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Ultrasound Physics > Colour Doppler > Flashcards

Colour Doppler Flashcards

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1
Q

Unlike spectral Doppler

A

Colour offers a wonderful survey tool to quickly assess large regions of the patient

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2
Q

Blessings of colour

A
  • 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
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3
Q

Curse of colour

A

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

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4
Q

Colour Doppler

A

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

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5
Q

Spectral Doppler

A

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

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6
Q

How is colour Doppler preformed

A

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.

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7
Q

what is created by repeatedly scanning a single line in the same direction

A

Colour packet

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8
Q

the packet is then

A

Scaned across the body to produce a frame

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9
Q

how is colour similar to 2D

A

packets of acoustic lines are scanned across the body

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10
Q

how is colour similar to spectral

A

A single line is transmitted repatedly in the same directin

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11
Q

Creating the colour scan step one

A

TTransmit pulse in a single line

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12
Q

creating the colour scan step two

A

Repeats this 4-12 times in the same line (colour packet)

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13
Q

creating the colour scan step three

A

Doppler information from the scan line is obtained by a series of range gates within each acoustic line of the packet

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14
Q

creating the colour scan step 4

A

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

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15
Q

creating the colour scan step 5

A

The direction of the line is then changed and a new packet is then transmitted in the new direction

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16
Q

creating the colour scan step 6

A

This process repeats until information is acquired from the scan region of interest

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17
Q

why is a packet of lines transmitted

A

So that an average velocity can be determined at each depth along the line

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18
Q

Colour has _______temporal resolution

A

Poor temporal reoslution

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19
Q

why does colour have a poor temporal resolution

A

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

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20
Q

A higher frame time

A

Causes lower frame frequency

A lower frame rate implies a greater likelihood of not capturing a short duration event

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21
Q

Creating the colour scan step 7

A

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

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22
Q

creating the colour scan step 8

A

Once the system determines the Doppler shift as it is assigned a colour based on the colour bar/scale (colour map)

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23
Q

Colour bar has

A

negative(-) and positive(+) direction
Positive-towards
Negative-away

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24
Q

Negative implies what

A

Negative frequency shift and the insonifcation angle is greater than 90

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25
Q

positive implies what

A

positive freuqency shift and the insonifcation angle of 0-90 degrees

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26
Q

in the center of the colour bar

A

black band which represents the baseline and colour wall filters

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27
Q

if no frequency shift is detected

A

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

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28
Q

Overgained

A

Random color speckle

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29
Q

what does aliasing result in

A

wrapping of the colours around the baseline

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30
Q

Colour wall filters

A

-no separate control for colour wall filters (unlike spectra)

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31
Q

how are most colour wall filters set

A

percentage of the color scale

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32
Q

As colour scale increases

A

Wall filters also increase, resulting in less ability to visualize lower velocity flow

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33
Q

Higher wall filter percntge

A

Larger black band

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34
Q

Determining flow direction

A

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.

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35
Q

Power angio

A

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.

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36
Q

before assessing flow direction

A

Must assess the colour bar

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37
Q

what is aliasing

A

Occurs when the Doppler shift excessds more than half the PRF

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38
Q

where is aliasing more likely to occur

A

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)

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39
Q

what does aliasing look like

A

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.

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40
Q

when is aliasing useful

A

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.

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41
Q

Colour persistence

A

technique in which frames are “averaged” over time.

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42
Q

are frames weighted equally in colour persistence

A

No

heavier weighting of the latest frames, and less weighting of earlier frames

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43
Q

Objective of persistence

A

improve signal to noise (increased sensitivity).

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44
Q

How does persistence affect duration of events

A

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.

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45
Q

what is the trade off of colour persitsence

A

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

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46
Q

Colour Priority

A

set by sonographer

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47
Q

what is colour priority

A

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

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48
Q

Higher colour priority implied what

A

higher grayscale amplitude threshold

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49
Q

what does colour prioroty use

A

Thresholds to dertremine what grayscale level 2D data is presented and below which colour data is presented

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50
Q

what is colour power doppler

A

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.

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51
Q

does colour power doppler give flow infomration

A

No

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52
Q

why is spectrum/PW Doppler needed

A

sort out the jumble of Doppler frequencies to allow quantitative information and Colour Doppler for qualitative information

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53
Q

Doppler spectrum

A

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).

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54
Q

what does doppler use to obtain information on velocity and frequency

A

Doppler angle

55
Q

Duplex Doppler: colour flow image

A

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

56
Q

Duplex Doppler: Colour flow information

A

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.

57
Q

Duplex doppler: Doppler Angle

A

The Doppler angle for the Spectral Doppler appears at the upper right of the display screen, in this case 60degrees.

58
Q

Duplex Doppler: Time

A

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.

59
Q

Duplex Doppler: Velocity

A

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.

60
Q

Duplex Doppler: Distribution of velocities

A

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

61
Q

Duplex Doppler: Flow direction

A

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.

62
Q

Duplex Doppler: Peak Velcouty Envelope

A

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.

63
Q

Duplex Dopper: Pulse Repition Freuqency

A

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).

64
Q

Auditory Spectrum

A

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!!!!

65
Q

Sample Volume

A

The spectrum shows blood flow information from a specific location called the Doppler sample volume

66
Q

Three characteristics of sample volume

A

. 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.
67
Q

Arterial spectral nalysis

A 
Peak velocity
Pulsatility
Arrthymias
Plaques formation
Aneurysms
Type of Flow 
Stenotic lesion
68
Q

Venus spectral analysis

A 
Spontaneous flow
Phasic flow
Respiratory changes
Valsalva 
Augmentation 
Unidirectional flow
Competency
69
Q

what is colour Tissue Doppler

A

modality that employs the Doppler effect to assess muscle wall characteristics throughout the cardiac cycle including velocity, displacement, deformation, and event timings

70
Q

what can tissue doppler meaurements be used to assess

A

Measurements can be used to assess myocardial performance in various disease states, monitor treatment response, and provide important prognostic information.

71
Q

TDI velocity and deformation assessment

A

measure myocardial with values that are highly influenced by loading conditions
Increased preloadincreases systolic tissue Doppler velocities while increased afterload reduces those velocities.

72
Q

What does TDI make possible

A

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.

73
Q

how can tissue Doppler be performed

A

pulsed Doppler, 2DColour Dopper, and M-mode colour mode Doppler.

74
Q

Pulsed Doppler tissue image

A

high level of temporal resolution and can therefore be used to analyze the temporal relationship between myocardium systolic and diastolic velocity waves

75
Q

Tissue Doppler display

A

Displays velocity over time

76
Q

PW Doppler does not

A

Measure strain directly

77
Q

what infor can tissue Doppler provide

A

Velocity and displacement information can be determined for the whole image because it is a scanned modality

78
Q

The perceived sensitivity on the image quality will vary depending on many system controls:

A 
Transducer
Positioning of transducer on phantom
Transmit power
Receiver gain
Focus depth
Post processing curves (compression/dynamic range)
Ambient Light
Monitor contrast setting
79
Q

when testing, msut ensure what

A

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

80
Q

Tissue equivalent phantoms are made of

A

graphite-filled aqueous gels or urethane rubber material

81
Q

Graphite partciles

A

Scatters, attenuation is similar to that for soft tissue and propagation speed

82
Q

Tissue phantoms

A

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

83
Q

What do tissue phantoms simulate

A 
Tissue properties
Assess detail resolution
Assess contrast resolution
Penetration
Dynamic range
TGC operation
84
Q

what aspects are tested with phantoms

A

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.)

85
Q

Testing for resolution

A

Must know axis/face the phantom the transducer is being placed

86
Q

general phantoms test for

A 
Dead zone
Axial resolution
Lateral resolution
Penetration
Image Uniformity
Distance accuracy
Focal zone
Cyst characteristics (size, shape, fill-in)
87
Q

What do general purpose phantoms do

A

mimic soft tissue characteristics close to the properties seen in a clinical setting

Propagation velocity
Scattering
Attenuation

88
Q

Multi-purpose tissue/cyst phantom

A

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
89
Q

Tissue equivalent phantom

A

With tissue-mimicking material the phantom can also be used for penetration tests, since this material has attenuation properties similar to tissue.

90
Q

Specialized phantoms

A

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

91
Q

Dead zone

A

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

92
Q

what is the dead zone distance

A

The dead zone is the distance from the front face of the transducer to the first identifiable echo

93
Q

what is not present in the dead zone

A

The tissue scatter from parenchyma is not present in the dead zone

94
Q

To test the dead zone

A

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

95
Q

Dead zone performance criteria

A

<3= <7mm
3-7=<5mm
>7=<3mm

96
Q

Axial resolution

A

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

97
Q

Axial resolution limit

A

The smallest space distance between the rods in the group determines the axial resolution/limit of the system to determine axial separation

98
Q

Lateral resolution

A

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

99
Q

Lateral resolution is assessed by…

A

closely spaced rods orientated horizontally

100
Q

lateral resolution limit is expressed as…

A

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

101
Q

Focal Zone

A

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

102
Q

How is focal zone assessed

A

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

103
Q

the focal zone can be

A

Electronically steered to reduce beam width and improve lateral resolution at different depths

104
Q

Focal zone banding

A

Brighter region and horizontal lines

seams between each of the lines that have been pasted together

105
Q

Vertical distance measurement

A

axis of the beam

106
Q

Vertical distance is determined by

A

The elapsed time between pulses transmitted and received is measured which allows the ultrasound machine to calculate distance to the interface

107
Q

Vertical distance measurement

A

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

108
Q

Measurement is used to identify….

A

Miscalibration because errors are more likely to occur with greater distances

109
Q

Vertical distance measurement should be accurate to

A

2% or 2mm

110
Q

What may contribute to phantom error (vertical distance meaurement)

A

Excessive pressure on the phantom

111
Q

Horizontal distance measurement

A

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

112
Q

Horizontal distance measurement depends on

A

Number of scan lines, pixel size, resolution of the display and beam width

113
Q

Change within the beam formation by a defective transducer or mechanical motor wear

A

Degrade the accuracy of horizontal distance measuring

114
Q

How is horizontal distance measured

A

A scan of the horizontal rods in the phantom is performed and the internal calipers are used to measure the rods

115
Q

Horizontal distance measurement should be

A

3% or 3mm

116
Q

CIRS ultrasound calibration phantom

A

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.

117
Q

Sensitivity (B-Mode)

A

the ability of the B-mode scanner to detect weak echoes from small scatterers located at specified depths in an attenuating medium

118
Q

Weak signals approaching the noise floor

A

Cannot be detected in the presence of noise

119
Q

Weak signals will…

A

degrade the ability of the beam to detect structures or detail within the organ or tissue of interest

120
Q

Most presets set the maximum penetration that the beam can resolve

A

Scan range, scan line density, deepest focal zone, time-gain-compensation

121
Q

Decreased Sensitivity

A

Decreases the maximum depth at which we can resolve structures

122
Q

Depth of penetration for a transducer should not shift more than

A

1cm for identical settings

123
Q

what decreases maximum depth of visualization

A

Variations of output intensity and loss of transducer channels reduce sensitivity

124
Q

Uniformity

A

Refers to the ability of the imaging system to display structures of equal reflectivity with the same brightness on the monitor

125
Q

Scan of uniform object should produce

A

An image with a consistent speckle pattern and brightness

126
Q

Uniformity test is…

A

Qualitative

No numerical value or grade

127
Q

Uniformity should be tested at

A

Different depths

128
Q

Defective scan lines

A

Become apparent from the phantom images

Usually from defective crystals, broken crystals or misfiring

129
Q

Simulated cysts or masses

A

The simulated cysts are evaluated for size, fill-in, accuracy of shape, enhancement

130
Q

How are simulated cysts and masses measured

A

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

131
Q

Needle biopsy phantom

A

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.

132
Q

Clear phantom gels (ONDA HIFU)

A

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.

133
Q

Image capture

A

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

134
Q

Dicom image reproducibility must be within

A

10%

Ultrasound Physics (10 decks)

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