Radiographic Film & Intensifying Screens Bushong Ch 11 & 13

Radiographic Film & Radiographic Film & Intensifying ScreensIntensifying Screens

Bushong Ch 11 & 13Bushong Ch 11 & 13

ObjectivesObjectives

Review FilmReview Film

Review Intensifying ScreensReview Intensifying Screens

Technique Changes for Screen SpeedsTechnique Changes for Screen Speeds

What is the function of radiographic film?What is the function of radiographic film?

What is exit radiation? What is another What is exit radiation? What is another name for exit radiation? name for exit radiation?

What is an IR? Name some examplesWhat is an IR? Name some examples

X-Ray FilmX-Ray Film

Film is a media that makes a Film is a media that makes a permanent record of the permanent record of the image.image.

Image recorded on film is Image recorded on film is caused by exposure to caused by exposure to photonsphotons

X-ray Film cont’dX-ray Film cont’d

Radiographic film is/was most Radiographic film is/was most common common image receptorimage receptor

Two parts:Two parts:

1. Base1. Base

2. Emulsion2. Emulsion

• FIRST “FILM”• GLASS PLATES• WW 1 • CELLULOSE NITRATE• HIGHLY FLAMMABLE• EASILY TORN• RESPONSIBLE FOR

MANY FIRES IN HOSPITAL BASEMENTS

• CELLULOSE TRIACETATE

Early Film baseCellulose Triacetate

• Highly Flammable• Emulsion would crack

& peel away from base when chemicals were too hot

• RETICULATION

Film Construction - BASEFilm Construction - BASE

Made of a polyester plasticMade of a polyester plastic Must be clear, strong, consistent Must be clear, strong, consistent

thicknessthickness Tinted pale blue or blue-gray (reduces Tinted pale blue or blue-gray (reduces

eye strain)eye strain) COATED ON 1 OR 2 SIDES WITH COATED ON 1 OR 2 SIDES WITH

EMULSIONEMULSION

Film Construction - EMULSIONFilm Construction - EMULSION

Film emulsion can be on one side or Film emulsion can be on one side or both sides of base (single emulsion / both sides of base (single emulsion / double emulsion)double emulsion)

Protective overcoat layered on top of Protective overcoat layered on top of emulsionemulsion

Emulsion is a gelatin containing the film Emulsion is a gelatin containing the film crystalscrystals

Emulsion is the “active” layer of filmEmulsion is the “active” layer of film

FILM COMPOSTIONFILM COMPOSTION

SINGLE OR DOUBLE EMULSIONSINGLE OR DOUBLE EMULSIONCOATED ON A BASECOATED ON A BASE

EMULSION : GELATIN EMULSION : GELATIN WITH SILVER HALIDE CRYSTALSWITH SILVER HALIDE CRYSTALS

BASE: SUPPORT (POLYESTER)BASE: SUPPORT (POLYESTER)

Film EmulsionFilm Emulsion

Made of mixture of gelatin Made of mixture of gelatin & silver halide crystals & silver halide crystals (fluorine, chlorine, (fluorine, chlorine, bromine, & iodine)bromine, & iodine)

Most x-ray film emulsions Most x-ray film emulsions made of :made of :

silver bromide silver bromide (98%) (98%) silver iodide (2%)silver iodide (2%)

Photographically active Photographically active layer – activated by light layer – activated by light & radiation to create & radiation to create imageimage

Silver halide crystalsSilver halide crystals

Crystals are cubic Crystals are cubic

in structurein structure

Crystal lattice Crystal lattice

containing ionscontaining ions

Film constructionFilm construction

Film is manufactured to have specific Film is manufactured to have specific characteristics of speed, contrast & characteristics of speed, contrast & resolutionresolution

Film is also manufactured to be sensitive Film is also manufactured to be sensitive to specific colors of light = spectral to specific colors of light = spectral matchingmatching

Direct-exposure film = thicker emulsion Direct-exposure film = thicker emulsion with more silver halide crystalswith more silver halide crystals

X-Ray Film Cross Section

FILM CONSTRUCTIONFILM CONSTRUCTION

BASE WITH EMULSIONBASE WITH EMULSION CAN BE ON 1 (SINGLE EMULSION)CAN BE ON 1 (SINGLE EMULSION) OR 2 SIDES (DOUBLE EMULSION)OR 2 SIDES (DOUBLE EMULSION)

MUST BE MATCHED WITH 1 OR 2 MUST BE MATCHED WITH 1 OR 2 SIDED INTENSIFYING SCREENSSIDED INTENSIFYING SCREENS

Image formationImage formation

X-ray photons converted to light X-ray photons converted to light photonsphotons

Image before processing = Image before processing = latent imagelatent image

Made visible by chemical processingMade visible by chemical processing

After proper chemical processing = After proper chemical processing = manifest manifest imageimage

IMAGE ON FILMIMAGE ON FILM

SINGLE EMULSION = BETTER DETAILSINGLE EMULSION = BETTER DETAIL

DOUBLE EMULISON = LESS DETAILDOUBLE EMULISON = LESS DETAIL

PARALLAX PARALLAX

With double emulsion – an image is With double emulsion – an image is created on both emulsions – then created on both emulsions – then superimposed – slight blurring of edgessuperimposed – slight blurring of edges

PARALLAX –PARALLAX –each emulsion has an imageeach emulsion has an image

single image overlaped – edges single image overlaped – edges less sharp less sharp

Radiation interacts releasing e-Radiation interacts releasing e-

Silver atoms buildup Silver atoms buildup at the sensitivity at the sensitivity center, building the center, building the latent image centerlatent image center

The group of silver The group of silver atoms is called the atoms is called the latent image centerlatent image center

LIGHT VS DARK AREAS ON FILMLIGHT VS DARK AREAS ON FILM

DARK SPOTS – SILVER HALIDE DARK SPOTS – SILVER HALIDE CRYSTALS THAT HAVE BEEN CRYSTALS THAT HAVE BEEN EXPOSED TO PHOTONS – TURN TO EXPOSED TO PHOTONS – TURN TO BLACK METALLIC SILVER AFTER BLACK METALLIC SILVER AFTER PROCESSINGPROCESSING

LIGHT AREAS – NO CRYSTALS LIGHT AREAS – NO CRYSTALS EXPOSED – SILVER HALIDE IS EXPOSED – SILVER HALIDE IS WASHED AWAY WITH PROCESSINGWASHED AWAY WITH PROCESSING

Processing Processing

The term applied to the chemical reactions The term applied to the chemical reactions that transform the latent image into a that transform the latent image into a manifest imagemanifest image

FILM FILM direct exposure & screen-film or film-screendirect exposure & screen-film or film-screen

SIZESSIZES

14 X 1714 X 17 14 X 1414 X 14 11 X 1411 X 14 10 X 1210 X 12 8 X 108 X 10

Film SizesFilm Sizes

Standard “inches”:Standard “inches”: 8” x 10”8” x 10” 10” x 12”10” x 12” 11” x 14”11” x 14” 14” x 17”14” x 17”

Metric:Metric: 18cm x 24cm18cm x 24cm 24cm x 30cm24cm x 30cm 30cm x 35cm30cm x 35cm 35cm x 43cm35cm x 43cm

Screen-FilmScreen-Film

Most widely used IR ?? Most widely used IR ??

Many Types of Film Used in Medical Many Types of Film Used in Medical Imaging Table 11-1Imaging Table 11-1

Screen-Film has several characteristics to Screen-Film has several characteristics to consider: contrast, speed, spectral consider: contrast, speed, spectral matching, anticrossover dyes, and safe matching, anticrossover dyes, and safe light requirementslight requirements

ContrastContrast

Manufactured in multiple levels Manufactured in multiple levels High-contrast (black-and-white image)High-contrast (black-and-white image) Low-contrast (more gray)Low-contrast (more gray)

Exposure LATITUDE = the range of Exposure LATITUDE = the range of exposure techniques that produce an exposure techniques that produce an acceptable image (medium, high or acceptable image (medium, high or higher)higher)

So what is the difference?So what is the difference?

Depends on the size and distribution of the Depends on the size and distribution of the silver halide crystalssilver halide crystals

High-contrast = smaller crystals, uniform High-contrast = smaller crystals, uniform grain sizegrain size

Low-contrast = larger crystals, wider range Low-contrast = larger crystals, wider range of sizes of sizes

Film SpeedFilm Speed

Single vs Double emulsionSingle vs Double emulsion

Size of CrystalsSize of Crystals

Thickness of emulsionThickness of emulsion

Intensifying screen usedIntensifying screen used

Screen Speed

• Efficiency of a screen in converting x-rays to light is Screen Speed.

Film SpeedFilm Speed

Greater efficiency = less exposure = fasterGreater efficiency = less exposure = faster

-Standard screen speed class of 100-Standard screen speed class of 100

-200 screen speed is twice as fast-200 screen speed is twice as fast Speeds for routine work: 200 – 800Speeds for routine work: 200 – 800 Speeds for high detail: 50 - 100Speeds for high detail: 50 - 100

Film CharacteristicsFilm Characteristics Size of silver halide crystals & Size of silver halide crystals &

emulsion thickness determine speed emulsion thickness determine speed of film and degree of resolutionof film and degree of resolution

Speed – the response to photonsSpeed – the response to photons Resolution – the detail seenResolution – the detail seen

Screen speed vs Spatial resolutionScreen speed vs Spatial resolution

Film Speed / Crystal sizeFilm Speed / Crystal size

Larger crystals or Thicker crystal Larger crystals or Thicker crystal layerlayer

Faster response= less detail, andFaster response= less detail, and

less exposure (chest x-ray)less exposure (chest x-ray) Finer crystals / thinner crystal layerFiner crystals / thinner crystal layer

=Slower response, greater detail, =Slower response, greater detail, more exposure (extremity)more exposure (extremity)

FILM SPEEDSFILM SPEEDS

FASTER SPEED – REDUCES PATIENT FASTER SPEED – REDUCES PATIENT EXPOSUREEXPOSURE

FASTER SPEED - REDUCES IMAGE FASTER SPEED - REDUCES IMAGE DETAIL DETAIL

IMAGE ON FILMIMAGE ON FILM

Crossover is when the exposure of the Crossover is when the exposure of the emulsion by light is from the opposite side emulsion by light is from the opposite side of the intensifying screen of the intensifying screen

Causes increased blur on the imageCauses increased blur on the image

CROSSOVERCROSSOVER

Reducing crossover Reducing crossover by adding a dye to the by adding a dye to the basebase

Reducing CrossoverReducing Crossover

Changing the shape of the crystal Changing the shape of the crystal improved light absorption and reduced improved light absorption and reduced crossovercrossover

Loss of DetailLoss of Detail

Spectral Sensitivity ORSPECTRAL MATCHING

Film is designed to be sensitive to the color of light emitted by the intensifying screens

• Blue – UV light sensitive film – CALCIUM TUNGSTATE screens

• Green, Yellow-Green light sensitive film -

RARE EARTH screens

Film is either blue-sensitive or Film is either blue-sensitive or green-sensitive green-sensitive

Rare earth-Rare earth-

green emittinggreen emitting

screens must screens must

use a red filteruse a red filter

Direct-Exposure FilmDirect-Exposure Film

Thicker emulsion and more crystalsThicker emulsion and more crystals Not sensitive to lightNot sensitive to light Not commonly used because of increased Not commonly used because of increased

patient dosepatient dose

Very detailed imagesVery detailed images

Laser FilmLaser Film

Uses the digital electronic signal Uses the digital electronic signal The intensity of the laser beam is varied in The intensity of the laser beam is varied in

direct proportion to the strength of the direct proportion to the strength of the image signal = image signal = LASER BEAM LASER BEAM MODULATIONMODULATION

The more intense the signal the darker the The more intense the signal the darker the imageimage

Laser printersLaser printers

Provide consistent image quality for Provide consistent image quality for multiple film sizes. Most lasers only print multiple film sizes. Most lasers only print on 14 X 17 regardless of initial IRon 14 X 17 regardless of initial IR

Printers can be linked to multiple users Printers can be linked to multiple users (CT, MRI, US & Computed Radiology)(CT, MRI, US & Computed Radiology)

Laser FilmLaser Film

Is silver halide film sensitive to the red light Is silver halide film sensitive to the red light emitted by the laseremitted by the laser

Laser film is light sensitiveLaser film is light sensitive

Laser film must be handled in the Laser film must be handled in the darkroom in total darkness… Why? darkroom in total darkness… Why?

Blue or Green filter would workBlue or Green filter would work

Duplicating filmDuplicating film

Single-emulsion film (active layer toward Single-emulsion film (active layer toward the initial radiograph)the initial radiograph)

Exposure to light reduces OD on Exposure to light reduces OD on duplicating film (short time = dark film)duplicating film (short time = dark film)

Light is exposed through the initial Light is exposed through the initial radiographradiograph

FILM BIN - STORAGEFILM BIN - STORAGE

Film StorageFilm Storage

Clean, dry location, light tight locationClean, dry location, light tight location 40 – 60 % Humidity 70 40 – 60 % Humidity 70 º º FahrenheitFahrenheit Away from chemical fumesAway from chemical fumes Safe from radiation exposureSafe from radiation exposure Standing on edgeStanding on edge Expiration date clearly visible. Film can be Expiration date clearly visible. Film can be

stored for about 45 days, use the first-in stored for about 45 days, use the first-in first-out rulefirst-out rule

Film Handling Film Handling

Do not bend or crease Do not bend or crease Hands must be cleanHands must be clean Film is sensitive to pressure and scratchesFilm is sensitive to pressure and scratches

What happens if any of these happen?What happens if any of these happen?

X-ray Film SensitivityX-ray Film Sensitivity

LightLightX-raysX-raysGamma RaysGamma RaysGasesGasesFumesFumes

HeatHeatMoistureMoisturePressurePressureStatic Static

ElectricityElectricityAgeAge

So what happens??

FILM FOG!!!!FILM FOG!!!!

Unintended Unintended uniform optical uniform optical density on a density on a radiograph radiograph because of x-rays, because of x-rays, light, or chemical light, or chemical contamination that contamination that reduces contrast & reduces contrast & affects densityaffects density

QUESTIONS ?

Intensifying ScreensIntensifying Screens

Bushong Ch 13Bushong Ch 13

CassettesCassettes

Cassettes serve 3 important functions:Cassettes serve 3 important functions:

1.1. Protect film from exposure to lightProtect film from exposure to light

2.2. Protect film from bending and scratching Protect film from bending and scratching during use.during use.

3.3. Contain intensifying screens, keeps film Contain intensifying screens, keeps film in close contact to screen during in close contact to screen during exposure.exposure.

CASSETTE or FILM HOLDERCASSETTE or FILM HOLDER

The CASSETTE is The CASSETTE is used to hold the film used to hold the film during examinations. during examinations. It consist of front and It consist of front and back intensifying back intensifying screens, and has a screens, and has a lead (Pb) backing. lead (Pb) backing. The cassette is light The cassette is light tighttight

Cassette Features - FrontCassette Features - Front

Exposure side of Exposure side of cassette is the “front”.cassette is the “front”.

Made of radiolucent Made of radiolucent material – easily material – easily penetrated by x-rays, penetrated by x-rays, lightweight metal alloy lightweight metal alloy or plastic material or plastic material made of resin.made of resin.

Intensifying screen Intensifying screen mounted to inside of mounted to inside of front.front.

Cassette FeaturesCassette Features Back Back

Back made of metal or plasticBack made of metal or plastic Inside back is a layer of lead foil – Inside back is a layer of lead foil –

prevents backscatter that could fog the prevents backscatter that could fog the filmfilm

Inside foil layer is a layer of padding – Inside foil layer is a layer of padding – maintains good film/screen contactmaintains good film/screen contact

Back intensifying screen mounted on Back intensifying screen mounted on paddingpadding

Has the ID blocker (patient identification)Has the ID blocker (patient identification)

Image creationImage creation

1% of xray photons that leave patient 1% of xray photons that leave patient Interact with phosphors of intensifying Interact with phosphors of intensifying

screens screens 100’s of light photons created to make 100’s of light photons created to make

image on filmimage on film Light photons expose silver halide crystals Light photons expose silver halide crystals

in the film emulsion in the film emulsion Turn black metallic silver after processionTurn black metallic silver after procession

Intensifying ScreensIntensifying Screens

Flat surface coated with Flat surface coated with fluorescent crystals fluorescent crystals called phosphorscalled phosphors

that glow, giving off that glow, giving off light when exposed to light when exposed to x-rays.x-rays.

Intensifying Screens PhosphorsIntensifying Screens Phosphors

RARE EARTH – (emits green light)RARE EARTH – (emits green light) Developed in 1980’sDeveloped in 1980’s Most efficient – most common in use todayMost efficient – most common in use today

CALCIUM TUNGSTATE (blue light)CALCIUM TUNGSTATE (blue light) Not as efficient Not as efficient

Rare Earth ScreensRare Earth Screens

GadoliniumGadoliniumLanthanumLanthanumYttriumYttriumFound in low Found in low

abundance in natureabundance in nature

Cardboard Cassettes Cardboard Cassettes

Direct x-ray exposure to film requiredDirect x-ray exposure to film required 25 to 400 times more radiation to create an 25 to 400 times more radiation to create an

image on the filmimage on the film

BETTER DETAIL THAN FILM SCREEN (NO BETTER DETAIL THAN FILM SCREEN (NO BLURRING OF IMAGE FROM LIGHT)BLURRING OF IMAGE FROM LIGHT)

ALL EXPOSURE MADE FROM X-RAY ALL EXPOSURE MADE FROM X-RAY PHOTONSPHOTONS

BIG DOSE TO THE PATEINTBIG DOSE TO THE PATEINT

INTENSIFYING SCREENSINTENSIFYING SCREENS

DISADVANTAGES:DISADVANTAGES: less detail than direct exposure less detail than direct exposure (detail better with rare earth than (detail better with rare earth than calcuim tungstate screens)calcuim tungstate screens)

ADVANTAGES:ADVANTAGES:

1.1. Reduce patient exposureReduce patient exposure

2.2. Increase x-ray tube lifeIncrease x-ray tube life

Screen ConstructionScreen Construction

Polyester plastic base – support layerPolyester plastic base – support layer Phosphor layer – active layerPhosphor layer – active layer Reflective layer – increases screen Reflective layer – increases screen

efficiency by redirecting light headed in efficiency by redirecting light headed in other directionsother directions

Protective coatingProtective coating

Intensifying screensIntensifying screens

Phosphor LayerPhosphor Layer

Active layer – x-ray photons Active layer – x-ray photons converted to light photonsconverted to light photons

*Photoelectric Effect*Photoelectric Effect

Screen SpeedScreen Speed

A relative number that describes how A relative number that describes how efficiently x-rays are converted into usable efficiently x-rays are converted into usable lightlight

Ranges from 100 (slow) to 1200 (fast)Ranges from 100 (slow) to 1200 (fast)

Screen SpeedScreen Speed

Greater efficiency = less exposure = fasterGreater efficiency = less exposure = faster

-Standard screen speed class of 100-Standard screen speed class of 100

-200 screen speed is twice as fast-200 screen speed is twice as fast Speeds for routine work: 200 – 800Speeds for routine work: 200 – 800 Speeds for high detail: 50 – 100Speeds for high detail: 50 – 100 Increasing speed also increases image Increasing speed also increases image

noisenoise

SCREEN SPEEDSSCREEN SPEEDS

FASTER SPEED – REDUCES PATIENT FASTER SPEED – REDUCES PATIENT EXPOSUREEXPOSURE

FASTER SPEED - REDUCES IMAGE FASTER SPEED - REDUCES IMAGE DETAIL INCREASES NOISE (LIGHT DETAIL INCREASES NOISE (LIGHT BLURING AROUND IMAGE) BLURING AROUND IMAGE)

Technique Changes Technique Changes

Relative Speed = Film speed & Screen Relative Speed = Film speed & Screen speedspeed

mAs 1 mAs 1 = = RS 2 RS 2 mAs 2 RS 1mAs 2 RS 1

They are inversely relatedThey are inversely related

Image NoiseImage Noise

Speckled background on the imageSpeckled background on the image Caused when fast screens and high kVp Caused when fast screens and high kVp

techniques are used. Noise reduces image techniques are used. Noise reduces image contrastcontrast

The percentage of x-rays absorbed by the The percentage of x-rays absorbed by the screen is the screen is the detective quantum efficiency detective quantum efficiency (DQE) (DQE)

The amount of light emitted for each x-ray The amount of light emitted for each x-ray absorbed is the absorbed is the conversion efficiency (CE)conversion efficiency (CE)

SCREEN SPEEDSSCREEN SPEEDS

Quantum Mottle causing a grainy, mottled Quantum Mottle causing a grainy, mottled or splotch imageor splotch image

Often results of using very fast-speed Often results of using very fast-speed screen-film systemsscreen-film systems

The light photons generated in the The light photons generated in the intensifying screen are emitted by intensifying screen are emitted by phosphor crystals. phosphor crystals.

These crystals are significantly larger These crystals are significantly larger than the silver halide crystals in the filmthan the silver halide crystals in the film

use of a screen reduces image use of a screen reduces image sharpness somewhatsharpness somewhat

Some examinations requiring Some examinations requiring extremely fine detail use screens with extremely fine detail use screens with small crystals. small crystals.

Image Quality

Rare Earth ScreensRare Earth Screens

Have higher DQE (detective quantum Have higher DQE (detective quantum efficiency). Higher x-ray absorption efficiency). Higher x-ray absorption abilities.abilities.

Have higher CE (conversion efficiency). Have higher CE (conversion efficiency). More light emitted per x-ray absorbed by More light emitted per x-ray absorbed by the screen. the screen.

Spatial resolution

• The use of intensifying screens lowers spatial resolution compared with direct-exposure radiographs.

• Spatial resolution

expressed by the

number of line pairs

per millimeter

(lp/mm)

The higher the lp/mm the smaller the object that can be imaged Very fast screens = 7 lp/mm

Fine-detail screens= 15 lp/mm

Direct-exposure screens = 50 lp/mm

Screen speed vs Spatial resolutionScreen speed vs Spatial resolution

Wire mesh test – check for screen-film contact. Good contact

Wire mesh test – check for screen-film contact.

• Warped cassette –poor contact

Care of ScreensCare of Screens

Image artifacts can appear if screens are Image artifacts can appear if screens are modifiedmodified

Small scratches can leave artifactsSmall scratches can leave artifacts Dirty screens can leave artifactsDirty screens can leave artifacts Screens should be cleaned once each Screens should be cleaned once each

month with manufacturer’s cleaner with month with manufacturer’s cleaner with antistatic compoundsantistatic compounds

Questions?