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

2. ALWAYS KEEP THE COLLIMATED AREA SMALLER THAN THE SIZE OF THE CASSETTE

3. Primary Radiation exit from tube 100 % enters patient 1% exits for form image on cassette below REMNANT Radiation

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

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

6. 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

7. 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.

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

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

10. 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

11. 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

12. 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

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

15. X-Ray Film Cross Section

17. 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

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

19. 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

21. 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

22. 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)

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

27. FILM BIN - STORAGE

28. 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

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

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

33. 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.

34. 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

35. 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

36. 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.

37. FILM ID PRINTER

38. 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

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

41. 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

42. Intensifying screens

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

44. 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

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

46. 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

47. 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

48. Intensifying Screen & Film Cross Section

49. 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.