X-Ray Films

KAMARUL AMIN ABDULLAH

LECTURE 6 (A)

What Is X-ray Film?

X-ray film is a photographic receptor consisting ofphotographically active or radiation sensitive emulsioncoated on a thin sheet like material, which is responsibleto record the physical impression of an object by whichwe can get detail about the object.

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Classification of the film

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MEDICAL X-RAY FILM

double-coated

screen type non-screen type

single-coated

screen type non-screen type

General radiographic film

Dental filmKidney surgery filmRadiation monitoring film

Mammographic film

CRT filmCopying filmLaser filmSubtraction film

Drystar FlmDryview film

Direct Exposure Film

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Used without intensifying screens

Used mainly for extremities, previously for mammography

Requires 10 – 100 times more the exposure dose

The emulsion is thicker than screen film

Renders excellent detail

Indirect Exposure Film

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These films are used in conjunction with pairs of I.S. .

The latent image being produced mainly by light emissionfrom screen phosphors.

A wide range of different films are available both the blue-sensitive and green - sensitive .

CHARACTERISTICS DIRECT EXPOSURE FILM INDIRECT EXPOSURE FILM

Exposed with Only by x-rays Mainly by vissible light

Used Without Screen With screen

Emulsion layer Thick Thin

Image formation In deep superficialy

Processing time more less

Resolution more less

Characteristic curve No apparent shoulder region in useful density range

Shoulder region within useful density range

Screen artifact no May possible

Exposure dose more less

Used in Orbit and extremities radiography. Also inIndustrial Radiography

General radiography

Difference B/W Non Screen & Screen Film

Type Of Direct Exposure Film

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A. Dental Film

B. Kidney Surgery Film

C. Radiation Monitoring Film

D. Industrial Film

Dental Film

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Periapical Dental Film:Used for single or group of Teeth

Occlusal Dental Fiim:Imaging mandibles or maxillae

Bitewing Dental film:Demonstrating the crown

Kidney Surgery Film

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This duplitized film non screen film is designed to enable toradiographic exposure of kidney .

Each packet contains two films ,one with a fast emulsion,the other slow.

10 CM

13 CM FOR RENAL VESSELS

Laser Film

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A laser printer uses digital electronic signal from an imagingdevice.

It is high-contrast single-emulsion film with extremely finegrain, also known as IR film.

Laser film is a silver halide film sensitized red light(Panchromatic) or laser light, e.g., HN Laser Film, IR LaserFilm.

Films Used With Cathode Ray

Tube Or TV Monitor

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These films are used with cathode ray tube camera andmulti-formatter.

The emulsions are orthochromatic of medium to highcontrast and made to match a wide variety of CRTphosphor.

The film sizes commonly used are 8” x 10”, 11”x14” and14”x17” .

contd...

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Used in following modalities:

Ultrasound

Computerized tomography

Magnetic resonance imaging

Nuclear medicine

Digital subtraction imaging

Substraction film

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A type of single emulsion film used with angiography

One type prepares a positive copy of the image

The other type enhances subject contrast and detail

Duplicating Film

It is used to duplicate the pre-existing film.

Duplicating film is a single emulsion film that is exposedto ultraviolet light or Visible light through existingradiograph to produce a copy.

Polaroid Film

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It is made up of positive and negative film sheets with a podof jellified processing chemistry.

Used particularly in ultrasound imaging.

The latent image is formed in the silver halide emulsion ofthe negative sheet. And the positive image formed due tomigration of Ag ions from the negative sheet.

The Dry View Film

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High quality silver based material coated.

The heat /laser light sensitive layer contains silver halide/silver behnate crystal.

DRYVIEW Film also a type of laser film having high-resolution,

It is infra red sensitive photothermographic film that needsno wet film processor.

The Drystar Film

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Direct thermal printing Drystar dry imaging films aredesigned to produce the highest diagnostic grayscalehardcopies. These images can represent the same "look andfeel" as conventional x-ray film.

Blue base

Maximum optical density > 3.5

Daylight film loading (films are insensitive to light)

Shelf life: to be used min. 18 months from packaging date

Storage temperature: 5 - 25 °C

Relative humidity: 30 - 60%

Extended term storage: minimum 20 years

Spectral Sensitivity

Spectral sensitivity is therange of wavelength of theelectromagnetic radiationthat the film will respond.

PEAK SENSITIVITY is therange of wavelength inwhich the film will exhibitits highest response

CUT-OFF SENSITIVITY isthe range of wavelengthbeyond which the film is nolonger sensitive.

Types Of Film According To

Sensitivity

MONOCHROMATIC - blue sensitive films

Contd…

ORTHOCHROMATIC - green sensitive film

Contd…

PANCHROMATIC - sensitive to all colors of the visiblespectrum

Layers Of Radiographic Film:

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Base

Subbing layer (Adhesive)

Emulsion layer

Supercoat

Film Construction

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0.0004”

0.0005”

0.007”0.008

TOTAL FILM THICKNESS =0.008 INCH

Double –sided emulsion film

Contd…

2323

0.0004”

0.0005”

0.007”0.008

Anti –Halation /non curl backing

Single –sided emulsion film

Difference b/w Single Coated And

Double Coated X-ray Film

Characteristic Single coated Double coated

Emulsion layer One side Both side

Patient Radiation dose More Less

Noncurl back layer Present Absent

Radiographic detail More Less

Average gradient (G) Very less more

Parallax effect No yes

Contrast Less more

Radiographic Film Base

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Initially X-RAY were taken on glass plates.

In 1918 cellulose nitrate bases film replaced glass,butdiscarded because of highly inflammable .

In 1920 cellulose tricetate or safety base was introduced.

Polyester base replaced cellulose tricetate in the 1960”s,

Now a days POLYETHYLENE TEREPHTHLATE RESIN areused.

FilmBase

.007”

Character Of Good Base Material.

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structural support for fragile emulsion low light absorption flexible, thick, & strong

• processing• handling• viewbox insertion / removal abuse

dimensional stability• in processing• For archival

varying humidity NON -FLAMMABLE

Function Of Base

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Provide support for emulsion layer.

To transmit light.

Subbing Layer (Adhesive Layer)

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Also called adhesive layer or Substratum layer.

Made of mixture of gelatin solution and solvent of filmbase.

It keeps emulsion layer and base adhered to each otherduring coating stage and processing.

When dye is added, it counteracts cross over effect.

Provides uniform surface over which the emulsion can becoated uniformly.

Emulsion Layer

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Emulsion is the heart of radiographic film .

The X-RAY or Light from I.S. interact with the emulsion andtransfer information to the film.

It consists of a very homogeneous mixture of gelatin andsilver crystal.

In typical emulsion 90 to 99% is AgBr and about 1 to 10% AgI .

NOTE:

• The presence of AgI produce an emulsion of muchsensitivity than a pure AgBr emulsion.

• It also contains traces of sulfur(ALLYLTHIOUREA).

EmulsionLayers

contd…

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Silver halide in a emulsion is in the form of small crystals.

Silver halide crystals may be tabular,globular,polyhedral,orirregular in shape.

Crystal size might vary from 1.0 –1.5 microns in dimeterwith about 6.3 x 1010 grains per centimeter of emulsion.

Grain Technology

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Globular Grain:spherical in shape and has a biggervolume.Use for blue sensitive film.

Tabular Grain:Has a table –top like structure that providesbigger surface but smaller volume.

Advantages Of Tabular Grain

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Increased RESOLUTION due to reduction in cross- over.

Reduction in silver coating weight.

Suitable for 45 s processing.

Grain Size And Distribution

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GRAIN SIZE and DISTRIBUTION affects the following:

SPEED: The bigger the average grain size, the higher thespeed of the film.

CONTRAST: Affected by size distribution. The moreavailable in the film, the lower the contrast.

GRAININESS: Graininess is the apparent clumping of thecrystal as seen on the radiograph. The bigger the crystal,thehigher the graininess o f the film.

Binder

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A binder is an ingredient used to bind together two or moreother materials in mixtures.

The common type of a binder which we can use is Gelatin.

Gelatin

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Gelatin is used as the suspending medium and bindingagent for the silver halide particles.

It comes collagen fiber in which primary source are thecartilage, skin and the protein matrix (ossein) of bone ofanimals.

Why We Use Gelatin As Binder?

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It is a medium in which SILVER NITRATE and SODIUMBROMIDE can react and the resulting AgBr get finely andevenly dispersed and remain suspended.

In warm state it can be easily spread on the film base.

On cooling, it sets firmly on the base as gel.

It is flexible and does not crack easily on bending.

It is optically transparent .

Gelatin does not react chemically with the silver halide .

It is porous so the processing chemicals can penetrate tothe silver halide crystals.

Some of the constituents in gelatin enhances the activity ofSilver bromide and some act as antifoggant.

contd…

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It is the great advantage of the gelatin in which it can setits intermolecular space a/c to the condition of theenvironment, While processing, gelatin swells up in contactwith water, allows processing chemicals to enter the layerand react with the grains of emulsion, & On drying itregains its former state.

It is believed that gelatin reduces the tendency of reversalof reaction of Silver bromide after exposure

Making Of The Film Emulsion

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The light sensitive layer of a film is termed the Emulsion. The preparation of emulsion is carried out in four stages:

Emulsification

Ripening

Washing

Digestion

Emulsification

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Aqueous solution of Silver nitrate and Potassium bromide ismixed with warm solution of gelatin.

AgNO3 + KBr AgBr + KNO3

Insoluble Silver bromide (AgBr) remains suspended inviscous gelatin.

More rapid process of mixing results small grain size, thatresults narrow grain size distribution hence there is lowgraininess & better resolution.

Note:

More bromide is used to increase the negative chargebarrier that helps in development process.

Ripening

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Emulsion is placed in certain temperature and more gelatinis mixed. Size of the grains and their even distribution isdetermined at this stage

Slow mixing with long ripening at high temp.=> Fast emulsion (with large grains)

Rapid mixing with short ripening at low temp.=> Slow emulsion (with fine grains)

Slow mixing with NH3 at low temp.=> Fast emulsion (with large grains)

Washing

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After ripening, emulsion is chilled to form thick gel.

This gel is shredded.

It is washed with water that remove KNO3 and excess KBr bydiffusion process.

Digestion

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Shredded and washed emulsion is re-heated to furtherincrease its sensitivity.

Re-heating also make the emulsion liquid and suitable tospread on the film base.

Supercoat (overcoat)

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Protective layer of gelatin

Provides sturdiness to unexposed radiographic film.

Antistatic

Reduces damage from scratches, pressure, orcontamination during storage, handling and processing.

Supercoating

Few Additives

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Preservative – Phenol as bacteriocide

Silver iodide – To extend sensitivity towards blue range.

Some dyes may extend Colour sensitivity further

Glycerin to make the emulsion pliable

Saponin – To make the emulsion receptive to the processingchemicals

Alcohol – To prevent frothing during coating

Coating The Film

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Different layers of film are coated on the base material withrollers and squeezers.

The film lengths are then passed over chilled rollers so thatliquefied gelatinous layers settle and harden.

Then The film lengths are hung like festoons in an airconditioned room to dry.

Mechanical cutters cut The film lengths in sheets ofdesirable sizes.

Anti- Halation Layer

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Halation : it is a phenomenon characterized by formation ofa diffuse image or halo around the proper image.

This occurs mainly in the single sided film.

Methods To Prevent Halation

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Adding a dye to base

Adding a dye to non-curling layer.

Non-curling Layer

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Preferred for single sided emulsion film.

This layer is not removed during development.

Adding A Dye To Base

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These dyes cannot be removed during development.

Dye introduced in the base is carefully controlled because itincrease the density and may interrupt the transparency ofthe film.

Note-dye used in this should be complementary to theexposing light. e.g.,red dye is used for greeen sensitivefilm,yellow dye is used for blue sensitive film .

Cross Over Effect

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It is a type of halation which occurs when film is used withintensifying screen.

Occurs only with double emulsion films and two screens.

Light from one screen expands in the form of a cone as itpasses through the screen and emulsion where a slightlyenlarged, less sharp image is formed.

contd

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Special dyes incorporated in the emulsion

Colored subbing layer is used.

Addition of magenta dye also reduces cross over effect.

Irradiation

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It is the sideway scattering of light within the crystal ofemulsion.

This contributes to unsharpness (blurring) of image.

How Film Records An Image

There are three steps

formation of subject contrast (Optical image)

Recording of latent image

Conversion of latent image into permanent image(processing)

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The Latent Image

The latent image is the invisible change in the silver halide crystals.

The interaction between the photons and the silver halide crystals produces the latent image or manifest image on the emulsion layer.

This interaction is sometimes referred to as the photographic effect.

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Formation Of Subject Contrast

Subject contrast:-the variation in intensity of x-ray beamafter passing the absorber.

Subject contrast depends upon atomic No., density,thickness of absorber and the energy of the x-ray beam.

Different intensity of beam react differently with thephotographic material of the film.

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The shape and lattice structure of silver halide are notperfect.

It causes some imperfection which results in imagingproperty of crystals.

So the sensivity specks is that low energy centre of thecrystal which acts as rest house for the 1º electron anddevelopment centre for the 2º electron.

Sensitivity Speck

For the formation of sensitivity specks impurity, usually aSilver-gold Sulfide is introduced by chemical sensitizationat or near the surface.

contd

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The image forming x-rays deposit energy by photoelectricinteraction with atoms of silver halide crystals.

Formation of latent image is given by Gurney-Mott theory

contd

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-

+

SENSITIVITY SPECK

SILVER HALIDE CRYSTAL

INTERSTITIAL Ag ION

1. Photon Absorption

6. Ag Ion Migration

3. Ag Ion Migration

2. Electron Trapping

+

-

4. Photon Absorption

-+

+

5. Electron Trapping

-

Producing the Latent Image

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Radiation interaction releases electrons.

Electrons migrate to the sensitivity center.

At the sensitivity center, atomic silver is formed byattracting an interstitial silver ion.

The process is repeated many times resulting in the build upof silver atoms.

The remaining silver halide is converted to silver duringprocessing.

The resulting silver grain is formed.

Silver halide that is not irradiated remain inactive. Theirradiated and non-irradiated silver halide produces thelatent image.

Conversion Of Latent Image Into

Visible Image

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This step is also known asprocessing. There are 4step in this processing:

1. Development

2. Fixing

3. Washing

4. Drying

Characteristics To Be Considered

While Selecting Film:

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Contrast

Speed

Crossover

Spectral matching

Bulk of purchase

Time of purchase

Care And Protection Of Film

Films should be protected from

Physical damage

Light

High temperature

High relative humidity

Harmful gases and fumes

X-rays and radioactive source

Fire and theft

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Resolving Power Of Films

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Ability of a photographic emulsion to record fine details

It is expressed as the number of line pairs per millimeterwhich can be distinguished in the image as separate entities

Factors affecting the resolution of an image are – Grain size,Processing, Diffusion of light inside the emulsion layer andModular transfer function

Line Pairs Per Millimeter

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A black and a white line make a line pair

A test pattern of slits cut on a metal plate with gradualfineness is exposed, processed and evaluated undermagnification.

Radiographic emulsions show 8 – 20 LP/mm

Photographic Fast emulsions show 40 – 50 LP/mm

• Medium emulsions show 70 – 100 LP/mm

• Slow emulsions show over 1000 LP/mm

Storage Of Film

STORAGE AREAS :-

The hospital or x-ray department

The dark room

The imaging room

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Handling And Storage Of

Radiographic Film

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X-ray film is a sensitive radiation detector and it must be handled in an area free of radiation.

Film storage must be shielded.

The darkroom adjacent to the x-ray room must be shielded.

If film use is low more shielding may be required.

Handling And Storage Of

Radiographic Film

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Improper handling of the film will result in poor image quality due to artifacts.

Avoid bending, creasing or otherwise rough handling the film. Avoid sharp objects contacting the film.

Hands must be clean and dry.

Avoid hand creams, lotions or water free hand cleaners.

Static electricity or a dirty processor can cause artifacts.

Artifacts must be avoided.

Handling And Storage Of

Radiographic Film

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Heat and Humidity must be controlled. Film is sensitive to heat and humidity from the time it is manufactured until the time it is viewed.

Heat and humidity causes fog or a loss of contrast. Film should be stored at 20º C (68º F).

Humidity should be between 40% and 60%.

Handling And Storage Of

Radiographic Film

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Light will expose the film. Film must be handled and stored in dark.

If low level diffuse light exposes the film, fog is increased.

Luminous watches, cell phone and darkroom light leaks should be avoided.

Bright light causes gross exposure.

Handling And Storage Of

Radiographic Film

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Shelf life. All film is supplied in boxes with an expirationdate.

Most film is supplied in boxes of 100 sheets.

The oldest film in stock should always be used first.Rotation is important.

Expired will loose speed and contrast and have increasedfog.

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