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118 Cards in this Set
- Front
- Back
- 3rd side (hint)
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How are frequency shift and velocity related?
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The magnitude of the frequency shift is related to velocity
↑ velocity = ↑ frequency shift. |
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How are frequency shift and velocity related?
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The magnitude of the frequency shift is related to velocity
increase in velocity = increase in frequency shift. |
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With a smaller angle what happens to the frequency shift?
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the higher the frequency shift (cosine)
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What does a 0 agree Doppler angle results in
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he maximum frequency shift
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what does a 60 degree Doppler angle results in
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half of the frequency shift
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What does a 90 degree doppler angle results in
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minimum frequency shift
• “No Doppler shift” |
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what happens as the Doppler angle decreases?
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the Doppler shift increases
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What happens with a smaller the Doppler angle?
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higher the frequency shift
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Transmitted frequency is directly or indirectly related to the Doppler frequency shift for any given velocity?
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Directly
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If the txr frequency increases, the Doppler frequency increases, what happens to velocity?
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velocity will NOT change
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DOPPLER EQUATION??
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∆f=2ft V Cos⊝
C |
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What is the pulse wave doppler rule of thumb?
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ALWAYS “HEEL and TOE” THE
VESSEL!!!!! |
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Which way do you steer the color box with doppler
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Steer the color box the same direction as the vessel angle
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When you“heel & toe” transducer, what are you accomplishing?
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adjustment to decrease Doppler angle to flow
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How will we know which way to steer the beam?
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Steer in a direction that will provide a lower angle
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what is the proper cursor alignment?
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parallel to the walls
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The cursor or “angle correct”
informs the ultrasound system of? |
the vessel angulations
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What happens with a 5 degree misalignment?
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5 degrees off at 40degrees=vel. calc =108cm/s
5 degrees off at 60degrees =vel. calc=118cm/s 5degrees off a t80degrees =vel. calc=195cm/s!! |
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What happen with an estimations over 70 degrees?
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> 70 degree Doppler angles overestimation of velocities is significant**
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How many piezo-electric crystals with CW doppler?
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2 piezo-electric crystals: one transmitting, one receiving
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Doppler equation for duplex imaging
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ooo
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Doppler equation for duplex imaging
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ooo
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What is the pulse wave doppler rule of thumb?
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ALWAYS “HEEL and TOE” THE
VESSEL!!!!! |
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Which way do you steer the color box with doppler
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Steer the color box the same direction as the vessel angle
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When you“heel & toe” transducer, what are you accomplishing?
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adjustment to decrease Doppler angle to flow
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How will we know which way to steer the beam?
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Steer in a direction that will provide a lower angle
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what is the proper cursor alignment?
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parallel to the walls
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The cursor or “angle correct”
informs the ultrasound system of? |
the vessel angulations
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What happens with a 5 degree misalignment?
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5 degrees off at 40degrees=vel. calc =108cm/s
5 degrees off at 60degrees =vel. calc=118cm/s 5degrees off a t80degrees =vel. calc=195cm/s!! |
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What happen with an estimations over 70 degrees?
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> 70 degree Doppler angles overestimation of velocities is significant**
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How many piezo-electric crystals with CW doppler?
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2 piezo-electric crystals: one transmitting, one receiving
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What is the advantage of using CW Doppler
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NO aliasing artifact
• Useful when taking systolic blood pressures |
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What is the disadvantage of using CW Doppler
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Range ambiguity
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Can continuous wave doppler create an image?
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NO
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How many elements does a PW doppler use?
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single element transmitting, then receiving
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What is range specificity
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Range “gate” or sample gate,
sample volume |
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What is PRF
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Number of pulse-echo cycles per second, different than the PRF used for imaging
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What is PRF linked to
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Linked to the scale
• Increased scale = increased PRF • Decreased scale = decreased PRF |
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What is PRF expressed in
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expressed in hertz (Hz)
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Why is PRF considered sensitive?
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Indirectly decreases the wall filters
when decreasing the PRF’s, therefore, considered more sensitive |
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When does aliasing occur?
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occurs when Doppler shift frequencies exceed 1/2 of PRF a.k.a. Nyquist limit
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How do you reduce of eliminate aliasing?
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Increase PRF
Decrease frequency shift with a higher Doppler angle Lower the Doppler transmit frequency (multi-freq. txr) or change tar Decrease sample volume depth Change from PW Doppler to CW Doppler |
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What does Fast-Fourier Transformation (FFT) do?
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Samples the Doppler signal •Processing and analyzing
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What does Fast-Fourier Transformation (FFT) display?
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• Doppler shift frequencies
(vertical axis) • Time (horizontal axis) • Amplitude or power (brightness) |
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What do Spectrum analyzers display?
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both the Doppler shift and velocity information
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What does FFT display
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Thousands of Doppler shifts are being sampled every second!!
• PRF = 10 KHz • 10,000 Doppler shifts |
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Can all the doppler shifts with FFT be displayed at the same time?
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NO
Doppler shifts CANNOT be displayed at the same time |
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How does FFT subdivide frequency shifts?
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into "bins"
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How are the frequencies divided in FFT?
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Signals that are traveling at similar
frequency shifts are grouped together into bins |
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How does the pixel display a high number of similar frequency shifts?
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The higher the number of similar frequency shifts in these bins, the brighter the pixel
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Name the Filters for spectral and color doppler
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• Wall filters
• High pass filters • “Thump” filters |
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What are wall filters important?
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essential in eliminating low frequency noise around the baseline,
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What happens if the wall filter is set improperly
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it can affect adversely waveform morphology
(black around baseline) |
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What is color doppler similar to?
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PW Doppler
• A lot of the same rules apply!! |
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With Color doppler, what happens with a small angle?
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As in PW Doppler, smaller Doppler angles result in higher frequency shifts
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How is a color image frame obtained?
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A color image frame is obtained by using multiple color scan lines
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How does color doppler work?
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Frequency shifts detected within sample sites along the scan lines are then color encoded
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What is the typical frame rates for color Doppler
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8 Hz or greater
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What make one frame?
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Color information obtained from one sweep of all scan lines equals one frame.
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What happens with high color scan line density?
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Small pixel size
Good spatial resolution |
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What happens with Low color scan line density?
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“brick” shaped pixels
Bad spatial resolution |
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does High scan line density have a slow or high frame rate?
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Slower frame rate
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Does Low scan line density have a slow or high frame rate?
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Higher frame rate
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Line averaging or fill-in interpolation work?
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Uses a low density scan line setting
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What happens to the missing information between scan lines?
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they interpolated and filled in
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Why is Line averaging or fill-in interpolation performed?
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to maintain higher frame rates
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What happen to frequency shifts with fast RBC?
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The faster the velocity in a RBC, the higher the frequency shift
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Is autocorrelation quantitative or semi-quantitative?
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semi-quantitative
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How is Color information is obtained
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by Autocorrelation
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with Autocorrelation, how is the doppler shift presented?
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Doppler shift is presented as an AVERAGE
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Autocorrelation derives:??
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• mean (average) frequency shift
• Considered semi quantitative!! • flow direction • Speed • aliasing |
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How many pulses per scan line with B-Mode
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1
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How many pulses per scan line with color
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3 - 20 (commonly 8 - 10) more pulses, more sound exposure to the patient!
!aka. Packet size Ensemble length Color sensitivity Color quality |
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With color, what does a high number of scan line look like? What is the frame rate?
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robust, full color, but lower frame rate
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With color, what does a low number of scan line look like? What is the frame rate?
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Low number = weak, inadequate color fill in,
but high frame rate |
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If color box is “opened” completely what will happen to frame rate and temporal resolution?
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• Frame rate is reduced
• Temporal resolution will decrease • “Cone down” to area of interrogation |
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Color frame rate
Variables pulses per lin (packet size) uses what setting? |
Minimum setting
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Color frame rate
Variables density of scan line uses what setting? |
Low setting
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Color frame rate
Variables...what does color box width do? |
reduces the number of functioning scan lines
• “Cone down” to area of interrogation |
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Color frame rate
Variables PRF uses what setting |
Minimum setting
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BART =
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Blue Away Red Towards
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What technique was used to establish color fill in?
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Doppler scale (PRF)
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Scale (PRF) is lowered to do what?
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Scale (PRF) is lowered to establish color “fill in” (aliasing)
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When you are adjusting PRF, what are you indirectly lowering?
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you are indirectly lowering the wall filter (more sensitive) and therefore processing lower Doppler shift information
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What is the first step you should perform to fill in color?
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increase color gain
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When do you start reducing PRF?
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Once your color gain is maximized, you may start decreasing the PRF color scale
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Can we obtain Doppler shifts if
the color box is “unsteered”? |
Yes. If you establish an adequate Doppler angle, you will establish a Doppler shift
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If you are having trouble filling in the vessel or have a weak spectral waveform what do you do?
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• First, increase your Doppler gain
• Verify that you are on the vessel! • If this does not improve the Doppler, then.. • Decrease the PRF scale |
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What is the Baseline settings for color flow Doppler:
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• color gain = 50 (%)
• Color scale (PRF) = .30 for arterial • Color scale (PRF) = .19 for venous • Filter = minimum or 1 step above minimum • Doppler frequency (if applicable) = decrease frequency for improved penetration! |
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Artifacts and color flow Doppler
What if your image is aliasing? |
increase color scale
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Artifacts and color flow Doppler
What if your image is bleeding? |
Decrease (color) Doppler gain
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Artifacts and color flow Doppler
What if your image has Flash / ghosting artifact |
increase wall filter
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Artifacts and PW Doppler
What is you image is aliasing? |
increase Doppler scale
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Troubleshooting with PW Troubleshooting with PW Doppler
you cannot see the Doppler signal BUT, you can hear it, what do you do? |
• Increase the (Doppler) gain • Adjust the scale
• look at the velocity scale adjacent to the spectrum • Always have the volume up so you can listen to the signal!! |
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Artifacts and PW Doppler
What if you have Noise or clutter around the baseline |
Increase wall filter
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Artifacts and PW Doppler
What if you have a Hyperechoic Doppler signal |
Decrease Doppler gain
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Artifacts and PW Doppler
What if you have an Absent Doppler signal |
Increase gain
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During Doppler sampling of deep vessels do you steer or unsteer the color box?
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unsteer the color box
• Allows for more color Doppler penetration |
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Power Doppler other names?
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• Ultrasound Angio tm
• Color Doppler Energy • Color Power Angio • Power Doppler Imaging • Convergence Power Doppler |
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Why use power doppler?
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• color encoding at 90 o
• more sensitive than color Doppler • Considered the MOST SENSITIVE of all Dopplers! • good wall definition (non-moving walls) • no aliasing |
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Power Doppler:
Current Limitations |
• wall definition - “bleeding” and/or “flash artifact”
• high persistence - slow frame rate • Information “drags” in frame • cannot detect increased velocity • Lack of aliasing • most systems do not encode for flow direction • differentiation of arterial /venous flow |
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Power Doppler
Clinical applications? |
• Tissue or organ perfusion - yes
• native kidney, liver, transplants, • Vascularity in tumors - yes • Transcranial Doppler - yes • “Trickle flow” - yes • Arterial stenosis – NO • Confirm fetal demise |
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Where are Mirror image artifact displayed?
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Displayed deeper compared to the real structure!!
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What do linear transducers display?
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Linear array transducers display a two dimensional image of a 3-dimensional object.
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What is Lateral resolution?
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The ability to distinguish two closely spaced objects in the horizontal plane
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What is Axial resolution determined by?
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spatial pulse length
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Good axial resolution is ?
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the ability to distinguish adjacent structures in the vertical axis
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The third dimension- the elevation is also known as?
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slice thickness
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slice thickness varies with...?
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depth
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focal point is fixed and determined by?
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transducer design and frequency
• Usually at mid level of beam |
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When small superficial vessels are being examined under ultrasound with a low frequency transducer, vessels are artifactually filled in with echoes. This artifact
typically occurs due to |
the slice thickness being wider than the vessel which is called the "partial volume effect"
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If the slice thickness is wider than the object...?
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the surrounding tissue may be displayed along with the object of interest.
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“Matrix” array or 2-D transducers can provide a more uniform...?
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elevation focal zone
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what does Intrinsic spectral broadening result in?
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an overestimation of true blood flow velocity
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Intrinsic spectral broadening is minimal at
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low Doppler angles.
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ntrinsic spectral broadening is severe at
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at angles greater than or equal to 70 degrees
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Manufacturers can double the PRF by?
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transmitting before echoes have returned
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Range Gate Ambiguity- High PRF creates?
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multiple, or phantom sample gates.
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