Chapter 5 Flashcards
average attenuation in soft tissue is?
0.5 dB every centimeter
if the question is with units of V, which ratio are we talking about?
amplitude/voltage
if the question is with W, which ratio are we talking about?
power
power ratio?
output power/input power
sample volume
the anatomic region from which pulsed Doppler echoes are accepted
saturation
the amount of hue present in a mix with white
spectral analysis
separation of frequencies in a Doppler signal for display as a Doppler spectrum; the application of the Fourier transform to determine the frequency components present in a Doppler signal.
spectral broadening
the widening of the Doppler-shift spectrum; that is, the increase in the range of Doppler-shift frequencies present that occurs because of a broadened range of flow velocities encountered by the sound beam. This occurs for disturbed and turbulent flow.
spectral-doppler display
the presentation of Doppler information in a quantitative form of Doppler shift versus time. Visual display of a Doppler spectrum.
spectrum analyzer
a device that derives a frequency spectrum from a complex signal
stenosis
narrowing of a vessel lumen.
streamlines
a line representing the path of motion of a particle of fluid.
turbulence
random, chaotic, multidirectional flow of a fluid with mixing between layers; flow that is not laminar.
variance
square of standard deviation; one of the outputs of the autocorrelation process; a measure of spectral broadening (i.e. spread around the mean).
helps highlight turbulent flow states.
usually appears green on display.
viscosity
resistance of a fluid to flow
volumetric flow rate
volume of fluid passing a point per unit of time (ie per second or minute).
wall filter
an electric filter that passes frequencies above a set level and eliminates strong, low-frequency Doppler shifts from pulsating heart or vessel walls or tissue motion.
window
an anechoic region appearing beneath echo frequencies presented on a Doppler spectral display..
inertia
resistance to acceleration
laminar flow
flow in which fluid layers slide over each other in a smooth, orderly manner, with no mixing between layers.
streamlines are straight and parallel
luminance
brightness of a presented hue and saturation.
parabolic flow
laminar flow with a profile in the shape of a parabola
while fluid flows down a tube
form of laminar flow
phase quadrature
two signals differing by one-fourth of a cycle
plug flow
flow with all fluid portions traveling with the same flow speed and direction
at entrance of tube
speed of fluid is constant
form of laminar flow
moves as a unit
poise
unit of viscosity
poiseuille equation
the math description of the dependence of volume flow rate on pressure, vessel length and radius, and fluid viscosity.
priority
the gray-scale echo strength below which color-Doppler information is shown preferentially on a display.
pulsatile flow
flow that accelerates and decelerates with each cardiac cycle.
pulsed Doppler
a Doppler device or procedure that uses pulsed-wave ultrasound
range gating
selection of the depth from which echoes are accepted based on echo arrival time
resistance
pressure difference divided by volume flow rate for steady flow
Doppler-power display
Color-Doppler display in which colors are assigned according to the strength (amplitude, power, intensity, energy) of the Doppler-shifted echoes.
Doppler shift
reflected frequency minus incident frequency; the change in frequency caused by motion.
Doppler spectrum
the range of frequencies present in Doppler-shifted echoes.
Duplex instrument
an ultrasound instrument that combines gray-scale sonography with pulsed Doppler and, possibly, continuous-wave Doppler.
eddies
regions of circular flow patterns present in turbulence
ensemble length
number of pulses used to generate one color-doppler image scan line.
fast fourier transform
digital computer implementation of the Fourier transform.
a math technique for separating a spectrum into its individual frequency components.
filter
an electric circuit that passes frequencies within a define range.
flow
to move in a stream; volume flow rate.
fluid
a material that flows and conforms to the shape of its container; a gas or liquid.
frequency spectrum
the range of Doppler-shift frequencies present in the returning echoes.
gate
a device that allows only echoes from a selected depth (arrival time) to pass.
hue
the color perceived based on the frequency of light.
autocorrelation
a rapid technique, used in most color-Doppler instruments, to obtain mean Doppler-shift frequency.
baseline shift
movement of the zero Doppler-shift frequency or zero flow speed line up or down on a spectral display
bernoulli effect
pressure reduction in a region of high-flow speed.
bidirectional
indicating Doppler instruments capable of distinguishing between positive and negative Doppler shifts (approaching and receding flow).
clutter
noise in the Doppler signal that generally is caused by high-amplitude, Doppler-shifted echoes from the heart or vessel walls.
Color-Doppler display
the presentation of 2D, real-time Doppler-shift information in color superimposed on a real-time, grayscale, anatomic, cross-sectional image. Flow directions toward and away from the transducer (ie positive and negative Doppler shifts) are presented as different colors on the display.
compliance
distensibility; nonrigid stretch-ability of vessels
continuous-wave Doppler
a Doppler device or procedure that uses continuous-wave ultrasound
disturbed flow
flow that cannot be described by straight, parallel streamlines.
Doppler angle
the angle between the sound beam and the flow direction
Doppler effect
a change in frequency caused by reflector motion
Doppler equation
the math description of the relationship between the Doppler shift, frequency, Doppler angle, propagation speed, and reflector speed.
ultrasound can detect and present?
motion information
motion is detected by using
the Doppler effect
insufficiency/regurgitation
valves allowing reverse flow by not closing completely
units for viscosity
poise
kg/ms
pressure
force/are
distributed equally throughout static fluids and exerts its force in all directions
what’s the normal viscosity for blood?
0.035 poise at 37 degrees Celsius
hydrostatic pressure
describes the force of gravity on static fluid
pressure difference required for flow to occur
pressure gradient
aka pressure difference
the greater the pressure difference, the greater the flow rate
pressure diff/distance between the 2 pressure points
volumetric flow rate
is the volume of blood passing a point per unit of time
adult blood flow rate is 5,000 mc/min
types of flow
plug flow
laminar flow
parabolic flow
non-parabolic flow
disturbed flow
turbulent flow
pulsatile flow
nonsteady flow with acceleration and deceleration due to the cardiac cycle (beating heart)
happens in the heart and the arterial side
relationship between pressure and flow rate depends on impedance (resistance), inertia, and compliance (expansion and contraction) of the vessel walls
windkessel effect
expansion and contraction of vessels that keeps blood flowing forward
flow reversal
when no valves are present to prevent it
it’s normal in distal veins during diastole
continuity rule
volumetric flow rate is constant at every unit
flow speed ____ at a stenosis and ____ can occur distal to it.
increases, turbulence
occlusion
vessel is blocked and there’s no flow
bernoulli effect
decreased pressure in regions of higher flow speed
necessary o allow fluid to accelerate into the stenosis and decelerate out of if
if flow speed increases, the magnitude of the pressure drop increases
Doppler effect
is a change in frequency (and wavelength) caused by motion of a reflector, receiver, or a sound source
amount of change in frequency depends on reflector motion speed, angle between the wave propagation direction and motion, and the frequency of the wave emitted by the source
if a reflector is moving towards the receiver, the echo has a ___ frequency
higher
if a reflector is moving away from the receiver, the echo has a ___ frequency
lower
doppler shift
the change in frequency caused by motion is called Doppler-shift frequency
is equal to the received frequency - the source frequency
difference between the emitted frequency and the echo frequency from moving scatterers
positive doppler shift
received frequency is greater than the emitted frequency
approaching reflector
higher frequency
moves against propagation speed
negative doppler shift
received frequency is smaller than emitted frequency
receding reflector
lower frequency
moves along the propagation speed
a higher operating frequency will have a ___ doppler shift
larger
the doppler shift depends on the ____ of the doppler angle.
cosine
only the portion of motion direction that is ____ to the beam contributes to the doppler effect
parallel
the ___ the doppler angle, the ____ the doppler shift
larger, less
angle 90 degrees means
0.0 cosine aka 0 doppler shift
angle 0 degrees means
1 cosine
60 degrees means
0.5 cosine
error in calculated flow speed increases with what?
with angle
the higher the angle, the higher the error
doppler shift measurements aren’t reliable at angles greater than
60 degrees
color doppler displays present information on?
the presence, direction, speed, and character of blood flow and on the presence, direction, and speed of tissue motion
presents 2d, cross-sectional, real-time blood flow or tissue motion
presents anatomic information in gray-scale form and detects doppler-shift frequencies at several locations along each scan line
is an extension of gray-scale sonography
presentations of doppler info
audible
color-Doppler
spectral Doppler
strip chart recording
color doppler principle
if an echo has a different frequency from that emitted, a doppler shift has occured
a 90 degree doppler angle yields no doppler-shift on vessels
phasing is used to steer the pulse
all pulses are steered at the same angle, resulting in a a parallelogram presentation
autocorrelation
math technique used in signal processor to detect doppler-shift echoes
determines the mean and variance of the doppler shift signal at each location along the scan line
typically 100-400 doppler samples per scan line are shown
a 3-pulse minimum is required for one speed estimate
more pulses improve the accuracy of estimates or to improve detection of slower flow
color controls
gain
color window location
width and depth
steering angle: permits avoidance of 90 degree angle
color-map inversion: alternates the color assignments on either side of the doppler shift baseline on color map
wall filter: eliminates clutter caused by tissue and wall motion
priority: selects gray-scale echo strength below which color will be shown at pixel location
baseline shift: allows shifting the baseline up or down to correct aliasing
velocity range (PRF): controlled by operator, sets the PRF and the limit at color bar extremes, low value permits slower flows to be viewed but high probability of aliasing for faster flows
color map selection
variance
smoothing: aka persistence, provides frame to frame averaging to reduce noise
ensemble length: is the number of pulses used for each color scan line, min is 3, 10-20 are the most common, higher lengths give better estimates of mean doppler shifts but lowers FR
average attenuation for each centimeter in soft tissue is?
0.5 dB
color-doppler limitations
it’s angle dependent
lower FR bc several pulses per scan line are required
lack of detailed spectral info
max permissible FR is:
max FR = 77,000 cm-s / pen x LPF x ensemble length
max permissible FR for color-doppler?
max FR = 77,000 cm-s / pen x LPF x ensemble length
doppler shift displays
hue represents the sing of the doppler shift
changes in hue, saturation, or luminance up or down represents high doppler shift magnitude
change in the hue from left to right on map represents variance
the doppler detector in color-doppler yields what?
the sign mean, variance, amplitude, and power of the doppler spectrum
need help with angle
help
other names for doppler power
power doppler, color power doppler, color-doppler energy, ultrasound angio, power angio
doppler power displays
present 2D doppler info by color-encoding the strength of the doppler shifts
assigns color values to doppler shift power values
the power of doppler shifts is determined by the concentration of moving scatterers producing doppler shifts
pros and cons of doppler power
pros:
free of aliasing
not angle dependent
more sensitive to slow flow and small/deep vessels bc lower PRF can be used
con:
shows only the presence of flow
spectral doppler displays
two types: CW and PW
used to image the heart and vessels
CW and PW present information in an audible and visual form corresponding to scatterer motion
PW spectral doppler
can use range gating
usually combined with gray-scale (called duplex scanning)
range gate definition
PW doppler has the ability to select information from a particular depth along the beam
bidirectionality
if the instrument can distinguish between positive and negative doppler shifts
CW spectral doppler
has 2 crystals or groups of crystals (one transmits constantly and the other listens constantly)
has CW oscillator and a doppler detector that detects doppler shifts
components of CW doppler system
oscillator
receiving crystal that produces voltages with frequencies equal to the returning echoes’ frequencies
the RF amplifier that increases the echo voltage amplitude
doppler detector
audio frequency amplifier that strengthen this different frequency
the phase quadrature detector
oscillator
part of the beam former for CW that produces a continuously alternating voltage that drives the source crystal
2-10 MHz
doppler detector
part of the signal processor
in the mixer, the sum and difference between the two frequencies is calculated
the filter removes the sum and leaves the difference which is the doppler shift frequency
echo frequency-oscillator frequency
phase quadrature detector
determines the direction and separates doppler shift voltages into separate reverse and forward channels
positive and negative doppler shifts are heard separately
voltages are sent to display
positive shifts=
toward the probe beam
negative shifts=
away from the probe beam
when angled 90 degrees, the doppler shifts are
equally positive and negative so they cancel each other out
angle incorporation or correction
must be accurate to correctly display the doppler shift speed vs time
angles at 30-60 degrees are best
most common is 60
wall filter
aka thump filter
rejects frequencies below a value
is used to remove clutter
adjustable over ranges of 25-32,000 Hz
what’s high intensity and has low frequency doppler shifts?
vessel wall or cardiac valve motion
pulsed-wave operation
pulser generates pulses 5-30 cycles long
echoes are processed in detector in which they’re amplified and doppler shifts determined
range gating
based on the echoes arrival time, echoes at a certain depth can be selected by the amplifier gate
enables depth selectivity and a smaller Doppler sample
operator controls gate length and location
longer gate lengths are used for what?
for searching for desired vessel and flow location
what determines the Doppler sample volume?
beam width at the sample volume depth,
gate length,
emitted pulse length
1/2 of a pulse length is added to gate length
spectral analysis
visual picture of what listeners hear from the loudspeaker
provides a more useful way to present doppler information visually
is in the form of a Doppler frequency spectrum
shorter wavelengths are used for what?
for spectral analysis and evaluation
improves spectral display quality
frequency spectrum
the breaking up of the frequency components of a wave/signal and putting them in order of increasing frequencies
define spectrum
an array of components of a wave, separated and arranged in order of increasing frequency
fast fourier transform
is the math technique the system uses to derive the Doppler spectrum from the echoes
can show spectral broadening
spectral displays
the amplitude/power of each doppler shift is presented as brightness
displays presentation of doppler spectra vs time aka doppler shifts vs time
doppler signal power is proportional to blood cell concentration
doppler spectra
doppler shift on horizontal axis
Power or Amplitude of each frequency on the vertical axis
in venous flow, the display is constant
spectral broadening
indicative of disturbed or turbulent flow (bc of their high variation of velocities) and can be related to a stenosis
can also be made by excessive doppler gain or excessive sample volume length or beam spreading (with wide aperture arrays)
downstream
distal
upstream
proximal
tardus-parvus waveform
is typical of flow with proximal stenosis
typical ranges for vascular?
flow speed, angles, operating f, doppler shift
flow speed: 10-100 cm/s
doppler angles: 30-60 degrees
operating frequency: 2-10 MHz
doppler shift: 100 Hz-11 kHz
flow is a ___ term
volumetric term
volume/time
another word for ensemble
packet
smaller angle means
better angle
the nyquist criterion is
1/2 the PRF
pros and cons of CW
pro: peak velocity obtainable bc CW has no nyquist limit
cons: no ability to do range gate
pros and cons of PW
pro: range discrimination (we can determine the depth)
nyquist limit and aliasing are cons
in spectral displays, the thickness of the mountains are called what
envelope
the thickness means the range of velocities
which is why spectral broadening means it’s detecting tons of different velocites/frequencies
when pressure decreases, velocity ____.
increases
the highest velocity occurs when?
during peak systole
_____ is represented on the horizontal or “x” axis on a spectral Doppler trace.
time
Peak systole corresponds to the:
highest velocity in the waveform
ΔF = +/- [(2 * v * fo) / c] * Cos θ
The symbol “delta F” in the Doppler equation represents which of the following?
Doppler shift
The Nyquist limit is equal to ____ the PRF.
One half
True or false? The Doppler effect is the change in the frequency of sound reflected off a moving target.
True
ΔF = +/- [(2 * v * fo) / c] * Cos θ
The symbol “fo” in the Doppler equation represents which of the following?
Transmitted frequency
True or false? Color Doppler provides accurate quantitative information regarding blood-flow velocities.
False
True or false? There is no spectral window on a continuous wave spectral Doppler graph.
True
Aliasing is a Doppler artifact that is characteristic of ____ systems.
Pulse wave
An advantage of continuous wave Doppler would be:
No Nyquist limit to the maximum velocity the system can record
True or false? Spectral Doppler provides accurate quantitative information regarding blood flow velocities.
True
The brightness of the spectral trace at any point on a spectral histogram represents:
The number of red blood cells traveling at that particular velocity at that point in time
Techniques to minimize/eliminate aliasing include all of the following except:
Reduce the overall gain
In the BART system of display, red signifies flow in which direction?
Flow detected moving towards the probe
A stenosis is defined as a/an:
Abnormal luminal narrowing
True or false? The sample volume is used to provide the Doppler angle information the system uses to calculate velocities.
False
True or false? A stenotic region in a vessel or across a valve causes blood flow acceleration.
True
The volumetric flow rate equation (Q = ?/?) relates which two of the following parameters?
A and B
pressure difference and resistance
What flow is associated with severe stenosis?
Turbulent
The standard for display on a spectral Doppler trace is _____.
Velocity
True or false? Aliasing on a spectral Doppler trace does not interfere with accurate velocity measurements.
False
True or false? It is always necessary to make the color box as wide as possible in order to optimize color Doppler sensitivity.
False
True or false? The range gate of the pulsed Doppler system is usually placed close to the vessel wall and away from the center stream, in order to obtain the fastest flow profile.
False
In the BART system of display, blue signifies flow in which direction?
Flow detected moving away from the probe
The wall filter control for spectral Doppler is used to:
Eliminate low velocity echoes from the spectral trace
ΔF = +/- [(2 * v * fo) / c] * Cos θ
The symbol “v” in the Doppler equation represents which of the following?
Velocity of the red blood cells
The cosine of 90° is ____.
0
True or false? Normal flow in a blood vessel is usually described as laminar flow.
True
True or false? The technique for color flow display known as power angio, is more sensitive to low flow states than Doppler.
True
True or false? The term antegrade refers to the normal direction of flow for a particular blood vessel.
True
True or false? The Doppler shifted frequency is directly proportional to blood flow velocity.
True
True or false? Spectral broadening occurs when there is a widening of the spectral envelope and filling in of the spectral window.
True
True or false? Flash artifact is a spectral Doppler phenomenon.
False
ΔF = +/- [(2 * v * fo) / c] * Cos θ
The symbol “c” in the Doppler equation represents which of the following?
Speed of sound in soft tissue
ΔF = +/- [(2 * v * fo) / c] * Cos θ
The “Cos theta” in the Doppler equation represents which of the following?
Doppler angle
True or false? For cardiac applications an angle of 20 degrees or less is acceptable for spectral Doppler studies.
True
True or false? The term retrograde refers to reverse flow detected in a particular vessel.
True
True or false? A spectral analysis graph is a histogram that relates velocity or frequency shift with time and allows accurate measurement of peak velocities.
True
True or false? The ultrasound PRF is determined by the voltage PRF applied to the transducer element.
True
The ultrasound pulse repetition frequency is equal to the voltage pulse repetition frequency of the pulser.
Causes of disturbed flow include which of the following?
Tortuous vessel
Vessel widening
Vessel branching
What flow is associated with severe stenosis?
Turbulent
The color Doppler display pattern that would accurately depict a normal physiologic flow in a normal vessel would be:
Brighter colors toward the center of the vessel with darker colors seen peripherally
what does the black band above and below the baseline represent in spectral display?
the signals attenuated by the wall filters
what’s the assumed Doppler angle in cardiac?
0 degrees
what does insonification angle mean?
doppler angle
color doppler yields what?
velocity information
work
total energy expended
power x time
poiseuille’s law deals with what kinds of tubes?
with long straight nonstenosis vessels
diameter of the entire vessel
continuity rule deals with what kinds of tubes?
with the diameter of a short section of the vessel
recommended angles for color doppler?
30-60 degrees
color flow
color doppler
where are the sing, mean, and variance of the Doppler signals stored?
addresses that correspond to anatomic locations.
BART
blue away, red towards
RABT
red away, blue towards
make the color box only as ___ as necessary
only as big as necessary
bc the larger it is, the lower the FR will be
velocity range
aka scale
adjust color PRF for Doppler signal
sector arrays are sent out in different directions so color has _____.
different Doppler angles
what is the best angle for gray-scale imaging?
90 degrees
what is the best angle for Doppler?
0 degrees
