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Vascular II & Physics II > Physics Ch 21 > Flashcards

Physics Ch 21 Flashcards

1
Q

An error in imaging

A

artifact

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2
Q

Causes of artifacts (4)

A

violation of assumptions, equipment malfunction, physics, operator error

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3
Q

Portions of an image that are brighter than surrounding tissues

A

hyperechoic

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4
Q

Portions of an image that are not as bright as surrounding tissues

A

hypoechoic

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5
Q

Without echoes

A

anechoic

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6
Q

Structures with equal echo brightness

A

isoechoic

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7
Q

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

A

homogenous

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8
Q

A portion of tissue or an image that has differing echo characteristics throughout

A

heterogenous

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9
Q

Artifacts appear when the assumptions are

A

not true

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10
Q

What are the 6 assumptions

A
  1. sound travels in a straight line 2. sound travels directly to a reflector and back 3. sound travels in soft tissue at exactly 1540 m/sec 4. reflections arise only from structures positioned in the beams main axis 5. imaging plan is very thin 6. strength of a reflection is related to the characteristics of the tissue creating the reflection
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11
Q

Appear on the display as multiple, equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positions parallel to the us system

A

reverberation

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12
Q

What assumption is not true with reverberation

A

2 sound travels directly to a reflector and back

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13
Q

Type of reverberation (ring down artifact) created when closely spaced reverberations merge

A

comet tail

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14
Q

Which assumption is not true with comet tail

A

2 sound travels directly to a reflector and back

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15
Q

Reverberation is located _____ to the sound beam main axis and at ______

A

parallel, increasing depths

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16
Q

Comet tail is located _____ to the sound beams main axis

A

parallel

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17
Q

Appears as a hypoechoic or anechoic region extending downward from a HIGHLY ATTENUATING structure

A

shadowing

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18
Q

Shadowing is _______ to the speed of sound in soft tissue

A

completely unrelated

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19
Q

Shadows are the same color as the image background, reflections missing are behind a _________ structure

A

highly attenuating

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20
Q

What assumption is not true with shadowing

A

6 strength of a reflection is related to the characteristic of the tissue creating the reflection

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21
Q

Type of shadowing (shadowing by refraction)

A

edge shadowing

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22
Q

Appears as a hypoechoic region extending down from the edge of a curved reflector

A

edge shadowing

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23
Q

What assumption is not true with edge shadowing

A

6 strength of a reflection is related to the characteristic of the tissue creating the reflection

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24
Q

Results when the beam spreads after striking a curved reflector

A

edge shadowing

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25
Q

Prevents visualization of true anatomy of the scan

A

edge shadowing

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26
Q

Appears as a hyperechoic region beneath tissue with abnormally LOW ATTENUATION

A

enhancement

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27
Q

Enhancement is completely _____ to the speed of sound in the tissue

A

unrelated

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28
Q

What assumption is not true with enhancement

A

6 the strength of a reflection is related to the characteristics of the tissue creating the reflection

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29
Q

Hyperechoic, result of too little attenuation, located beneath a structure with abnormally LOW attenuation

A

enhancement

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30
Q

Type of enhancement, focal banding, side to side region of an image that appears brighter than tissues at other depths

A

Focal enhancement

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31
Q

Has the appearance of incorrect use of TGCs

A

focal enhancement

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32
Q

In focal enhancement, where is focal banding most prominent and why

A

at the focus, where the sound beam intensity is greatest

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33
Q

What assumption is not true with focal enhancement

A

6 the strength of a reflection is related to the characteristics of the tissue creating the reflection

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34
Q

Hyperechoic side to side region, results from increased intensity at the focus

A

focal enhancement

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35
Q

Created when sound reflects off a strong reflector and is redirected toward a second structure. The redirection causes a replica of the structure to incorrectly appear on the image

A

mirror image

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36
Q

This artifact is located deeper than the real structure

A

mirror image

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37
Q

Another name for mirror image that is seen with color and spectral doppler

A

crosstalk

38
Q

What assumption is not true with mirror image

A

1 sound travels in a straight line #2 sound travels directly to a reflector and back to the transducer

39
Q

Second copy of a true reflector, a bright reflector lies on a straight line between the artifact and the transducer

A

mirror image

40
Q

In mirror image, the true reflector and artifact are

A

equal distances from the mirror

41
Q

Created when a sound wave propagates through the medium at a speed other than that of soft tissue. The correct number of reflectors are displayed, but they appear at different depths

A

Speed error/prop speed error

42
Q

Speed errors appear as a ______ as if structures are _____ or ______

A

step off, split, cut

43
Q

What assumption is not true with speed error

A

3 Sound travels in soft tissue at exactly 1540 m/s

44
Q

Correct number of reflectors, improper depth, appears as a step off

A

speed error/prop speed error

45
Q

In speed error, when the medium’s speed is slower than average speed in soft tissue (3)

A

go-return time is longer, reflectors placed too deep on image, distances are overestimated

46
Q

In speed error, when the medium’s speed is faster than average speed in soft tissue (3)

A

go-return time is short, reflectors are located too shallow on the image, distances are underestimated

47
Q

This artifact appears when the sound energy is transmitted in a direction other than along the beams main axis

A

lobes

48
Q

Lobe artifacts degrade _____ resolution

A

lateral

49
Q

Lobes are weaker than the primary beam and do not typically

A

create reflections that appear on an image

50
Q

Can lobes create a reflection ever? When?

A

Yes, when a strong reflector is in the path of the lobe

51
Q

What assumption is not true with lobe

A

4 reflections only arise from structures positioned in the beams main axis

52
Q

Lobes are located

A

side by side and at the same depth

53
Q

Lobes created by mechanical probe are called

A

side lobes

54
Q

Lobes created by array transducers are called

A

grating lobes

55
Q

How to reduce grating lobes

A

subdicing, apodization

56
Q

Dividing the PZT element into small pieces

A

subdicing

57
Q

An extension of subdicing where elements are applied at different voltages-elements close to the center of the sound beam are excited with higher voltages, while the outermost elements are excited with lower voltages

A

apodization

58
Q

Created when a sound pulses changes direction during transmission

A

refraction

59
Q

Refraction occurs when a sound wave strikes a boundary with ______ and the media has ______. AKA _____

A

oblique incidence, different prop speeds, “transmission with a bend”

60
Q

Refraction artifact degrades _____ resolution

A

lateral

61
Q

What assumption is not true with refraction

A

1 Sound travels in a straight line

62
Q

Related to dimension of the beam that is PERPENDICULAR to the imaging plan

A

slice thickness

63
Q

What are the other names for slice thickness

A

section thickness, partial volume

64
Q

Slice thickness artifact is involved with

A

elevational resolution

65
Q

Elevational resolution is determined by the thickness of

A

the imaging plane

66
Q

What assumption is not true with slice thickness

A

5 the imaging plane is very thin

67
Q

The true reflector lies either above or below the assume imaging plan, but is displayed within the image. FILLS IN FLUID FILLED STRUCTURES

A

slice thickness

68
Q

Reducing slice thickness artifact involves

A

using a 1 1/2 dimensional array transducer which provides a thinner imaging plane

69
Q

Occurs when a pair of side by side reflectors are closer than the width of the sound beam

A

lateral resolution artifact

70
Q

What is another name for lateral resolution artifact

A

point spread artifact

71
Q

Lateral resolution artifact reflectors are also called

A

point spread artifact

72
Q

Lateral resolution reflectors are positioned _____ and depend on _____

A

perpendicular to the sound beam, beam width (least likely to occur at the focus where the beam is the smallest)

73
Q

_____ occurs when a long pulse strikes two closely spaced structures ____ to the sound beam and only ____ will appear on the image

A

axial resolution, parallel, one reflection

74
Q

Reducing axial resolution artifact involves

A

higher frequency transducer (shorter pulses, less ringing)

75
Q

Created when sound pulses glance off a second structure on the way to or from the primary reflector. As a result, the transmit path length differs from the return path length

A

Multipath artifact

76
Q

What assumption is not true with multipath artifact

A

2 sound travels directly to a reflector and back

77
Q

Subtle nonspecific changes that cannot be explicitly identified on the image

A

multipath artifact

78
Q

When sound beam strikes a curved or oblique reflector, some of the reflected sound may be directed away from the transducer. The amplitude of the reflection received by the transducer may be less than expected

A

Curved and Oblique reflectors

79
Q

Reflections may be absent on the image, may appear too weak on the image, may appear different from other similar reflecting boundaries

A

curved and oblique reflectors

80
Q

Results in less accurate positioning of moving reflectors

A

temporal resolution artifact

81
Q

Spatial resolution is related to

A

overall detail

82
Q

Spatial resolution is determined by

A

line density, axial/lateral resolution

83
Q

With spatial resolution and high line density, greater number of _______ per frame and _______, the image exhibits great detail and the spatial resolution is _____

A

horizontal scan lines, high pixel density, exceptional

84
Q

With spatial resolution and low line densit, the imafe exhibits _______ and the spatial resolution is _____

A

less detail, poor

85
Q

Occurs when a reflecting structure is located deeper than the imaging depth of the image. This reflector is placed at a shallow location on the image

A

range ambiguity artifact

86
Q

Small amplitude choes and results from many sources (including electrical interference, signal processing and spurious reflection)

A

noise

87
Q

Noise is more likely to affect ______ hypoechoic regions rather than bright echogenic areas

A

low level

88
Q

What are the two types of noise

A

speckle, clutter

89
Q

Results from constructive and destructive interference of small sound wavelets. Give image a grainy appearance, especially in shallow portions of an ultrasound image

A

Speckle

90
Q

Presence of false echo signals arising from locations outside of the main sound beam. Side lobes, grating lobes and section thickness artifact are sources of this

A

Clutter

91
Q

Reducing noise involves using

A

harmonic imaging

92
Q

The goal of harmonic imaging is to selectively distinguish meaningful _________ and this _____ the signal-to-noise ratio

A

reflections from noise, increases

Vascular II & Physics II (21 decks)

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