HDR104

SCHOOL OF MEDICAL IMAGINGFACULTY OF HEALTH SCIENCES

PREPARED BY:MR KAMARUL AMIN BIN ABDULLAH

CHAPTER 3

RADIOGRAPHIC EQUIPMENT AND IMAGE RECORDING 1

RADIOGRAPHIC FILMS

LEARNING OUTCOMES

At the end of the lesson, 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

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.

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 film2. Kidney

surgery film

3. Radiation monitoring film

1. Mammographic film

1. CRT film2. Copying film3. Laser film4. Subtraction

film5. Drystar Flm6. Dryview film

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.

5

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 emission from 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 in Industrial Radiography

General radiography

Difference B/W Non Screen & Screen Film

Type Of Direct Exposure Film

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1. Dental Film

2. Kidney Surgery Film

3. Radiation Monitoring Film

4. Industrial Film

Dental Film

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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

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

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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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.

• 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

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.

14

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.

Types Of Film According To Sensitivity

• MONOCHROMATIC - blue sensitive films

• ORTHOCHROMATIC - green sensitive film

• PANCHROMATIC - sensitive to all colors of the visible spectrum

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

2323

0.0004”

0.0005”

0.007”0.008

Anti –Halation /non curl backing

Single –sided emulsion 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

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

• 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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FilmBase

.007”

Radiographic Film Base

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).

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EmulsionLayers

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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.

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 cross- over.

• 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.

36

Why We Use Gelatin As Binder?

• 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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38

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

Why We Use Gelatin As Binder?

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.

40

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)

41

Ripening

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

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.

46

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.

47

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 greeen 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.

51

52

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.

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.

55

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.

58

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

-

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

Characteristics To Be Considered While Selecting Film:

Contrast

Speed

Crossover

Spectral matching

Bulk of purchase

Time of purchase

63

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

64

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.

69

Handling And Storage Of Radiographic Film

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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Handling And Storage Of Radiographic Film

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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Handling And Storage Of Radiographic Film

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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FILM BIN - STORAGE

KAAB (C)

KAAB (C)

KAAB (C)

X-RAY FILMS

Standard SizesInches• 14’ X 17’• 14’ X 14’• 12’ X 15’• 10’ X 12’• 8’ X 10’

Metric• 18cm x 24cm• 24cm x 30cm• 30cm x 40cm• 35cm x 40cm• 35cm x 43cm

EXAMPLES OF POOR STORAGE AND HANDLING

KAAB (C)

FILM FOG!!!!

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

KAAB (C)

KAAB (C)

POOR SCREEN CONTACT

• FOAM BACKING HELPS TO PLACE INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM – NO GAPS

• IF GAPS – MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAIL

KAAB (C)

KAAB (C)

KAAB (C)

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.