X-RAY FILMS

Mamita SakhakarmiB.Sc. MIT (4th Batch)

4th yearChitwan Medical College

Objectives

• Historical background of X-ray film and its construction.

• Duplitized/Single X-ray film with its advantage and disadvantage.

• Explain film for medical imaging.•

CONSTRUCTION OF A MEDICAL X-RAY FILM

• ADHESIVE (Substratum) LAYER– Thin coat of gelatin

• EMULSION– Silver halide crystal in

gelatin binder

• SUPERCOAT– Hardened gelatin

History of film base• 1st x-ray film base is glass plate by using roentgen

original film base.• 1917 – cellulose nitrate film base is widely adopted

but flammable • 1923 – cellulose triacetate ‘safe film base’- kodak.• 1932 – Blue tint is added x-ray film• 1960 – polyester base film – ‘Dupont’ – as cellular

triacetate but it is more resistant (polyethylene terephthalate )

Characteristic of base

• Transparent• Flexible• Untreatable• Uniform thickness & colour• Impermeable in water & processing solution• Non inflammable• Chemically inactive• Dimensionally stable throughout processing.• Thickness- 150-300µm

Function of base

• Functions of film base1. To provide support for emulsion layer.2. To transmit light to view image

Adhesive layer

• Preparation used is gelatin solution and solvent of film base.

• Colour dyes may be used sometimes to prevent crossover or transmission effect

• Ensures that emulsion adheres to base during manufacture and processing.

Emulsion• Microscopic crystals of silver-bromide &

silver iodide suspended in gelatin.• Gelatin – treated with mustard oil

1. Improves sensitivity2. Keeps silver halides uniformly dispersed3. Readily penetrated by processing chemical and

water

Super-coat

• Thin layer of clear gelatin.

• Emulsion1. Anti-abrasive layer2. Provide suitable surface characteristics

Types of films1. Duplitized emulsion films

a. Direct exposure (non-screen films) Dental films

1. Periapical2. Occlusal 3. Bitewing

Kidney surgery films Radiation monitoring films

b. Screen type films • Monochromatic/ Orthochromatic films

Duplitized films

Duplitized films

• Advantages

1. Increased sensitivity2. Increase image contrast3. Low machine load4. Low radiation dose to staff and patients5. No curling effect

Duplitized films

• Disadvantages

1. Loss of image qualitya. Crossover effectb. Parallax effect

2. Economic reasons

Dental films• Periapical Film: 31 x 41 mm for single or group of Teeth

• Occlusal Film: 57 x 76 mm film - mandibles or maxillae

• Bitewing film: 31 x 41 - Demonstrating the crown

Kidney 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.

Radiation Monitoring Film• Similar to the dental film in appearance but very important.• Different one side of the base is high speed of emulsion and

another for wide used of exposure level to be recorded.

Screen Type Film

• Pair intensifying screen• The lateral image being produce by light emission

from the screen and phosphor.• Wide range of different manufactures film are

available.1)Blue light sensitive- monochromatic2) Green light sensitive – orthochromatic

Single emulsion film1. Screen type –

a. Mammography

2. Non-screen typea. Photofluorography type – cine filmsb. Cathode ray tube (CRT) type –

USG, CT, MRI, DSA, Nuclear Medicinec. Duplication films – copy radiographd. Subtraction filmse. Polaroid films – Old USG filmsf. Laser imaging films

Single emulsion film

• To help identify the emulsion side of single coated film in darkroom, the manufacturer cuts a small notch into one edge of each film

Single emulsion film

• Advantages1. Good image quality2. Less expensive

• Disadvantages1. Curling problem

FILM FORMATS AND PACKAGING

• Standard Sizes– 8x10 in.– 10x12– 11x14– 14x14– 14x17

Other Sizes 8x12 in. 12x14 4x4 70 mm roll/sheet film 35 mm roll film

Packaging Available in 25 50, 100, and 500 sheets AFW (Alternate folded wrapped) NIF ( non-interleaved films)

Screen type film

• Used in conjunction with a cassette fitted with a single intensifying screen.

• Particular application mammography.• The film speed is medium to high contrast.• It is capable of demonstrating micro

calcification in soft tissue.

Non-screen type film

a) Photofluorography film: cine film, roll filmThese are films used to record the image produce at i)The output phosphor of an image intensifier tube.ii) The fluorescent screen of a camera system.

b) Cathode ray tube (CRT)• 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- USG, CT, MRI, Nuclear medicine, Digital subtraction imaging

c) Subtraction film 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

d) Duplication film 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 copy.

e) 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.

f) 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.

Non-curl backing• Present in single sided emulsion

films only.

• As emulsion swells during processing film tends to curl.

• Prevented by adding subbing and gelatin layer on opposite side of emulsion

Halation ?

• The ghost image produced out side the proper image, by the light transmitted through the base and reflected back from the base-air interface is called halation.

Anti-halation layer

• Depending upon angle at which the light strikes it may– Pass completely out of base.– Get reflected back producing halo around the proper image.

• Halation causes un-sharpness of image.

• Methods to prevent Halation1. Adding dye to non-curl backing2. Adding dye to base

Anti-halation layer

• When a colour dye is added to the anti-curl layer to prevent the effect of halation, it is called an anti-halation layer

Halation

Light from screen

emulsion

base

True image

Halation

Crossover effect

• Type of halation occurring in films used with intensifying screens.

• Prevented by adding dye which effectively absorbs incident light e.g. Magenta dye in Kodak x-ray films.

• Dye is removed during processing.

Crossover effect

Irradiation

• Sideways scattering of light within the emulsion due to striking of light on halides present in emulsion.

• Causes un-sharpness of image.

• Can be prevented by thinly coated emulsion.

Irradiation• This is the sideways scattering of light within the

emulsion itself as a result of the light striking the grains of silver halide

• This light contributes nothing to the image proper but becomes a source of image unsharpness.

• The use of thin emulsion layers produce less irradiation.

Parallax Effect

• When double emulsion film exposure light the image is formed in different position same object.

• More common in double emulsion film.