Chapter 19 Flashcards
Doppler & color doppler
Doppler shift is the apparent change in the ____ of a wave as a result of relative motion between the sound source and the observer.
Frequency
____ ____ is the principle used to measure the velocity of blood moving in the body.
Doppler shift
Doppler Shifts are created when transmitted sound waves strike moving ____ ____ ____.
Red blood cells
What is the equation for doppler shift?
Doppler shift (Hz) = reflected freq. – transmitted freq.
With a positive doppler shift, the red blood cells are moving ____ the transducer.
Towards
With a negative doppler shift, the red blood cells are moving ____ the transducer.
Away from
Doppler frequencies indicate ____ NOT speed.
Velocity
____ is a magnitude, indicates distance but not direction. Units are cm/sec.
Speed
____ is a magnitude and a direction (north, south, towards, away).
Velocity
The equation for velocity is:
Doppler shift x (1540 m/s) / 2 x transducer frequency x cosine angle
Doppler shift is ____ related to the velocity of the blood cells.
Directly
Doppler shift is ____ related to the transmitted frequency.
Directly
Doppler shift is ____ related to the Doppler angle.
Inversely
If the sound beam and flow direction are not parallel, the percentage of the true velocity that is measured depends on the ____ between the sound beam and the direction of motion.
Cosine of the angle
Doppler shift is ____ related to the cosine of the angle between flow direction and direction of sound.
Directly
If flow is perpendicular (90˚), then the cosine = ____.
0
With flow parallel to the sound beam, the angle would be ____ or ____.
0° or 180°
With flow perpendicular to the sound beam, the angle would be ____.
90°
____ doppler distinguishes the presence and direction of flow.
Bidirectional
Most common clinical Doppler devices are ____.
Bidirectional
____ ____ is a commonly used signal processing technique for bidirectional Doppler.
Phase quadrature
Continuous wave doppler requires how many crystals in the transducer?
Two
Main advantage of ____ doppler is its ability to accurately measure very high velocities.
CW
The main disadvantage of CW is ____ ____, which is the inability to determine the exact location of the moving red blood cells that are creating the waveform.
Range ambiguity
Pulsed wave doppler requires how many crystals in the transducer?
One
A major advantage for ____ doppler is range resolution.
PW
____ ____ is the ability to determine the exact location of the moving red blood cells that are creating the waveform.
Range resolution
Aliasing exists only with ____ Doppler.
PW
____ is when the PW Doppler sampling rate is too low in comparison to measured blood velocity, therefore cells moving at high velocities are displayed as moving in the wrong direction.
Aliasing
____ ____ is the highest Doppler velocity that can be measured without the appearance of aliasing.
Nyquist limit
How to you calculate the nyquist limit?
PRF/2
Higher frequency transducers create ____ aliasing because they create higher Doppler shifts
More
Lower frequency transducers create ____ aliasing because they create lower Doppler shifts.
Less
What are the five techniques that may be used to avoid aliasing?
- Adjust the waveform scale to its maximum
- Move the baseline shift up or down so that the entire waveform fits in the appropriate area
- Select a new ultrasound view with a shallower sample
- Select a lower frequency transducer
- Use continuous wave Doppler
The grey shades on a Doppler spectrum are related to the ____ of the reflected signal, or number of ____ creating the reflection.
Amplitude; redblood cells
____ imaging is simultaneous anatomic imaging (2D greyscale image) and Doppler.
Duplex
Best type of transducers for duplex imaging are ____.
Arrays
____ doppler simply measures the presence of moving blood cells by detecting a Doppler shift. Does not distinguish direction of flow.
Power
____ dopper is a form of two-dimensional Doppler. The velocity of blood flow is coded into colors and superimposed on a 2D greyscale, anatomic image.
Color flow doppler
Color Doppler reports ____ velocities.
Average
Pulsed and continuous wave doppler report ____ velocities.
Peak
The colors in a velocity mode map present information on flow ____.
Direction
The black region in the middle indicates ____ Doppler shift.
No
The colors above the black region indicate blood cells moving ____ the transducer (positive Doppler shifts).
Toward
The colors below the black region indicate blood cells moving ____ the transducer (negative Doppler shifts).
Away from
Colors closer to the black region indicate ____ velocities, while colors further from the black region indicate ____ velocities.
Lower; higher
Top and bottom (yellow and green on bar to left) represent the ____ ____.
Nyquist limit
The ____ maps display different colors side to side.
Variance
With variance maps, colors from the left side of the map indicate ____ flow.
Laminar
With variance maps, colors from the right side of the map indicate ____ flow.
Turbulent
With color Doppler, multiple ultrasound pulses are used to accurately determine blood cell velocities. These multiple pulses are called a ____ or ____.
Packet or ensemble
On spectral displays (doppler graph), the low frequency doppler shift artifacts are called ____.
Clutter
On color doppler, the low frequency doppler shift artifacts are called ____.
Ghosting
____ ____ (aka high pass filters) eliminate low frequency Doppler shifts from moving anatomy rather than blood flow.
Wall filters
Crosstalk is a special form of mirror image artifact that arises only with ____ doppler.
Spectral
____ appears as an identical Doppler spectrum both above and below the baseline.
Crosstalk
____ ____ is a tool that breaks the complex signal into its basic “building blocks” and identifies the individual velocities that make up the reflected doppler signal.
Spectral analysis
Two methods of spectral analysis are:
- Fast Fourier Transform (FFT)
- Autocorrelation
Fast Fourier Transform (FFT) is a digital (computer-based) technique used to process both ____ and ____ wave doppler signals.
Pulsed and continuous
Because ____ displays all the individual frequencies, the spectral display can distinguish laminar flow from turbulent flow.
FFT
Autocorrelation is the digital technique used to analyze ____ doppler. It determines the mean velocity.
Color flow
____ is used to analyze color Doppler because of the huge amounts of data that is processed.
Autocorrelation
Autocorrelation is ____ accurate than FFT but ____ at processing large amounts of data.
Less; faster
