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Ultrasound Physics > Ch 21: Artifacts > Flashcards

Ch 21: Artifacts Flashcards

1
Q

Artifacts result from:

  1. violations of __
  2. __ malfunction
  3. __ of ultrasound
  4. operator __
A

assumptions
equipment
physics
error

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2
Q

Assumption #1: Sound travels in…

A

in a straight line.

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3
Q

Assumption #2: Sound travels directly…

A

to a reflector and back.

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4
Q

Assumption #3: Sound travels in soft tissue…

A

at exactly 1540 m/s.

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5
Q

Assumption #4: Reflections arise only from…

A

structures positioned in the beam’s main axis.

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6
Q

Assumption #5: The imaging plane is…

A

very thin.

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7
Q

Assumption #6: The strength of a reflection is related to…

A

the characteristics of the tissue creating the reflection.

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8
Q

These appear on the display as multiple equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the u/s beam.

A

reverberation

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9
Q

Reverb violates which assumption?

A

2 (sound travels directly to the reflector and back)

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10
Q

This artifact appears in multiples, equally spaced, and are located parallel to the sound beam’s main axis, at ever-increasing depths.

A

reverberation

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11
Q

This appears as a solid hyperechoic line directed downward.

A

comet tail aka ring down

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12
Q

This artifact is created when closely spaced reverberations merge.

A

comet tail

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13
Q

Comet tail violates which assumption?

A

2 (sound travels directly to the reflector and back)

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14
Q

Two characteristics of comet tail?

A
  1. a single long hyperechoic echo

2. located parallel to the beams main axis

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15
Q

This appears as a hypoechoic or anechoic region extending downward from a highly attenuating structure.

A

shadow

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16
Q

Shadows are the same color as the…

A

image background.

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17
Q

Shadows appear when the __ in the tissue above the shadow than in the surrounding tissue.

A

attenuation is higher

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18
Q

Shadowing violates which assumption?

A

6 (reflection strength is related to the tissue creating the reflections)

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19
Q

This artifact is located beneath the structure with abnormally high attenuation and prevents visualization of true anatomy on the scan.

A

shadowing

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20
Q

T/F? Shadowing is unrelated to the speed of sound in a medium.

A

true

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21
Q

This is a special form of shadowing that appears as a hypoechoic region extending down from the edge of a curved reflector.

A

edge shadow aka shadowing by refraction

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22
Q

Edge shadowing violates which assumption?

A

6 (reflection strength is related to the tissue creating the reflections)

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23
Q

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

A

enhancement

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24
Q

Enhancement violates which assumption?

A

6 (reflection strength is related to the tissue creating the reflections)

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25
This artifact is the opposite of shadowing.
enhancement
26
T/F? Enhancement artifact is entirely unrelated to the speed at which sound travels in a medium.
true
27
This is a special form of enhancement in which a side-to-side region of an image appears brighter than tissues at other depths.
focal enhancement aka focal banding
28
Focal enhancement violates which assumption?
#6 (reflection strength is related to the tissue creating the reflections)
29
This is created when sound reflects off a strong reflector and is redirected toward a second structure.
mirror image
30
The 'mirror image' is located (deeper/shallower) than the real structure.
deeper
31
Mirror image violates which assumption?
#1 (sound travels in a straight line) and #2 (sound travels directly to the reflector and back)
32
The mirroring structure lies __ between the artifact and the transducer.
on a straight line
33
This is a mirror image artifact that appears on a spectral Doppler display.
crosstalk
34
This is created when a sound wave propagates through a medium at a speed other than that of soft tissue.
speed error aka range error artifact
35
When the medium's speed is __ than soft tissue, the reflector appears deeper than it really is.
slower
36
When the medium's speed is __ than soft tissue, the reflector appears shallower than it really is.
faster
37
Speed error violates which assumption?
#3 (sound travels at 1540 m/s in soft tissue)
38
Speed errors appear as a...
step-off, as if structures are 'split' or 'cut'.
39
This appears when sound energy is transmitted in a direction other than along the beam's main axis.
lobe artifact
40
Lobe artifacts __ lateral resolution.
degrade
41
Lobe artifacts degrade __ resolution.
lateral
42
Lobe artifact violates which assumption?
#2 (sound travels directly to the reflector and back)
43
The lobe artifact and the true reflector are located __ at the __.
side-by-side, same depth
44
Lobes created by a single crystal transducer are called...
side lobes.
45
Lobes created by array transducer are called...
grating lobes.
46
This process reduces grating lobes by dividing each PZT element into small pieces.
subdicing
47
This process reduces grating lobes by exiting the element with different voltages.
apodization
48
This is created when a sound pulse changes direction during transmission.
refraction
49
Refraction violates which assumption?
#1 (sound travels in a straight line)
50
The refraction artifact and the true reflector are located __ at the __.
side-by-side, same depth
51
This artifact occurs when a sound wave strikes a boundary obliquely and the media on either side of the boundary have different speeds.
refraction
52
Slice thickness is also known as...
section thickness or partial volume.
53
This is related to the dimension of the beam that is perpendicular to the imaging plane.
slice thickness
54
This is determined by the thickness of the imaging plane.
elevational resolution
55
Slice thickness artifact violates which assumption?
#5 (the imaging plane is very thin)
56
Slice thickness is reduced with...
1.5 D array transducers
57
This occurs when a pair of side-by-side reflectors are closer than the width of the sound beam.
lateral resolution artifact aka point spread
58
T/F? Lateral resolution artifact is least likely to occur at th focus.
true
59
This is created when a long pulse strikes two closely spaced structures, where one is in front of the other.
axial resolution artifact
60
Transducers that create __ minimize axial resolution artifact.
short pulses (high frequency, less ringing)
61
This is created when sound pulses glance off a second structure on the way to or from the primary reflector.
multipath artifact
62
This is a subtle artifact tat often cannot be explicitly identified on the image.
multipath
63
Multipath violates which assumption?
#2 (sound travels directly to the reflector and back)
64
What kind of reflectors direct reflected sound away from the transducer?
curved or oblique reflectors
65
Spatial resolution is affected by the number of...
horizontal scan lines per frame.
66
This occurs when a reflecting structure is located deeper than the imaging depth of the image.
range ambiguity artifact
67
Range ambiguity artifact is eliminated by increasing the...
PRP.
68
This appears as small amplitude echoes and results from many sources, including electrical interference, signal processing and spurious reflections.
noise
69
This is noise resulting from the constructive and destructive interference of small sound wavelets.
speckle
70
This is an effective tool to reduce speckle.
spatial compounding
71
This is the presence of false echo signals arising from locations outside of the main sound beam.
clutter
72
Name three examples of clutter.
side lobes, grating lobes, and section thickness
73
This reduces an image's noise content.
harmonic imaging

Ultrasound Physics (23 decks)

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