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Physics REVIEW > Artifacts > Flashcards

Artifacts Flashcards

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1
Q

Main categories of artifacts (4)

A

Resolution
Attenuation
Doppler
Propagation/location

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2
Q

Refraction and redirection or reverberation of sound waves is what type of artifact

A

Propagation

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3
Q

Degrade lateral resolution of artifact - which type of artifact

A

Propagation

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4
Q

With multipath artifact where is the second copy of the reflector placed?

A

At a DEEPER location

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5
Q

Which artifact occurs when it hits a rounded surface?

A

Multipath

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6
Q

How do you fix a double aorta

A

Change the window

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7
Q

Artifacts caused by air (2)

A

Ring down and comet tail

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8
Q

Adenomyomatosis will have this artifact

A

Comet tail

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9
Q

Emphysematous or pneumobilia will have this artifact

A

Ring down

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10
Q

Sound reflecting off a strong reflector causes what artifact? How does this occur

A

Mirror image

Interrogation at 90 degrees

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11
Q

Side lobes vs grating lobes

A

Side lobes are single element probes

Grating lobes are transducer arrys

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12
Q

How to fix grating lobes (3) explain

A

Apodization - decrease voltage and thus amplitudes on outer elements

Subdicing - each element is divided into subelements and wired together as single element

Dynamic aperture - use only few elements narrow the beam info returned

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13
Q

What is vertical misregistration

A

Propagation speed error

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14
Q

If the prop speed is faster than 1540 m/s, where will the reflector be placed?

A

Reflector will be closer

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15
Q

With propagation speed error, the reflector will be placed deeper when the prop speed is (faster or slower than 1540)

A

When it is slower, it will be placed deeper

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16
Q

How to fix section thickness artifact

A

THI

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17
Q

What is the assumption with section thickness artifact

A

The beam is razor thin

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18
Q

Assumptions with US (6)

A
  1. Sound travels in a straight line and at a constant speed in soft tissue
  2. Sound travels to and from a transducer
  3. Echoes only originate from the central sound beam
  4. Intensity of the echo corresponds to the strength of a reflector
  5. The imaging plane (elevation plane) is thin
  6. Distance to the reflector is proportional to the time it takes an echo to return
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19
Q

What artifacts are caused by attenuation (3)

A

Posterior enhancement
Posterior shadowing
Edge shadow

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20
Q

6 assumptions of US

A
  1. Sound always travels in a straight line (path)
  2. Sound always travels directly to and from a reflector (path)
  3. Sound travels exactly 1540 m/s in soft tissue (speed)
  4. Reflectors are always positioned in the central axis of the beam (reflector position)
  5. Strength/intensity of reflection is related only to the characteristics of the object causing the reflection (other reflectors)
  6. Imaging plane (elevation) infinitely thin
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21
Q

Resolution artifacts are related to

A

The ability of the US system

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22
Q

Resolution artifacts are related to

A

Ability to distinguish objects in the 3 imaging dimensions

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23
Q

Resolution artifact assumptions (2)

A
  1. Reflectors are always positioned in the central axis of the main beam
  2. The imaging plane is infinitely thin
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24
Q

Location/propagation speed artifacts create

A

creating an image of a differently shaped sized object

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25
Q

attenuation artifacts are the group of artifacts that create (2)

A

creating an object in an incorrect position

creating an object of incorrect brightess

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26
Q

Attenuation artifact assumption

A

The assumption that the strength / intensity of the reflection is related only to the characteristics of the object causing the reflection - what artifact?

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27
Q

spectral doppler artifact relates to

A

velocity measurement error

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28
Q

colour doppler error

A

presence/absence of a signal error

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29
Q

elevation resolution is determined by the thickness of the crystal and increases with distance away from the focal zone

A

true

30
Q

location/prop speed artifacts include (6)

A
  1. multipath
  2. mirror image
  3. refraction
  4. reverberation
  5. side lobes/grating lobes
  6. speed error/range ambiguity

MMRRSS

31
Q

attenuation artifacts (3)

A
  1. acoustic shadowing
  2. enhancement
  3. speckle
32
Q

double aorta is an example of what artifact

A

refraction artifact example

33
Q

Gas in colon is an example of what artifact

A

reverberation

34
Q

comet tail and ring down artifacts are examples of what artifact

A

reverberation

35
Q

ring down artifact occurs when

A

an ultrasound beam passes through a group of small air bubbles - reverb occurs between the reflective interfaces between the bubbles

36
Q

ring down distinguished by the appearance of

A

a posterior tail that does not taper in width or decrease in brightness

37
Q

comet tail is when there is reverberation of

A

high amplitude echoes within a small object (ilke a surgical clip or small metallic foreign body)

38
Q

multipath assumption

A

sound pulse always travels directly to the structure and back to the transducer

39
Q

where is the echo placed in multipath

A

deeper than the actual structure (travel time is longer than expected if the pulse strikes a second structure on the way out or way back)

40
Q

side lobes/grating lobes assumption

A

all reflectors lie in the central axis of the main beam

41
Q

what happens with side/grating lobes

A

low intensity off-axis sound beams produce a weak reflected signal. objects that reflect echoes arising from these lobes are misplaced as though they are lying in the main axis

42
Q

shadowing occurs when

A

sound waves strike a medium with extremely high attenuation

43
Q

enhancement occurs when

A

sound waves strike a medium with extremely low attenuation

44
Q

speckle is the result of

A

constructive/destructive interference and resultant scattering that creates bright and dark spots not related to a true anatomic structure

45
Q

anterior reverberation AKA

A

main bang

46
Q

lateral position errors are caused by

A

refraction

47
Q

range ambiguity artifacts occurs when

A

2nd pulse sent out before all echoes returned from the 1st pulse

48
Q

range ambiguity places structures closer or further?

A

closer

49
Q

if sound travels in a medium faster than 1.54, the echo will be placed ___

A

too close

50
Q

if sound travels in a medium slower than 1.54, the echo will be placed

A

too deep

51
Q

how to reduce spectral mirror image (AKA cross talk)

A 
decrease gains/power output
decrease angle (near 90degrees will show flow on either side of BL)
52
Q

acoustic shadowing is what type of artifact

A

attenuation

53
Q

shadowing is caused by

A
  1. increased attenuation

2. increased reflection (IRC)

54
Q

aliasing occurs when

A

the doppler shift exceeds the nyquist limit

55
Q

how do you fix aliasing (5)

A
  1. shift baseline down
  2. lower the operating frequency
  3. increase PRF (possiblity of range ambiguity)
  4. increase doppler angle (possibility of error)
  5. use continuous wave
56
Q

flash artifact is caused by

A

___ caused by motion - anything thats moving may cause a doppler shift

57
Q

Grating lobes duplicates structures ____ to the real structure

A

Lateral

58
Q

propagation speed error displaces objects ______

A

Axially

59
Q

What 2 artifacts displaces structres laterally

A

Grating lobes

Refraction (2)

60
Q

What creates slice thickness artifact?

What can the artifact look like?

A

The beam width - echoes received from the centre of the beam are averaged in with echoes received from off centre, creates a “fill-in” effect.

false echoes (debris) in an echo free area

61
Q

What is speckle?
What does the artifact look like?
How is it reduced? (2)

A

Produced by constructive/destructive interference patterns caused by scatterers in tissue
Looks like granular appearance
Reduced by compounding, persistence

62
Q

What causes reverberation?

What does it look like?

A

Multiple reflections between strong reflectors

Display of additional reflectors (not real) beneath the real reflector with equal separation intervals

63
Q

What is comet tail?

What does it look like?

A

A form of reverb; series of closely spaced discrete echoes

A comet, brightest closest to transducer, fading away from it

64
Q

How does ring down differ from comet tail artifact?

A

Ring down caused by the resonating or vibrating gas bubble after it is bombarded by US pulse.
Comet tail is produced as sound ping pongs between two reflectors

65
Q

What creates mirror image artifact?

What does mirror image look like?

A

A strong reflector creates mirror image

There will be a duplicate structure on the other side of the reflector

66
Q

What creates refraction artifact?

What does it look like?

A

Different propagation speeds between different tissues

Structures are displaced laterally from the correct locations and can be doubled

67
Q

What is side lobe?
What is grating lobe?
What do side lobe/grating lobe artifacts look like?
How is this artifact reduced?

A

Side lobe- beams that propagate from a single element outside the primary beam
Grating lobe - similar to side lobes but for multi-element transducers
Look like - a duplicate of the true reflector appears on the image as its correct depth, but is positioned laterally from the true anatomy
Reduce - apodization, subdicing (gating lobes), THI

68
Q

What creates propagation speed error?

What does it look like?

A

When the speed through the tissue isnt 1.54 mm/us

The structure can have the incorrect shape and/or be positioned too close or too far

69
Q

What causes range ambiguity
What does it look like
What corrects this artifact

A

When echoes are received from the previous pulse
Structures shown too close to the surface
Decrease PRF

70
Q

What reduces enhancement and shadowing artifacts

A

Spatial compounding

71
Q

What is nyquist limit (not formula)

A

Upper limit of the detectable doppler shift

Physics REVIEW (14 decks)

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