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Physics 2 > Module 6 : Artifacts > Flashcards

Module 6 : Artifacts Flashcards

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1
Q

artifacts

A
  • anything that does not correctly display the structures or functions that are imaged
  • need to know what they look like and how to compensate for them if we can
  • some are useful some are bad
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2
Q

factors creating artifacts

A
  • malfunctioning equipment
  • defective recording device
  • improper operation of equipment
  • acoustic properties of tissues and propagation of sound waves
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3
Q

why artifacts occur

A
  • many artifacts occur because of assumptions made about how sound propagates in tissue
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4
Q

assumptions that create artifacts

A
  • all tissue have same velocity (not true)
  • the sound beam always travels in a straight line
  • echo strength indicates organ echogenicity only
  • distance to each reflector equals the round trip
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5
Q

categories of artifacts

A
  • not real (not repressing actual interfaces)
  • missing
  • improperly located
  • improper brightness shape or size
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6
Q

2 main groups of artifacts

A
  • the propagation group

- the attenuation group

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7
Q

propagation artifacts

A
  • axial resolution
  • lateral resolution
  • section thickness
  • acoustic speckle
  • reverberation
    + comet tail
    + ring down
  • mirror image
  • multipath
  • refraction
  • grating and side lobes
  • speed error
  • range ambiguity
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8
Q

axial resolution

A
  • objects less than 1/2 the SPL apart in the axis of the beam are demonstrated as single echo
  • fix = increase frequency
  • limit = penetration
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9
Q

lateral resolution

A
  • beam width artifact that is also called POINT SPREADING or IMAGE BROADNING
  • reflectors appeared smeared across the screen in areas where beam is wide can be accentuated with increased gain or TGC
  • to correct for this artifact Lowe overall gain and TGC and scan in near zone with proper focus
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10
Q

slice thickness

A
  • VOLUME AVERAGING
  • can account for filling in Ian anechoic structure with false debris
  • happens beacaseu assumption that all echoes come back from centre of beam echoes come from front behind structure compressed 2D
  • repositioning probe so narrowest portion of Z axis at desired location
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11
Q

acoustic speckle

A
  • result of several off axis reflections from the scatter reflection in parenchyma
  • constructive and destructive interference occurs creates heterogeneous brightness in image
  • PERSISTANCE is the control that averages out frames to help homogenize tissue brightness
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12
Q

reverberation

A
  • reflection of sound between transducer and a strong interference often seen near the probe surface in fluid filled structures
  • will appear as multiple equally spaced linear lines that get weaker with depth and look like the rungs of ladder
  • changing your window and using HARMONICS is best way to help eliminate artifact
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13
Q

comet tail reverb

A
  • specifically a short range reverb between 2 closely spaced specular reflectors
  • metal clips
  • metal pellets
  • biopsy needle
  • iucd
  • calcium cholesterol
  • useful artifact to diagnose
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14
Q

ring down reverb

A
  • similar to comet tail without discrete echoes and instead appears as continuous stream of echoes
  • resonance phenomenon associated with gas bubbles in which gas vibrates and becomes new source of sound
  • can be useful in diagnosis
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15
Q

mirror image artifact

A
  • results in duplication of object due to odd angled strong reflector
  • diaphragm causes mirror image
  • may not always be able to correct to awareness is key
  • assumes all sound travels in straight line
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16
Q

multipath artifact

A
  • result of assumptions that beam travels in straight line
  • reality beam may take several off axis vectors before returning probe resulting in incorrect location of echoes
  • solution to correct for this is get more perpendicular
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17
Q

refractive artifacts

A
  • refers to redirection of beam when an interface is struck at an angle and both media have different velocities
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18
Q

types of refractive artifacts

A
  • edge shadowing
  • refractive duplication
  • refractive malposition
  • refractive enhancement
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19
Q

edge shadowing

A
  • shadows seen at edges of strong curved reflectors because the beam changes direction with non perpendicular incidence
  • to correct try changing window to come at interact from different angle
  • helpful and hurtful
20
Q

refractive duplication

A
  • create the appearance lateral duplication of echo interface on either side of true location
  • occurs because of refraction of beam by strong interface as beam is swept the lines of sight are angled
  • rectus abdominus can act like an acoustic lens and create this
  • must get perpendicular to structure of interest and move away from cause
  • hurtful
21
Q

side lobes

A
  • linear echogenic bands or sheets in anechoic structures
  • result of radial mode vibration in in single disc probe
  • echoes that return from weal side beams are placed along axis of the main beam
  • insulator rings are used to suppress the radial mode vibrations along with TGC and gain
  • HURTFUL
22
Q

grating lobes

A
  • length and width vibration of the array elements and crosstalk
  • looks just like side lobe artifact
  • corrected with apodization and sub dicing and using harmonics
23
Q

propagation speed error

A
  • result of machine assumption of propagation speed (everything at 1540)
  • results in misallocation of reflectors proximal or distal to actual location
  • usually in FAT
  • no way to correct it
24
Q

propagation speed error - faster medium

A
  • if sound travels faster in a medium than 1540 then the structure will be placed closer to the probe
25
Q

propagation speed error - slower medium

A
  • if sound travels slower in medium than 1540 then structures posterior are pushed farther
26
Q

range ambiguity

A
  • rare 2D scanning but can make echoes appear closer to transducer than actually are
  • most common in DOPPLER
  • occurs when pulse is emitted before all echoes return
  • PRF TOO HIGH EXCEEDING LIMIT SET BY DEPTH
  • CORRECT = REDUCE RAME RATE OR PRF
27
Q

attenuation artifacts

A
  • shadowing
  • enhancement
  • focal enhancement
  • edge shadowing
28
Q

shadowing

A
  • lack of echoes beneath highly attenuating structure because of ABSORPTION reflection or scattering
  • use different window to correct
  • HELPFUL AND HURTFUL
29
Q

shadowing helpful

A
  • helpful in diagnosing (stones)
  • increase amount of shadowing by using
    + higher frequency
    + focus at source of shadow
    + reduce overall gain
30
Q

enhancement

A
  • posterior brightness to structures that attenuate less (cyst or solid)
  • extremely rare that solid structure enhances
  • also HELFUL for diagnosis
31
Q

focal enhancement

A
  • false brightening to a particular area of the image at the focal zone
  • known as FOCAL BANDING
  • happens because the intensity of sound is hight as this point
  • HURTFUL
  • TGC to compensate
32
Q

doppler artifacts

A
  • aliasing
  • slice thickness
  • reverberation
  • mirror imaging
  • flash or clutter
  • noise
  • refraction
33
Q

aliasing

A
  • in color and spectral
  • occurs because we are not sampling fast enough
  • can be HELPFUL or HURTFUL
34
Q

helpful aliasing

A
  • can let us know something is wrong if very high velocity or turbulence
35
Q

correcting for aliasing

A 
\+ baseline
\+ increase PRF or scale
- CW
- increase angle
- decrease operating frequency
36
Q

doppler slice thickness

A
  • beam is 3D so is sampling volume
  • multiple flow profiles seen within one flow envelope because of beam width phenomenon
  • to correct less gain or move sample volume
37
Q

doppler reverberation

A
  • similar appearance to 2D reverb seen as buzzing or equidistant color lines
  • reverberation between front and back wall of stone produce mosaic color deep to flow
  • HELPFUL
38
Q

twinkle artifact reverb

A
  • very helpful type of reverb
  • aid in diagnosing calculus or CALCIUM
  • looks like comet tail or wizard beard
39
Q

doppler mirror image

A
  • can effect both color and spectral
  • spectral mirror causes the exact same flow to be seen on other side of baseline
  • in color mirror a false vessel will appear deep to real one can sample and get trace
  • caused by OVER GAINING or ANGLE OF INCIDENCE CLOSE TO 90
40
Q

doppler flash or clutter

A
  • low level echoes in the color flow seen in the tissue as result of tissue movement like heart wall valve or vessel wall motion
  • filters are present in machine to eliminate (wall filter)
  • if filter set to high can lose real info
41
Q

doppler noise

A
  • doppler gain set too high causing color to blossom outside of the vessel or appear in anechoic structure with no flow
  • in spectral can increase peak systolic velocities which can impact diagnosis (halo effect0)
42
Q

artifacts due to equipment

A
  • electronic interference
  • faulty software
  • faulty scan converter
  • faulty equipment
43
Q

electronic interference

A
  • may see echo patter either low/high intensity that can be irregular/regular (geometric/random)
  • usually radio signals generated by other equipment
44
Q

60 Hz bandwidth artifact

A
  • low level echoes on spectral trace seen because of cell phone interference
45
Q

reasons for faulty equipment

A
  • malfunctioning crystal elements
  • cracked dampening material
  • defective recording device
  • improper transducer sheilding

Physics 2 (8 decks)

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