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Physics Test 3 > Module 7- Imaging Features & Artifacts > Flashcards

Module 7- Imaging Features & Artifacts Flashcards

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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

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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

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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

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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
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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)

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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

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7
Q

TRUE/FALSE: Scanning a medium at oblique incidence can cause axial displacement.

A

FALSE (it can cause LATERAL displacement)

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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)

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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
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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)
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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
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12
Q

Is it better to have a high or low value with spatial resolution?

A

Low

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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)

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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
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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
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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
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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

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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
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19
Q

What interferes with the ability of the system to detect low-level contrast objects?

A

Acoustic speckle

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20
Q

What is section thickness?

A

Thickness of the scanned tissue volume perpendicular to the scan plane

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21
Q

What are other names form section thickness?

A
  • Slice thickness
  • Out-of-plane focusing
  • Elevational resolution
  • Width focusing
  • Z plane
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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)

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23
Q

What is temporal resolution?

A

The ability to precisely position a moving structure

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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

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25
Q

What are the names for axial resolution?

A

-Longitudinal
-Axial
-Range
-Radial
-Depth
(LARRD)

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26
Q

What are the names for lateral resolution?

A

-Lateral
-Angular
-Transverse
-Azimuthal
(LATA)

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27
Q

What transducer component reduces the “ringing” of the crystal, improves axial resolution and reduces spatial pulse length?

A

Backing material

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28
Q

What are the artifacts associated with propagation?

A
  • 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)
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29
Q

What is reverberation artifact?

A
  • Appears as more interfaces than actually exist

- Multiple, equally spaced reflections decreasing in intensity

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30
Q

What are some forms of reverberation artifacts?

A
  • Comet-tail artifact

- Ring-down artifact

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31
Q

What is comet-tail artifact?

A
  • Type of reverberation artifact
  • Caused by metal objects within the body (surgical clips, prosthetic valves, bullet)
  • Appears as multiple small bands
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32
Q

What is ring-down artifact?

A
  • 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
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33
Q

How can reverberation artifacts be overcome?

A

Harmonics

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34
Q

What is mirror-image artifact?

A
  • 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
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35
Q

How can you try to overcome mirror-image artifacts?

A

Try to come from a different location/angle

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36
Q

What is multipath artifact?

A
  • 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
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37
Q

How does multipath artifact appear?

A
  • Results in incorrect axial location of an interface due to the increased time the signal takes to return to the receiver
  • Improper brightness
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38
Q

How can you try to overcome multipath artifact?

A

Come through a different structure

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39
Q

The diaphragm appearing as 3 lines instead of one is an example of what kind of artifact?

A

Multipath artifact

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40
Q

How do artifacts due to refraction appear?

A
  • Echoes received after refraction appear on the screen in improper locations
  • Produces shadowing at the edges of structures that are curved
41
Q

What is ghost image artifact?

A
  • 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
Q

The celiac axis appearing as two structures is an example of what kind of artifact?

A

Ghost image artifact (refraction)

43
Q

How can you overcome refraction artifacts?

A

Scan from a different angle

44
Q

What is side lobe/grating lobe artifact?

A
  • 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
Q

How do side lobe/grating lobe artifacts appear?

A
  • Reflection appears at the correct depth, but is lateral from the true anatomy
  • Reflected structure appears weaker than the real structure is
46
Q

Why are array transducers not commonly seen?

A
  • Due to corrective processes

- Sub-dicing and Apodization (which is performed during the transducer manufacturing process)

47
Q

Why is range ambiguity an artifact?

A

-The misplacement of an interface when the assumption that each echo is derived from the most recent pulse is violated

48
Q

What is range ambiguity artifact?

A

Depth placement error that occurs because the time between the transmitted pulse and the detected echo is not measured correctly

49
Q

What is the cause of range ambiguity artifact?

A

PRF is set too high

50
Q

How can you overcome range ambiguity artifact?

A
  • Decrease the PRF

- Come from a different angle

51
Q

What is another name for propagation speed errors?

A

Speed of sound artifact

52
Q

What is speed of sound artifact?

A
  • Causes improper location of interfaces

- Reflectors appear in the correct number but at improper depths

53
Q

If the speed of sound is _____ than 1540 m/s within the mass, the reflector will be placed too far from the transducer.

A

Less

54
Q

If the speed of sound is ______ than 1540 m/s within the mass, the reflector will be placed too close to the transducer.
greater

A

Greater

55
Q

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?

A

Speed of sound artifact

56
Q

What are the artifacts associated with attenuation?

A
  • Acoustic shadowing
  • Acoustic enhancement
  • Focal banding
57
Q

What is acoustic shadowing?

A
  • 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
Q

TRUE/FALSE: Both shadowing and enhancement are useful artifacts.

A

TRUE

59
Q

What is acoustic enhancement?

A
  • 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
Q

What is focal banding?

A
  • 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
Q

How can you overcome focal banding?

A

Smoothing out the TGC curve

62
Q

What is near field artifact?

A
  • Caused by reverberation

- Seen in anterior walls of organs very close to the skin surface

63
Q

How can you overcome near field artifact?

A

Turning on Harmonics

64
Q

What are some operator caused artifacts?

A
  • Excessive gain or TGCs

- Excessive reject

65
Q

What is the result of excessive gain or TGCs?

A
  • Alteration of the normal echogenicity of structures present on the image
  • Contrast resolution is diminished
66
Q

What is the result of excessive reject?

A
  • 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
Q

What is something that can cause electrical interference?

A

Other equipment in the room such as patient monitors

68
Q

How does electrical interference appear?

A

An arc of vibrating bands across the monitor when the image is live (whether the operator is scanning or not)

69
Q

What is the result of electrical interference?

A

Degradation of contrast resolution

70
Q

TRUE/FALSE: Aliasing is an artifact with both Pulse Wave Doppler and Color Doppler.

A

TRUE

71
Q

What are some artifacts of Doppler?

A
  • Aliasing
  • Mirror imaging or ghosting (color)
  • mirror imaging or crosstalk (spectral)
  • Color registration (ghosting or flash, blossoming, color noise/clutter)
  • Incident beam angle
72
Q

What is aliasing?

A
  • 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
Q

How does Mirror imaging or ghosting with color Doppler appear?

A

Color Doppler image shows the true vessel closest to the transducer with the duplicate (artifact) vessel below it

74
Q

How does Mirror imaging or crosstalk with spectral Doppler appear?

A

Spectral Doppler shows waveform above and below the baseline

75
Q

What causes mirror imaging or crosstalk with spectral Doppler?

A
  • The Doppler gain is set too high

- The Doppler angle is close to 90 degrees

76
Q

What is ghosting or flash artifact with color Doppler?

A
  • Color is improperly assigned to stationary structures

- May be caused by any movement of the transducer, structure, or patient (breathing or talking)

77
Q

How does ghosting or flash artifact with color Doppler appear?

A

A sudden burst of color that encompasses the frame

78
Q

How is ghosting or flash artifact with color Doppler suppressed?

A
  • 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
Q

What is Color bleed also called?

A

Blossoming

80
Q

What is blossoming?

A

The extension of color beyond the region of flow to the adjacent tissue

81
Q

How can you overcome blossoming?

A

Decreases the transmit power and color gain

82
Q

What is color noise also called?

A

Clutter

83
Q

What is color noise?

A

A random variation in signal detection which causes areas with no color flow to be encoded

84
Q

How can you overcome color noise?

A

Filter or threshold may eliminate the low level echoes

85
Q

How does artifact caused by the incident beam angle appear?

A

Improper Doppler angle will result in little or no waveform on the spectral tracing, and no color or black in the vessel

86
Q

What can interfere with the reconstruction process for some 3-D and 4-D applications?

A

Clutter or noise on the 2-D slices

87
Q

A feature that appears on the image but does not correspond to an anatomical structure is called:

A

Artifact

88
Q

The artifact that interferes with the ability to detect a low-contrast object is known as:

A

Acoustic speckle

89
Q

The artifact that occurs from the thickness of the scanned tissue volume perpendicular to the scan plane is called:

A

Elevational resolution (section thickness)

90
Q

Multiple, equally-space reflections on the image decreasing in intensity is called:

A

Reverberation

91
Q

A type of reverberation artifact due to metal within the body is called:

A

Comet-tail

92
Q

Acoustic energy emitted in a direction different than from the main axis of the sound beam is called:

A

Side lobes

93
Q

If the speed of sound is greater than 1540 m/s, the echo will be placed:

A

Too close to the transducer

94
Q

The absence or reduced intensity of echo information distal to the reflector is called:

A

Shadowing

95
Q

An example of an artifact helpful in diagnosis is:

A

Shadowing (also enhancement)

96
Q

The extension of color beyond the region of flow to the adjacent tissue is called:

A

Blossoming (color bleeding)

97
Q

Low-level echo image artifact caused by other electrical equipment is called:

A

Banding

98
Q

Harmonics can be used to eliminate:

A

Reverberation

99
Q

When the Doppler gain is set too high which artifact can appear on the image?

A

Crosstalk

Physics Test 3 (2 decks)

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