Module 7- Imaging Features & Artifacts Flashcards
1
Q
What are artifacts?
A
Structures and features (echoes) that appear on the image but do not have a one-to-one correspondence to an anatomical structure
2
Q
What are the assumptions of ultrasound imaging systems?
A
(1) Sound travels in a straight line
(2) Reflections are produced by structures along the main axis of the sound beam
(3) Intensity of an echo corresponds to a reflector’s scattering strength
(4) Imaging plane is thin
(5) Sound travels directly to and from a reflector
(6) Sound always travels at 1.54 mm/μsec in soft tissue
3
Q
What can cause non-structural echo signals to be seen on the display?
A
Interference from outside sources can add noise to the image
4
Q
What can cause the image to be missing real structural echoes on the display?
A
- Strongly reflecting objects create shadowing which appears as black where normal anatomy should be seen
- An improper operating crystal can produce black lines on the image which obscure the normal anatomy
5
Q
What can cause the displacement of echo signals on the display?
A
Scanning a medium with oblique incidence (can cause lateral displacement of structures)
6
Q
What can cause a distortion of the echo signal on the display?
A
An increase or decrease of the amplitude of the signal can be caused by wave interference
7
Q
TRUE/FALSE: Scanning a medium at oblique incidence can cause axial displacement.
A
FALSE (it can cause LATERAL displacement)
8
Q
TRUE/FALSE: When wave interference causes an echo signal to be distorted, it is either increasing or decreasing the frequency of the signal.
A
FALSE (wave interference can cause an increase or decrease in the AMPLITUDE of the signal)
9
Q
What are the mechanisms of artifact production?
A
- Ultrasound equipment assumptions
- Viewer assumptions and/or errors
- Equipment malfunction
- Operator error
- Improper use of equipment
10
Q
How can axial resolution be improved?
A
Shorten SPL
Can be accomplished by:
- Use a thin element transducer (higher frequency)
- Increase the frequency (because it will have a shorter wavelength)
- Shorter wavelength
- Reduce PD (by reducing the # of cycles per pulse)
- Reduce the # of cycles per pulse (reduced by adding damping)
11
Q
How can lateral resolution be improved?
A
- Changing the focus (this makes the beam width narrowest in the area of interest)
- Decreasing the depth
- Higher frequency
12
Q
Is it better to have a high or low value with spatial resolution?
A
Low
13
Q
TRUE/FALSE: Axial resolution is the ability to distinguish structures that are in close proximity to each other from front to back.
A
TRUE (axial resolution is anterior to posterior (on one top of the other on the screen)
14
Q
What is artifact of axial resolution?
A
- Occurs when multiple structures are along the main axis of the beam and appear only as one reflector on the image
- Contributes to incorrect representation of size and shape of interfaces and to missing interfaces
15
Q
What is artifact of axial resolution?
A
- Occurs when multiple structures are along the main axis of the beam and appear only as one reflector on the image
- Contributes to incorrect representation of size and shape of interfaces and to missing interfaces
16
Q
What is artifact of lateral resolution?
A
- Occurs when side-by-side structures are not producing two distinct echoes, but one
- Contributes to incorrect representation of size and shape of interfaces and to missing interfaces
17
Q
Why is acoustic speckle considered to be an artifact?
A
Because a one-to-one correspondence between image brightness and scanned objects does not exist
18
Q
What is acoustic speckle?
A
- The granular appearance of images and spectral displays
- Caused by constructive and deconstructive interference of scattered sound waves
- Dominates the near face of the transducer
- Interferes with the ability of the system to detect low- contrast objects
19
Q
What interferes with the ability of the system to detect low-level contrast objects?
A
Acoustic speckle
20
Q
What is section thickness?
A
Thickness of the scanned tissue volume perpendicular to the scan plane
21
Q
What are other names form section thickness?
A
- Slice thickness
- Out-of-plane focusing
- Elevational resolution
- Width focusing
- Z plane
22
Q
How can section thickness cause artifact?
A
May cause misdiagnosis when echo fill-in occurs in a cystic structure (ex. debris appearance in the gallbladder that is not real)
23
Q
What is temporal resolution?
A
The ability to precisely position a moving structure
24
Q
What is an artifact of temporal resolution?
A
Low frame rates result in less accurate positioning of reflectors in motion
(Depth, # of Focus, # of Scan Lines) x Frame rate = <77,000
25
What are the names for axial resolution?
-Longitudinal
-Axial
-Range
-Radial
-Depth
(LARRD)
26
What are the names for lateral resolution?
-Lateral
-Angular
-Transverse
-Azimuthal
(LATA)
27
What transducer component reduces the "ringing" of the crystal, improves axial resolution and reduces spatial pulse length?
Backing material
28
What are the artifacts associated with propagation?
- Reverberation artifacts (comet tail/ring down)
- Mirror-image artifacts
- Multipath
- Refraction (shadowing, ghost image)
- Side lobes / grating lobes
- Range ambiguity
- Proagation speed errors (speed of sound)
29
What is reverberation artifact?
- Appears as more interfaces than actually exist
| - Multiple, equally spaced reflections decreasing in intensity
30
What are some forms of reverberation artifacts?
- Comet-tail artifact
| - Ring-down artifact
31
What is comet-tail artifact?
- Type of reverberation artifact
- Caused by metal objects within the body (surgical clips, prosthetic valves, bullet)
- Appears as multiple small bands
32
What is ring-down artifact?
- Type of reverberation artifact
- Caused by small gas bubbles, such as air, in the biliary tree
- Appears as a single, long, strong, echo behind the reflector
33
How can reverberation artifacts be overcome?
Harmonics
34
What is mirror-image artifact?
- Reflector and object (true and false image) are equidistant from the strong reflector
- Mirror image duplicate (false image) always appear DEEPER than the true anatomic structure
35
How can you try to overcome mirror-image artifacts?
Try to come from a different location/angle
36
What is multipath artifact?
- Relates to paths to and from a reflector that are not the same
- The beam strikes an interface at an angle and is reflected from a second or third interface before being reflected to the transducer
37
How does multipath artifact appear?
- Results in incorrect axial location of an interface due to the increased time the signal takes to return to the receiver
- Improper brightness
38
How can you try to overcome multipath artifact?
Come through a different structure
39
The diaphragm appearing as 3 lines instead of one is an example of what kind of artifact?
Multipath artifact
40
How do artifacts due to refraction appear?
- Echoes received after refraction appear on the screen in improper locations
- Produces shadowing at the edges of structures that are curved
41
What is ghost image artifact?
- Type of refraction
- Rectus abdominus muscle can cause the beam to be refracted
- Causes a duplication of structures that appear side-by-side (ex. two celiac axis)
42
The celiac axis appearing as two structures is an example of what kind of artifact?
Ghost image artifact (refraction)
43
How can you overcome refraction artifacts?
Scan from a different angle
44
What is side lobe/grating lobe artifact?
- Acoustic energy is emitted in a direction different than the main axis of the sound beam
- Energy off the main axis of a single crystal transducer (for side lobes) or arrays (for grating lobes) can introduce positioning artifacts
45
How do side lobe/grating lobe artifacts appear?
- Reflection appears at the correct depth, but is lateral from the true anatomy
- Reflected structure appears weaker than the real structure is
46
Why are array transducers not commonly seen?
- Due to corrective processes
| - Sub-dicing and Apodization (which is performed during the transducer manufacturing process)
47
Why is range ambiguity an artifact?
-The misplacement of an interface when the assumption that each echo is derived from the most recent pulse is violated
48
What is range ambiguity artifact?
Depth placement error that occurs because the time between the transmitted pulse and the detected echo is not measured correctly
49
What is the cause of range ambiguity artifact?
PRF is set too high
50
How can you overcome range ambiguity artifact?
- Decrease the PRF
| - Come from a different angle
51
What is another name for propagation speed errors?
Speed of sound artifact
52
What is speed of sound artifact?
- Causes improper location of interfaces
| - Reflectors appear in the correct number but at improper depths
53
If the speed of sound is _____ than 1540 m/s within the mass, the reflector will be placed too far from the transducer.
Less
54
If the speed of sound is ______ than 1540 m/s within the mass, the reflector will be placed too close to the transducer.
greater
Greater
55
The diaphragm located posterior to a fatty tumor in the liver appears displaced too far from the transducer. This is an example of what type of artifact?
Speed of sound artifact
56
What are the artifacts associated with attenuation?
- Acoustic shadowing
- Acoustic enhancement
- Focal banding
57
What is acoustic shadowing?
- The absence or reduced intensity of echo information distal to the reflector
- Caused by the sound beam intersecting a highly attenuating (highly reflective) structure
58
TRUE/FALSE: Both shadowing and enhancement are useful artifacts.
TRUE
59
What is acoustic enhancement?
- The increase in echo brightness posterior to the structure
| - Occurs when the sound beam intersects a very low-attenuating (weak) reflector (such as fluid)
60
What is focal banding?
- Focusing characteristics of the transducer creates a region of increased brightness
- Caused by the greater intensity in the focal zone or incorrect TGC settings
61
How can you overcome focal banding?
Smoothing out the TGC curve
62
What is near field artifact?
- Caused by reverberation
| - Seen in anterior walls of organs very close to the skin surface
63
How can you overcome near field artifact?
Turning on Harmonics
64
What are some operator caused artifacts?
- Excessive gain or TGCs
| - Excessive reject
65
What is the result of excessive gain or TGCs?
- Alteration of the normal echogenicity of structures present on the image
- Contrast resolution is diminished
66
What is the result of excessive reject?
- Boundaries and bright reflectors are seen but the low level echoes (parenchyma of organs) are eliminated
- Alteration of the normal echogenicity of structures present on the image
- Contrast resolution is diminished
67
What is something that can cause electrical interference?
Other equipment in the room such as patient monitors
68
How does electrical interference appear?
An arc of vibrating bands across the monitor when the image is live (whether the operator is scanning or not)
69
What is the result of electrical interference?
Degradation of contrast resolution
70
TRUE/FALSE: Aliasing is an artifact with both Pulse Wave Doppler and Color Doppler.
TRUE
71
What are some artifacts of Doppler?
- Aliasing
- Mirror imaging or ghosting (color)
- mirror imaging or crosstalk (spectral)
- Color registration (ghosting or flash, blossoming, color noise/clutter)
- Incident beam angle
72
What is aliasing?
- A wrap-around of the color display resulting gin an apparent reversal of the flow direction
- Occurs when the Doppler shift frequency exceeds half of the PRF (Nyquist limit)
73
How does Mirror imaging or ghosting with color Doppler appear?
Color Doppler image shows the true vessel closest to the transducer with the duplicate (artifact) vessel below it
74
How does Mirror imaging or crosstalk with spectral Doppler appear?
Spectral Doppler shows waveform above and below the baseline
75
What causes mirror imaging or crosstalk with spectral Doppler?
- The Doppler gain is set too high
| - The Doppler angle is close to 90 degrees
76
What is ghosting or flash artifact with color Doppler?
- Color is improperly assigned to stationary structures
| - May be caused by any movement of the transducer, structure, or patient (breathing or talking)
77
How does ghosting or flash artifact with color Doppler appear?
A sudden burst of color that encompasses the frame
78
How is ghosting or flash artifact with color Doppler suppressed?
- Increasing the color filter
- Decreasing the persistence
- Reducing the width of the color field of view
- Having the patient hold their breathe or stop talking
79
What is Color bleed also called?
Blossoming
80
What is blossoming?
The extension of color beyond the region of flow to the adjacent tissue
81
How can you overcome blossoming?
Decreases the transmit power and color gain
82
What is color noise also called?
Clutter
83
What is color noise?
A random variation in signal detection which causes areas with no color flow to be encoded
84
How can you overcome color noise?
Filter or threshold may eliminate the low level echoes
85
How does artifact caused by the incident beam angle appear?
Improper Doppler angle will result in little or no waveform on the spectral tracing, and no color or black in the vessel
86
What can interfere with the reconstruction process for some 3-D and 4-D applications?
Clutter or noise on the 2-D slices
87
A feature that appears on the image but does not correspond to an anatomical structure is called:
Artifact
88
The artifact that interferes with the ability to detect a low-contrast object is known as:
Acoustic speckle
89
The artifact that occurs from the thickness of the scanned tissue volume perpendicular to the scan plane is called:
Elevational resolution (section thickness)
90
Multiple, equally-space reflections on the image decreasing in intensity is called:
Reverberation
91
A type of reverberation artifact due to metal within the body is called:
Comet-tail
92
Acoustic energy emitted in a direction different than from the main axis of the sound beam is called:
Side lobes
93
If the speed of sound is greater than 1540 m/s, the echo will be placed:
Too close to the transducer
94
The absence or reduced intensity of echo information distal to the reflector is called:
Shadowing
95
An example of an artifact helpful in diagnosis is:
Shadowing (also enhancement)
96
The extension of color beyond the region of flow to the adjacent tissue is called:
Blossoming (color bleeding)
97
Low-level echo image artifact caused by other electrical equipment is called:
Banding
98
Harmonics can be used to eliminate:
Reverberation
99
When the Doppler gain is set too high which artifact can appear on the image?
Crosstalk
