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:– 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:

– 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

– 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).– 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 sensitivity- requires 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