated into individual frequency components using FAST FOURIER TRANSFORM
- displayed as a spectrum or “image” of the doppler frequency
+ time = horizontal axis (x)
+ velocity = vertical axis (y)
+ brightness of pixel - the z axis ( proportional to the # of rbc’s)
Quadrate detection
- processes the signal as a (+) or (-) value depending on direction of flow relative to the doppler beam
peak systole
- peak velocity of the cardiac cycle
dicrotic notch
- early diastole flow reversal signifies closing of the aortic valve
end diastole
- velocity at end diastole just prior to systole
envelope
- white line that outlines the changes in frequencies
- determined by the number of blood cells in a sample
window
- Clear area below the envelope that displays no frequencies
spectral broadening
- ” thickness” of the white line up to “filing in” of window
Pulsatility
- relationship of peak minimum velocities over the mean velocity of an entire cycle
- can be low, moderate, and high
resistivity
- relationship of peak systolic velocity to end diastolic velocity
- low or high resistance waveforms
low resistivity
- has diastolic flow above zero
- organs that need flow constantly have low resistance wave forms
- high resistance
- usually shows reversed flow in early diastole
laminar flow
- MOST COMMON
- all blood particles move forward
- blood moves in concentric layers
- highest velocities at the centre and crease in speed as you move toward the wall
- AVERAGE VELOCITY IS 1/2 THE MAX VELOCITY
- stationary layer against vessel wall
- parabolic, plug, blunt
factors affecting flow
- velocity
- change in diameter
- curves, bifurcation, branch origins
disturbed pattern
- friction and energy loss disrupt laminar flow
- still forward flow but with diverging direction
- mild version of turbulence but still considered normal
turbulent
- non linear flow
- multiple directions
- multiple velocities
- considered abnormal
spectral optimization
- gain, baseline, wall filter, scale/prf/velocity range,
gain - spectral
- adjust to allow visualization of signal without unwanted noise
- too high of gain will create false spectral broadening or unwanted noise artifacts
baseline
- adjust to allow entire spectral signal to be seen
- too high of baseline may cause aliasing
wall filter
- eliminates low frequency noise
- adjust to ensure low velocities not missed
scale, prf, velocity range
- adjust to demonstrate peak and minimum velocities
- too low of prf will cause aliasing
- increase prf to correct aliasing
power doppler
- power or intensity measured instead of direction
- based on density of RBC not speed
- no ailiasing
- more sensitive and no doppler angle
- asses small vessels with little flow
- less subject to blooming
- ## slow frame rate
color doppler
- stationary reflectors make up gray scale portion
- interference with moving RBCs create doppler shift
- represents mean frequency
- doppler shifts are cooler coded corresponding to direction and velocity
- hundreds of sample lines
- autocorrelation
- qualitative not quantitative
- reduces prf
- fram rate decrease
color flow display
- map
- optimization of color
maps
- bar or wheel
- various color maps
- SHIFTING HUE MOST COMMON (diff colours diff frequency)
- CHANGING SHADE (saturation) same color but different shade
- VARIANCE MAPS tag certain frequencies
optimization of color
- velocity range
- doppler angle
- field of view
- color box size
- color scale
- gain
- color priority
- wall filter
- baseline
- maps
- power
- invert
velocity range- color
- high flow / high prf and low flow/ low prf
doppler angle
- steer probe and or color box
field of view
- greater depth to area of interest degrades image and ability to display flow
color box size
- smaller is better , height has no effect on frame rate
- width decrease frame rate
color scale prf
- to low prf result in aliasing
- to high prf no flow detected or vessel not filled in
gain - color
- insufficient gain result in poor color fill in
- increase till bleeding then go back to threshold
color priority
- image processing priority tray scale vs color
wall filter - color
- high setting may eliminate low flow info
baseline - color
- adjusted from middle of scale to accommodate more red or blue velocities
maps - color
- ise map to help assess flow
power / angio
- in case of trickle or low flow
invert
- observe orientation of vessel to transducer
color artifactis
- mirror image
- blooming
- color flash
- aliasing
- visible bruit
mirror image artifact
- seen in gray scale, color and spectral
- mirror of real vessel
blooming/ bleeding
- due to high gain setting may obscure pathology
color flash
- transmitted pulsations or adjacent motion will cause color to flash outside of vessel
aliasing
- inappropriate prf setting may cause color to exceed high velocity threshold
visible bruit
- soft tissue vibration adjacent to area of high flow
