Module 3 : Principles Of Color And Spectral Doppler Flashcards
1
Q
Who first described the Doppler effect/ Doppler shift
A
- Christian johann Doppler
2
Q
What was the Doppler guy studying when he discovered the Doppler principle
A
- he was studying the varying color of the stars to determine if they were moving toward or away from the earth
3
Q
What is the Doppler effect
A
- change in frequency of sound, light, or other waves caused by the motion of the source or the observer
4
Q
Ultrasound Doppler shift is caused by what
A
- change in frequency of sound caused by the motion of red blood cells
5
Q
The Doppler shift is the difference between what two frequencies
A
- difference between the transmitted frequency and the received frequency
6
Q
What is the transmitted frequency
A
- transducer frequency
7
Q
What is the received frequency
A
- reflected or echo frequency
8
Q
Frequency shift when the RBCs move toward the transducer
A
- the echo frequency will be larger/higher than the transducer frequency (antegrade flow)
9
Q
Frequency when the RBCs are moving away from the transducer
A
- the echo frequency will be smaller/lower than the transducer frequency (retrograde flow)
10
Q
What is beat frequency
A
- method used to measure the Doppler shift is based on wave interference
- the reflected wave will vary slightly from the original transmitted wave the algebraic sum give off beat frequency
11
Q
In which part of the vessel are cells moving the fastest
A
- the cells at the center of the vessel move the fastest while those at the sides move the slowest
12
Q
How is a spectral trace created with the beat frequency
A
- there are many different frequencies within the beat frequency due to the different velocities of RBCs that are plotted on a graph to form spectral trace
13
Q
Complicated Doppler shift equation
A
^F = 2Fo x V x Cos0 / C
14
Q
^ F
A
Doppler shift
15
Q
Fo
A
Transducer operating frequency
16
Q
V
A
- velocity if moving RBCs
17
Q
Cos0
A
- angle of insonation
18
Q
C
A
- speed of sound through soft tissue
19
Q
What is the Nyquist limit
A
- upper limit to the Doppler shift that can be detected by pulsed instruments
- 1/2 PRF
20
Q
What must be exceeded if aliasing occurs
A
- the nyquist limit hast to be exceeded
21
Q
Why does aliasing occur
A
- PRF is too slow for the true Doppler shift and is sampling the flow to late so its only capturing parts of it
22
Q
Aliasing on color Doppler
A
- color wraps around the color bar showing both colors with no separation
23
Q
5 ways to compensate for aliasing
A
- move the baseline
- increase PRF (scale)
- increase Doppler angle (not good)
- lower the operating frequency
- change to CW
24
Q
What is high PRF mode
A
- allows the machine to send out subsequent scan lines before the first is returned
25
High PRF mode can lead to what downfall
- range ambiguity
26
What is range ambiguity
- machine does not know what depth the echoes are being returned and could show misrepresented echoes on the display
27
3 ways Doppler info can be represented
- spectral
- color
- sound
28
Characteristics of spectral Doppler
- graphed information shown on display
| - QUANTITATIVE (can measure speed) using FFT
29
What is fast Fourier transformation (FFT)
- means if taking complex beat frequency and dissecting it into its component waves
- each wave is the result of a reflection off a moving blood cell within the sample volume
30
Color Doppler characteristics
- visualize flow by sending out two set of scan lines (one for 2D one for color)
- Doppler info is OVERLAID the 2D
- obtained using autocorrelation
- qualitative
31
What velocity does color Doppler represent
- mean flow velocity
| - different colors represent positive or negative Doppler shift and give the direction of flow
32
Characteristics of Doppler sound
- Doppler info can be heard
| - helps us detect changes in flow
33
Characteristics of CW
- sounds waves emitted continuously from ONE crystal and is continuously received by another crystal
- zone of sensitivity
34
What is the zone of sensitivity
- in CW the velocities received come from a large overlap zone
- area where transmitted and received sound is overlapped
35
Advantages to CW
- no nyquist limit so can scan really high velocity with no aliasing
36
Disadvantages to CW
- no range resolution
| - no 2D image
37
PW characteristics
- one crystal is used to fire and then listens for returning echoes
38
Advantage to PW
- we know how fast the sound is traveling so we can determine at what depth we would like to sample
39
PW sample volume increase in size causes what
- increases ring time
| - increases spectral broadening
40
PW sample size decrease in size does what
- decreases ring time
| - samples a more discrete area of flow and the spectral waveform displays less spectral broadening
41
Power Doppler characteristics
- overlay of color onto the 2D image
- power Doppler uses amplitude of returning Doppler signals to detect flow
- very sensitive to low flow states and independent of angle
- directional power Doppler has been introduced
