X-RAY FILMS

Dr. Pankaj Kaira JR – I Radiodiagnosis SRMSIMS,Bareilly.

Introduction-The X-Ray films, help us to record the

information regarding the object (tissue) through which the x-rays passes & hence they greatly help in diagnosis, & treatment of the patient problem.

Image recorded on film is caused by

exposure to photons.

X-RAY FILM

X-RAY FILM

HISTORY- The first x-rays were recorded on

glass plates. These were coated with emulsion on

one side only. The exposure dose was quite high. In 1839, the phenomenon of

development was discovered by Louis Daguerre

One year later, it was discovered that treating exposed silver chloride paper with sodium chloride would make the image permanent.

Nitrocelluose based film was used in 1914 for recording x-rays.

This film was single-emulsion but was quiet flammable

It was later discovered that double-emulsion responded to x-rays faster.

In 1924, safety film made of cellulose triacetate replaced the nitrocellulose based film.

COMPOSITIONX- ray film

Adhesive Base

Polyester polyethyle

ne terephthal

ate

Emulsion

Silver halide grains

Vehicles matrix

X-RAY FILM- CROSS SECTION

BASE -FILM

It is a transparent supporting material.

POLYESTER POLYETHYLENE TEREPHTHALATE RESIN are used.

Thickness - 0.18 mmFilmBase 0.18 mm

IDEAL PROPERTIES BASE MATERIAL

1. Structural support for fragile emulsion.

2. Low light absorption : Should not produce visible pattern on the radiograph.

3. Flexible, thick, & strong.

4. Dimensional stability : Maintain size and shape during processing, handling and storage.

5. Non - Flammable.

Triacetate and Polyester are clear and colorless.

Adopted in 1933, blue tint was added to the x-ray film in an effort to produce a film that was “easier” to look at.Causes less eye strain.Blue tint can be added to either to the base or to the emulsion.All present x ray films are blue tinted.

TINTED FLUE FILM

FUNCTIONS OF BASE

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Provide support for emulsion layer.

To transmit light.

ADHESIVE LAYER

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Also called subbing layer or Substratum layer.

Made of mixture of gelatin solution and solvent of film base.

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

Provides uniform surface over which the emulsion can be coated uniformly.

EMULSION LAYER

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Has 2 principle components – I. Silver halide grainsII. Vehicle matrix

It consists of a homogeneous mixture of gelatin and silver halide crystals.

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

EmulsionLayers

The presence of AgI produce an emulsion of much higher sensitivity than a pure AgBr emulsion.

It also contains traces of sulfur (ALLYLTHIOUREA).

How silver halide crystals are made … ???

Dissolve Metallic silver in nitric acid.

to form

Silver nitrate

by mixing

silver nitrate + KBr = Ag-Br + potassium nitrate

……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, or irregular in shape.

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

Silver Iodo Bromide Crystals

• An Imperfect crystal (perfect crystal has almost no photographic sensitivity).

• Several types of crystal defects noted.

Crystal Defects

A Point defect consists of a Silver Ion that has moved out of its normal position in crystal lattice (Interstitial Ions).

Crystal Defects

A dislocation is a line imperfection in the crystal.

Cause a strain in the wall structure.

Iodine ion strains the crystal in this way

Chemical sensitization

Chemical sensitization of the crystals are produced by adding allythiourea, a sulfur containing compound to the emulsion , which reacts with silver halide to form silver sulfide. This Silver Sulphide is usually located on surface of the crystals and is referred as “sensitivity speck”.It is the sensitivity speck that traps elctrons to begin formation of the latesnt image centers.

Point defect in cubic lattice.

Sensitivity speck by Silver sulfide

The sensitivity speck traps electron and form Latent image.

The Latent Image

Remnant radiation interacts with the silver halide crystals

Mainly by the photoelectric interaction The energy deposited into the film is in the same

pattern as the subject that was exposed to radiation

This invisible image is known as the latent image A latent image on photographic (radiographic)

film is an invisible image produced by the exposure of the film to light (radiation).

By chemically processing the latent image it is made visible known as the manifest image.

Formation of Latent Image

Metallic silver is black, so it is this metallic silver that produces black areas on a developed films.

Exposure of silver-iodo-bromide grains to light photons emitted by screen / direct x-ray exposure initiates the formation of atomic silver to form a visible pattern.

Latent Image Formation: Gurney-Mott

Energy absorbed from Light photon ejects Br electron

Electron trapped at sensitivity speck where it is trapped and temporarily fixed .

Negative electron attracts interstitial Ag+ ion

Ag+ and e- combine to form neutral (black) Ag

If >6-10 Ag0 accumulate at speck, it becomes a latent image center: ie, it is developable.

Gurney Mott hypothesis

This process repeats.

GRAIN SIZE AND DISTRIBUTION

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GRAIN SIZE and DISTRIBUTION affects the following: SPEED: The bigger the average grain size, the

higher the speed of the film. CONTRAST: Affected by size distribution. The

more available in the film, the lower the contrast. GRAININESS: Graininess is the apparent clumping

of the crystal as seen on the radiograph. The bigger the crystal, the higher the graininess o f the film.

GELATIN Gelatin is used as the suspending medium

and binding agent for the silver halide particles.

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

WHY WE USE GELATIN AS BINDER…?

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It is a medium in which SILVER NITRATE and SODIUM BROMIDE can react and the resulting AgBr get finely and evenly 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 to the silver halide crystals. Some of the constituents in gelatin enhances the

activity of Silver bromide and some act as antifoggant.

?

SUPERCOAT (OVERCOAT)

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Protective layer of gelatin Provides sturdiness to unexposed

radiographic film. Antistatic Reduces damage from scratches,

pressure, or contamination 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 processing chemicals Alcohol – To prevent frothing during coating

TYPES OF X-RAY FILM -1. According to their USES –

Intraoral filmsPeriapical films

No. 0 – childrenNo. 1 – anterior adultNo.2 – standard adult

Occlusal filmsBitewing films

Extraoral films

2. According to SPEED –Slow film

Speed A Speed B Speed C

Fast film D – ultra speed E – ekta speed F – ultra ekta speed

Hyper speed G

3. According to emulsion layer -Single coated Double coated

4. According to packaging –Single film packet

Double film packet

TYPES OF X-RAY FILM -Based on their application.

1) Screen Films :

Most commonly used Sensitive to blue light emitted by

intensifying screens and direct actions of x-rays.

Used in cassettes with intensifying screens

High speed.

2) Non-screen / Direct exposure films:

Has thicker coat of emulsion used without intensifying screen.

Depends mainly on action of x-ray. Four times faster than that of screen

films so requires 1/4th exposure only. Must be manually processed because of

thick emulsion.

Uses : A)In limb radiography. B)To detect intra-ocular foreign body. C)In dental with intra-oral cardboard.

3) Mammography film: Single coated Fine grain Slow speed High contrast Designed to be used with single

intensifying screen Combination must be fast to deliver

minimum dose to the glandular tissue.

4) Duplicating Film : Used to copy radiograph. Original cassette to be copied is inserted

into a cassette whose opaque front has been replaced by pane of clear glass.

Special duplicating film is placed with emulsion side down onto radiograph and lid closed.

Exposure made.

What is speed of X-RAY FILM …???

It is defined as the amount of the radiation required to produce the radiograph of adequate density.

Slow film – Require more exposure & vice versa.

Factors affecting film speed – Size of crystals Shape of grains Thickness of emulsions

Difference b/w Single Coated and Double Coated

X-ray FilmCharacteristic Single coated Double coated

Emulsion layer One side Both side

Patient Radiation dose

More Less

Radiographic detail More Less

Average gradient (G)

Very less more

Parallax effect No yes

Contrast

Less more

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