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Doppler physics 2 > Chapter 21 Artifacts > Flashcards

Chapter 21 Artifacts Flashcards

1
Q

What is an error in imaging or something that doesn’t belong called?

A

Artifact

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2
Q

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

A

Hyperechoic

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3
Q

Portions of an image that are not as bright as surrounding tissues, or tissues that appear less bright than normal?

A

Hypoechoic

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4
Q

An extreme form of hypoechoic, meaning entirely without echoes (echo free)

A

Anechoic

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5
Q

Describes structures with equal echo brightness

A

Isoechoic

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6
Q

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

A

Homogeneous

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7
Q

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

A

Heterogeneous

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8
Q

Multiple, equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasound beam

A

Reverberation

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9
Q

Artifact that . .

  • appears in multiples
  • appears equally spaced
  • located parallel to the sound beam’s main axis
  • located at ever increasing depths
A

Reverberation

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10
Q

With reverberations, which of the echoes are real if any?

A

First two

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11
Q

This appears as a solid, hyperechoic line directed downward, created when closely spaced reverberations merge (aka, Ring down artifact)

A

Comet tail

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12
Q

artifact that . . .

  • appears as a single long hyperechoic echo
  • located parallel to the sound beam’s main axis
A

Comet tail

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13
Q

This appears as a hypoechoic or anechoic region extending downward from a very strong attenuating medium

A

Shadow

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14
Q

Artifact that . .

  • results from too much attenuation
  • hypo or anechoic
  • located beneath the structure with abnormally high attenuation
  • prevents visualization of true anatomy on the scan
A

shadow

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15
Q

Is shadowing related to the speed of sound in a medium?

A

No

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16
Q

This appears as a hypoechoic region extending along the edge of a curved reflector. The sound beam refracts at the edge resulting in an intensity drop

A

Edge Shadow (Shadowing by refraction)

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17
Q

Artifact that . . .

  • results when the beam spreads after striking a curved reflector
  • hypo or anechoic
  • extends downward from the curved reflector’s edge parallel to the beam
  • prevents visualization of true anatomy
A

Edge shadow (shadowing by refraction)

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18
Q

This appears as a hyperechoic region beneath tissues with abnormally low attenuation

A

Enhancement

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19
Q

In enhancement related to the speed of sound in the medium?

A

NO

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20
Q

Name the artifact:

  • Hyperechoic
  • results from too little attenuation
  • located beneath the structure with abnormally low attenuation
A

Enhancement

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21
Q

This appears when side to side region of the image appears brighter than tissues at other depths

A

Focal enhancement (focal banding)

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22
Q

What is most often the cause of focal enhancement?

A

A TGC pod is set too high

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23
Q

Name the artifact:

  • a hyperechoic side to side region
  • results from increased intensity at the focus
A

Focal enhancement ( focal banding)

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24
Q

This appears when sound reflects off of a strong reflector and is redirected toward a second structure, causing a replica to incorrectly appear on the image

A

Mirror image

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25
Q

In the case of mirror images, which one is the artifact?

A

Deeper image is the artifact

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26
Q

Name the artifact:

  • a second copy of a true reflector
  • copy 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
A

Mirror image

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27
Q

This appears as a mirror image artifact on a spectral doppler display

A

Crosstalk

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28
Q

This appears when a sound wave propagates through a medium at a speed other than that of soft tissue (1.54Km/s): the correct number of reflectors are displayed, but at incorrect depths

A

Speed error (Range error artifact)

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29
Q
  • go return time is too short
  • System assumes reflectors are close to the transducer
  • reflectors are too shallow
  • distances are underestimated (too small)
A

Medium’s speed is Faster than that of soft tissue

30
Q
  • go return time is too long
  • system assumes reflectors are far from the transducer
  • reflectors are too deep
  • distances are overestimated (too large)
A

Medium’s speed is slower than that of soft tissue

31
Q

Name the artifact:

  • Correct number of reflectors
  • improper depth
  • appears as a step off
A

Speed error (range error artifact)

32
Q

This appears when sound energy is transmitted in a direction other than the sound beam’s main axis, degrading lateral resolution

A

Lobe artifacts

  • side lobes
  • grating lobes
33
Q

Side lobes

A

one crystal

34
Q

Grating lobes

35
Q

Name the artifact:

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

Lobe artifacts

  • side lobes (one crystal)
  • grating lobes (arrays)
36
Q

What are two methods for reducing lobe artifacts?

A

Subdicing

Apodization

37
Q

Dividing each crystal into small pieces

38
Q

Differential excitation: inner elements receive higher voltages while outer elements receive lower voltages

A

Apodization

39
Q

This appears when a sound pulse changes direction during transmission, degrading lateral resolution

A

Refraction

40
Q

Name the artifact:

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

Refraction

41
Q

This appears when reflections from structures above or below the assumed imaging plane appear in the image, or hollow structures appear filled in

A

Slice thickness artifact/ elevational resolution

42
Q

How can slice thickness artifact/ elevational resolution problems be reduced?

A

1 1/2 dimensional array transducers (matrix) which create thinner imaging planes

43
Q

This appears when a beam is wider than the distance between two reflectors that are located side by side. In this case, the two objects appear as one reflection

A

Lateral resolution

44
Q

This appears when a long pulse strikes two closely spaced structures, where one is in front of the other. Only one reflection will appear if the structures are closer together than 1/5 the SPL

A

Axial Resolution artifact

45
Q

What type of transducers reduce axial resolution artifacts?

A

Higher frequency

46
Q

This appear when sound pulses glance off a second structure on the way to of from the primary reflector, resulting in a transmit path length different from the receive path length and subtle, non-specific errors

A

Multipath artifacts

47
Q

This appears when a sound beam strikes a curved or oblique reflector, causing some of the reflected sound to be directed away from the transducer

A

Curved/ oblique reflectors

48
Q

Name the artifact:

  • Reflections are absent or
  • Reflections appear too weak or
  • Reflections appear different than other similar reflecting boundries
A

Curved /oblique reflectors

49
Q

This appears as a result of low frame rates and causes less accurate positioning of reflectors in motion

A

Temporal resolution artifacts

50
Q

This appears as a result of low line density causing less detail in the image

A

Spatial resolution artifact

51
Q

When the image is in analog format for display on a CRT how is spatial resolution determined?

A

Number of scan lines fer frame (more the better)

52
Q

When the image is in digital format, how is spatial resolution determined?

A

Pixel density (more the better)

53
Q

Closely packed sound pulses, image exhibits great detail, spatial resolution is exceptional

A

High line density

54
Q

Each pixel is large and the spatial resolution degrades

A

Low pixel density

55
Q

Wider gaps between the sound pulses, the image exhibits less detail, spatial resolution is poor

A

Low line density

56
Q

Each pixel is small resulting in a detailed image with excellent spatial resolution

A

High pixel density

57
Q

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

A

Range ambiguity artifact

58
Q

Range ambiguity is eliminated by increasing the ________

59
Q

Longer PRP means ________ imaging and decreased PRF

60
Q

Small amplitude echoes resulting from many sources including electrical interference, signal processing and spurious reflections. Most likely affects low-level hypoechoic regions

61
Q

A form of noise arising from small amplitude sound waves interfering with each other; Most likely to appear close to the transducer
- grainy appearance that is not directly related to the actual biologic tissue

62
Q

A form of noise associated with Doppler

63
Q

A high-tech solution for reducing an image’s noise content:

selectively distinguish meaningful reflections from noise, thereby improving signal to noise ratio

64
Q

What are the six assumptions of imaging systems

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 1540m/s
  4. Reflections arise only from 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 reflections
65
Q

Anatomic reflectors are absent on image

A
  • shadowing
  • shadowing by refraction
  • lateral resolution
  • Axial resolution
66
Q

Anatomic reflector appears multiple times on image. Artifact positioned deeper than the true anatomy

A
  • Comet tail
  • Ring down
  • Reverberation
  • Mirror image
67
Q

Anatomic reflector appears multiple times on image. Artifact displaced to the side of the true anatomy

A

Refraction
Side lobe
Grating lobe

68
Q

Anatomic reflectors appear with abnormal brightness

A

Enhancement (hyperechoic)
Banding (hyperechoic)
Shadowing (hypoechoic)
Shadowing by refraction (hypoechoic)

69
Q

Anatomic structures appear at incorrect depth

A

Speed errors

Range ambiguity

70
Q

Anatomic structures appear in the incorrect imaging plane

A

Slice or section thickness

71
Q

Anatomic structures do not correspond to echoes on the image

A

acoustic speckle

Multipath

Doppler physics 2 (5 decks)

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