Radiographic recording
Film Materials
Film groups


X-ray films
• Films exposed to X-radiation alone –
(Direct exposure film)
• Films exposed to x-radiation and light –
(Screen type film)
(these are usually of double sided
emulsion)
Films exposed to light only. E.g.
fluorographic films, duplicating films, Cine
films
(these are of single sided emulsion)
Film structure
Double sided
emulsion
Base
Single sided
emulsion
Base
Super coat
Emulsion
Substratum
Anti halation/curl
Film base




Polyester made from polyethlene
terepthalate resin is used now
It is extremely strong and untearable
Demonstrate high dimensional
stability
Cellulose triacetate was used before
Functions of film base


To provide a support for the emulsion
layer
To transmit light so that an image
can be viewed
Desirable characteristics of film base
1. Transparent, free from any defect,
uniform transmission of light
2. Strong but flexible to
1. Withstand mechanical stress during
processing and handling
2. be made thinner to minimize parallax
(0.18 mm for sheet film, 0.08 for roll
film)
3. Uniform in thickness
4. Dimensionally stable during
processing
Desirable characteristics of film base
5. Impermeable to water or
processing solutions
6. Non- flammable
7. Chemically inactive
8. Uniform in colour, if a colour tone is
added during manufacture
The subbing layer / adhesive layer

This is required,
1. To ensure that emulsion layer adheres
to the smooth and shiny base during
manufacture
2. To prevent any separation of the
emulsion layer from the base during
processing

A mixture of gelatin solution and
solvent of the film base is used
The emulsion layer





This is a layer of silver halide suspended in
gelatin
It is coated on the subbing layer
The shape of crystals is important , it
affects the sensitivity of the film and the
sharpness of the image
Kodak is pioneer in producing flat grain
emulsion
Light absorbing magenta dye is added to
the surface of the grains to increase the
sensitivity and to absorb the irradiating
light within the emulsion so that
unsharpness produce by that way is
reduced
The supercoat


This is a thin layer of gelatin which is
applied to the emulsion
The prime functions are:
• To protect the emulsion from the effect
of pressure or abrasion.
• To provide suitable surface
characteristics; sufficiently glossy to
reduce accumulation of dust; not too
glossy as to prevent the grip by the
rollers of processor.
Non-curl backing




Present only in single emulsion sheet film.
Function is to prevent the tendency of the
film to curl when the emulsion swells
during processing.
This is a gelatin layer coated on a subbing
layer
It swells equally as the emulsion layer and
counteract the swelling of emulsion on the
other side.
Anti-halation layer

When a colour dye is added to the
anti-curl layer to prevent the effect
of halation, it is called an antihalation layer
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.
Light from screen
emulsion
base
True image
Halation
Halation
Prevention of Crossover effect




Crossover effect is a type of halation occur
when using double sided emulsion films
with two intensifying screens.
I.e. The light from one screen crosses the
base and produces a ghost image on the
opposite emulsion
To prevent this a colour dye (magenta for
green sensitive films) is added to the
surface of the emulsion.
The dye has the effect of reducing the
light scattering within the emulsion and,
at the same time limiting crossover and
thus image unsharpness
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.
Films for medical imaging

Duplitized emulsion films
• Direct exposure films :- Dental x-ray films,
Radiation-monitoring films
• Screen type films used with two intensifying
screens:- General radiography films

Single emulsion films
• Screen type film used with single screen
• Photofluorography films :- Cine film, 70mm & 105
mm roll film, 100 mm sheet film
• Cathode ray tube (CRT) photography films
• Duplication films
• Subtraction films
• Laser imaging films
End