Exam 2 Flashcards by Angela Mel

Source (transducer) determines the ______ of the wave

Frequency

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The medium (RBC’s) determines the ________

Propagation speed

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Wavelength equation

c
—
f

c= propagation speed
f=frequency

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Stationary source, transducer =

Reference signal

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Reflector is moving

RBC’s flowing through vessels

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Positive Doppler shift the reflector is moving ________ the transducer

Toward

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Positive Doppler shift the reflected frequency is_________ than the transmitted frequency

Higher

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Positive Doppler shift
- positive or negative shift?
- above or below baseline?
- higher or lower frequency?

positive
above
higher

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Negative Doppler shift:
- positive or negative shift
- above or below baseline
- higher or lower frequency

negative
below
lower

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If reflector is moving away from the transducer the reflected freq is _________ than transmitted freq

Lower

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Doppler shift equation (frequency)

Doppler shift (Hz) = reflected - transmitted

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Is the Doppler frequency range within the audible range?

Yes, Doppler shift between 200 Hz & 15,000 Hz

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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

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Doppler frequency is ___________ proportional to the reflector velocity

Directly

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Reflector velocity doubles = _________ of Doppler frequency

Double

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Higher transmit frequency = ________ frequency shift
(higher/lower)

Higher

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Lower transmit frequency = ___________ frequency shift

Lower

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When distance between source & observer is increasing the relative motion is “away” and a ___________ occurs

Decompression

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Distance between source & observer decreases, the relative motion is “towards” & a __________ occurs

Compression

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Compression leads to ________ frequency & a ________ frequency shift
(higher/lower) (positive/negative)

Higher
Positive

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Decompression leads to a _________ frequency & __________ frequency shift
(higher/lower) (positive/negative)

Lower
Negative

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Faster velocity will result in a _________(greater or lesser) frequency shift

Greater

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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

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Where is insonification angle (angle of insonation) measured?

Between the beam steering direction and the direction of the flow

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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

1. Accuracy 2. 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..

1. Raise speed limit - increase scale 2. Reduce Doppler shift (speed)

Nyquist is ______ PRF

1/2 (half)

Methods to reduce aliasing..

1. Increase PRF/scale - (raises nyquist limit) 2. Get closer - adjust depth 3. Lower transducer freq 4. Shift the baseline 5. 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