Doppler Principles Flashcards
The doppler effect was first described by who, when
Christian Andreas Doppler
1803-1853
Doppler proposed a theory in what year to explain the observed differences of the colour of some stars
1842
What are some examples of how doppler is used
Radar
Sonar
Ultrasound
A change in —— results from relative motion of the source of the sound or the receiver
Pitch
When a sound source is moving towards you the wave crests are closer or farther apart and the pitch is higher or lower
Wave crests closer
Pitch is higher
When a sound source is moving away from you the wave crests are closer or farther apart and the pitch is higher or lower
Wave crests are further apart
Pitch is lower
Doppler info is primarily used to assess blood flow what two ways
Qualitatively
Quantitatively
Doppler can give you what three pieces of information
Presence of flow
Direction of flow
Quality of flow
Presence, direction and quality of flow through doppler is provided in what three ways
Spectral tracing
Color imaging
Audible sound
Direction of flow moving away is represented as a positive or negative shift in frequency
Negative
Direction of flow moving towards is represented as a positive or negative shift in frequency
Positive
Conventially on the machines what acronym is commonly used to show blood flow and what does it mean
BART
BA. Blue away
RT. Red towards
When scanning both 2D image and doppler simultaneously it is called what
Duplex scanning
When the display shows the image and a spectral tracing at the same time this is called
Duplex scanning
When scanning both the 2D image and colour doppler is on simultaneously this is referred to as
Triplex scanning
Sound reflecting off of moving blood cells does what to returning frequency
It alters the returning frequency
The amount of change to the frequency returning from reflecting off of blood cells depends on what two things
Direction
Speed
Of red blood cells
Is this change in frequency within our hearing range
Yes
What is the typical diameter of a red blood cell
7 um
Since blood cells diameter is smaller then a typical wavelength what type of scatter occurs
Rayleigh scatter
The intensity of scattered sound is directly proportional to —— and therefore indicates the quantity of blood in the sample
To the number of red blood cells
The doppler shift is based on what principle
The principle of wave interference
A reflected wave varies slightly in frequency from the transmitted wave what results
A beat frequency is the result
What is the most basic level formula used to calculate the doppler shift
Doppler shift = received f - transmitted f
What is the more detailed formula for doppler shift and what does it show the relationship between
(2*operating frequency)(velocity)(cos feta)
Doppler shift = ———————————————————
Speed of sound
In the doppler shift equation what is the most meaningful component to sonographers
V (velocity of RBC)
The operating frequency has a —— relationship with the doppler effect
Linear
If the operating frequency increases what happens to the doppler
Shift
Doppler shift increases as well
If frequency is higher/increases what happens to resolution and penetration
Increase resolution Decrease penetration (due to attenuation)
Since RBC return very little intensity a lower or higher frequency probe is needed for doppler
Lower frequency
In duplex scanning does the image or doppler use higher or lower frequencies
Image - higher
Doppler - lower
RBC has what kind of relationship with the doppler shift
Linear relationship
As RBC move faster the difference in the returning frequency increases therefore the doppler shift ——
Increases as well
What is extremely important in doppler
Angle
The cosine of 90 degrees is zero. Therefore when the beam is perpendicular to the vessel what happens to doppler shift
Doppler shift cannot be calculated
What impacts the velocity calculated in the equation? Because it must be consistent for proper patient care
Angle of insonation
What is the most accurate angle for the correct calculation of velocity
Zero degrees (cosine 1)
As —— increases so does the percent error for velocity
Angle of insonation
The calculation of RBC velocity is only as good as the accuracy of the
Angle
How does a sonographer ensure the angle is accurate
Setting the angle to 60 degrees and heel toe probe until the angle indicator line is parallel to flow
What is the limit reached when the RBC velocities are faster then the machines ability to sample called
Nyquist limitation
The rate at which pulses are sent out are limited by
The speed of sound in tissue
The nyquist limit is equal to
1/2 the PRF
1/2 PRF usually falls in which range
5-30 kHz
An artifact that occurs when the Nyquist limit is exceeded is known as
Aliasing
Aliasing is shown like what on a graph
Parts of the signal are wrapped around the baseline
Blood cells are not being sampled fast enough so false readings occur
Correcting aliasing can be done in which 5 ways
Move baseline (real life) Increase PRF (real life) Increase doppler angle - heel toe probe Lower the operating frequency Change to continuous wave
It is possible to send out the second wave before the first comes back but by doing so we are at risk of what occurring
Range ambiguity
What should be positioned in the middle of the vessel, or where the fastest velocity flow occurs
The gate
—— allows several depths to be sampled simultaneously
Multi-gating
The sample volume is created because of the
Range equation
The sample volume is determined by what 3 factors
The beam width
The receiver gate length
The length of the emitted pulse (number of cycles in pulse)
The overall sample volume is equal to what
1/2 pulse length. Plus. Gate length
If the gate length is reduced what must happen to the pulse length
Pulse length must also be reduced
A bigger/smaller gate length will improve spectral display
Smaller
Longer/shorter pulses are required to improve the accuracy of the doppler shift
Longer
To achieve a more accurate beat frequency the pulse duration must be
Longer
A minimum of —— cycles/pulse are required for color and spectral
4 (typically at 30)
In 2D scanning a short or long pulse duration is best
Short
Range gating is not possible with what kind of doppler
Continous wave
CW doppler sample is found at the intersection of the transmitted and received beam and tends to be about how big
5-6 cm
The zone where the transmitted and received beams intersect is known as the
Zone of sensitivity
With a large sample volume it is possible to do what and it would result in a very complex spectral tracing
Possible to pick up more then one vessel
When the beam intersects flow, echos are produced and many different ——— are returned to the vessel
Doppler shifts
The spectrum created is a range of generated doppler shift frequencies from —— that pass through the sample volume
From each RBC
What term means “to take part”
Analysis
The spectrum is an array of the components of a wave arranged in order of ———— over ——
Increasing frequency over time
The spectral tracing of doppler frequencies generated by moving blood that we see are plotted along the following 3 axes
Time (x)
Frequency or velocity (y)
Power (z)
The power (Z-axis) is represented by what
Brightness of pixels
The brightness of pixels (power)(z-axis) is proportional to
The number of cells moving at one velocity at a given time
The greater the number of RBC contained in a sample the —— the waveform
Brighter
The way in which the system creates the spectral trace is through a process of
Fast Fourier Transform (FFT)
What is FFT
A mathematical technique that separates the individual doppler shifts from the complex beat frequency
The Y-axis can represent what two things
Frequency of doppler shift
Velocity of RBC
Frequency is expressed in what units
Velocity is expressed in what units
Frequency kHz
Velocity cm/s m/s
Is frequency or velocity preferred for on the y-axis and why
Velocity. Because it compensates for variations in vessel alignment relative to surface and more meaningful to technologist
When assessing flow direction on a spectral trace it is relative to
The transducer
What word means, flow towards the probe and is expressed as positive number on Y-axis
Antegrade
Which word means flow away from probe and is expressed as negative value on Y-axis
Retrograde
On spectral analysis (graph) the peak systolic velocity is where
The top “peak” of the spikes
On spectral analysis (graph) the envelope is where
All the white lines because it is the range of velocities
On spectral analysis (graph) the window is where
Is the black part below the envelope (white stuff) and above the baseline
On spectral analysis (graph) the dicrotic notch is where
The little second bump of the graph after the peak systolic velocity but before the end diastolic velocity
On spectral analysis (graph) the end diastolic velocity is where
After the diacrotic notch the low part right before the peak systolic velocity
