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RTEC A Fall 2012

Learn about the different types of x-ray film, their construction, and the role of film cassettes and intensifying screens in image formation. Discover the characteristics of film, including speed and resolution, as well as proper film storage techniques.

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RTEC A Fall 2012

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  1. RTEC A Fall 2012 FILM CASSETTES & INTENSIFYING SCREENS WEEK 9

  2. FIRST “FILM” GLASS PLATES CELLULOSE ACETATE HIGHLY FLAMMABLE EASILY TORN RESPONSIBLE FOR MANY FIRES IN HOSPITAL BASEMENTS

  3. SIZES 14 X 17 11 X 14 10 X 12 8 X 10 FILM

  4. Standard “inches”: 8” x 10” 10” x 12” 11” x 14” 14” x 17” Metric: 18cm x 24cm 24cm x 30cm 30cm x 35cm 35cm x 43cm Film Sizes

  5. X-Ray Film • Film is a media that makes a permanent record of the image. • Image recorded on film is caused by exposure to photons.

  6. Image Formation • X-ray photons converted to light photons • Image before processing • Latent image • Made visible by chemical processing • Manifest image

  7. X-ray Film cont’d • Radiographic film was most common image receptor • Two parts: 1. Base 2. Emulsion

  8. Film Construction - BASE • Made of a polyester plastic • Must be clear, strong, consistent thickness • Tinted pale blue or blue-gray (reduces eye strain) • COATED ON 1 OR 2 SIDES WITH EMULSION

  9. Film Construction - EMULSION • Film emulsion can be on one side or both sides of base (single emulsion / double emulsion) • Protective overcoat layered on top of emulsion • Emulsion is a gelatin containing the film crystals

  10. Film Emulsion • Made of mixture of gelatin & silver halide crystals • Most x-ray film emulsions made of : silver bromide (90%) silver iodide (10%) • Photographically active layer – activated by light & radiation to create image

  11. FILM COMPOSTION • SINGLE OR DOUBLE EMULSION COATED ON A BASE EMULSION : GELATIN • WITH SILVER HALIDE CRYSTALS • BASE: SUPPORT POLYESTER

  12. X-Ray Film Cross Section

  13. IMAGE ON FILM • SINGLE EMULSION = BETTER DETAIL • DOUBLE EMULSION = LESS DETAIL • PARALLAX – single image • With double emulsion – an image is created on both emulsions – then superimposed – slight blurring of edges

  14. PARALLAX –each emulsion has an imagesingle image overlapped – edges less sharp

  15. LIGHT VS DARK AREAS ON FILM • DARK SPOTS – SILVER HALIDE CRYSTALS THAT HAVE BEEN EXPOSED TO PHOTONS – TURN TO BLACK METALLIC SILVER AFTER PROCESSING • LIGHT AREAS • NO CRYSTALS EXPOSED • SILVER HALIDE IS WASHED AWAY WITH PROCESSING

  16. Film Characteristics • Size of silver halide crystals & emulsion thickness determine speed of film and degree of resolution • Speed – the response to photons • Resolution – the detail seen

  17. Film Speed / Crystal size • Larger crystals or Thicker crystal layer • Faster response= less detail, and less exposure (chest x-ray) • Finer crystals / thinner crystal layer • Slower response, greater detail, more exposure (extremity)

  18. Amount of Crystals • More silver halide crystals = faster film • Less silver halide crystals= slower film

  19. FILM BIN - STORAGE

  20. Film Storage • Clean, dry location • 40 – 60 % Humidity 70 º Fahrenheit • Away from chemical fumes • Safe from radiation exposure • Standing on edge • Expiration date clearly visible

  21. Light X-rays Gamma Rays Gases Fumes Heat Moisture Pressure Static Electricity Age X-ray Film Sensitivity So what happens??

  22. FILM FOG!!!! • Unintended uniform optical density on a radiograph • Get a long scale of contrast

  23. Cassettes Cassettes serve 3 important functions: • Protect film from exposure to light • Protect film from bending and scratching during use. • Contain intensifying screens, keeps film in close contact to screen during exposure.

  24. Cardboard Cassettes Direct x-ray exposure to film required • 25 to 400 times more radiation to create an image on the film • BETTER DETAIL THAN FILM SCREEN (NO BLURRING OF IMAGE FROM LIGHT) • ALL EXPOSURE MADE FROM X-RAY PHOTONS • BIG DOSE TO THE PATEINT

  25. CASSETTE or FILM HOLDER • The CASSETTE is used to hold the film during examinations. • It consist of front and back intensifying screens, and has a lead (Pb) backing. • The cassette is light tight

  26. Cassette Features - Front • Exposure side of cassette is the “front”. • Has the ID blocker (patient identification) • Made of radiolucent material • Intensifying screen mounted to inside of front.

  27. Cassette Features - Back • Back made of metal or plastic • Inside back is a layer of lead foil – prevents backscatter that could fog the film • Inside foil layer is a layer of padding – maintains good film/screen contact • Back intensifying screen mounted on padding

  28. FILM CONSTRUCTION • MUST BE MATCHED WITH 1 OR 2 SIDED INTENSIFYING SCREENS • Single emulsion film is used with single intensifying screen.

  29. Screen Construction • Polyester plastic base – support layer • Phosphor layer – active layer • Reflective layer – increases screen efficiency by redirecting light headed in other directions • Protective coating

  30. Intensifying screens

  31. Intensifying Screens • Flat base coated with fluorescent crystals called phosphors • Active layer- (phosphors) give off light when exposed to photons (x-rays)

  32. Intensifying Screens Phosphors • RARE EARTH – (emits green light) • Developed in 1980’s • Most efficient • Most common in use today • CALCIUM TUNGSTATE (blue light) • Not as efficient • Not used as often

  33. Rare Earth Screens • Gadolinium • Lanthanum • Yttrium • Found in low abundance in nature

  34. INTENSIFYING SCREENS DISADVANTAGES: • less detail than direct exposure (detail better with rare earth than calcium tungstate screens) ADVANTAGES: • Reduce patient exposure • Increase x-ray tube life

  35. Spectral Sensitivity ORSPECTRAL MATCHINGFilm is designed to be sensitive to the color of light emitted by the intensifying screens • Blue – UV light sensitive film – CALCIUM TUNGSTATE screens • Green, Yellow-Green light sensitive film - RARE EARTH screens

  36. Intensifying Screen & Film Cross Section

  37. The light photons are emitted by phosphor crystals. • These crystals are significantly larger than the silver halide crystals in the film • Screen reduces image sharpness • Exams requiring extremely fine detail use screens with small crystals.

  38. Screen Speed • Efficiency of a screen in converting x-rays to light is Screen Speed.

  39. Screen Speed • Greater efficiency • less exposure - faster • Standard screen speed class of 100 • 200 screen speed is twice as fast • Speeds for routine work: 200 – 800 • Speeds for high detail: 50 - 100

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