Colour Doppler Flashcards
Unlike spectral Doppler
Colour offers a wonderful survey tool to quickly assess large regions of the patient
Blessings of colour
- Quick survey of large area of patient
- Detection of disease
- Blood flow detection in malignant/benign tumors can demonstrated
- Provides spatial dimension over large area
Curse of colour
Yields only an estimate of the mean velocity
Does not give full spectrum information
Can appear normal visually while spectral depicts presence of disease
Must be used with spectral Doppler to interpret disease in vascular studies
Does not provide peak velocities, velocity gradients or spectral broadening
Colour Doppler
Colour Doppler allows flow information over a large spatial areas
Scanned modality
Provides lateral dimension
In colour, after the transmit pulse, it listens with a series of range gates which spans the entire time until the next transmit pulse
Colour, received pixel-by-pixel information to determine the spatial data for the depth
Spectral Doppler
Spectral Doppler provides information along a specific line or with a specified gate range
Non-scanned modality
Does not provide lateral dimension
In Spectral, after the transmit pulse, it listens to only the specified rage gate at a specific depth
How is colour Doppler preformed
Color Doppler utilizes Doppler techniques to provide flow information over a scanned region of the patient.
Unlike PW and CW Doppler, color Doppler does not provide spectral information.
Color Doppler provides an estimate of the mean velocity.
what is created by repeatedly scanning a single line in the same direction
Colour packet
the packet is then
Scaned across the body to produce a frame
how is colour similar to 2D
packets of acoustic lines are scanned across the body
how is colour similar to spectral
A single line is transmitted repatedly in the same directin
Creating the colour scan step one
TTransmit pulse in a single line
creating the colour scan step two
Repeats this 4-12 times in the same line (colour packet)
creating the colour scan step three
Doppler information from the scan line is obtained by a series of range gates within each acoustic line of the packet
creating the colour scan step 4
Correlation is then made using each of the lines within the packet to yield an estimated mean velocity at each range gate along the line
creating the colour scan step 5
The direction of the line is then changed and a new packet is then transmitted in the new direction
creating the colour scan step 6
This process repeats until information is acquired from the scan region of interest
why is a packet of lines transmitted
So that an average velocity can be determined at each depth along the line
Colour has _______temporal resolution
Poor temporal reoslution
why does colour have a poor temporal resolution
Since every colour line displayed on the screen represents an entire packet of acoustic lines, creating an entire colour scan requires many more acoustic lines than creating an entire conventional 2D scan
A higher frame time
Causes lower frame frequency
A lower frame rate implies a greater likelihood of not capturing a short duration event
Creating the colour scan step 7
Once the packet has been transmitted and correlation performed the data is filtered and colours assigned on a pixel-by-pixel basis based on a colour scale/bar. The colour bar is a key which relates mean frequency shifts detected with a colour
creating the colour scan step 8
Once the system determines the Doppler shift as it is assigned a colour based on the colour bar/scale (colour map)
Colour bar has
negative(-) and positive(+) direction
Positive-towards
Negative-away
Negative implies what
Negative frequency shift and the insonifcation angle is greater than 90
positive implies what
positive freuqency shift and the insonifcation angle of 0-90 degrees
in the center of the colour bar
black band which represents the baseline and colour wall filters
if no frequency shift is detected
If no frequency shift is detected or a low frequency is detected it is filtered out and will display an absence of colour in the image
Overgained
Random color speckle
what does aliasing result in
wrapping of the colours around the baseline
Colour wall filters
-no separate control for colour wall filters (unlike spectra)
how are most colour wall filters set
percentage of the color scale
As colour scale increases
Wall filters also increase, resulting in less ability to visualize lower velocity flow
Higher wall filter percntge
Larger black band
Determining flow direction
Notice in this example that the flow is not changing in direction or speed (constant velocity) yet the flow looks very different traversing the vessel. This appearance is the result of the changing angle to flow formed between the constant flow direction and the varying steering angle.
Power angio
disadvantage of not conveying flow direction information, but is advantageously much less sensitive to angle effects. Angio is frequently used when there are low velocity flows, especially in small vessels.
before assessing flow direction
Must assess the colour bar
what is aliasing
Occurs when the Doppler shift excessds more than half the PRF
where is aliasing more likely to occur
High velocity flow (like center stream of vessel)
Regions of acceleration (bends, kinks, twists, narrowings,
convergence)
Angles which result in greater frequency shifts (close to 0 and 180
degrees)
Higher frequency transducers (recall fDop is proportional to fo)
what does aliasing look like
Notice that both the “towards” and “away” colors appear simultaneously (near the vessel walls and in the center of the vessel) even though the angle to flow is the same.
when is aliasing useful
Aliasing is often useful in recognizing reverse flow patterns as in this case of mitral regurgitation.
Since the colors on either side of the baseline usually present a sharp contrast, flow that is aliased is easy to distinguish for non-aliased surrounding flow.
Colour persistence
technique in which frames are “averaged” over time.
are frames weighted equally in colour persistence
No
heavier weighting of the latest frames, and less weighting of earlier frames
Objective of persistence
improve signal to noise (increased sensitivity).
How does persistence affect duration of events
The effects of persistence are opposite for short duration events than for longer duration events. The use of higher persistence can make short duration events completely disappear, while making longer duration events persist even longer than reality.
what is the trade off of colour persitsence
The trade-off is temporal resolution
Signals present in many frames may only be present in one frame
Using a higher persistence may allow an event to be missed
Colour Priority
set by sonographer
what is colour priority
When a pixel has both a grayscale signal and a colour signal, this function determines if the colour is displayed or the grayscale is displayed
Higher colour priority implied what
higher grayscale amplitude threshold
what does colour prioroty use
Thresholds to dertremine what grayscale level 2D data is presented and below which colour data is presented
what is colour power doppler
Color power Doppler offers improved flow sensitivity, especially to low flow states, and tends to be less angle dependent than conventional color Doppler. Color power Doppler encodes the flow based on the power of the reflected flow signal.
does colour power doppler give flow infomration
No
why is spectrum/PW Doppler needed
sort out the jumble of Doppler frequencies to allow quantitative information and Colour Doppler for qualitative information
Doppler spectrum
The echoes that return to the transducer from a blood vessel contain only Doppler frequency shift information; yet the Doppler Spectrum often displays both velcity(cm/sec or m/sec) and Frequency (kHz).
what does doppler use to obtain information on velocity and frequency
Doppler angle
Duplex Doppler: colour flow image
The vessel, the sample volume, and the Doppler line of sight are shown in the colour flow image at the top of the display screen
Duplex Doppler: Colour flow information
The colour bar to the right of the image shows the relationship between the direction of blood flow toward the transducer. This is logical as this part of the bar is nearest to the transducer. The red is toward and blue is away.
Duplex doppler: Doppler Angle
The Doppler angle for the Spectral Doppler appears at the upper right of the display screen, in this case 60degrees.
Duplex Doppler: Time
The time is represented on the horizontal (x) axis of the Doppler spectrum at the base of the display. The lines represent divisions of a second. The space between on large line to another is a second.
Duplex Doppler: Velocity
Blood flow velocity is shown on the vertical (y) axis of the spectrum. In this case it is demonstrated on either side of the y axis. On some systems, one side is velocity and the other (y) is the frequency.
Duplex Doppler: Distribution of velocities
The distribution within the sample volume is illustrated by the brightness of the spectral display (z-axis). It is proportionate to the number of blood cells at that specific point in time causing the frequency shift. It distributes the flow energy, power and amplitude
Duplex Doppler: Flow direction
The direction of flow is shown in relation to the spectrum baseline. In this case, flow toward the transducer is shown above the baseline, and flow away from the transducer is shown below the baseline.
Duplex Doppler: Peak Velcouty Envelope
The peak velocity throughout the cardiac cycle is shown by the green line outlining the Doppler spectrum. You may also achieve this by placing a caliper at the highest/mean aspect of the spectrum.
Duplex Dopper: Pulse Repition Freuqency
The PRF for the colour flow image is shown at the left of the image
The PRF for the spectral Doppler is much higher as shown to the right of the image
The difference illustrates the fact that the colour flow image is based on the average Doppler frequency shift or velocity (lower), while the spectral Doppler are shown as absolute without averaging (higher).
Auditory Spectrum
The human ear was the spectrum instrument for Doppler initially
The ear is a highly capable spectrum analysis instrument which is evident in its ability to distinguish one person’s voice from another
High grade stenosis has a distinctive whining or whistling sound and this can be heard by us!
However, the ear is purely qualitative and is not equipped with a hard copy output for permanent storage!!!!
Sample Volume
The spectrum shows blood flow information from a specific location called the Doppler sample volume
Three characteristics of sample volume
. It is a volume and contains three dimensions, although thickness is not displayed on our duplex image and may cause localizations artifacts. Adjacent vessels may be within this sample volume and we may not be aware.
2. the actual shape and size of the sample volume may be somewhat different from the linear representation shown on the duplex image. 3. Doppler sample volume displays flow information only within the sample volume and does not provide information about flow in other portions of the blood vessel that are visible on the ultrasound image.
Arterial spectral nalysis
Peak velocity Pulsatility Arrthymias Plaques formation Aneurysms Type of Flow Stenotic lesion
Venus spectral analysis
Spontaneous flow Phasic flow Respiratory changes Valsalva Augmentation Unidirectional flow Competency
what is colour Tissue Doppler
modality that employs the Doppler effect to assess muscle wall characteristics throughout the cardiac cycle including velocity, displacement, deformation, and event timings
what can tissue doppler meaurements be used to assess
Measurements can be used to assess myocardial performance in various disease states, monitor treatment response, and provide important prognostic information.
TDI velocity and deformation assessment
measure myocardial with values that are highly influenced by loading conditions
Increased preloadincreases systolic tissue Doppler velocities while increased afterload reduces those velocities.
What does TDI make possible
makes it posisble to record lower Doppler shift freuqencies of high energy generated by ventricular wall motion that are purposely filtered out in standard Doppler blood flow stidues.
how can tissue Doppler be performed
pulsed Doppler, 2DColour Dopper, and M-mode colour mode Doppler.
Pulsed Doppler tissue image
high level of temporal resolution and can therefore be used to analyze the temporal relationship between myocardium systolic and diastolic velocity waves
Tissue Doppler display
Displays velocity over time
PW Doppler does not
Measure strain directly
what infor can tissue Doppler provide
Velocity and displacement information can be determined for the whole image because it is a scanned modality
The perceived sensitivity on the image quality will vary depending on many system controls:
Transducer Positioning of transducer on phantom Transmit power Receiver gain Focus depth Post processing curves (compression/dynamic range) Ambient Light Monitor contrast setting
when testing, msut ensure what
All the controls ate the same
If the perceived sensitivity will changes, leading to incorrect conclusion that the system performance has degraded
Care must be taken when testing to make certain that the derived conclusion if based on actual system variation and not a change in procedure
Tissue equivalent phantoms are made of
graphite-filled aqueous gels or urethane rubber material
Graphite partciles
Scatters, attenuation is similar to that for soft tissue and propagation speed
Tissue phantoms
echo-free (cystic) regions or various diameters and thin nylon lines for measuring detail resolution and distance accuracy
Cones or cylinders may also be used to demonstrate hyperechoic or hypoechoic objects
What do tissue phantoms simulate
Tissue properties Assess detail resolution Assess contrast resolution Penetration Dynamic range TGC operation
what aspects are tested with phantoms
Detail resolution (lateral, axial, and elevation)
Sensitivity
Contrast resolution
The dead zone (area close to the transducer dominated by reverberation)
Dimensional measurement accuracy (depth, diameter, area, volume, etc.)
Testing for resolution
Must know axis/face the phantom the transducer is being placed
general phantoms test for
Dead zone Axial resolution Lateral resolution Penetration Image Uniformity Distance accuracy Focal zone Cyst characteristics (size, shape, fill-in)
What do general purpose phantoms do
mimic soft tissue characteristics close to the properties seen in a clinical setting
Propagation velocity
Scattering
Attenuation
Multi-purpose tissue/cyst phantom
Can be used to test many different aspects of the ultrasound system
Dead Zone Detail resolution (lateral and axial) Depth accuracy Measurement accuracy Contrast resolution Penetration
Tissue equivalent phantom
With tissue-mimicking material the phantom can also be used for penetration tests, since this material has attenuation properties similar to tissue.
Specialized phantoms
Specific applications
Contrast Resolution
Slice thickness
Elasticity
Beam shape determination
Specialty imaging such as breast, thyroid, prostate, heart and fetus’
Contrast resolution phantoms assess object size resolvability for varying levels of contrast
Dead zone
Corresponds to the region adjoining the transducer in which no useful information s collected in part because of the pulse length and reverb from the transducer phantom interface
what is the dead zone distance
The dead zone is the distance from the front face of the transducer to the first identifiable echo
what is not present in the dead zone
The tissue scatter from parenchyma is not present in the dead zone
To test the dead zone
The depth of the rod that can visualized closest to the surface or the depth at which texture is visualized indicates the axial extend of the dead zone
Dead zone performance criteria
<3= <7mm
3-7=<5mm
>7=<3mm
Axial resolution
Ability of the system to resolve two closely spaced objected along the axis of the beam
SPL-which depends on the power, transmit frequency and length of ringing
This is assessed by evaluating closely spaced rods oriented vertically
Axial resolution limit
The smallest space distance between the rods in the group determines the axial resolution/limit of the system to determine axial separation
Lateral resolution
Ability to distinguish two objects adjacent to each other within the scan place in the direction perpendicular to the beam axis
Decreasing beam width by focusing improves the lateral resolution
Small beam with high scan line density allows small objects to become distinguiabl
Lateral resolution is assessed by…
closely spaced rods orientated horizontally
lateral resolution limit is expressed as…
smallest distance between any rods resolved at a particular depth
Because the rods are seen at different depths, using the focus lets us determine the lateral resolution at specific depths with focusing the beam
Focal Zone
The maximum intensity and narrowest beam width occur at the focal point
best lateral resolution
Beam pattern is obtained by scanning equally spaced vertical rods
How is focal zone assessed
Each rod appears as a line on the display in which the length of the line signifies the width of the beam at that depth
the focal zone can be
Electronically steered to reduce beam width and improve lateral resolution at different depths
Focal zone banding
Brighter region and horizontal lines
seams between each of the lines that have been pasted together
Vertical distance measurement
axis of the beam
Vertical distance is determined by
The elapsed time between pulses transmitted and received is measured which allows the ultrasound machine to calculate distance to the interface
Vertical distance measurement
Is checked by comparing distance indictors in the vertical direction with the known separation between rods in a phantom
Image is analyzed b measuring the distance between rods located at the extremes of the field of view
Measurement is used to identify….
Miscalibration because errors are more likely to occur with greater distances
Vertical distance measurement should be accurate to
2% or 2mm
What may contribute to phantom error (vertical distance meaurement)
Excessive pressure on the phantom
Horizontal distance measurement
Perpendicular to the beam axis within the scan plane
Ultrasound is a composite of many scan lines-each representing the depth information gathered along the axis of the beam
Image depicts spatial relationships perpendicular to the beam axis
Horizontal distance measurement depends on
Number of scan lines, pixel size, resolution of the display and beam width
Change within the beam formation by a defective transducer or mechanical motor wear
Degrade the accuracy of horizontal distance measuring
How is horizontal distance measured
A scan of the horizontal rods in the phantom is performed and the internal calipers are used to measure the rods
Horizontal distance measurement should be
3% or 3mm
CIRS ultrasound calibration phantom
The large and small eggs are used for volume measurements and contrast. The wire targets are used to measure linear and curved dimensions. The wires can also be used to determine image uniformity and depth of penetration.
Sensitivity (B-Mode)
the ability of the B-mode scanner to detect weak echoes from small scatterers located at specified depths in an attenuating medium
Weak signals approaching the noise floor
Cannot be detected in the presence of noise
Weak signals will…
degrade the ability of the beam to detect structures or detail within the organ or tissue of interest
Most presets set the maximum penetration that the beam can resolve
Scan range, scan line density, deepest focal zone, time-gain-compensation
Decreased Sensitivity
Decreases the maximum depth at which we can resolve structures
Depth of penetration for a transducer should not shift more than
1cm for identical settings
what decreases maximum depth of visualization
Variations of output intensity and loss of transducer channels reduce sensitivity
Uniformity
Refers to the ability of the imaging system to display structures of equal reflectivity with the same brightness on the monitor
Scan of uniform object should produce
An image with a consistent speckle pattern and brightness
Uniformity test is…
Qualitative
No numerical value or grade
Uniformity should be tested at
Different depths
Defective scan lines
Become apparent from the phantom images
Usually from defective crystals, broken crystals or misfiring
Simulated cysts or masses
The simulated cysts are evaluated for size, fill-in, accuracy of shape, enhancement
How are simulated cysts and masses measured
Vertically and horizontally
Shape and brightness are noted
Measured size should be within 1mm of the actual size
Should be able to differentiate between solid and cystic masses
Needle biopsy phantom
The breast phantom can be used to practice aspirating and biopsying. The cysts can be aspirated once, and each solid mass can be biopsied multiple times.
Clear phantom gels (ONDA HIFU)
imaging intentionally produces high intensities so as to cause bioeffect lesions. These clear gel phantoms produce lesions of the same position, size, and shape as those produced in real tissue.
Image capture
The collection if standards is called
Digital Imaging and Communication in Medicine
(DICOM)
DICOM established standardized file formats for patient data and images as well as criteria for the transfer, storage and display of this information
Images obtained with phantoms can be transferred to the PACS to evaluate reproducibility
Dicom image reproducibility must be within
10%
