Exam 2 Flashcards
Source (transducer) determines the ______ of the wave
Frequency
The medium (RBC’s) determines the ________
Propagation speed
Wavelength equation
c
—
f
c= propagation speed
f=frequency
Stationary source, transducer =
Reference signal
Reflector is moving
RBC’s flowing through vessels
Positive Doppler shift the reflector is moving ________ the transducer
Toward
Positive Doppler shift the reflected frequency is_________ than the transmitted frequency
Higher
Positive Doppler shift
- positive or negative shift?
- above or below baseline?
- higher or lower frequency?
- positive
- above
- higher
Negative Doppler shift:
- positive or negative shift
- above or below baseline
- higher or lower frequency
- negative
- below
- lower
If reflector is moving away from the transducer the reflected freq is _________ than transmitted freq
Lower
Doppler shift equation (frequency)
Doppler shift (Hz) = reflected - transmitted
Is the Doppler frequency range within the audible range?
Yes, Doppler shift between 200 Hz & 15,000 Hz
Doppler shift equation (velocity)
fDOP = 2f0V
——
c
fDOP = Doppler shift
2 = round trip of the sound
f0 = transmitted freq
V = velocity
c = speed of sound in tissue
Doppler frequency is ___________ proportional to the reflector velocity
Directly
Reflector velocity doubles = _________ of Doppler frequency
Double
Higher transmit frequency = ________ frequency shift
(higher/lower)
Higher
Lower transmit frequency = ___________ frequency shift
Lower
When distance between source & observer is increasing the relative motion is “away” and a ___________ occurs
Decompression
Distance between source & observer decreases, the relative motion is “towards” & a __________ occurs
Compression
Compression leads to ________ frequency & a ________ frequency shift
(higher/lower) (positive/negative)
Higher
Positive
Decompression leads to a _________ frequency & __________ frequency shift
(higher/lower) (positive/negative)
Lower
Negative
Faster velocity will result in a _________(greater or lesser) frequency shift
Greater
Doppler equation (angle):
fdop = 2foV cos(o)
—————
c
fdop = Doppler shifted frequency
fo = transmit frequency
V = velocity
c = speed of sound through medium
Cos = angle effect
(0) = angle or flow
Where is insonification angle (angle of insonation) measured?
Between the beam steering direction and the direction of the flow
When blood cells are moving parallel to a sound beam, how much of the velocity is being measured?
Entire velocity is measured
Flow direction toward transducer = (positive or negative) _______ shift
Positive
Flow direction away from transducer = (positive or negative) _______ shift
Negative
Perpendicular (90 degree) incidence can not be measured. What is the velocity measured?
Velocity measured = 0
Angle of incidence must be _____ (≤ ≥) ______ degrees
≤
60
Ability to correctly identify the insonification angle is critical for these reasons:
- determine flow direction
- Doppler measurement accuracy
- minimize Doppler error sources
- likelihood of artifact related issues (spectral broadening)
What does the Spectral Display, display?
The blood flow measurements
- Displaying flow velocities recorded over time (graphically)
Spectral display allows for evaluating the following:
Blood flow direction - towards or away
Blood flow characteristics - whether flow has high or low resistance & pulsatile and phasic
Quality of flow - turbulent or laminar
Quantification of blood flow - peak or mean velocities
What is the difference between the transmit frequency and the received frequency?
Doppler shift /effect/frequency
Doppler tracing has a “y-axis” representing ________ and “x-axis” representing _________
Y - velocity (m/sec)
X - time
High resistance flow =
Systolic flow
Low resistance flow =
Diastolic flow
Phasic flow is driven by….
Respiratory pump
Spectral broadening is usually caused by
Turbulence
- results in “fill in” of trace window
- hallmark feature of post stenotic flow
Fast Fourier Transform (FFT) can distinguish _______ flow from _______ flow
Laminar
Turbulent
Two advantages of FFT
- Accuracy
- Displays individual velocity components that make up the reflected signal
Laminar flow travels at _______ and displays _______
Similar velocities
Narrow, well-defined tracing
Turbulent flow is _______
displays______
Chaotic, goes in all directions & velocities
Spectral broadening
Sample volume:
Keep cursor ______
Ideal gate size =
Center of vessel
1/2 the lumen
Range resolution (range ambiguity)
Ability to detect signals from a specific area
PRP =
(1)
—-
PRF
PRF is determined by
- Speed of sound
- Distance it travels
What is necessary to measure reflectors moving w/high velocity & producing large Doppler shifts
High PRF
High PRF allows the pulses to be sent out frequently:
Shallow location
Low PRF allows the pulses to be sent out less frequently:
Deeper location
Regurgitant jet velocity is (higher or lower) ________ than the nyquist limit
Higher
PRF limit where aliasing occurs is called?
Nyquist limit
Aliasing occurs if the velocity of blood exceeds the? -
Nyquist limit
Aliasing appears when the Doppler shift (speed) exceeds the?
Nyquist limit (speed limit)
Two ways to avoid aliasing..
- Raise speed limit - increase scale
- Reduce Doppler shift (speed)
Nyquist is ______ PRF
1/2 (half)
Methods to reduce aliasing..
- Increase PRF/scale - (raises nyquist limit)
- Get closer - adjust depth
- Lower transducer freq
- Shift the baseline
- Use CW probe
PW Doppler review
One Crystal that alternates between sending & receiving
Backing material
Range ambiguity/specificity
Limited on detecting high velocities
PRF/2 = nyquist limit
Lower sensitivity
Duty Factor of CW probe
1 - (100%)
CW Doppler review
2 crystals/elements
1 constantly transmits
1 constantly receives
Able to detect small Doppler shifts
Accurately measure high velocities
No nyquist limit = no aliasing
No range ambiguity
DF = 1 (100%)
High sensitivity
CW probe
Non imaging
No backing material
-longer ring
-high Q-factor
-low bandwidth (narrow)
-one frequency
-higher sensitivity
Scale
Varies the range of velocity that can be displayed on the spectral recording
Increasing the scale _______ the display range
Increases
Sweep speed
Alters the speed at which the x-axis (time) is displayed on the screen
Higher sweep speed displays…
Fewer waveforms
Lower sweep speed display….
More waveforms
Wall filter
Allows the removal of high-intensity but low-velocity signals (clutter) from the Doppler spectrum
Short PRP = ______ PRF
High
Long PRP= ______ PRF
Low
An increase in the velocity between the source and receiver causes a _______ (greater or less) change in the received frequency
Greater
PRP short = PRF _____
PRP long = PRF ______ (takes system longer to listen)
PRF high
PRF low
How can you eliminate clutter
Increasing wall filter
What does mirroring & cross talk result from?
- Doppler gain set to high
- incident angle near 90 degrees
Doppler effect
A shift or change in frequency of an interrogating wave caused by relative motion between an observer & object
