04 - Artifacts 2011
Transcript of 04 - Artifacts 2011
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Radiographic Artifacts
NOT ESPECIALLY
OLD ORVALUABLE
Chris Ober, DVM,PhD, DACVR
14 February 2011
Artifacts Defined
Any opacity on the radiograph that does
not correspond to an actual anatomicstructure
Any misrepresentation of an actual
anatomic structure
Anything decreasing radiographic quality
Quick CR primer
Cassette exposed by x-
rays; storage phosphors
excited
Quick CR primer
Cassette exposed by x-
rays; storage phosphors
excited
Cassette put into reader
Quick CR primer
Laser shines onto
detectors
Quick CR primer
Laser shines onto
detectors
Excited phosphors give
off light photons
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Quick CR primer
Laser shines onto
detectors
Excited phosphors give
off light photons
Light photons travel
through light guide
Quick CR primer
Laser shines onto
detectors
Excited phosphors give
off light photons
Light photons travel
through light guide
Image produced by
computer
Quick DR primer
Panel exposed by x-
rays, detectors
excited
Data sent directly to
computer via cord
Image created
Sequence: Film-Screen
Film storage &
handling
Positioning
Exposure
Film handling
Film processing
Manual
Automatic
Image archiving
Sequence: CR (With Cassette)
Cassette storage
Positioning
Exposure Postexposure
Cassette reading
Workstation
Sequence: DR (No Cassette)
Panel storage
Positioning
Exposure Image reading &
transfer
Workstation
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Another Classification System
Color
Black White
Distribution
Focal
Regional or Global
Storage & Pre-Exposure Handling
Artifacts
Screen-Film
Pressure Abrasions & Scratches
Fingerprints
Static electricity
Material in cassette
Fog
Light leak
CR & DR
Storage scatter (CR)
Pressure Artifacts
Film Crease Crescents (SF)
Black & focal
Cause: rough
handling
Pressure from crease
causes activation of
crystals
NOT caused by
fingernail (usually)
Pressure Artifacts
Film Crease Crescents (SF)
Abrasions & Scratches (SF)
Black or white, focal
Cause: rough handling
Black: pressure from
abrasion activatescrystals
White: emulsion has
been removed (scratch)
Can feel texture in
emulsion
Fingerprints (SF)
Focal
White: most common
Oil on fingertips blocksdeveloper
OR
Fixer on fingertips
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Fingerprints (SF)
Focal
White: most common
Oil on fingertips blocks
developer
OR
Fixer on fingertips
Fingerprints (SF)
Black: less common
Developer onfingertips
Prevent:
Keep fingers dry and
clean
Touch only film edges
Hogge JP, et al.
RadioGraphics 1999.
Static Electricity (SF)
Black & focal
Two patterns
Branching
Smudge / Spot
Cause: electrical
discharge
Static Electricity (SF)
Prevent:
Moderate humidity
Avoid friction while
handling film
Antistatic cassette
cleaners
Static Electricity (SF)
Hogge JP, et al.
RadioGraphics 1999.
Material in Cassette /
Dirty Screen (SF) White & focal
Sharp margins (close
to film no
penumbra) Cause: Visible light
photons from screen
cant reach and
expose film emulsion
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Material in Cassette /
Dirty Screen (SF) THUS radiolucent
material can stillcause this artifact
Common causes
Hair
Dust
Fog (SF)
Increased blackness,
usually regional orglobal
Definition: any
unwanted film
exposure /
development
Decreased image
contrast and detail
Fog (SF)
Causes:
Light exposure
Heat
(store at < 68 F)
Humidity
(keep at 30-50%)
Radiation (including
scatter)
Chemicals
Old film
Fog (SF)
Hogge JP, et al.
RadioGraphics 1999.
Light Leak (SF)
Black, focal to global
A form of fog
Sources:
Storage bin (along 1edge)
Cassette not closed (1
edge or corner)
Overhead light
Safelight filter crack
Storage Scatter (CR)
Black & global
Like fog unwanted
exposure of CR plate
Causes: Background radiation
Scatter from imaging
procedure
Jimnez DA, et al.
Vet Radiol Ultrasound 2008.
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Positioning Artifacts
Screen-Film
Magnification Foreshortening /
distortion
Patient rotation
Upside-down cassette
Grid cutoff
CR & DR
Magnification Foreshortening /
distortion
Patient rotation
Upside-down cassette
(CR) or panel (DR)
Grid cutoff
Magnification
Object closer to film:
Closer to normal size Sharper margins
Object farther from
film:
Magnified
Less distinct margins
Foreshortening / Distortion
X-ray beam does not
pass perpendicular to
long axis of structure
Differential
magnification of
structure
Foreshortening / Distortion
Patient Rotation
A form of distortion
Lesions may bemasked by atypical
superimposition onnormal anatomy
Unusual projection ofnormal anatomy maybe incorrectlydiagnosed asabnormal
Upside-down Cassette (SF)
White & focal
Springs & latches onback of cassette block
x-ray beam
Global lightness
Lead backing absorbssome x-ray photons(film appearsunderexposed)
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Upside-down Cassette (SF) Upside-down Cassette (SF)
Upside-down Cassette (CR)
White & multifocal
Construction of
cassette back
absorbs x-rays
Pattern depends on
manufacturer
Upside-down Cassette (CR)
Upside-down Panel (DR)
White & multifocal
Electronics in the
back of the panel
absorb x-rays
Grid Cutoff (SF, CR, DR)
White, regional to
global
Orientation of lead
strips in grid requiresappropriate geometry
relative to x-ray beam
Wrong geometry
lead strips attenuate
more x-rays
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Laterally Decentered
Focused Grid
Result: Too white across
entire image
Off-Level Focused Grid
Result: Too white across
entire image
Upside-Down Focused Grid
Result: OK in the center,Severely too white at periphery
Distance Decentered
Focused Grid Similar to upside-
down grid
OK in the center,
Markedly too white at
periphery
Often not as severe
as upside-down grid
Combined Lateral and Distance
Decentering of Grid
Result: OK on one side,
Gradually whiter toward
other side
Exposure Artifacts
Screen-Film
Motion
Double exposure
Overexposure
Underexposure
Material obstructing x-ray
beam
CR & DR
Motion
Double exposure (CR)
Overexposure(Saturation)
Underexposure
Material obstructing x-ray
beam
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Motion (SF, CR, DR)
Blurring of moving
parts Exposure does have
a finite interval
Reduce with:
Better restraint
Sedation
Decreased exposure
time
Motion (SF, CR, DR)
Double Exposure (SF, CR)
Appearance of 2
summated images
Cause: Cassette
inadvertently exposed
more than once
Press exposure trigger
twice
Forget to change
cassette after first view
Double Exposure (SF, CR)
SF: Black, global
2 exposures =
overexposure artifact
CR: Normal grayscale
Wide latitude can
usually accommodate
the overexposure
DR: Cant happen
Image is transferred to
computer immediately
Double Exposure (SF, CR) Overexposure (SF)
Black & global
Patient info label
normal
Cause: Too muchactivation of emulsion
crystals
High mAs or kVp
Line surge
Double exposure, Fog
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Saturation (CR, DR)
Black, may only beapparent in parts ofimage
Just like SFoverexposure
High exposure maxesout sensitivity rangeof detector
Anatomy (esp. thinnerparts) may be burnedthrough
Saturation (CR, DR)
Black, may only beapparent in parts ofimage
Just like SFoverexposure
High exposure maxesout sensitivity rangeof detector
Anatomy (esp. thinnerparts) may be burnedthrough
Paradoxical Overexposure,
Saturation, & Planking (DR)
Paradoxical Overexposure,
Saturation, & Planking (DR)
Underexposure (SF)
White & global
Patient info label
normal
Cause: Too littleactivation of emulsion
crystals
Low mAs or kVp
General x-ray
obstruction
X-ray tube troubles
Underexposure:
Quantum Mottle (CR, DR) Noisy & global
Computer algorithms
adjust image to
remain gray Low signal level
causes grainy
appearance and poor
contrast & sharpness
Cause: As with SF
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Underexposure:
Quantum Mottle (CR, DR)Material Obstructing
X-Ray Beam (SF, CR, DR)
White, focal
Cause: Anyradiopaque structure
in the path of the x-
ray beam
On patient
In patient
On table
On cassette
Material Obstructing
X-Ray Beam (SF, CR, DR)
OMG!
Its a fracture fragment!
Material Obstructing
X-Ray Beam (SF, CR, DR)
or gravel on the table.
Material Obstructing
X-Ray Beam (SF, CR, DR)
Material Obstructing
X-Ray Beam (SF, CR, DR)
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Insufficient Mixing (SF) Inadequate Fixation (SF)
Initially film is cloudy
and milky Over time appears
yellow/brown
Dichroic stain
Incomplete Washing / Rinsing (SF)
Fixer remains
Cloudy, sticky residue
Yellow-brown stain
Sulfur smell
Kissing Defects (SF)
Dirty Light Guide (CR)
White & focal
Sharp white line
Cause:
Light emitted fromplate reaches lightguide
Dirt blocks path for anentire line of data
No light along that line= assumption thatthere was no exposure
Dirty Light Guide (CR)
White & focal
Sharp white line
Cause:
Light emitted fromplate reaches lightguide
Dirt blocks path for anentire line of data
No light along that line= assumption thatthere was no exposure
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Dirty Light Guide (CR)
White & focal
Sharp white line Cause:
Light emitted fromplate reaches lightguide
Dirt blocks path for anentire line of data
No light along that line= assumption thatthere was no exposure
Cassette Debris (CR)
White & focal
Sharp margins Essentially the same
as FS dirty cassette
EXCEPT
Cassette Debris (CR)
Problem is that
photons emitted from
plate during reading
dont reach
photomultiplier tube
(Contrast with FS,
where light photons
from screen dont
reach film)
Workstation Artifacts
Screen-Film
Not Applicable
CR & DR
Faulty Transfer (DR)
Clipping
Planking
Uberschwinger
Faulty Transfer (CR, DR)
Appearance: Anything
goes, generally
distorted anatomy
Cause: Problems indata transfer to
workstation
Memory problems
Communication errors
(e.g. loose cables)
Power fluctuation
Faulty Transfer (DR)
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Uberschwinger (CR, DR)
Black & focal
Black lines occuraround dense
structures
Can be mistaken for
loosening or infection
of implants
Cause: Certain
processing algorithms
(edge-enhancement)
Uberschwinger (CR, DR)
What Have We Learned?
People can manage to screw up any stage
of the radiographic process.
Recognizing artifacts and when they occur
is the only way to make good radiographs.
Look up Mr. Yuk on Wikipedia for a video
that scarred my childhood.