Download - Radiographic Artifacts - Canvas

Radiographic Artifacts

NOT ESPECIALLY OLD OR VALUABLE

• Chris Ober, DVM, PhD, DACVR

• 14 February 2011

Artifacts Defined

• Any opacity on the radiograph that does not correspond to an actual anatomic structure

• 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


• Excited phosphors give off light photons

Quick CR primer



• Light photons travel through light guide

Quick CR primer



• 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

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 activates crystals

• White: emulsion has been removed (scratch)

• Can feel texture in emulsion

Fingerprints (SF)

• Focal

• White: most common– Oil on fingertips blocks

developer

OR– Fixer on fingertips

Fingerprints (SF)

• Focal

• White: most common– Oil on fingertips blocks

developer

OR– Fixer on fingertips

Fingerprints (SF)

• Black: less common– Developer on

fingertips

• 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


• Prevent:– Moderate humidity

– Avoid friction while handling film

– Antistatic cassette cleaners



Material in Cassette /Dirty Screen (SF)

• White & focal

• Sharp margins (close to film – no penumbra)

• Cause: Visible light photons from screen can’t reach and expose film emulsion

Material in Cassette /Dirty Screen (SF)

• THUS “radiolucent”material can still cause this artifact

• Common causes– Hair

– Dust

Fog (SF)

• Increased blackness, usually regional or global

• 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)


Light Leak (SF)

• Black, focal to global

• A form of fog

• Sources:– Storage bin (along 1

edge)

– 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

Jiménez DA, et al.Vet Radiol Ultrasound 2008.

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 be

masked by atypical superimposition on normal anatomy

• Unusual projection of normal anatomy may be incorrectly diagnosed as abnormal

Upside-down Cassette (SF)

• White & focal• Springs & latches on

back of cassette block x-ray beam

• Global lightness• Lead backing absorbs

some x-ray photons (film appears underexposed)

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 requires appropriate geometry relative to x-ray beam

• Wrong geometry lead strips attenuate more x-rays

Laterally DecenteredFocused Grid

Result: Too white acrossentire image

Off-Level Focused Grid

Result: Too white acrossentire image

Upside-Down Focused Grid

Result: OK in the center,Severely too white at periphery

Distance DecenteredFocused 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 towardother 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

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: Can’t happen– Image is transferred to

computer immediately

Double Exposure (SF, CR) Overexposure (SF)

• Black & global

• Patient info label normal

• Cause: Too much activation of emulsion crystals– High mAs or kVp

– Line surge

– Double exposure, Fog

Saturation (CR, DR)

• Black, may only be apparent in parts of image

• Just like SF overexposure

• High exposure maxes out sensitivity range of detector– Anatomy (esp. thinner

parts) may be “burned through”

Saturation (CR, DR)

• Black, may only be apparent in parts of image

• Just like SF overexposure

• High exposure maxes out sensitivity range of detector– Anatomy (esp. thinner

parts) may be “burned through”

Paradoxical Overexposure, Saturation, & Planking (DR)

Paradoxical Overexposure, Saturation, & Planking (DR)

Underexposure (SF)

• White & global

• Patient info label normal

• Cause: Too little activation 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

Underexposure:Quantum Mottle (CR, DR)

Material ObstructingX-Ray Beam (SF, CR, DR)

• White, focal

• Cause: Any radiopaque structure in the path of the x-ray beam– On patient

– In patient

– On table

– On cassette


OMG!It’s a fracture fragment!


…or gravel on the table.




Material Obstructing X-Ray Beam

Post-Exposure Handling Artifacts

Screen-Film

• Pressure

• Abrasions

• Fingerprints

• Static electricity

• Fog

• Light leak

CR & DR

• Not Applicable

Processing / Reading Artifacts

Screen-Film

• Overdevelopment

• Underdevelopment

• Insufficient mixing

• Incomplete fixation

• Incomplete washing

• Pi lines (LAB)

• Guide shoe lines (LAB)

• Kissing defects

CR & DR

• Dirty light guide (CR)

• Cassette debris (CR)

Overdevelopment (SF)

• Black & global

• Patient info label also black

• Cause: Too much metallic Ag forms in emulsion crystals– Developer too hot

– Developed too long

Underdevelopment (SF)

• White & global

• Patient info label also white

• Cause: Too little metallic Ag forms in emulsion crystals– Developer too cold

– Developed too little time

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 from plate reaches light guide

– Dirt blocks path for an entire line of data

– No light along that line = assumption that there 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 don’t reach photomultiplier tube

• (Contrast with FS, where light photons from screen don’t 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 in data transfer to workstation– Memory problems

– Communication errors (e.g. loose cables)

– Power fluctuation

Faulty Transfer (DR)

Uberschwinger (CR, DR)

• Black & focal

• Black lines occur around 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.