Module 6 : Artifacts Flashcards
(45 cards)
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
2
Q
factors creating artifacts
A
- malfunctioning equipment
- defective recording device
- improper operation of equipment
- acoustic properties of tissues and propagation of sound waves
3
Q
why artifacts occur
A
- many artifacts occur because of assumptions made about how sound propagates in tissue
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
5
Q
categories of artifacts
A
- not real (not repressing actual interfaces)
- missing
- improperly located
- improper brightness shape or size
6
Q
2 main groups of artifacts
A
- the propagation group
- the attenuation group
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
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
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
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
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
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
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
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
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
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
17
Q
refractive artifacts
A
- refers to redirection of beam when an interface is struck at an angle and both media have different velocities
18
Q
types of refractive artifacts
A
- edge shadowing
- refractive duplication
- refractive malposition
- refractive enhancement
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
propagation speed error - slower medium
- if sound travels slower in medium than 1540 then structures posterior are pushed farther
26
range ambiguity
- 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
attenuation artifacts
- shadowing
- enhancement
- focal enhancement
- edge shadowing
28
shadowing
- lack of echoes beneath highly attenuating structure because of ABSORPTION reflection or scattering
- use different window to correct
- HELPFUL AND HURTFUL
29
shadowing helpful
- helpful in diagnosing (stones)
- increase amount of shadowing by using
+ higher frequency
+ focus at source of shadow
+ reduce overall gain
30
enhancement
- posterior brightness to structures that attenuate less (cyst or solid)
- extremely rare that solid structure enhances
- also HELFUL for diagnosis
31
focal enhancement
- 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
doppler artifacts
- aliasing
- slice thickness
- reverberation
- mirror imaging
- flash or clutter
- noise
- refraction
33
aliasing
- in color and spectral
- occurs because we are not sampling fast enough
- can be HELPFUL or HURTFUL
34
helpful aliasing
- can let us know something is wrong if very high velocity or turbulence
35
correcting for aliasing
```
+ baseline
+ increase PRF or scale
- CW
- increase angle
- decrease operating frequency
```
36
doppler slice thickness
- 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
doppler reverberation
- 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
twinkle artifact reverb
- very helpful type of reverb
- aid in diagnosing calculus or CALCIUM
- looks like comet tail or wizard beard
39
doppler mirror image
- 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
doppler flash or clutter
- 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
doppler noise
- 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
artifacts due to equipment
- electronic interference
- faulty software
- faulty scan converter
- faulty equipment
43
electronic interference
- may see echo patter either low/high intensity that can be irregular/regular (geometric/random)
- usually radio signals generated by other equipment
44
60 Hz bandwidth artifact
- low level echoes on spectral trace seen because of cell phone interference
45
reasons for faulty equipment
- malfunctioning crystal elements
- cracked dampening material
- defective recording device
- improper transducer sheilding
