Physics Ch 21 Flashcards
1
Q
An error in imaging
A
artifact
2
Q
Causes of artifacts (4)
A
violation of assumptions, equipment malfunction, physics, operator error
3
Q
Portions of an image that are brighter than surrounding tissues
A
hyperechoic
4
Q
Portions of an image that are not as bright as surrounding tissues
A
hypoechoic
5
Q
Without echoes
A
anechoic
6
Q
Structures with equal echo brightness
A
isoechoic
7
Q
A portion of tissue or an image that has similar echo characteristics throughout
A
homogenous
8
Q
A portion of tissue or an image that has differing echo characteristics throughout
A
heterogenous
9
Q
Artifacts appear when the assumptions are
A
not true
10
Q
What are the 6 assumptions
A
- 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
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
12
Q
What assumption is not true with reverberation
A
2 sound travels directly to a reflector and back
13
Q
Type of reverberation (ring down artifact) created when closely spaced reverberations merge
A
comet tail
14
Q
Which assumption is not true with comet tail
A
2 sound travels directly to a reflector and back
15
Q
Reverberation is located _____ to the sound beam main axis and at ______
A
parallel, increasing depths
16
Q
Comet tail is located _____ to the sound beams main axis
A
parallel
17
Q
Appears as a hypoechoic or anechoic region extending downward from a HIGHLY ATTENUATING structure
A
shadowing
18
Q
Shadowing is _______ to the speed of sound in soft tissue
A
completely unrelated
19
Q
Shadows are the same color as the image background, reflections missing are behind a _________ structure
A
highly attenuating
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
21
Q
Type of shadowing (shadowing by refraction)
A
edge shadowing
22
Q
Appears as a hypoechoic region extending down from the edge of a curved reflector
A
edge shadowing
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
24
Q
Results when the beam spreads after striking a curved reflector
A
edge shadowing
25
Prevents visualization of true anatomy of the scan
edge shadowing
26
Appears as a hyperechoic region beneath tissue with abnormally LOW ATTENUATION
enhancement
27
Enhancement is completely _____ to the speed of sound in the tissue
unrelated
28
What assumption is not true with enhancement
#6 the strength of a reflection is related to the characteristics of the tissue creating the reflection
29
Hyperechoic, result of too little attenuation, located beneath a structure with abnormally LOW attenuation
enhancement
30
Type of enhancement, focal banding, side to side region of an image that appears brighter than tissues at other depths
Focal enhancement
31
Has the appearance of incorrect use of TGCs
focal enhancement
32
In focal enhancement, where is focal banding most prominent and why
at the focus, where the sound beam intensity is greatest
33
What assumption is not true with focal enhancement
#6 the strength of a reflection is related to the characteristics of the tissue creating the reflection
34
Hyperechoic side to side region, results from increased intensity at the focus
focal enhancement
35
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
mirror image
36
This artifact is located deeper than the real structure
mirror image
37
Another name for mirror image that is seen with color and spectral doppler
crosstalk
38
What assumption is not true with mirror image
#1 sound travels in a straight line #2 sound travels directly to a reflector and back to the transducer
39
Second copy of a true reflector, a bright reflector lies on a straight line between the artifact and the transducer
mirror image
40
In mirror image, the true reflector and artifact are
equal distances from the mirror
41
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
Speed error/prop speed error
42
Speed errors appear as a ______ as if structures are _____ or ______
step off, split, cut
43
What assumption is not true with speed error
#3 Sound travels in soft tissue at exactly 1540 m/s
44
Correct number of reflectors, improper depth, appears as a step off
speed error/prop speed error
45
In speed error, when the medium's speed is slower than average speed in soft tissue (3)
go-return time is longer, reflectors placed too deep on image, distances are overestimated
46
In speed error, when the medium's speed is faster than average speed in soft tissue (3)
go-return time is short, reflectors are located too shallow on the image, distances are underestimated
47
This artifact appears when the sound energy is transmitted in a direction other than along the beams main axis
lobes
48
Lobe artifacts degrade _____ resolution
lateral
49
Lobes are weaker than the primary beam and do not typically
create reflections that appear on an image
50
Can lobes create a reflection ever? When?
Yes, when a strong reflector is in the path of the lobe
51
What assumption is not true with lobe
#4 reflections only arise from structures positioned in the beams main axis
52
Lobes are located
side by side and at the same depth
53
Lobes created by mechanical probe are called
side lobes
54
Lobes created by array transducers are called
grating lobes
55
How to reduce grating lobes
subdicing, apodization
56
Dividing the PZT element into small pieces
subdicing
57
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
apodization
58
Created when a sound pulses changes direction during transmission
refraction
59
Refraction occurs when a sound wave strikes a boundary with ______ and the media has ______. AKA _____
oblique incidence, different prop speeds, "transmission with a bend"
60
Refraction artifact degrades _____ resolution
lateral
61
What assumption is not true with refraction
#1 Sound travels in a straight line
62
Related to dimension of the beam that is PERPENDICULAR to the imaging plan
slice thickness
63
What are the other names for slice thickness
section thickness, partial volume
64
Slice thickness artifact is involved with
elevational resolution
65
Elevational resolution is determined by the thickness of
the imaging plane
66
What assumption is not true with slice thickness
#5 the imaging plane is very thin
67
The true reflector lies either above or below the assume imaging plan, but is displayed within the image. FILLS IN FLUID FILLED STRUCTURES
slice thickness
68
Reducing slice thickness artifact involves
using a 1 1/2 dimensional array transducer which provides a thinner imaging plane
69
Occurs when a pair of side by side reflectors are closer than the width of the sound beam
lateral resolution artifact
70
What is another name for lateral resolution artifact
point spread artifact
71
Lateral resolution artifact reflectors are also called
point spread artifact
72
Lateral resolution reflectors are positioned _____ and depend on _____
perpendicular to the sound beam, beam width (least likely to occur at the focus where the beam is the smallest)
73
_____ occurs when a long pulse strikes two closely spaced structures ____ to the sound beam and only ____ will appear on the image
axial resolution, parallel, one reflection
74
Reducing axial resolution artifact involves
higher frequency transducer (shorter pulses, less ringing)
75
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
Multipath artifact
76
What assumption is not true with multipath artifact
#2 sound travels directly to a reflector and back
77
Subtle nonspecific changes that cannot be explicitly identified on the image
multipath artifact
78
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
Curved and Oblique reflectors
79
Reflections may be absent on the image, may appear too weak on the image, may appear different from other similar reflecting boundaries
curved and oblique reflectors
80
Results in less accurate positioning of moving reflectors
temporal resolution artifact
81
Spatial resolution is related to
overall detail
82
Spatial resolution is determined by
line density, axial/lateral resolution
83
With spatial resolution and high line density, greater number of _______ per frame and _______, the image exhibits great detail and the spatial resolution is _____
horizontal scan lines, high pixel density, exceptional
84
With spatial resolution and low line densit, the imafe exhibits _______ and the spatial resolution is _____
less detail, poor
85
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
range ambiguity artifact
86
Small amplitude choes and results from many sources (including electrical interference, signal processing and spurious reflection)
noise
87
Noise is more likely to affect ______ hypoechoic regions rather than bright echogenic areas
low level
88
What are the two types of noise
speckle, clutter
89
Results from constructive and destructive interference of small sound wavelets. Give image a grainy appearance, especially in shallow portions of an ultrasound image
Speckle
90
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
Clutter
91
Reducing noise involves using
harmonic imaging
92
The goal of harmonic imaging is to selectively distinguish meaningful _________ and this _____ the signal-to-noise ratio
reflections from noise, increases
