Chapter 20-21 Flashcards Preview

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Flashcards in Chapter 20-21 Deck (138):
1

What is the term used for when the color gain is set to an inappropriately high level, color appears throughout the color box?

color confetti

2

When there is color confetti, what should you adjust?

lower the color Doppler gain

3

What appears on the image when the pulsed Doppler gain is set too high?

gray scale noise

4

What should be considered when a possible source of peculiar color variation, whenever the color changes directly from red to blue or vice versa?

aliasing

5

According to the color map, when will you see flow reversal?

flow reversal is present in a vessel when the colors red, black, and blue are next to each other
on the color map if the colors touch each other and they they go through the maps middle

6

on the color map, when can you tell aliasing?

if the colors that touch each other go around the outside of the map

7

What is the most effective way to eliminate aliasing on a color flow image?

increase the velocity scale

8

What effect does increasing the scale have on a color Doppler image?

decreases sensitivity

9

What does increasing the wall filter do?

eliminates low frequency Doppler shifts.
leaves high velocity flows unchanged.
can eliminate ghosting artifact

10

What does increasing the wall filter do in spectral Doppler?

eliminate low frequency Doppler shifts near the baseline.
does not affect higher velocity flows

11

What is an artifact?

an error in imaging

12

What are the types of artifacts?

artifacts include reflections that are described as
-not real
-not seen on the image
-incorrect shape or size
-incorrect position
-incorrect brightness

13

What are causes of artifacts?

violation of assumptions
equipment malfunction or poor design
the physics of US
operator error

14

What is hyperechoic?

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

15

what is hypoechoic?

portions of an image that are not as bright as surround tissues, or tissues that appear less bright than normal

16

what is anechoic?

an extreme form of hypoechoic, meaning entirely without echoes or echo free

17

What is isoechoic?

describes structures with equal echo brightness

18

What is homogeneous?

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

19

What is heterogeneous?

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

20

What are six assumptions that are used in 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 1,540 m/s
4. reflections arise only form 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 reflection

21

How do you know if something is an artifact?

it will appear in some views and disappear in others, whereas actual anatomy always remains visible no matter the imaging plane

22

What is a reverberation?

they appear on the display as multiple, equally spaces echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasound beam

23

What is the assumption that is invalid with reverb?

sound travels back directly to a reflector and back

24

What are some characteristics of reverberation?

appear in multiples
appear equally spaced
are located parallel to the sound beams main axis
are located at ever increasing depths

25

What does reverb resemble?

a ladder or venetian blind

26

Which reflections are real with reverb?

the first and second reflections, closest to the transducer are real, but the remaining echoes (which appear deeper) do not correctly correspond to true anatomic structures

27

What is a comet tail?

described as "reverb with the spaces squeezes out" appears as a solid hyperechoic line directed downward.

28

Another name for comet tail?

ring down artifact

29

When is the comet tail artifact created?

when closely spaced reverbs merge.

30

Where is comet tail artifact more likely to appear?

when the reflecting surfaces are located in a medium with a very high propagation speed, such as a mechanical heart valve

31

Where can comet tail arise from?

from resonance, or vibration, of small structures such as gas bubbles after they have been bombarded by a sound pulse

32

What assumption does comet tail break?

same as reverb
sound travels directly to a reflector and back

33

What are characteristics of comet tail?

appears as a single long hyperechoic echo
is located parallel to the sound beams main axis

34

What is shadowing?

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

35

What happens when too much attenuation occurs?

deep reflecting surfaces do not appear on the image, thus shadowing prevents the display of true anatomic stuctures

36

When does shadowing appear?

when the attenuation is higher in the tissue above the shadow than in the surrounding tissue

37

What assumption is invalid for shadowing?

the intensity of a reflection is related to the tissue creating the reflection

38

What are characteristics of shadowing?

hypo or anechoic (background color)
the result of too much attenuation
located beneath the structure with abnormally high attenuation
prevents visualization of true anatomy on the scan

39

What can shadowing and enhancement provide?

provide valuable diagnostic info that helps to characterize tissue

40

how is shadowing and speed of sound in a medium related?

unrelated

41

What is edge shadow?

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

42

With edge shadowing, what does the sound beam do?

the sound beam refracts (transmits with a bend) at the edge of a curved reflector.

43

What happens with edge shadowing?

the beam simultaneously diverges, resulting in a drop in intensity. this decrease in intensity causes edge shadowing.

44

What is another name for edge shadowing?

shadowing by refraction

45

What are characteristics of edge shadowing artifact?

hypo or anechoic (background color)
results when the beam spreads after striking a curved reflector
extends downward from the curved reflectors edge, parallel to the beam
prevents visualization of true anatomy on the scan

46

What assumption is invalid with edge shadowing?

the intensity of a reflection is related to the characteristics of tissue creating the reflection

47

Define enhancement

an artifact that appears as a hyperechoic region beneath tissues with abnormally low attenuation

48

Shadowing is the same color as ____ whereas enhancement is the same color as ____

background
foreground (echoes)

49

What is the relationship between enhancement and speed of sound in a medium?

unrelated

50

What are characteristics of enhancement?

hyperechoic (same color as foreground)
the result of too little attenuation
located beneath a structure with abnormally low attenuation

51

What is focal enhancement?

a special form of enhancement in which a side by side region of an image appears brighter than tissues at other depths

52

Another name for focal enhancement

focal banding

53

What appearance does focal banding have?

has the same appearance as an incorrect TGC setting

54

where is focal banding more prominent?

at the focus
when the beam is strongly focused, the intensity in the focal zone is increased

55

What assumption does enhancement break?

the intensity of a reflection is related to the characteristics of tissue creating the reflection

56

What are characteristics of focal enhancement?

a hyperechoic side to side or horizontal region (appears the same as the foreground)
results from increased intensity at the focus

57

What is mirror image artifact created?

created when sound reflects off a strong reflector (mirror) and is redirected toward a second structure

58

How does the mirror image artifact appear?

appears as a replica of a true reflector. the artifact is always deeper than the true anatomy

59

where is the mirror located?

the mirror is always located along a straight line between the transducer and the artifact

60

where is the mirror image artifact located?

located deeper than the real structure

61

What imaging places can mirror image appear?

gray scale
color doppler

62

What assumptions are invalid with mirror image artifact?

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

63

What are the characteristics of mirror image?

a second copy of a true reflector
the artifact 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

64

What is an artifact of mirror image that appears on spectral Doppler display?

crosstalk

65

When is speed error artifact created?

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

66

What appearance does a speed error artifact have?

a step off as if structures are split or cut

67

What happens when the mediums speed is slower than that in soft tissue?

-sound travels slower than the US system expects
-pulses return from their trip in the body-SLOW
-Go return time is too long
-system assumes reflectors are far from transducer
-reflectors placed too deep on image
-distances are overestimated (reported number is too large)

68

What happens when the mediums speed is faster than that in soft tissue?

-sound travels faster than the US system expects
-pulses return from their trip in the body -FAST
-Go return time is too short
-system assumes reflectors are close to the transducer
-reflectors are located too shallow on image
-distances are underestimated (reported number is too small)

69

What are other names for speed error artifact?

propagation speed error or range error artifact

70

What assumption is invalid with speed error?

sound travels at a speed of exactly 1540 m/s

71

What are characteristics of speed error?

correct number of reflectors
improper depth
appears as a step off

72

When do lobe artifacts appear?

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

73

What does lobe artifact degrade?

lateral resolution

74

What assumption is invalid with lobe artifact?

reflections arise from structures located along the beams main axis

75

What are characteristics of lobe artifact?

a second copy of the true reflector
the artifact and the true reflector are located side by side at the same depth

76

Lobes created by a single crystal transducer, such as mechanical probe are called what?

side lobes

77

Lobes created by an array transducer are called what?

grating lobes

78

What ways can grating lobes be reduced?

subdicing
apodization

79

What is subdicing?

dividing each PZT element into small pieces

80

What is apodization?

exciting the subdiced elements with different voltage

81

What is refraction artifact?

created when a sound pulse changes direction during transmission

82

What assumption is invalid with refraction artifact?

sound travels in a straight line

83

What should we remember about refraction?

refraction is transmission with a bend

84

What resolution is degraded with refraction artifact?

lateral resolution

85

What are characteristics of refraction artifact?

a second copy of the reflector
the copy is side by side, or at the same depth as the true reflector

86

What are other names for slice thickness?

section thickness artifact or partial volume artifact

87

What is slice thickness artifact related to?

related to the dimension of the beam that is perpendicular to the imaging plane

88

What is determined by the thickness of the imaging plane?

elevational resolution

89

What does slice thickness artifact fill in?

fills in hollow structures such as cysts

90

What can reduce slice thickness artifact?

reduced with thinner imaging planes such as using a 1.5 D array transducer

91

What assumption is invalid with slice thickness?

the imaging plane is extremely thin

92

Define slice thickness artifact

the true reflector lies either above or below the assumed imaging plane, but is displayed within the image

93

When is lateral resolution artifact created?

occurs when a pair of side by side reflectors are closer than the width of the sound beam
reflectors are positioned perpendicular to the beam

94

how do objects appear with lateral resolution artifact?

two objects appear as one reflection on the image

95

What is another name for lateral resolution artifact?

point spread artifact

96

Where is lateral resolution artifact least likely to occur?

at the focus where the beam is narrow
more likely to occur where the beam is wide

97

where is lateral resolution artifact more likely to occur?

more likely to occur where the beam is wide

98

Lateral resolution artifact may display what?

display a small reflector as a wide line rather than a narrow dot

99

When is axial resolution artifact created?

when a long pulse strikes two closely spaced structures, where one is in front of the other. the structures are parallel to the beams main axis.

100

How many reflections appear on the image if the structures are closer together than one half the SPL?

one

101

axial resolution artifact creates what?

one reflection on the image from two closely spaced reflectors

102

What minimizes axial resolution artifact?

shorter pulses such as using a higher freq transducer and less ringing

103

When is multipath artifact 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

104

When does multipath artifact appear?

appears when some pulses travel directly to and from a reflector while others do not

105

What assumption is invalid with multipath artifact?

a pulse travels directly to a structure and then back to the transducer

106

What often results in multipath artifact?

results in subtle, nonspecific changes that cannot be explicitly identified on the image

107

What do curved or oblique reflectors do?

they redirect sound waves in direction other than back toward the transducer

108

When the amplitude of the reflection received by the transducer may be less than expected, what happens?

reflectors are
-absent on the image
-appear too weak on the image or
-appear different from other similar reflection boundaries

109

What does poor temporal resolution result in?

results in less accurate positioning of moving reflectors

110

high line density results in better what?

spatial resolution

111

What is spatial resolution related to?

overall detail in an image

112

What is spatial resolution determined by>

line density, axial resolution and lateral resolution

113

What is spatial resolution affect by?

affected by the number of horizontal scan lines per frame

114

Spatial resolution is better with a ____number of scan lines

greater

115

When the image info is in digital form, spatial resolution is related to ____

pixel density

116

spatial resolution improves with a __ number of pixels in an image of fixed size which is called _____

large and high pixel density

117

What does lower pixel density do to the spatial resolution?

degrades spatial resolution

118

With low pixel density, each pixel is ___

large

119

When does spatial resolution artifact occur?

when the pixel size is greater than the size of the reflector

120

When does range ambiguity artifact occur?

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

121

How is range ambiguity artifact eliminated?

increasing the PRP. longer PRP means deeper imaging and decreased PRF

122

How does noise appear?

appears as small amplitude echoes and results from many sources, including electrical interference, signal processing and spurious reflections

123

What does noise most likely affects?

affects low level hypoechoic regions rather than bright echogenic areas

124

What is acoustic speckle?

noise resulting from the constructive and destructive interference of small sound wavelets

125

What is the appearance and speckle

the displayed images will contain fake detail, such as grainy tissue like texture.
speckled or grainy appearance
salt and pepper

126

What can reduce speckle artifact?

spatial compounding

127

What is clutter?

another form of noise
the presence of false echo signals arising from locations outside of the main sound beam

128

What are sources of clutter?

side lobes, grating lobes and section thickness artifact

129

What is clutter with Doppler?

a contamination of valid Doppler signals with high amplitude reflections from vessel walls or heart muscle. These high amplitude reflections overpower the true Doppler signals created by moving blood.

130

What does harmonic imaging do?

reduces an images noise content

131

What is the goal of harmonic imaging?

is to selectively distinguish meaningful reflections from noise, thereby increasing the signal to noise ratio

132

What are some possible causes of an anatomic reflector absent on image?

shadowing
shadowing by refraction
lateral resolution
axial resolution

133

What are some possible causes of anatomic reflectors appears multiple time on image. Artifact positioned deeper than the true anatomy?

comet tail
ring down
reverb
mirror image

134

What are some possible causes of an anatomic reflector appears multiple time on image. Artifact displaced to the side of true anatomy?

refraction
side lobe
grating lobe

135

What are some possible causes of anatomic reflector appear with abnormal brightness?

enhancement (hyper)
banding (hyper)
shadowing (hypo)
shadowing by refraction (hypo)

136

what are some possible causes of anatomic structures appear at incorrect depth?

speed errors
range ambuigity artifact

137

What are some possible causes of anatomic structures appear in the incorrect imaging plane?

slice thickness artifact

138

What are some possible causes of anatomic structures do not correspond to echoes on the image?

acoustic speckle
multipath