Dmi 50 b_intensifying_screens

Intensifying ScreensIntensifying Screens

Kyle ThorntonKyle Thornton DMI 50BDMI 50B

History Of Intensifying History Of Intensifying ScreensScreens

First developed by Thomas EdisonFirst developed by Thomas Edison Calcium tungstate was used as the Calcium tungstate was used as the

phosphorphosphor Converted x-rays to ultraviolet-blue Converted x-rays to ultraviolet-blue

lightlight First screens were flawed in designFirst screens were flawed in design Screen design was perfected in the Screen design was perfected in the

1920’s1920’s

What Is An Intensifying What Is An Intensifying Screen?Screen?

Part of the radiographic cassettePart of the radiographic cassette Screens contain phosphors that emit Screens contain phosphors that emit

visible light when struck with x-ray visible light when struck with x-ray photonsphotons

Depending on the phosphor used, the Depending on the phosphor used, the screen will emit light in the blue or screen will emit light in the blue or green spectrumgreen spectrum

Usage of screens result in lowered Usage of screens result in lowered patient dosespatient doses

Screen ConstructionScreen Construction

Protective coatingProtective coating• Layer closest to filmLayer closest to film• about 10 - 20 micrometers thickabout 10 - 20 micrometers thick

Phosphor layerPhosphor layer• Active layerActive layer• emits lightemits light

Reflective layerReflective layer• 25 micrometers thick25 micrometers thick• Intercepts light and redirects it to filmIntercepts light and redirects it to film

BaseBase• Provides supportProvides support• Farthest from filmFarthest from film

Screen ConstructionScreen Construction

Cassette ConstructionCassette Construction

LuminescenceLuminescence

The emission of visible lightThe emission of visible light Two types of visible lightTwo types of visible light

• FluorescenceFluorescence– Emitted only during stimulation of Emitted only during stimulation of

phosphorsphosphors

• PhosphorescencePhosphorescence– Continues to emit light after stimulationContinues to emit light after stimulation– Afterglow or screen lagAfterglow or screen lag– A flaw with early screensA flaw with early screens

Intensifying Screen Intensifying Screen CharacteristicsCharacteristics

X-ray absorptionX-ray absorption Screen conversion efficiencyScreen conversion efficiency Image noiseImage noise Spatial resolutionSpatial resolution Image blurImage blur Screen speedScreen speed

Intensification FactorIntensification Factor

Compares patient dosage with Compares patient dosage with screens to without screensscreens to without screens

A reduction in dose is expectedA reduction in dose is expected Technical factors must be modified Technical factors must be modified

to accommodate changes in to accommodate changes in screen speedscreen speed

Screen speedScreen speed

Also depends on speed of film usedAlso depends on speed of film used Assigned speeds - 100, 200, 400, 800, Assigned speeds - 100, 200, 400, 800,

and 1000and 1000 Screen speed depends on:Screen speed depends on:

• Number of x-rays interacting with Number of x-rays interacting with phosphor layerphosphor layer

• Conversion of x-ray energy to visible lightConversion of x-ray energy to visible light• This is interrelated with phosphor This is interrelated with phosphor

distribution and sizedistribution and size

Manufacturer’s Design Of Manufacturer’s Design Of Intensifying ScreensIntensifying Screens

Phosphor compositionPhosphor composition• Rare earth elements are Rare earth elements are

most efficientmost efficient Phosphor thicknessPhosphor thickness

• The number of x-rays The number of x-rays converted to light converted to light increases with phosphor increases with phosphor thicknessthickness

Reflective layerReflective layer• Increases conversion Increases conversion

efficiency but adds to efficiency but adds to image blurimage blur

DyeDye• Controls spread of lightControls spread of light• Improves spatial Improves spatial

resolutionresolution Crystal sizeCrystal size

• Larger phosphors Larger phosphors produce more lightproduce more light

Concentration of Concentration of phosphor crystalsphosphor crystals• Higher crystal Higher crystal

concentration results in concentration results in higher conversion higher conversion efficiencyefficiency

X-Ray AbsorptionX-Ray Absorption

The percent absorption of x-rays in The percent absorption of x-rays in the phosphor layer of intensifying the phosphor layer of intensifying screensscreens

Conversion EfficiencyConversion Efficiency

The efficiency of converting x-ray The efficiency of converting x-ray to visible lightto visible light

Increase in conversion efficiency Increase in conversion efficiency will make a screen brighter and will make a screen brighter and affects image receptor speedaffects image receptor speed

Conversion EfficiencyConversion Efficiency

Image NoiseImage Noise

Deterioration of the imageDeterioration of the image Affected byAffected by

• mAs - or number of x-rays usedmAs - or number of x-rays used• limited absorption efficiencylimited absorption efficiency• randomness of conversionrandomness of conversion

Quantum mottleQuantum mottle• Noisy appearance of an imageNoisy appearance of an image• More apparent in fluoroscopyMore apparent in fluoroscopy• Raising mAs tends to overcome Q.M.Raising mAs tends to overcome Q.M.

Spatial Resolution/Image Spatial Resolution/Image BlurBlur

Measured in line pairs/mmMeasured in line pairs/mm Direct exposure film has highest Direct exposure film has highest

lp/mmlp/mm The slower the speed, the more The slower the speed, the more

lp/mmlp/mm

Resolution Test ToolResolution Test Tool

CompatibilityCompatibility

Film must match the screenFilm must match the screen Each screen exposes the emulsion Each screen exposes the emulsion

that it is nearestthat it is nearest

Advantages Of Screen Advantages Of Screen FilmFilm

IncreasedIncreased• Adjustment of radiographic contrastAdjustment of radiographic contrast• Spatial resolution w/small focal spotsSpatial resolution w/small focal spots• Ability for magnification radiographyAbility for magnification radiography• Flexibility of kVp selectionFlexibility of kVp selection• X-ray tube lifeX-ray tube life

DecreasedDecreased• Patient dosePatient dose• Occupational exposureOccupational exposure• Heat productionHeat production• Exposure timeExposure time• Tube mATube mA

• Focal spot sizeFocal spot size

Elements UsedElements Used

Rare earthRare earth• Gadolinium - GreenGadolinium - Green• Lanthanum - BlueLanthanum - Blue• Yttrium - BlueYttrium - Blue

– Very high conversion efficiencyVery high conversion efficiency– 15 - 20%15 - 20%

Recent DevelopmentsRecent Developments

Asymmetric cassettesAsymmetric cassettes Advantages in:Advantages in:

• Chest Chest • PediatricPediatric• Portable radiographyPortable radiography

Care Of Intensifying Care Of Intensifying ScreensScreens

Handle with careHandle with care Must be cleaned periodicallyMust be cleaned periodically

• Special cleaning fluid must be usedSpecial cleaning fluid must be used Must be tested for screen-film Must be tested for screen-film

contactcontact• Wire mesh testWire mesh test

Wire-Mesh Test ResultsWire-Mesh Test Results