Module 3 : Doppler Principles Flashcards
1
Q
doppler principle
A
change in frequency of sound, light, or other waves caused by the motion of the source or the observer
2
Q
Doppler effect - ultrasound
A
- 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)
3
Q
movement toward transducer
A
- echo frequency larger than transducer frequency
- ANTEGRADE FLOW
4
Q
movement away transducer
A
- echo frequency will be smaller than transducer frequency
- RETROGRADE FLOW
5
Q
methods used to detect and analyze doppler shifts
A
- color flow
- spectral waveforms
- audible sounds
6
Q
doppler shift basic equation
A
Fd = Fr - Fo
7
Q
doppler shift dependent factors
A
- transmitted (sent) frequency
- velocity of the moving blood
- angle between the moving blood and the sound beam
8
Q
complex doppler shift equation
A
Fd = 2 x Fo x V x cos0 / c
9
Q
angle of insonation
A
- 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
10
Q
correct doppler angle
A
30 - 60 to the blood vessel
- REDUCE MARGIN OF ERROR, REPRODUCIBLE
11
Q
doppler angle greater than 60
A
- doppler shifts difficult to quantify due to large margin of error
- lead to errors in estimates of peak frequency
12
Q
venous flow assessment
A
- angle is not important
- velocities are not used
- angle correct is set to zero
13
Q
continuous wave doppler (CW)
A
- 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
14
Q
pulsed wave doppler
A
- 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
15
Q
nyquist limit
A
- doppler shift exceeds 1/2 the PRF
- occurs when insufficient amount of time to collect the returning signal information before next pulse is sent
16
Q
spectral display
A
- 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)
17
Q
Quadrate detection
A
- processes the signal as a (+) or (-) value depending on direction of flow relative to the doppler beam
18
Q
peak systole
A
- peak velocity of the cardiac cycle
19
Q
dicrotic notch
A
- early diastole flow reversal signifies closing of the aortic valve
20
Q
end diastole
A
- velocity at end diastole just prior to systole
21
Q
envelope
A
- white line that outlines the changes in frequencies
- determined by the number of blood cells in a sample
22
Q
window
A
- Clear area below the envelope that displays no frequencies
23
Q
spectral broadening
A
- ” thickness” of the white line up to “filing in” of window
24
Q
Pulsatility
A
- relationship of peak minimum velocities over the mean velocity of an entire cycle
- can be low, moderate, and high
25
resistivity
- relationship of peak systolic velocity to end diastolic velocity
- low or high resistance waveforms
26
low resistivity
- has diastolic flow above zero
| - organs that need flow constantly have low resistance wave forms
27
- high resistance
- usually shows reversed flow in early diastole
28
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
29
factors affecting flow
- velocity
- change in diameter
- curves, bifurcation, branch origins
30
disturbed pattern
- friction and energy loss disrupt laminar flow
- still forward flow but with diverging direction
- mild version of turbulence but still considered normal
31
turbulent
- non linear flow
- multiple directions
- multiple velocities
- considered abnormal
32
spectral optimization
- gain, baseline, wall filter, scale/prf/velocity range,
33
gain - spectral
- adjust to allow visualization of signal without unwanted noise
- too high of gain will create false spectral broadening or unwanted noise artifacts
34
baseline
- adjust to allow entire spectral signal to be seen
| - too high of baseline may cause aliasing
35
wall filter
- eliminates low frequency noise
| - adjust to ensure low velocities not missed
36
scale, prf, velocity range
- adjust to demonstrate peak and minimum velocities
- too low of prf will cause aliasing
- increase prf to correct aliasing
37
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
-
38
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
39
color flow display
- map
| - optimization of color
40
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
41
optimization of color
- velocity range
- doppler angle
- field of view
- color box size
- color scale
- gain
- color priority
- wall filter
- baseline
- maps
- power
- invert
42
velocity range- color
- high flow / high prf and low flow/ low prf
43
doppler angle
- steer probe and or color box
44
field of view
- greater depth to area of interest degrades image and ability to display flow
45
color box size
- smaller is better , height has no effect on frame rate
| - width decrease frame rate
46
color scale prf
- to low prf result in aliasing
| - to high prf no flow detected or vessel not filled in
47
gain - color
- insufficient gain result in poor color fill in
| - increase till bleeding then go back to threshold
48
color priority
- image processing priority tray scale vs color
49
wall filter - color
- high setting may eliminate low flow info
50
baseline - color
- adjusted from middle of scale to accommodate more red or blue velocities
51
maps - color
- ise map to help assess flow
52
power / angio
- in case of trickle or low flow
53
invert
- observe orientation of vessel to transducer
54
color artifactis
- mirror image
- blooming
- color flash
- aliasing
- visible bruit
55
mirror image artifact
- seen in gray scale, color and spectral
| - mirror of real vessel
56
blooming/ bleeding
- due to high gain setting may obscure pathology
57
color flash
- transmitted pulsations or adjacent motion will cause color to flash outside of vessel
58
aliasing
- inappropriate prf setting may cause color to exceed high velocity threshold
59
visible bruit
- soft tissue vibration adjacent to area of high flow
