Oral Radiology L02-2, 3

  1. Latent Image
    • The photons altered the chemical composition of the silver bromide in the film emulsion.
    • The altered silver bromide crystals contain the information that will become the radiographic image.
    • Until the film has been processed, the data is called the latent image - can't see it, looks same as unexposed film.
  2. Emulsion
    • Primarily silver bromide crystals in gelatin
    • Trace amounts of silver iodide, sulfur compounds, free silver ions.
    • Both sides of film are coated for maximum sensitivity to reduce the dose.
  3. Mechanism
    • Compton and Photoelectric interactions within the emulsion removes an electron from Br ion, forming Br atom.
    • Sulfur compounds and iodides produce sensitivity sites, which traps the free electrons moving through the crystal.
    • Silver ion reaches the sensitivity site and is reduced to a neutral silver atom, forming a latent image site, which becomes visible after processing.
  4. Developer
    • Converts these latent image sites into grains of solid silver by reducing the silver ions of AgBr around the sites to metallic Ag grains, the area becomes dark on the radiograph by blocking the light.
    • The darker areas are interpreted as radiolucency, corresponding to the tissue where the photons go through.
    • Developer does not work on the unexposed sites, and the areas remain clear on radiograph - radiopacity.
    • The pattern of dark and clear areas correspond to the radiographic properties of the tissues.
  5. Fixer
    Removes unexposed AgBr crystals, creating clear areas on the film, interpreted as areas of radiopacity.
  6. Film Processing
    • In a light-tight environment - darkroom.
    • Automated processors - miniature darkrooms.
    • Safelights - Film emulsions are relatively insensitive to certain wavelengths of light. Small light sources, with filters corresponding to these wavelengths used during processing.
    • Processing steps, manual or automated:
    • – Film is immersed in developer…
    • – Rinsed in a water bath (skipped in automated processing)…
    • – Immersed in fixer…
    • – Washed in a water bath …
    • – Dried
  7. Developing Solution
    • 4 components dissolved in water.
    • 1. Developer - Converts exposed AgBr in silver grains; unexposed crystals unaffected.
    • 2. Activator - Raises pH of developer to ~10 to activate it; gelatin swells, developer can infiltrate and interact with AgBr crystals.
    • 3. Preservative - Prevents developer to be oxidized and
    • extends its useful life; usually Sodium sulfite (Na2SO3).
    • 4. Restrainer - KBr and Benzotriazole, prevents development of unexposed AgBr crystals - overall fogging.
  8. RINSE
    • With water, drops the pH, stops developer activity.
    • Prevents deactivation of the fixer, which has an acid pH.
    • Automated processors skip this step, using fixers to stop developing.
  9. FIXER
    Dissolves and removes undeveloped silver halide crystals from the emulsion. Otherwise the film remains dark and nondiagnostic.
  10. FIXER components
    • 1.Clearing Agent - NH4 thiosulfate [(NH4)2S2O3], clears unexposed AgBr.
    • 2.Acidifier - acetic acid buffering system, maintains a constant acidic pH; inactivates any remaining developer.
    • 3.Preservative - Amonium sulfate, prevents oxidation of the thiosulfate clearing agent.
    • 4.Hardener - Aluminum sulfate combines w/ the gelatin, makes the emulsion less prone to damage from handling.
  11. Wash
    Removes thiosulfate ions and silver thiosulfate, which will cause brown stains on the radiographs if left in the emulsion. The stains only show up a week or two later.
  12. Darkroom
    • Light-tight.
    • Clean (Should not double as the lab! dust-free)
    • Controlled temperature - critical for the chemicals.
    • Proper ventilation.
    • Lockable door or maze to prevent unwanted white light from entering.
  13. Safelights
    • Not for a long time, will fog if > 5 min
    • <15 Watt, minimum 4 feet from opened and unprocessed films, prevents fogging
    • X-ray films are sensitive to blue-green light, a red GBX-2 safelight filter is used.
  14. Processing Tanks
    • One large tank with water - rinsing, washing, as well as a water jacket to maintain proper temperature for the developer and fixer.
    • Two smaller tanks - inserts for the developer and fixer.
    • Developer is placed at the left side and Fixer at the right.
    • The large tank should have a water inlet and a drain to provide continuous fresh water.
    • The tanks should be constructed of stainless steel (or certain plastics) to minimize chemical reaction with the processing chemicals.
    • Tanks should be covered when access is not required to reduce the premature oxidation of the chemicals.
  15. Film Hangers
    • Used to hold film while it is manually processed.
    • Uses either clips or slides to hold the film securely.
  16. Steps in Manual Processing - Get Ready!
    • Replenish or replace solutions as necessary.
    • Agitate solutions - do settle
    • Check temperatures and refer to chart.
    • Close door and turn on safelight.
    • Open and mount films on hanger - fast
    • Set timer.
  17. Steps in Manual Processing - Develop and Rinse
    • Immerse films in developer, agitate to dislodge air bulbs, and allow films to develop undisturbed.
    • At the end of the developing time, immediately remove the films from the developer and place them in the running water bath. Agitate the films for 30 seconds.
  18. Steps in Manual Processing - Fix and Wash
    • Immerse the film hanger in the Fixer solution. Agitate the films for 5 seconds every half minute to eliminate air bubbles and to bring the emulsion in contact with fresh fixer. Films are fixed for 10 minutes, or twice the developing time.
    • Rinse the film in running water for 15 minutes (3x developing time) to remove residual fixing and to ensure archival processing.
  19. Steps in Manual Processing - Dry
    • Dry the film on the hanger away from dust.
    • Shake the excess water from the film to avoid water spots.
  20. Automated Processor - Roller Transport
    • Carries the unwrapped film from one section of the automated processor to the next.
    • Squeegee action of the rollers may increase the energy of the developer, boosting resultant film speed from E to F.
  21. The Downside of automated processing
    • Grainy images due to higher temperatures.
    • Roller marks.
    • Mechanical breakdowns.
    • Need for meticulous care of processors
  22. Types of image receptors
    • Film
    • Digital receptors - Photostimuable Storage Phosphor (PSP), CCD/CMOS sensors
  23. Dr. Kells used impression compound to take the impression and used it as a bite tray to position and stabilize the film during exposure.
  24. Modern film is composed of
    • 1. The base - plastic, supports the emulsion; the thickness may create an offset in the double-sided images when viewed from an angle and appears as unsharpness.
    • 2. The emulsion - sensitive to x-radiation and light; on both sides of base (double-sided to decrease exposure time), covered by a gelatin overcoat to protect the emulsion from scratch
  25. Dose reduction
    Ability of film to absorb x-radiation and create an image. Has been quite low since 1960's
  26. Emulsion
    • Flexible to allow film to bend.
    • Thin homogenous mixture of pure gelatin containing silver halide grains sensitive to light and photons.
    • Trace amounts of gold- or sulfur-containing
    • compounds - improve the sensitivity of the silver.
  27. AgBr crystals
    • The size (microscopic) and shape affect the characteristics of the film.
    • Insight® film - tabular grains, oriented parallel to the film surface, to maximize their exposed surface area and shorten the exposure time.
    • Larger crystal, more efficient, lower image quality
    • Active constituents of the emulsion.
    • 95% silver bromide, 5% silver iodide.
    • High atomic number compared to base.
    • AgBr - sensitive to radiation, white light & pressure, hence fingernail mark artifact.
  28. Gelatin
    • Very pure (made from cattle bones).
    • Allows light and energy to penetrate unattenuated.
    • Vehicle to keep silver halide crystals evenly suspended.
    • Should not dissolve in water. It swells, allowing chemicals to penetrate and interact with silver halide crystals.
    • Shrinks evenly, leaving a smooth surface as it dries.
  29. Protective Coating
    • Very thin, non-abrasive, transparent layer of pure gelatin.
    • Covers both sides of film to protect emulsion from mechanical damage.
    • Without this layer, silver halide grains can react to gentle pressure of abrasion leading to dark spots or patches on the processed film.
  30. Film types
    • All x-ray film is sensitive to both x-ray photons and visible light.
    • direct exposure film - Intraoral film; intended to be exposed by X-ray photons only; produces high resolution images; requires a high dose of radiation; fives sizes (size 0 - 4).
    • - 0 is very tiny, don’t really see
    • - 1 is for kids
    • - 2 is regular periapical
    • - 3 is bitewing
    • - 4 is occlusal
  31. Film packet
    • Light-tight
    • Moisture-proof
    • Color-coded: speed and number of film
    • - pink: F, 2 films
    • - purple: F, 1 film
    • - red: E, 2 films
    • - gray: D, 2 films; prettier than E/F, not necessarily better diagnostically
    • - light blue: D, 1 film
  32. Film packet content - front to back
    • Tube-side, facing the radiation source
    • - White
    • - Matte or slightly pebbly to prevent slippage in the mouth.
    • - Embossed/raised Indicating Dot: distal for bitewings, occlusal/incisal for periapical; on the film(s), can be felt on the outside of the packet
    • Film - 1 or 2 sheets, surrounded by black, lightproof paper on both sides; black paper must be removed before processing.
    • Embossed lead foil backing - right next to the back side of the packet; Attenuates beam; Absorbs scattered radiation (back scatter) so it does not strike the film emulsion a second time from the back of the film; Tire track, herringbone or series of squares appear on the processed film if the film is reversed in the mouth and the image will lack density.
    • Back side of the packet is color coded
  33. Screen film
    • Extraoral imaging.
    • Always used with intensifying screens.
    • Sensitive to both x-ray and visible light
    • Special dyes in the emulsion sensitive to certain wavelengths of light, which is emitted by the intensifying screens.
    • Decreased resolution compared to direct film.
    • Lower dose radiation used - less exposure to the patient; shorter time, less movement during exposure; sharper image.
    • Common Oral & Maxillofacial applications:
    • – Panoramic.
    • – Lateral and Postero-antero cephalometric.
    • – Skull films (seldom used):
    • • PA.
    • • Townes.
    • • Waters.
    • • Lateral oblique
  34. Intensifying screens
    • Sheets of plastic coated with fluorescent phosphors, such as calcium tungstate or gadolinium or lanthanum.
    • Glow at a specific wavelength when hit with x-ray photons. The glow stops when the incident radiation stops.
    • Placed in intimate contact (short distance, makes the image as sharp as possible) with both sides of the film and held together like a sandwich in a cassette.
    • When the exposure is made, the intensifying screens fluoresce in proportion to the incident radiation. Some scatters but good enough for the purpose. The film is exposed by both the light and the incident x-ray photons. Less radiation to the patient.
    • Must match the film
Card Set
Oral Radiology L02-2, 3
Oral Radiology L02-2 Processing Radiographic Film Oral Radiology L02-3 X-ray receptors: films and screens