radiographic (x-ray) films - xraykamarul · pdf filehdr 104 chapter 3 radiographic equipment...

HDR 104

CHAPTER 3

RADIOGRAPHIC EQUIPMENT AND IMAGE RECORDING 1

RADIOGRAPHIC (X-RAY) FILMS

PREPARED BY:MR KAMARUL AMIN BIN ABDULLAH

SCHOOL OF MEDICAL IMAGINGFACULTY OF HEALTH SCIENCE

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CHAPTER 3: Radiographic (X-ray) Films

LEARNING OUTCOMES

At the end of the lesson, the student should be able to:-

Describe types of medical imaging films

Describe the usage and difference of films

Define of monochromatic, orthochromatic and panchromatic

Explain the process of identifying emulsion side for a single emulsion film

Explain the emulsion formation process and film packing

Describe the type of grains in emulsion

Explain problems associated with films and methods of overcoming them

Explain Quality Assurance (QA) test

Compare the relative speed of two films

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3

What is X-ray Film?

X-ray film is a photographic receptor consisting of photographically active or

radiation sensitive emulsion coated on a thin sheet like material.

It is responsible to record the physical impression of an object by which we

can get detail about the object.

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Classification of the Films

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MEDICAL X-RAY FILM

Double-coated

screen type non-screen type

Single-coated

screen type non-screen type

1. General

radiographic

film

1. Dental film

2. Kidney

surgery film

3. Radiation

monitoring

film

1. Mammographic

film

1. CRT film

2. Copying film

3. Laser film

4. Subtraction

film

5. Drystar Flm

6. Dryview film

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Direct Exposure Film

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.

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Indirect Exposure Film

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

The latent image being produced mainly by light emission from screen

phosphors.

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

green - sensitive.

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0

2

4

6

8

10

12

14

Series 3

Series 2

Series 1

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 in

Industrial Radiography

General radiography

Difference B/W Non Screen & Screen Film

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Type Of Direct Exposure Film

1. Dental Film

2. Kidney Surgery Film

3. Radiation Monitoring Film

4. Industrial Film

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Dental Film

1. Periapical Dental Film: Used for single or group of teeth

2. Occlusal Dental Film: Imaging mandibles or maxillae

3. Bitewing Dental Film: Demonstrating the crown

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Kidney Surgery Film

This duplitized film non screen film is designed to enable to radiographic

exposure of kidney .

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

10

10 CM

13 CM FOR RENAL VESSELS

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Laser Film

A laser printer uses digital electronic signal from an imaging device.

It is high-contrast single-emulsion film with extremely fine grain, 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 Laser Film.

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Films Used With Cathode Ray Tube OR TV Monitor

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

The emulsions are orthochromatic of medium to high contrast and made

to match a wide variety of CRT phosphor.

The film sizes commonly used are 8” x 10”, 11”x14” and 14”x17”.

Used in following modalities:

1. Ultrasound

2. Computerized tomography

3. Magnetic resonance imaging

4. Nuclear medicine

5. Digital subtraction imaging

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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.

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• It is used to duplicate the pre-existing film.

• Duplicating film is a single emulsion film that is exposed to ultraviolet.

light or Visible light through existing radiograph to produce a copy.

Duplicating Film

Substraction film

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Polaroid Film

It is made up of positive and negative film sheets with a pod of jellified

processing chemistry.

Used particularly in ultrasound imaging.

The latent image is formed in the silver halide emulsion of the negative sheet.

And the positive image formed due to migration of Ag ions from the negative

sheet.

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The Dry View Film

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 needs no wet film

processor.

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The Drystar Film

Direct thermal printing Drystar dry imaging films are designed to produce the

highest diagnostic grayscale hardcopies. These images can represent the same

"look and feel" 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

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Spectral Sensitivity

Spectral sensitivity is the range of

wavelength of the electromagnetic

radiation that the film will respond.

PEAK SENSITIVITY is the range

of wavelength in which the film

will exhibit its highest response

CUT-OFF SENSITIVITY is the

range of wavelength beyond

which the film is no longer

sensitive.

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Types Of Film According To Sensitivity

MONOCHROMATIC - blue sensitive films

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ORTHOCHROMATIC - green sensitive film

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PANCHROMATIC - sensitive to all colors of the visible spectrum

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Layers of Radiographic Film

1. Base

2. Subbing layer (Adhesive)

3. Emulsion layer

4. Supercoat

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Film Construction

22

0.0004”

0.0005”

0.007”0.008

TOTAL FILM THICKNESS=0.008 INCH

Double –sided emulsion film

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2323

0.0004”

0.0005”

0.007”0.008

Anti –Halation /non curl backing

Single –sided emulsion film

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0

2

4

6

8

10

12

14

Series 3

Series 2

Series 1

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

Difference b/w Single Coated And Double Coated X-ray Film

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Radiographic Film Base

Initially X-RAY were taken on glass plates.

In 1918 cellulose nitrate bases film replaced glass,but discarded 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 are used.

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Film

Base

.007”

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Character of Good Base Material

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

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Function of Base

Provide support for emulsion layer.

To transmit light.

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Subbing Layer (Adhesive Layer)

Also called Adhesive 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.

When dye is added, it counteracts cross over effect.

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

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Emulsion Layer

Emulsion is the heart of radiographic film .

The X-RAY or Light from I.S. interact with the emulsion and transfer

information to the film.

It consists of a very homogeneous mixture of gelatin and silver crystal.

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

NOTE:

• The presence of AgI produce an emulsion of much sensitivity than a

pure AgBr emulsion.

• It also contains traces of sulfur(ALLYLTHIOUREA).

Emulsion

Layers

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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 dimeter with about 6.3 x

1010 grains per centimeter of emulsion.

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Grain Technology

Globular Grain:spherical in shape and has a bigger volume.Use for blue

sensitive film.

Tabular Grain:Has a table –top like structure that provides bigger surface but

smaller volume.

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Advantages of Tabular Grain

Increased RESOLUTION due to reduction in crossover.

Reduction in silver coating weight.

Suitable for 45 s processing.

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Grain Size And Distribution

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.

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Binder

A binder is an ingredient used to bind together two or more other materials in

mixtures.

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

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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.

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Why We Use Gelatin As Binder?

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.

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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.

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It is the great advantage of the gelatin in which it can set its intermolecular

space a/c to the condition of the environment, While processing, gelatin

swells up in contact with water, allows processing chemicals to enter the

layer and react with the grains of emulsion, & On drying it regains its former

state.

It is believed that gelatin reduces the tendency of reversal of reaction of

Silver bromide after exposure

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Making of The Film Emulsion

The light sensitive layer of a film is termed the Emulsion.

The preparation of emulsion is carried out in four stages:

1. Emulsification

2. Ripening

3. Washing

4. Digestion

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Emulsification

Aqueous solution of Silver nitrate and Potassium bromide is mixed with warm

solution of gelatin.

AgNO3 + KBr AgBr + KNO3

Insoluble Silver bromide (AgBr) remains suspended in viscous gelatin.

More rapid process of mixing results small grain size, that results narrow grain

size distribution hence there is low graininess & better resolution.

Note:

More bromide is used to increase the negative charge barrier that helps in

development process.

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Ripening

Emulsion is placed in certain temperature and more gelatin is mixed. Size of

the grains and their even distribution is determined 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)

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Washing

After ripening, emulsion is chilled to form thick gel.

This gel is shredded.

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

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Digestion

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

Re-heating also make the emulsion liquid and suitable to spread on the film

base.

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Supercoat (Overcoat)

Protective layer of gelatin

Provides sturdiness to unexposed radiographic film.

Antistatic

Reduces damage from scratches, pressure, or contamination during

storage, handling and processing.

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Supercoating

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Few Additives

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

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Coating The Film

Different layers of film are coated on the base material with rollers and

squeezers.

The film lengths are then passed over chilled rollers so that liquefied

gelatinous layers settle and harden.

Then The film lengths are hung like festoons in an air conditioned room to

dry.

Mechanical cutters cut The film lengths in sheets of desirable sizes.

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Anti- Halation Layer

Halation : it is a phenomenon characterized by formation of a diffuse image or

halo around the proper image.

This occurs mainly in the single sided film.

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Methods To Prevent Halation

Adding a dye to base

Adding a dye to non-curling layer.

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Non-curling Layer

Preferred for single sided emulsion film.

This layer is not removed during development.

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Adding A Dye To Base

These dyes cannot be removed during development.

Dye introduced in the base is carefully controlled because it increase the

density and may interrupt the transparency of the film.

Note-dye used in this should be complementary to the exposing light. e.g.,

red dye is used for green sensitive film, yellow dye is used for blue sensitive

film .

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Cross Over Effect

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

Occurs only with double emulsion films and two screens.

Light from one screen expands in the form of a cone as it passes through the

screen and emulsion where a slightly enlarged, less sharp image is formed.

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Cross Over Effect (Cont’d)

Special dyes incorporated in the emulsion

Colored subbing layer is used.

Addition of magenta dye also reduces cross over effect.

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Irradiation

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

This contributes to unsharpness (blurring) of image.

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How Film Records An Image

There are three steps:-

1. Formation of subject contrast (Optical image)

2. Recording of latent image

3. 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 beam after 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 the photographic material

of the film.

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Sensitivity Speck

The shape and lattice structure of silver halide are not perfect.

It causes some imperfection which results in imaging property of crystals.

So the sensitivity specks is that low energy centre of the crystal which acts as

rest house for the 1º electron and development centre for the 2º electron.

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Sensitivity Speck (Cont’d)

• For the formation of sensitivity specks impurity, usually a Silver-gold Sulfide is

introduced by chemical sensitization at or near the surface.

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Sensitivity Speck (Cont’d)

The image forming x-rays deposit energy by photoelectric interaction with

atoms of silver halide crystals.

Formation of latent image is given by Gurney-Mott theory

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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

-

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Producing the Latent Image

Radiation interaction releases electrons.

Electrons migrate to the sensitivity center.

At the sensitivity center, atomic silver is formed by attracting an interstitial

silver ion.

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

The remaining silver halide is converted to silver during processing.

The resulting silver grain is formed.

Silver halide that is not irradiated remain inactive. The irradiated and non-

irradiated silver halide produces the latent image.

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Conversion Of Latent Image Into Visible Image

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

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1. Development

2. Fixing

3. Washing

4. Drying

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Characteristics To Be Considered While Selecting Film:

Contrast

Speed

Crossover

Spectral matching

Bulk of purchase

Time of purchase

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Care And Protection Of Film

Films should be protected from:-

1. Physical damage

2. Light

3. High temperature

4. High relative humidity

5. Harmful gases and fumes

6. X-rays and radioactive source

7. Fire and theft

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Resolving Power of Films

Ability of a photographic emulsion to record fine details

It is expressed as the number of line pairs per millimeter which 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 and Modular

transfer function

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Line Pairs Per Millimeter

A black and a white line make a line pair

A test pattern of slits cut on a metal plate with gradual fineness is

exposed, processed and evaluated under magnification.

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

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STORAGE AREAS :-

The hospital or x-ray department

The dark room

The imaging room

Storage Of Film

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Handling and Storage Of Radiographic Film

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.

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Handling and Storage of Radiographic Film

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.

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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%.

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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.

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Shelf life. All film is supplied in boxes with an expiration date.

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 increased fog.

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References

No. REFERENCES

1 Richard R. Carlton, Arlene McKenna Adler (2005) Principles of

Radiographic Imaging, Delmar

2 Bushong, S. C. (2008). Radiologic science for technologists. Canada:

Elsevier.

radiographic (x-ray) films - xraykamarul · pdf filehdr 104 chapter 3 radiographic equipment...

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