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DMST 265 VASC 1 > Module 3 Doppler review > Flashcards

Module 3 Doppler review Flashcards

1
Q

What does Doppler tell the sonographer? 6

A
  1. The presence of flow
  2. The direction of flow
  3. The quality of flow
  4. The velocity of the RBC
  5. Resistances/ pulsatility
  6. Timing
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2
Q

What is doppler?

A

A change in frequency of a sound wave in a moving source

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3
Q

How can we relate doppler to RBC’s?

A

We can use doppler to determine the direction RBCs are moving

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4
Q

When RBCs are moving towards the transducer what happens?

A

Received frequency will be higher than the transmitted frequency
antegrade to the transducer or positive shift

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5
Q

When RBCs are moving away from the transducer what happens?

A

Received frequency will be less than the transmitted frequency
retrograde flow or negative shift

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6
Q

How is doppler shift calculated?

A

We can calculate D/S by subtracting the transmitted frequency from the received frequency

D/S = Fr - Ft

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7
Q

What is the more detailed formula for Doppler shift?

A

D/S = ((2)(Fo)(v)(cos))/c

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8
Q

If the operating frequency or RBC velocity increase, what happens to D/S?

A

It increases?

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9
Q

If the angle of insoation increases, what happens to doppler?

A

It decreases

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10
Q

Doppler shift frequencies are processed by what?

A

Fast fourier transform (FFT)

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11
Q

Doppler shifts or velocities are plotted on what?

A

The Y axis over time

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12
Q

Stationary reflectors make up what?

A

Gray scale

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13
Q

Moving RBCs create the doppler shift and are color coded to mean what?

A

Color coded relative to their direction and mean velocity

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14
Q

Each scan line is sampled how many times to do what?

A

Sampled hundreds of times to create an image of color

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15
Q

Autocorrelation is what?

A

The technique that analyzes pulses in a scan line

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16
Q

Autocorrelation is similar to what?

A

FFT

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17
Q

How does RBCs create a doppler shift and how doe we use this?

A

Moving RBCs creates a doppler shift and are colour coded relative to their direction and mean velocity

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18
Q

Each scan line is sampled how many times to do what?

A

Each scan line is sampled hundreds of times to create an image of color

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19
Q

Stationary reflectors make up what?

A

Gray scale

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20
Q

What is autocorrelation?

A

The technique that analyzes pulses in a scan line

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21
Q

How is autocorrelation and FFT similar?

A

It is a mathematical means of obtaining the sign and mean velocity of the blood flow

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22
Q

Since mean frequencies are obtained, the information is what?

A

Qualitative

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23
Q

With multiple pulses required to obtain the mean, there is a reduction of what?

A

PRF effecting the temporal resolution

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24
Q

Framerate determines what kind of resolution?

A

Temporal resolution

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25
In terms of flow we have only considered arterial flow. Flow in the venous system compare how?
It will be quite different since the mechanical for flow are different and varied
26
Venous flow needs to demonstrate 4 characteristics to be normal?
1. Spontaneous 2. Unidirectional 3. Respirophasic 4. Augmentable
27
What are some controls we use to optimize the image when performing doppler? 6
1. Gain 2. Scale (PRF) 3. Baseline 4. Angle 5. Gate size 6. Wall filter
28
Why should gain be used to assist in doppler?
Used to overcome the attenuation of small RBCs and scatter
29
What happens if gains are set to low?
1. poor visualization of the spectral trace 2. Poor color fill 3. Make for weak signals
30
When we set gain to high what will happen?
We create artifacts
31
What is scale also known as?
Velocity range
32
How should we adjust scale to assist in doppler?
Adjust so that peak and minimum velocities are seen
33
A Scale that is set to low will result in what (for doppler)?
Aliasing
34
A scale that is set to high will do what (in terms of doppler)?
1. Make the spectral trace to small to interpret 2. Make it difficult to see low velocity shifts in the color
35
How can we use baseline to assist in doppler?
Adjusted to allow entire spectral signal to be seen (forward and reverse components)
36
Typically where do we have the baseline?
1/4 of the space above the baseline and 3/4 of the space below for venous **this is the opposite for arterial**
37
For most studies the color baseline will not be what?
Adjusted **The exception is in echo**
38
How can the angle/ box angle help doppler?
Since doppler requires a non-perpendicular angle to detect doppler shifts, an angle is crucial to scanning
39
With venous flow, we do not need what?
To angle correct since velocities are not important
40
How should we adjust gate size help for doppler?
Gate size in a pulsed system should be approximately 1/3 the size of the vessel if possible **some vessels are very small and this becomes impossible**
41
When the gate size is to big, what may happen?
Spectral broadening occurs
42
When the gate is too small, what might happen?
It might become difficult to interrogate the true middle of the vessel
43
For doppler what should we do with box size/ position?
The color box should be sized to maximize the FOV without compromising the framerate **this will vary with the exam being performed**
44
How should we position the box? for doppler?
Should be positioned so that the vessels fit in it completely
45
How will wall filter assist in doppler?
1. Eliminates low frequency noise 2. Adjust so that low velocities are not missed in arterial or venous flow states
46
What is the priority control?
A control that can give more emphasis to the color when overwriting the grayscale
47
If the priority is high what happens?
The color will be displayed
48
If the priority to low what happens?
The grayscale shows instead of the color
49
Is priority something that we typically adjust on modern day equipment?
Nope
50
When scanning vessels, we typically do what? 2
1. We keep the veins blue and the arteries red regardless of the direction of flow relative to the probe 2. We show venous flow below the baseline and arterial flow above it
51
What are some doppler artifacts we see? 4
1. Noise or blooming 2. Flash or clutter 3. Aliasing 4. Mirror image
52
What is noise/blooming?
This occurs when the doppler gains are set too high causing the color to blossom outside the vessel or appear in anechoic structures that how no flow
53
With spectral, the over gaining can artificially do what?
Artificially increase the peak systolic velocities which can impact the diagnosis
54
How can we get a halo effect in terms of doppler?
Over gaining the spectral trace
55
What is doppler flash or clutter?
This appears as low level echoes in the color flow seen in the tissue as the result of tissue movement like the heart wall, valve or vessels wall motion.
56
How can we control doppler flash or clutter?
There are filters present within the machine to help eliminate this motion as their velocities are usually lower then the flowing of blood **if we set them too high there is a risk of eliminating real low flow info**
57
What is aliasing? How do we get it?
An artifact that occurs if the nyquist limit is exceeded
58
What is the nyquist limit?
1/2 the PRF
59
When the Nyquist limit is exceeded, what happens?
The blood cells are not being sampled fast enough so a false reading occurs and parts of the signal are wrapped around the baseline
60
1/2 PRF usually falls between what frequencies?
5-30 kHZ
61
How can we correct for nyquist limitation? 5
1. **Move the baseline** 2. **Increase the PRF** 3. Increase the doppler angle (heel or toe probe) 4. Lower the operating frequency 5. Change the continuous wave
62
In the LE venous study, aliasing is expected when?
Expected in the normal limb when we augment the flow
63
What is a doppler mirror image?
This is an artifact that can affect both color and spectral tracing
64
Spectral mirroring has doppler flow where?
on both sides of the baseline and is caused by over gaining or having a angle of incidence too close to 90 degrees
65
With color doppler a false vessel will appear how?
Deep to the real one due to a deeper strong specular reflector
66
What is power doppler?
Power or intensity of signal is measured rather than doppler shift
67
What is power doppler based on?
Density of RBCs, not on speed
68
What is Power doppler used to assess? 3
1. Small vessel 2. Tissue perfusion 3. Slow flow
69
Power doppler has how much aliasing?
No aliasing and is more sensitive to low flow states
70
How dependent is power doppler on doppler angle?
Less dependent
71
The sensitivity to low flow during power doppler is more subject to what?
Flash from other slow moving structures, like bowel
72
Pulsed vs continuous wave. Compare the element use?
PW has one and CW has two
73
Pulsed vs continuous wave. Compare the images
PW produces an image CW does not
74
Pulsed vs continuous wave. Compare the depth
PW has a specific depth, CW samples in zones of sensitivity
75
Pulsed vs continuous wave. Compare Aliasing?
PW: Aliasing is possible; CW: No aliasing

DMST 265 VASC 1 (19 decks)

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