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Understanding Ultrasound Physics/Edelman Ch 19 Part 2
Understanding Ultrasound Physics
69
Medical
09/27/2010

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Term
The following factors relate to what type of doppler?
- range resolution
- sample volume
- limited maximum velocity (Nyquist)
- aliasing
Definition
Pulsed Doppler
Term
The following factors relate to what type of doppler?
- range ambiguity
- region of overlap
- unlimited maximum velocity
- no aliasing
Definition
CW Doppler
Term
The following factors relate to what type of transducer?
- at least one crystal
- damped PZT
- low Q-factor
- wide bandwidth
- lower sensitivity
Definition
Pulsed Doppler Transducer
Term
The following factors relate to what type of transducer?
- at least two crystals
- undamped PZT
- high Q-factor
- narrow bandwidth
- higher sensitivity
Definition
CW Doppler Transducer
Term
The following factors relate to what general type of modality?
- normal incidence
- higher frequency
- pulsed wave only
- minimum of 1 crystal
Definition
Imaging
Term
The following factors relate to what general type of modality?
- 0/180 degrees
- lower frequency
- pulsed or CW
- min of 1 (pulsed) or 2 (CW) crystals
Definition
Doppler
Term
In this modality, velocity information is coded into colors and superimposed on a 2D grayscale, anatomic image
Definition
Color Flow Doppler
Term
Is spectral doppler considered qualitative or quantitative?
Definition
Quantitative
Term
Is color flow doppler considered qualitative or quantitative?
Definition
Qualitative
Term
Since color flow doppler is based on ___ techniques, it has the same advantages (___) and disadvantage (___)
Definition
Pulsed Wave
+ Range Resolution/Specificity
- Aliasing
Term
What type of velocities does color doppler report?
Definition
Average/Mean Velocities
Term
What does RABT stand for?
Definition
Red Away Blue Towards
Term
What does BART stand for?
Definition
Blue Away, Red Towards
Term
What type of velocities does PW and CW doppler report?
Definition
Peak Velocities
Term
In color doppler, the color represents what?
Definition
Flow Direction
Term
What does black represent in color doppler?
Definition
No doppler shift
Term
Colors above the black stripe represent blood cells moving in what direction?
Definition
Toward the Transducer
Term
Colors below the black stripe represent blood cells moving in what direction?
Definition
Away from the Transducer
Term
Flow toward the transducer is what kind of doppler shift?
Definition
Positive Doppler Shift
Term
Flow away from the transducer is what kind of doppler shift?
Definition
Negative Doppler Shift
Term
Colors closer to the black stripe represent what?
Definition
Slower speeds
Term
Colors farther away from the black stripe represent what?
Definition
Faster speeds
Term
In addition to direction and velocity, what additional information does variance mode offer?
Definition
Laminar vs Turbulent Flow
Term
In variance mode, what do the colors on the left side represent?
Definition
Laminar Flow
Term
In variance mode, what do the colors on the right side represent?
Definition
Turbulent Flow
Term
In color doppler, multiple pulses are used to accurately determine blood velocities. What are these multiple pulses called?
Definition
Packets
Ensembles
Term
The following advantages apply to what type of packets/ensembles?
- more accurate velocity measurements
- more sensitive to low flow
Definition
Larger Packets
Longer Ensemble Lengths
Term
The following disadvantages apply to what type of packets/ensembles?
- more time needed to acquire data
- reduced frame rate
- decreased temporal resolution
Definition
Larger Packets
Longer Ensemble Lengths
Term
Flows detected at angles closer to 0 degrees will be ___ than those detected closer to 60 degrees
Definition
Brighter
Term
This modality only identifies the presence of a doppler shift, not speed or direction
Definition
Power Doppler
Energy Mode
Color Angio
Term
In this modality, the strength/amplitude of the reflected signal is processed, which is directly related to the number of moving blood cells
Definition
Power Doppler
Energy Mode
Color Angio
Term
What are 3 advantages of power doppler?
Definition
1. increased sensitivity to low velocities
2. unaffected by doppler angles (unless 90 degrees exactly)
3. no aliasing
Term
What are 3 disadvantages of power doppler?
Definition
1. no velocity or direction information
2. lower frame rates / temporal resolution
3. susceptible to motion / flash artifacts
Term
In addition to moving blood, very low frequency doppler shifts may be produced by ___ or ___
Definition
Moving Anatomy
Pulsating Vessels
Term
On spectral displays, low frequency doppler shift artifacts called what?
Definition
Clutter
Term
On color displays, low frequency doppler shift artifacts are called what?
Definition
Ghosting
Term
How is clutter or ghosting eliminated?
Definition
Wall Filter
Term
Wall Filters
Definition
These exclude low frequency doppler shifts around the baseline, but have no effect on higher doppler frequency shifts commonly created by blood cell motion
Term
Crosstalk
Definition
This is a special form of mirror image artifact that only appears with spectral doppler; while the flow pattern appears identical above and below the baseline, the true pattern in unidirectional
Term
The following cause what type of artifact?
- doppler receiver gain too high
- incident angle near 90 degrees between the beam and the flow direction
Definition
Crosstalk
Term
This is the tool that breaks up a complex signal into the individual velocities which make up the reflected doppler signal
Definition
Spectral Analysis
Term
FFT (Fast Fourier Transform)
Definition
This doppler analysis tool is exceedingly accurate and displays all individual velocity components from the reflected signal; it is used with PW and CW doppler
Term
Using FFT, a laminar flow will produce what in the display?
Definition
Spectral Window
Term
Using FFT, a turbulent flow will produce what in the display?
Definition
Spectral Broadening
Term
This doppler analysis tool is less accurate but substantially faster than FFT; it is used with color flow doppler
Definition
Autocorrelation
Correlation Function
Term
When the spectral window is filled in, this is called what? and results from what?
Definition
Spectral Broadening
Turbulent Flow
Term
Can a patient be so severely anemic that a doppler exam cannot be performed?
Definition
No
Term
Is FFT quantitative or qualitative?
Definition
Quantitative
Term
Is autocorrelation quantitative or qualitative?
Definition
Qualitative
Term
Resistivity Index (RI)
Definition
This ratio is a quantitative, doppler-derived measurement of the vascular resistance of a segment of the arterial system. It requires min/max velocities
Term
Pulsatility Index (PI)
Definition
This ratio is a quantitative, doppler-derived measurement of the vascular resistance of a segment of the arterial system. It requires min/mean/max velocities
Term
The following are advantages of what?
- based on mathematical measurements
- based on waveform shapes; unaffected by doppler angles
Definition
Resistivity Index (RI)
Pulsatility Index (PI)
Term
The doppler effect is presented as a ___ when the source and the receiver are ___
Definition
Frequency Shift
Moving relative to each other
Term
Starting from the same point, the sound source is moving east at 12 miles/hour and the receiver is moving west at 10 miles/hour. The doppler shift is ___
Definition
Negative
Term
Starting from the same point, the receiver is moving west at 12 miles/hour and the source is moving west at 10 miles/hour. The doppler shift is ___
Definition
Negative
Term
Doppler shift produces information about ___
Definition
Velocity
Term
At what angle between the sound beam and the direction of motion will the doppler shift be at a maximum?
Definition
0/180 degrees
Term
At what angle between the beam and the direction of motion will the doppler shift be a minimum?
Definition
90 degrees
Term
What is the difference between speed and velocity?
Definition
Speed = magnitude
Velocity = magnitude & direction
Term
What is the current method of processing doppler signals?
Definition
FFT for spectral doppler
Autocorrelation for color doppler
Term
What is the typical range of doppler shift found in diagnostic imaging?
Definition
20 Hz - 20 kHz (in the audible range)
Term
The phenomenon where high velocities appear negative is called what?
Definition
Aliasing
Term
The frequency at which aliasing occurs is called what?
Definition
Nyquist Limit
Term
The area of interrogation in a pulsed doppler exam is called what?
Definition
Sample Volume
Term
T/F: the higher the emitted frequency, the more likely a pulsed wave signal is to alias
Definition
True
Term
T/F: shallower sample volumes result in more aliasing
Definition
False
Term
T/F: only pulsed wave doppler exams have a sample volume
Definition
True
Term
An 8 MHz transducer with a PRF of 5,000 Hz is imaging to a depth of 7 cm. What is the Nyquist frequency?
A. 4 MHz
B. 3.5 Hz
C. 2.2 kHz
D. 2.5 dB
E. 5 kHz
Definition
C. 2.2 kHz
Term
An 8 MHz transducer with a PRF of 5,000 Hz measures a doppler shift of 7 kHz. The study is repeated with a 4 MHz transducer. What doppler shift will be measured?
A. 4 MHz
B. 3.5 Hz
C. 4 kHz
D. 3.5 dB
E. 3,500 Hz
Definition
E. 3,500 Hz