2. History
 By the time x-rays were discovered, photography
was already an art.
 Photographic film with a nitrocellulose base was
already being marketed by George Eastman.

3.  The first x-rays were recorded on glass plates.
 These were coated with emulsion on one side
only.
 The exposure dose was quite high.

4.  Glass plates were used until World war I.
 During WWI, nitrocellulose based film was found
to be a more feasible choice for recording x-rays.
 This film was single-emulsion.

5.  It was later discovered that double-emulsion
responded to x-rays faster.
 The flaw with nitrocellulose based film was its
easy flammability.
 In 1924, cellulose acetate replaced the
nitrocellulose based film.

6. The Radiographic Film
 A Radiographic film is similar in construction and
characteristics to a photographic film.
 Its spectral response is different from
photographic film but its mechanism of
operation is the same.

7.  The film is sandwiched between the radiographic
intensifying screens in a protective cassette.
 The intensifying screens change the x-rays into
visible light. The visible light exposes the
radiographic film.

8. Film Structure
Radiographic Film has
two basic parts.
 Base
 Emulsion
Most films have two
layers of emulsion so
these are referred as
Double Emulsion Film.

9. An adhesive layer
attaches the emulsion
to the base.
The emulsion is
enclosed in a
protective layer of
gelatin called the
overcoat.

11. Transparent Base
 It is the foundation of
the film. 150 to 300 µm
thick.

12. Transparent Base
 Provides a surface and support for the
emulsion.
 It must have strength, but it should be flexible.
 Most film bases are composed of polyester.

13.  Polyester can withstand higher temperatures
and is more fireproof.
 The base is usually tinted blue to reduce light
glare.
 Amount of tint varies per specifications of
different manufacturers.

14. Emulsion
 The emulsion is the heart of the film.
 The x-rays or light from the intensifying screens
interact with the emulsion and transfer
information to the film.
 A homogeneous mixture of gelatin and silver
halide crystals and is about 3 to 5 µm thick.

15. Gelatin
 The gelatin is clear so it transmits the light to the
silver halide crystals.
 It is porous so the processing chemicals can
easily penetrate to the silver halide crystals.
 The primary function of the gelatin is to provide
a support medium for the silver halide crystals by
holding them in place.

16. Silver Halide Crystals
 98% Silver Bromide
 2% Silver Iodide
 May be
tabular,cubic,octahedr
al,polygonal in shape.
 Tabular shape used
most commonly for
general radiography.
 About 0.1µm thick and
1µm in diameter.

17. Silver Halide Crystals
 The differences in speed, contrast and resolution
depends upon the process by which the silver
halide crystals are manufactured.
 From the time the emulsion ingredients are
brought together until the film is packaged, the
whole process occurs in complete darkness.

18. The Latent Image
 Invisible image produced on the film after
exposure prior to development.
 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.

19. The Latent Image Formation
 This interaction is sometimes referred to as the
photographic effect.
 This process is not well understood and is still
under research.
 The Gurney-Mott theory is presently an
acceptable explanation of the photographic
effect.

20.  Ionic structure of silver halide crystal
 Bromide and iodide ions are mostly
concentrated on the surface of crystal giving it a
negative charge.
 The silver ions are inside known as interstitial
silver ions,so inside is positively charged.

21. The Latent Image Formation
A Radiation interaction
releases electrons.
B Electrons migrate to
the sensitivity
center(contaminant in
the silver halide
crystal,usually silver
sulfide).

22. C At the sensitivity
centre, atomic silver is
formed by attracting an
interstitial silver ion---
latent image centre.

23. D The process is
repeated many times
resulting in the build up
of silver atoms.
E The remaining silver
halide is converted to
silver during
processing.

24. F 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.

25. Types of Films
 Screen films most commonly used.
 Screen film used with intensifying screens.
 Single emulsion- emulsion on one side of base.
 Double emulsion used with two screens.
 Direct exposure film or non-screen film.
 Special purpose films

26. Standard screen-film sizes
English Units SI Units
7 x 7 in 18 x 18 cm
8 x 10 in 20 x 25 cm
10 x 12 in 24 x 30 cm
14 x 14 in 35 x 35 cm
14 x 17 in 35 x 43 cm

27. Screen Film Factors
 Main factors to be considered when selecting
film
a) Contrast & Speed
b) Crossover
c) Spectral matching
d) Reciprocity Law
e) Safelights

28. Contrast
 Contrast of a film depends on its latitude.
 Latitude is the range of exposure techniques that
produce an acceptable image.
 Latitude is inversely proportional to contrast.

29.  High contrast film has low latitude
 Medium contrast film has medium latitude
 Low contrast film has high latitude
 High contrast has small uniform grains
 Low contrast has larger grains and wide range in
size.

30. Speed
 It is the sensitivity of film to x-rays and light.
 The size and shape of the silver halide crystals
are the main factors that determine speed.
 Faster speed films are almost always double
emulsion.
 Light spectrum from screens must match to
achieve optimum speed.

31. Crossover
 Crossover is the
exposure of an
emulsion by light from
the opposite
radiographic
intensifying screen.

32.  Reducing crossover by
adding a dye to the
base

33.  Crossover causes blurring of the image.
 Can be reduced by
 Tabular grains---flat, large surface area to vol
ratio
 Addition of a light absorbing dye in crossover
control layer.

34. Spectral Matching
 The most important consideration in selecting
screen film is spectral absorption matching.
 The material in the screen will determine the
color of light emitted by the screen.
 Special dyes in the film are used to match the
screen to the film.

35. Spectral Matching
 Calcium Tungstate screens emit blue and blue
violet light.
 Replaced by Rare earth screens.
 Rare earth screens emit ultraviolet, blue, green
and red light.

36. Spectral Matching
 If the light spectrum does not match, there will
be a significant loss of speed alongwith increased
patient dose.

37. Reciprocity Law
 In radiography, it is generally assumed that the
total exposure of a film depends only on the total
quantity of radiation (mAs) and not on the
exposure time. This is known as the reciprocity
law.
 Reciprocity law
Exposure=intensity x time
=Constant Optical Density

38. Reciprocity Law
 The reciprocity law is true for film exposed
directly to x-rays.
 It fails when film is exposed to light from
radiographic intensifying screens.

39.  Reciprocity law failure is important when the
exposure times are very long (as in
mammography)or very short (angiography).
 The result is a loss of speed.
.

40. Safelights
 Working with film in
the darkroom requires
special lighting to
avoid exposure of the
film.
 Filters are used to
avoid exposure of the
film.

41. Safelights
 An amber filter can be used for blue sensitive
film only.
 A red filter is used for blue-green sensitive film.
 The color is not the only concern, the wattage of
the bulb and distance between the lamp and
work surface is also very important.

42. Special Film Types
 Direct exposure film: used without intensifying
screen.
 were used for small body parts.
 Requires 10 to 100 times more exposure. The
emulsion is thicker than screen film.
 Renders excellent detail. No longer used.

43.  Single emulsion film: once used for extremities
but now most extremity cassettes are double
screen type.
 Again required more exposure.

44.  Mammography Film: Only single emulsion film
currently used in modern radiography.
 Laser Film: Used in with a laser printer for digital
radiography, CT and MRI.

45.  Subtraction Film: used in angiography to do
subtraction where the bone is removed for
better visualization of the arteries.

46.  Spot film: Special roll film of 70 to 105 mm width
used in fluoroscopy.
 Can be processed in x-ray film processor.

47.  Cine film:
 35 mm black & white film supplied in rolls of 100
and 500 ft
 used in coronary angiography.
 Requires motion picture film processor.

48. 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.

49.  Improper handling of the film will result in poor
image quality due to artifacts.
 Avoid bending, creasing or rough handling of
the film.
 Avoid sharp objects contacting the film.

50.  Hands must be clean and dry.
 Avoid hand creams, lotions or water free hand
cleaners.
 Static electricity or a dirty processor can cause
artifacts.

51.  Film is sensitive to heat and humidity.
 Heat and humidity causes fog or a loss of
contrast.
 Film should be stored at less than 20º C (68ºF)
 Humidity should be between 40% and 60%.

52.  Film must be handled and stored in the dark.
 Low level diffuse light causes fog.
 Bright light causes gross exposure.
 Luminous watches, cell phone and darkroom
light leaks should be avoided.

53.  Films should be used no longer than the stated
Shelf life.
 The oldest film in stock should always be used
first.
 Expired film results in loss of speed and contrast
and an increase in fog.