Transcript Radiographic Film

Chapter 19
Radiographic Film
Radiographic Film
• Diagnostic radiographic film is manufactured by
coating both sides of a base material with an
emulsion containing photosensitive crystals.
• Several other materials are also used to improve
the performance and permanence of the film:
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Base
Adhesive
Emulsion with crystals
Supercoat
Film Base
• Originally composed of a glass plate.
• Cellulose nitrate once used but extremely
flammable.
• Nonflammable cellulose triacetate introduced in
1920s.
• Modern plastic bases (polyester introduced by
DuPont in the 1960’s) solve problems such as
cut fingers from broken films and strained backs
from carrying and filing stacks of heavy
radiographs.
Film Base
• Flexible yet tough
– Permit easy handling in the darkroom.
– Make good contact with cassette pressure pads.
• Stable
– Does not change its dimension during the heating and
immersion in chemicals required for processing.
• Rigid
– To be placed onto viewbox.
• Uniformly lucent
– Permits transmission of light without adding artifacts
to the diagnostic image.
Reflections
• Crossover effect: blurring of the image caused
by light from one screen crossing into the light
from another screen.
• Halation: an effect on a radiographic image
caused when light that is reflected from the air
interfaces on the back of the base material.
– Antihalation coating: a substance applied to the back
of a single-emulsion film designed to absorb light
coming from the emulsion and preventing
backscatter, (removed by the processing chemicals to
permit light to be transmitted through the film for
viewing).
Adhesive
• Designed to glue the emulsion to the base
and prevent bubbles or other distortion
when the film is bent during processing or
handling, or when it is wet and heated
during development.
Emulsion
• Composed of gelatin in which photosensitive
silver halide crystals are suspended.
– Acts as a nonreactive, neutral lucent suspension
medium for the silver halide crystals (silver bromide,
silver iodide, and silver chloride) that must be
separated from one another to permit processing
chemicals to reach them.
– Distributes the crystals evenly over the surface of the
film- preventing clumps that would make one area of
the film more photosensitive than another.
Supercoat
• Layer of hard protective gelatin designed
to prevent the soft emulsion from being
abused physically or chemically.
Manufacturing
• Radiographic film is manufactured in four
stages:
– Crystal production
– Ripening
– Mixing
– Coating
Crystal Production
• AgNO3 + KBr
AgBr + KNO3
• Gelatin must be present:
– A medium to permit the crystals to form
– Limit oxidation and reduce crystal surface tension
– Facilitate other reactions
• Conventional grain
• Tabular grain:
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Larger more evenly dispersed
Absorption of a greater portion of the exposing photons
Reduced light crossover from one emulsion to the other
Reduced silver coating requirements
Crystal Structure
• Structure permits both free
silver atoms and free
electrons to drift through the
lattice- key to the formation
of the latent image.
• Negatively charged surfaces
• Positively charged exteriors
• Sensitivity speck: must be
present to provide film
sensitivity
– Serve as electrodes to attract
the free silver ions
• Bromide: serve as ion pumps
to assist in the deposition of
silver.
Ripening
• Period during which silver halides are
allowed to grow
• Size of the crystal determines their total
sensitivity.
• At the proper time, emulsion is cooled,
shredded, and washed to remove KNO3
(potassium nitrate)
Mixing
• Colored dyes: improve the sensitivity of the
silver halides to match the wavelengths of
photons that will be striking the emulsions during
exposure.
– Panchromatic: sensitive to al colors
– Orthochromatic: not sensitive to the red spectrum
• Hardeners: to prevent physical trauma
• Bactericides and fungicides
• Antifogging agents: to decrease sensitivity to
environmental factors, such as heat.
Latent image formation
• The latent image is the unseen change in the
atomic structure of the crystal lattice that results
in the production of a visible image.
Latent image formation
Types Of Film
• Direct Exposure/ nonscreen films
• Intensifying screen films
• Special Application Films
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Mammography
Detail extremity radiography
Contact surgical radiography
Cathode Ray Tube (CRT) imaging
Laser Films
Duplication Films
Fluoroscopic spot filming
Direct Exposure/ Nonscreen films
• Used primarily for industrial nondestructive testing (NDT)
radiography.
• When extremely fine detail is critical to the diagnostic
quality of the image (extremely high radiation exposure).
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Dental
Reconstructive surgery of the hands
Biopsy specimen
Forensics
• Single emulsion, extremely fine grain silver halide
crystals, much greater silver content.
• Thicker emulsion layer to achieve sufficient sensitivityrequires manual processing.
Intensifying Screen Films
• Wide variety of speeds (controlled by the
size of the crystals and the thickness of
the emulsion), contrast ranges, latitudes,
and resolutions.
– Larger crystals and thicker emulsions usually
provide lower contrast, wider latitude, and
less resolution.
• Double emulsion
Special Application Films
• Fine grain films sensitive to a single screen:
– Mammography: x-ray examination of the breast
– Detail extremity radiography: imaging that uses
slower speed films
• Contact surgical radiography: nonscreen film in
sterilized packages
• Cathode Ray Tube (CRT) imaging Video
imaging): requires a film that is sensitive to the
light emitted by the CRT
Special Application Films
• Lasers films: directly exposed by the laser used in the
imaging camera
– Film must be sensitive to the frequency of light emitted by the
particular camera.
– Produces near distortion free images
• Duplication film: designed to provide an exact image of
the original film.
– Single emulsion
– Chemically fogged to D-Max – further exposure decreases
optical density (OD).
• Fluoroscopic spot filming: imaging that is done with 70
mm roll film or 105 mm film chips that are sensitive to
green light.
Film Storage and Handling
• Film should be stored at a temperature of 68* F
or lower at all times.
• Films must be brought to room temperature in
advance of use.
• Humidity must be maintained between 30 and
60 percent.
• Photosensitive materials must be protected from
unfiltered light.
– Lead lining of storage area.
• Film should be stored on end.
Film Identification
• Should be permanently identified with
medical record information.
– Date of exposure
– Full name of patient
– Institution exposure made
– Referring physician
– Patient identification number
– Examination ordered