Film/Screen ImagingComputed RadiographyDigital Radiography

IMAGE RECEPTOR SYSTEMS

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Image Capture

Image Receptor

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Image Receptor Types Film/Screen Systems

Computed Radiography Systems

Direct Digital Systems

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Image Receptor Types

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Film/Screen, CR, DR systems

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Terminology•I

mage receptor•I

mage capture•B

eam absorption•A

ttenuation•P

rimary radiation•S

econdary radiation•S

catter radiation•R

emnant radiation•E

xit radiation•L

atitude•L

atent image•M

anifest image

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Film/Screen Imaging

Film constructionCassette constructionFilm captureFilm developingFilm Interpretation/Storing

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FIRST “FILM”

•Early Years:• Glass plates • Break easily• Difficulty in storage• Expensive

•Developments:• Cellulose acetate• Highly flammable• Easily torn

• Polyester Base• Highly flammable• Easily torn

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Today’s Modern Film

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Film Sizes

Standard:

•8” x 10”

•10” x 12”

•11” x 14”

•14” x 17”

Metric:

•18cm x 24cm

•24cm x 30cm

•30cm x 35cm

•35cm x 43cm

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X-ray Film •T

wo basic parts:

1. Base

2. Emulsion and Topcoat

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Film Construction - BASE

• Made of a polyester plastic

• Must be clear, strong, consistent thickness

• Tinted pale blue or blue-gray (reduces eye strain)

• Uniform lucency

• COATED ON 1 OR 2 SIDES WITH EMULSION

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Film Construction - EMULSION

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

• Protective overcoat layered on top of emulsion-topcoat, supercoat

• Emulsion is a gelatin containing the film crystals---THE HEART OF THE FILM

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Film Emulsion• Made of mixture of

gelatin & silver halide crystals

• Silver halide crystals made of silver bromide (90%) and silver iodide (10%)

• Photographically active layer – activated by light & radiation to create image

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Latent Image•I

maged Formed by:• Direct x-ray interaction with

film

• Indirect interaction with light from cassette

•Image is not seen until developed chemically developed by processor.

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Film Storage•C

lean, dry location

•40 – 60 % Humidity 70 º Fahrenheit

•Away from chemical fumes

•Safe from radiation exposure

•Standing on edge

•Expiration date clearly visible

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CASSETTES FUNCTION

Protect film from exposure to light

Protect film from bending and scratching during use.

May contain intensifying screens, keeps film in close contact to screen during exposure.

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FILM CASSETTE or FILM HOLDER

•The CASSETTE is used to hold the film during examinations.

•It consist of front and back intensifying screens, and has a lead (Pb) backing.

•The cassette is light tight

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Cardboard Cassettes

Direct x-ray exposure to film:

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equires 25 to 400 times more radiation to create an image on the film

•Better detail than film screen (no blurring of image from light)

•All exposure made from x-ray photons

• Very large dose to the patient

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CASSETTE CONSTRUCTION

•Exposure side of cassette is the “front”.

•Has the ID blocker (patient identification)

•Made of radiolucent material

•Intensifying screen mounted to inside of front

•Back made of metal or plastic

•Inside back is a layer of lead foil – prevents backscatter that could fog the film

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

•Back intensifying screen mounted on padding

CASSETTE FRONT CASSETTE BACK

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Cassette Construction

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Screen Construction

•Polyester plastic base – support layer

•Phosphor layer – active layer

•Reflective layer – increases screen efficiency by redirecting light headed in other directions

•Protective coating

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Intensifying Screens Phosphors

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

•CALCIUM TUNGSTATE (blue light)• Not as efficient • Not used as often

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INTENSIFYING SCREENS

DISADVANTAGES:• less detail than direct exposure

ADVANTAGES:

• Reduce patient exposure• Increase x-ray tube life

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•The light photons are emitted by phosphor crystals.

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

•Screen reduces image sharpness

• Exams requiring extremely fine detail use screens with small crystals.

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Image creationLatent Image

•1% of x-ray photons that leave patient

•Interact with phosphors of intensifying screens

•100’s of light photons created to make image on film

•Light photons expose silver halide crystals in the film emulsion –

•Turn black metallic silver after procession

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Film Development

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Process of X-ray Image

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FILMX

-RA

Y

LATENT IMAGE

PRO

CE

SSO

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MANIFEST IMAGE

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Developing is the stage where the latent image is converted to the manifest (visible)Image.

Phenidone Developing AgentHydroquinone Developing AgentSodium Carbonate ActivatorPotassium Bromide Restrainer

Developing Agents help change ionic silver to metallic silver (black). Silver ion is said to be reduced. Only crystals that contain the latent image are reduce tometallic silver.

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The stage of processing where the film gets treated so that the image will not fadebut will remain permanently is called fixing.

Acetic acid activatorAmmonium thiosulfate(hypo) clearing agentPotassium alum hardenerSodium sulfite preservativeWater solvent

Fixing the film CLEARS the film of all undeveloped silver halides.It is important to stop the developing process because with time, all the ionic silverwill be reduced to metallic silver, thus ruining our image. Our latent image mustbe processed in a timely fashion or we will have image degradation.

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The function of the wash cycle is to remove ANY residual chemicalsfrom the film. Water is used as the washing agent. Failure to completelywash the residual chemicals could result in film fog, hypo retention, yellowing of films, fading of films,

The final step of the processing is to dry the film before it leaves theprocesser. Failure to do so occasionally results in sticky films which eventually cause artifacts.

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ReplenishmentReplenishment : As chemistry is used up by the processing of image, the proper chemical balance is needed to be maintained.As a film enters the first stages of processing, the replenishmentsystem turns on and the chemistry in both developer and the fixerare added to as needed according to prescribed rates.

Silver Recovery: Silver Recovery: As the latent image is developed into the manifestimage, the unaffected silver halide crystals will be washed off. Eachprocessor will have a silver recovery system in place. This is economically soundand environmentally helpful. It also helps prevent the processor from breaking down due to clogging of the system by metallic silver.

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Film Storage

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You will need to bring to class an object or objects to image during week 12 and week 13. Each student will produce one image.

YOUR XRAY IMAGE

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Any Questions ??????

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