Doppler edelman ch 19 and color doppler pp, spectral analysis pp Flashcards
doppler shift is also called _________
doppler frequency
the process of extracting the low doppler frequency from the transducer carrier frequency is called ____________
demodulation
doppler shift(Hz) equation
doppler shift(Hz)= reflected frequency - transmitted frequency
if doppler shift is positive (frequency higher than the transmitted frequency), what does that mean
blood cells are traveling toward the transducer
doppler frequencies indicate __________, not speed
velocity
speed vs velocity
speed in magnitude
velocity is magnitude and direction
when velocity is halved, the doppler shift is __________
halved
flow towards transducer is where on baseline
above baseline
simultaneous anatomic imaging and doppler is called _______________
duplex imaging
what term is used for bidirectional doppler
phase quadrature or quadrature detection
what is the most common error associated with doppler ultrasound
aliasing
what is the very top or very bottom of the spectral display called
nyquist limit
what is the part of the spectrum that appears on the the opposite side after reaching its limit
aliasing
can aliasing happen with continuous wave doppler
No, only with pulsed doppler
nyquist limit (hz) equaltion
= PRF(HZ) / 2
2 ways to avoid aliasing are
raise the nyquist limit
reduce the doppler shift
produces a continuously alternating voltage that drives the element
Oscillator
detects the difference between source and reflected frequency & determines the Doppler shift (Doppler shift are normally in the audible range and are applied to a loudspeaker)
Doppler detector
analyzes the spectrum for visual display
Spectrum analyzer
Doppler detector that has the ability to determine positive and negative shifts contained in incoming echoes and to separate them into two channels for display
-Two output channels
-Represents forward (positive Doppler shift) and reverse flow (negative Doppler shift)
Phase quadrature detector
Performed by a high-pass (wall) filter
-Eliminates high-intensity, low-frequency
Doppler shift echoes resulting from
vessel or heart wall motion
-Rejects strong echoes that obstruct
weaker echoes
Wall filter
ADJUST WALL FILTER WHEN NEAR WALL
Same crystal to both transmit and receive
Presents one-dimensional information audibly and visibly
Has the ability to select listening depth
PULSED WAVE DOPPLER
Allows operator to separate flow information from two vessels or to localize within a vessel
-Uses a “gate”
-When open, allows the passage of voltages representing echoes; when closed, prevents the passage of voltages
- Determined using echo-arrival time (corresponds to depth of reflector)
-Gate should be open to 1/2 width of the vessel to prevent artifactual spectral broadening
Range selectivity -
Pulser generates pulses of ___________ cycles
PULSED WAVE DOPPLER
5-30 cycles
Autocorrelation is a ______________ that is used to compare each echo to the corresponding echo from the previous pulse to determine motion
Autocorrelation is used with color Doppler because of the enormous amount of Doppler information that requires processing. Typically 100 to 400 Doppler samples per scan line (more pulses = improved accuracy)
Autocorrelation is slightly less accurate, but substantially faster, than FFT
Decreases frame-rate as it is displayed as an over-lay on the gray scale image
digital process
3 components of color flow
Hue
Saturation
Luminance
perceived color, can demonstrate flow disturbances and turbulence
hue
Hue used to indicate the ________________
Blue: negative shift (away from transducer)
Red: Positive shift (towards transducer)
direction of flow
_____________ – the amount of color in a mix with white, represents magnitude (# of RBCs) moving at that velocity
Saturation
______________ – brightness of color represents echo amplitude (velocity)
Luminance
top color indicates blood coming to/away from transducer
to
how to increase color fill in……3 ways
Angle color box with vessel (decreases Doppler <)
Decrease scale (too low if aliasing)
Increase color Doppler gain until get “speckle” then decrease until speckle is gone
___________ or color bleed artifact occurs when the color signal indicating blood flow extends beyond its true boundaries,
spreading into adjacent
regions with no actual flow.
Blooming
The packet size is the number of sound bursts (pulses) transmitted per color scan line to determine blood velocities and assign a color.
How Many?
The number of pulses per line is termed: ensemble length, packet size, dwell time or shots per line (these are synonymous names).
How Long:
The number of pulses transmitted in one second is the pulse repetition frequency (PRF). How many of those pulses are fired on each scan line is the ensemble length.
Doppler (Color) Packets info
just read
color doppler energy Also called Ultrasound Angio, Power Doppler, Power Angio
demonstrates or does not demonstrate direction?
does not
Frequencies of complex signal separated through process of ____________
spectral analysis
what does spectral mean
collection or assortment
what does analysis mean
to analyze or examine
The technique for identifying frequency components in a complex signal or waveform and spreading them out in frequency order
spectral analysis
Spectral analysis is performed in a Doppler Instrument _________ and __________
electronically and mathematically
spectral analysis is accomplished digitally by the __________
Fast Fourier Transform (FFT)
A mathematical technique
Identifies individual components that comprise the complex signal
Process of separating a waveform into a series of single frequency sine-wave components
Fast Fourier Transform (FFT)
___________ - each analysis presented as a single vertical line representing the bandwidth
Frequency
__________ - represented by the various brightness levels; represents the number of RBCs moving at that velocity
Magnitude
_________ - dimension of time obtained by sampling the Doppler signal repeatedly in small increments of a few milliseconds
Time
Random movement of RBCs causes many different Doppler shift frequencies to be detected
RBC Doppler shift frequencies normally grouped together, forming a spectral tracing that is narrow in systole and wide in late diastole
doppler waveform wording on board
what are some organs with low resistant blood flow
brain, liver, kidneys
will take all the blood they can get
spectral window is good. when spectral window starts closing it means _________
stenosis
________________ and window reduction are equivalent terms.
spectral broadening
Narrow spectra are seen in the center of the vessel and broad spectra are seen near the walls (slower flow)
Narrow spectra are seen in large vessels and broad spectra are seen in small vessels
This is because in a small vessel we are forced to sample the fastest flow (center) because of the size of the vessel
dont quite understand it
Spectral broadening can be produced
artifactually by ____________________
Can also be produced by using a large gate
(including flow across the vessel)
excessive Doppler receiver gain.
_____________ provide information about flow at the site of measurement and distal to it (resistance)
Peak flow speeds and degree of spectral broadening indicate the degree of stenosis
Spectral tracings
Accurate identification of spectral tracing requires minimum __________ samples per second
two
High velocities appear as negative sine - called _______________
A wrap-around of the Doppler signal
aliasing
if you cant change nyquist limit scale anymore then change ______________
focal zone amount or depth
3 parts of triphasic flow
Systole - high frequency; large forward velocity peak produced by systole
Early diastole - Brief phase of flow reversal
Late diastole - Low- velocity forward flow
A _____________ will have abnormally high peak systolic frequency signal
stenosis
___________ to stenosis or occlusion - single forward velocity component, flow remains above baseline (no reversal)
Distal
(decreased/Increased) peripheral resistance - peak systolic frequency lower than normal, waveform flat and rounded
increased
___________ ultrasound is the machines ability to display real time scanning with Doppler Spectral analysis at the same time.
Duplex
____________ ultrasound is the machines ability to display real time scanning with Doppler Spectral analysis and color overlay all at the same time.
Triplex
Boards: Tardus parvus refers to a pattern of Doppler ultrasound spectral waveform resulting from arterial stenosis. The phenomenon is observed downstream to the site of stenosis, and is due to reduced magnitude of blood flow through the narrowed vessel during ventricular systole
type of waveform pulsatile, phasic, non phasic, aphasic
pulsatile
type of waveform pulsatile, phasic, non phasic, aphasic
phasic
type of waveform pulsatile, phasic, non phasic, aphasic
nonphasic
type of waveform pulsatile, phasic, non phasic, aphasic
aphasic
Pathologic causes of nonphasicity may be considered including:
Cirrhosis
Spectral broadening is due to the narrowed caliber of compressed hepatic veins
Hepatic vein thrombosis (Budd-Chiari syndrome)
hepatic vein thrombosis is much less common than portal vein thrombosis.
When nyquist limit is increased so is _______
Prf
Higher prf (increases/reduces) sensitivity to low velocities
Reduces
The ___________ is a change in frequency that occurs when a wave hits a moving reflector
Doppler effect
The change in frequency caused by motion is called the _____________________
Doppler shift frequency
received freq minus source frequency =
doppler shift frequency
2 things that makes the doppler shift frequency positive
received frequency greater than transmitted frequency
If the RBC’s (a.k.a. scatterer, reflector, receiver) are approaching the
transducer
2 things that makes the doppler shift frequency negative
➢ If the received frequency is less than the transmitted frequency: negative
shift
➢ If the RBC’s (a.k.a. scatterer, reflector, receiver) are moving away from the
transducer: negative shift
Know all three formulas for Doppler equation on p. 180 in Kremkau
Doppler shift is proportional to:
➢ Flow speed
➢ Operating frequency
The Doppler shift is dependant on the Doppler angle in the form of Cosine.
➢ The ___________ the Doppler angle the less the Doppler shift
➢ Said differently: If the Doppler angle increases the frequency decreases.
larger
Typical Ranges
➢ Flow speeds: 10-100cm/s
➢ Doppler angles 30-60 °
➢ Operating frequencies 2-10 MHz
➢ Doppler shifts in range of 100 Hz to 11kHz (vascular studies)
➢ Range of intensities 0.2-400 mW/cm2
does continuous wave doppler have aliasing or nyquist limit?
no
Aliasing occurs more easily with higher/lower transducer frequencies.
higher
Lower frequency
transducers are not as likely to reach the Nyquist limit.
A Doppler instrument that can distinguish between positive and negative shifts is
called _________.
bi-directional
A pulse echo system should have a ______ Q factor. A ________ Q factor implies a short spatial pulse length, which means higher spatial resolution.
low
At least ________ samples per cycle are required to accurately identify a sine or cosine
wave.
two
____________ means a vertical thickening of the spectral trace.
Spectral Broadening
Duplex scanning
B scan and spectral analysis
Triplex scanning
B scan, spectral and color all displayed
These high intensity, low frequency Doppler shifted echoes from the wall are often called ____________
‘clutter’
