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Ultrasound Physics > Quiz 4 Chapter 21 > Flashcards

Quiz 4 Chapter 21 Flashcards

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1
Q

What is an artifact in imaging?

A

An artifact is essentially an error in imaging

Artifacts can distort the representation of the actual object being imaged.

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2
Q

List some characteristics of artifacts in imaging.

A
  • Not real
  • Not seen on the image
  • Incorrect shape or size
  • Incorrect position
  • Incorrect brightness

These characteristics can lead to misinterpretation of the images.

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3
Q

What causes artifacts in ultrasound?

A

Artifacts are caused by:
* Violation of assumptions
* Equipment malfunction or poor design
* The physics of ultrasound
* Operator error

Each of these factors can lead to misleading images or data in ultrasound imaging.

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4
Q

What is hyperechoic ?

A

Portions of an image that are brighter than surrounding tissues

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5
Q

What is hypoechoic?

A

Portions of an image that are NOT as bright as the surrounding tissues

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6
Q

What is anechoic?

A

Extreme form of hypoechoic.
No echoes

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7
Q

What is isoechoic?

A

Structures with equal echo brightness

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8
Q

What is homogeneous?

A

Portion of tissue or image that has similar echo characteristics throughout

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9
Q

What is heterogeneous?

A

Portion of tissue or image that has differing echo characteristics throughout

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10
Q

What are the 6 assumptions of imaging?

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 1,540 m/s
  4. Reflections happen only from structures positioned in beams main axis
  5. Imaging plane is thin
  6. Strength of reflection is related to the characteristics of the tissue creating the reflection
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11
Q

In axial resolution high frequency means ______ wavelength?

A

Shorter wavelength

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12
Q

In lateral resolution a _____ beam equals better lateral resolution?

A

Narrow

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13
Q

A _____ beam = better Elevational resolution

A

Thin

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14
Q

What is temporal resolution ?

A

How quickly the system can show images

Competes with spatial resolution

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15
Q

What is spatial resolution?

A

The ability of the system to distinguish between two closely spaced structures.

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16
Q

What do reverberations look like?

A

Multiple, equally spaced echos
(Look like a ladder)

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17
Q

What is the cause of reverberations?

A

Sound waves bouncing between two reflectors parallel to the beam

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18
Q

What does a comet tail look like?

A

Solid hyperechoic line directed downward

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19
Q

What is the cause of a comet tail?

A

Closely spaced reverberations merge and are located parallel to the beams main axis

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20
Q

When are comet tails most likely to occur?

A

When reflected surfaces are located in a medium with a high propagation speed

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21
Q

What does a shadow artifact look like?

A

Appears hypoechoic or anechoic

Located beneath a highly attenuated structure

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22
Q

What causes shadow artifacts?

A

Too much attenuation in the tissue above the shadow

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23
Q

What does an Edge shodow artifact look like?

A

Appears as a hypoechoic region extending downward

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24
Q

What is the cause of an edge shadow artifact?

A

When the beam spreads after striking a curved reflector

Decrease in intensity

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25
What does an enhancement artifact look like?
Appears hyperechoic (Opposite of shadowing)
26
What causes enhancement ?
Low attenuation of a structure
27
Examples of media with low attenuation?
Blood, urine, fluids etc.
28
T/F Can enhancement be used to provide clinically useful information to help characterize a tissue?
True
29
What does a focal enhancement artifact look like?
Hyperechoic horizontal region Appears brighter than structures at other depths
30
What is the cause of focal enhancement?
Increased intensity at the focus
31
What is another name for focal enhancement?
Focal banding
32
What is another name for edge shadow?
Shadowing by refraction
33
What is another name for comet tail?
Ring down artifact
34
What does a mirror image look like?
A replica of the structure that is located deeper than the real structure
35
What is the cause of mirror an image?
Sound reflects off a strong reflector and is redirected towards a second structure causing a replica to appear
36
A bright reflector (mirror), lies on a _______ line between the artifact and the transducer.
Straight
37
True reflector and artifact are_______ distances from the mirror.
Equal
38
What does a crosstalk artifact look like?
Appears as an identical Doppler spectrum above and below the baseline
39
What is the cause of crosstalk?
Doppler gain is set too high Incident angle is near 90 degrees between the sound beam and the flow direction
40
What does a speed error look like?
Appear as if structures are split or cut
41
What is another name for speed error artifact?
Range error artifact
42
What is the cause of speed error?
When a sound wave propagates through a medium at any other speed other than soft tissue (1,540m/s).
43
In speed error, the correct number of reflectors are displayed but appear at ______ _____?
Incorrect depths
44
What happens when the mediums speed is slower than soft tissue?
-Pulses return slow -sound travels slower than system expects -go-return time is too long -system assumes reflectors are far from transducer -reflectors are too deep on images -distances are overestimated
45
What happens when the mediums speed is faster than soft tissue?
-sound travels faster than system expects -pulses return fast -go-return time is too short -system assumes reflectors are close to the transducer -reflectors are too shallow on the image -distances are underestimated
46
When do Lobe artifacts appear?
When sound energy is transmitted in a direction other than along the beams main axis Side by side at same depth
47
What happens to lateral resolution in a lobe artifact?
Degrades lateral resolution
48
How can you tell the difference between the true reflector and the Lobe artifact?
It is impossible to tell them apart
49
Why should you use multiple views when a lobe artifact occurs?
The real anatomy will appear in all views The artifact will only appear in a few views
50
What do Lobe artifacts look like?
A second copy of the true reflector Located side by side
51
What transducers create side lobes?
Single crystal transducer
52
What transducer creates grating lobes?
Array transducer
53
What 2 things are used to reduce grating lobes?
Subdicing Apodization
54
What is subdicing?
Dividing PZT into smaller pieces
55
How does apodization work?
Exciting the subdued elements with different voltages Elements closer to beam get higher voltages Elements further from beam get lower voltages
56
What does a refraction artifact look like?
A second copy of a true reflector at the same depth
57
What is the cause of a refraction artifact?
When a pulse changes direction during transmission Occurs when a sound wave strikes a boundary at an oblique angle The media on either side of the boundary have different propagation speeds
58
How does refraction affect lateral resolution?
It degrades lateral resolution
59
What are other names for slice thickness?
Section thickness artifact Partial volume artifact
60
What is slice thickness artifact?
Reflections from structures above or below the assumed image plane may appear in the image
61
How is slice thickness reduced?
With thinner imaging planes (Ones created with a 1 1/2 D array transducer)
62
What is elevational resolution determined by?
Thickness of the imaging plane
63
Why does a lateral resolution artifact occur?
When a pair of side by side reflectors are closer than the width of the sound beam
64
Where is a lateral resolution artifact LEAST likely to occur?
At the focus
65
Where is a lateral resolution artifact MOST likely to occur?
Where the beam is wide
66
What is the other name for lateral resolution artifact?
Point spread artifact
67
What does a lateral resolution artifact look like?
Two object appear as one reflection on an image -displays a small reflector as a wide line instead of small dot
68
Why does an axial resolution artifact occur?
When a long pulse strikes two closely spaced structures when one is in front of the other Structures are parallel to beams main axis
69
What does an axial resolution artifact look like?
Appears as one reflector in the image if they are closer together than 1 1/2 the SPL
70
Transducers that create _____ pulses minimize axial resolution artifacts.
Short
71
How are Multipath artifacts created?
When pulses glance off a second structure on the way to or from the primary reflector
72
What do multipath artifacts look like?
Can not be identified on the image, change is too subtle
73
In a multipath artifact, the transmit pulse length _______ from the return path length.
Differs
74
How does a curved and oblique reflector artifact occur?
When a sound beam strikes a curved or oblique reflector, some of the reflected sound is directed away from transducer
75
What happens to the amplitude of the received reflection in a curved / oblique reflector artifact?
Less than expected
76
What happens to the reflectors in a curved and oblique reflector artifact ?
-absent on image -too weak to see
77
Temporal resolution is best with _______ frame rate.
High
78
Poor temporal resolution causes ________ accurate position of moving reflectors.
Less
79
What is spatial resolution determined by?
Line density Axial resolution Lateral resolution
80
What is high line density?
Closely packed sound pulses
81
High line density provides greater what?
Detail and spatial resolution
82
What is low line density?
Wider gaps between sound pulses
83
Low line density provides _____ detail and _____ spatial resolution.
Less detail Poor spatial resolution
84
When does spatial resolution artifact occur?
When the pixel size is greater than the size of the reflector
85
What is high pixel density?
Lots of pixels in an image Improved spatial resolution Pixels are small resulting in detailed image
86
What is low pixel density?
Each pixel is large Degrades spatial resolution Pixels
87
When do Range ambiguity artifacts occur?
When a reflecting structure is deeper than the imaging depth
88
Where is the reflector placed on an image when range ambiguity occurs?
Reflector is placed at a shallow location
89
How is range ambiguity eliminated?
By increasing PRP
90
In range ambiguity, longer PRP = deeper imaging and ______ PRF.
decreased
91
What does Noise look like?
Small amplitude echoes
92
Where does noise come from?
Electrical interference Signal processing Spurious reflections
93
Noise affects low level _______ regions rather than ______ regions.
Hypoechoic Echogenic
94
What is speckle?
Noise resulting from constructive and deconstructive interference of small sound waves
95
What does speckle look like on an image?
Contain fake detail Looks grainy in texture
96
How is speckle reduced?
Spatial compounding
97
What is clutter?
False echo signals from locations outside the main sound beam
98
What causes clutter?
Side lobes Grating lobes Slice thickness artifact
99
What is clutter with Doppler?
The contamination of Doppler signals with high amplitude reflections from vessel walls or heart muscle
100
What is harmonic imaging?
Reduces noise Selectively distinguishes meaningful reflections from noise

Ultrasound Physics (7 decks)

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