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Doppler physics 2 > Chapter 21 Artifacts > Flashcards

Chapter 21 Artifacts Flashcards

1
Q

What is an error in imaging or something that doesn’t belong called?

A

Artifact

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2
Q

Portions of an image that are brighter than surrounding tissues, or that appear brighter than normal?

A

Hyperechoic

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3
Q

Portions of an image that are not as bright as surrounding tissues, or tissues that appear less bright than normal?

A

Hypoechoic

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4
Q

An extreme form of hypoechoic, meaning entirely without echoes (echo free)

A

Anechoic

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5
Q

Describes structures with equal echo brightness

A

Isoechoic

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6
Q

a portion of tissue or an image that has similar echo characteristics throughout

A

Homogeneous

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7
Q

a portion of tissue or an image that has differing echo charateristics throughout

A

Heterogeneous

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8
Q

Multiple, equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasound beam

A

Reverberation

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9
Q

Artifact that . .

  • appears in multiples
  • appears equally spaced
  • located parallel to the sound beam’s main axis
  • located at ever increasing depths
A

Reverberation

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10
Q

With reverberations, which of the echoes are real if any?

A

First two

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11
Q

This appears as a solid, hyperechoic line directed downward, created when closely spaced reverberations merge (aka, Ring down artifact)

A

Comet tail

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12
Q

artifact that . . .

  • appears as a single long hyperechoic echo
  • located parallel to the sound beam’s main axis
A

Comet tail

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13
Q

This appears as a hypoechoic or anechoic region extending downward from a very strong attenuating medium

A

Shadow

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14
Q

Artifact that . .

  • results from too much attenuation
  • hypo or anechoic
  • located beneath the structure with abnormally high attenuation
  • prevents visualization of true anatomy on the scan
A

shadow

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15
Q

Is shadowing related to the speed of sound in a medium?

A

No

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16
Q

This appears as a hypoechoic region extending along the edge of a curved reflector. The sound beam refracts at the edge resulting in an intensity drop

A

Edge Shadow (Shadowing by refraction)

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17
Q

Artifact that . . .

  • results when the beam spreads after striking a curved reflector
  • hypo or anechoic
  • extends downward from the curved reflector’s edge parallel to the beam
  • prevents visualization of true anatomy
A

Edge shadow (shadowing by refraction)

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18
Q

This appears as a hyperechoic region beneath tissues with abnormally low attenuation

A

Enhancement

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19
Q

In enhancement related to the speed of sound in the medium?

A

NO

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20
Q

Name the artifact:

  • Hyperechoic
  • results from too little attenuation
  • located beneath the structure with abnormally low attenuation
A

Enhancement

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21
Q

This appears when side to side region of the image appears brighter than tissues at other depths

A

Focal enhancement (focal banding)

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22
Q

What is most often the cause of focal enhancement?

A

A TGC pod is set too high

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23
Q

Name the artifact:

  • a hyperechoic side to side region
  • results from increased intensity at the focus
A

Focal enhancement ( focal banding)

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24
Q

This appears when sound reflects off of a strong reflector and is redirected toward a second structure, causing a replica to incorrectly appear on the image

A

Mirror image

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25
In the case of mirror images, which one is the artifact?
Deeper image is the artifact
26
Name the artifact: - a second copy of a true reflector - copy appears deeper than the true reflector - a bright reflector, the mirror, lies on a straight line between the artifact and the transducer - true reflector and artifact are equal distances from the mirror
Mirror image
27
This appears as a mirror image artifact on a spectral doppler display
Crosstalk
28
This appears when a sound wave propagates through a medium at a speed other than that of soft tissue (1.54Km/s): the correct number of reflectors are displayed, but at incorrect depths
Speed error (Range error artifact)
29
- go return time is too short - System assumes reflectors are close to the transducer - reflectors are too shallow - distances are underestimated (too small)
Medium's speed is Faster than that of soft tissue
30
- go return time is too long - system assumes reflectors are far from the transducer - reflectors are too deep - distances are overestimated (too large)
Medium's speed is slower than that of soft tissue
31
Name the artifact: - Correct number of reflectors - improper depth - appears as a step off
Speed error (range error artifact)
32
This appears when sound energy is transmitted in a direction other than the sound beam's main axis, degrading lateral resolution
Lobe artifacts - side lobes - grating lobes
33
Side lobes
one crystal
34
Grating lobes
arrays
35
Name the artifact: - a second copy of the true reflector - artifact and the true reflector are located side by side at the same depth
Lobe artifacts - side lobes (one crystal) - grating lobes (arrays)
36
What are two methods for reducing lobe artifacts?
Subdicing | Apodization
37
Dividing each crystal into small pieces
Subdicing
38
Differential excitation: inner elements receive higher voltages while outer elements receive lower voltages
Apodization
39
This appears when a sound pulse changes direction during transmission, degrading lateral resolution
Refraction
40
Name the artifact: - a second copy of the reflector - the copy is side by side or at the same depth as the true reflector
Refraction
41
This appears when reflections from structures above or below the assumed imaging plane appear in the image, or hollow structures appear filled in
Slice thickness artifact/ elevational resolution
42
How can slice thickness artifact/ elevational resolution problems be reduced?
1 1/2 dimensional array transducers (matrix) which create thinner imaging planes
43
This appears when a beam is wider than the distance between two reflectors that are located side by side. In this case, the two objects appear as one reflection
Lateral resolution
44
This appears when a long pulse strikes two closely spaced structures, where one is in front of the other. Only one reflection will appear if the structures are closer together than 1/5 the SPL
Axial Resolution artifact
45
What type of transducers reduce axial resolution artifacts?
Higher frequency
46
This appear when sound pulses glance off a second structure on the way to of from the primary reflector, resulting in a transmit path length different from the receive path length and subtle, non-specific errors
Multipath artifacts
47
This appears when a sound beam strikes a curved or oblique reflector, causing some of the reflected sound to be directed away from the transducer
Curved/ oblique reflectors
48
Name the artifact: - Reflections are absent or - Reflections appear too weak or - Reflections appear different than other similar reflecting boundries
Curved /oblique reflectors
49
This appears as a result of low frame rates and causes less accurate positioning of reflectors in motion
Temporal resolution artifacts
50
This appears as a result of low line density causing less detail in the image
Spatial resolution artifact
51
When the image is in analog format for display on a CRT how is spatial resolution determined?
Number of scan lines fer frame (more the better)
52
When the image is in digital format, how is spatial resolution determined?
Pixel density (more the better)
53
Closely packed sound pulses, image exhibits great detail, spatial resolution is exceptional
High line density
54
Each pixel is large and the spatial resolution degrades
Low pixel density
55
Wider gaps between the sound pulses, the image exhibits less detail, spatial resolution is poor
Low line density
56
Each pixel is small resulting in a detailed image with excellent spatial resolution
High pixel density
57
When a reflecting structure is located deeper than the imaging depth of the image. This reflector is placed on a shallow location on the image
Range ambiguity artifact
58
Range ambiguity is eliminated by increasing the ________
PRP
59
Longer PRP means ________ imaging and decreased PRF
Deeper
60
Small amplitude echoes resulting from many sources including electrical interference, signal processing and spurious reflections. Most likely affects low-level hypoechoic regions
Noise
61
A form of noise arising from small amplitude sound waves interfering with each other; Most likely to appear close to the transducer - grainy appearance that is not directly related to the actual biologic tissue
Speckle
62
A form of noise associated with Doppler
Clutter
63
A high-tech solution for reducing an image's noise content: | selectively distinguish meaningful reflections from noise, thereby improving signal to noise ratio
Harmonics
64
What are the six assumptions of imaging systems
1. Sound travels in a straight line 2. Sound travels directly to a reflector and back 3. Sound travels in soft tissue at exactly 1540m/s 4. Reflections arise only from structures positioned in the beams main axis 5. The imaging plane is very thin 6. The strength of a reflection is related to the characteristics of the tissue creating the reflections
65
Anatomic reflectors are absent on image
- shadowing - shadowing by refraction - lateral resolution - Axial resolution
66
Anatomic reflector appears multiple times on image. Artifact positioned deeper than the true anatomy
- Comet tail - Ring down - Reverberation - Mirror image
67
Anatomic reflector appears multiple times on image. Artifact displaced to the side of the true anatomy
Refraction Side lobe Grating lobe
68
Anatomic reflectors appear with abnormal brightness
Enhancement (hyperechoic) Banding (hyperechoic) Shadowing (hypoechoic) Shadowing by refraction (hypoechoic)
69
Anatomic structures appear at incorrect depth
Speed errors | Range ambiguity
70
Anatomic structures appear in the incorrect imaging plane
Slice or section thickness
71
Anatomic structures do not correspond to echoes on the image
acoustic speckle | Multipath

Doppler physics 2 (5 decks)

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