Radiographic film

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
ARadiation interaction
releases electrons.
BElectrons 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. DThe process is
repeated many times
resulting in the build up
of silver atoms.
EThe remaining silver
halide is converted to
silver during
processing.

24. FThe 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.