1. FILM CASSETTES & INTENSIFYING SCREENS WEEK 9
RTEC A Spring 2009
FILM
CASSETTES
& INTENSIFYING SCREENS
WEEK 9

2. Creating the IMAGE
When x-rays pass through a patient's body, three things can happen:
(1) the x-ray photon is transmitted, passing through the body, interacting with the film, and producing a dark area on the film;
(2) the x-ray photon is absorbed in an area of greater tissue density, producing lighter areas on the film; and
(3) the x-ray photon is scattered and reaches the film causing an overall gray fog.

4. Radiographic Images AIR, CO2 , Lungs BARIUM, IODINE, Bones
RADIOLUCENT - dark on image
AIR, CO2 , Lungs
RADIOPAQUE - white on image
BARIUM, IODINE, Bones

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

7. 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.

8. Image formation Remnant x-ray photons converted to light photons
Image before processing = Latent image
Made visible by chemical processing = Manifest image

9. 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

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

12. Cassette Features - Front
Exposure side of cassette is the “front”.
Has the ID blocker (patient identification)
Made of radiolucent material – easily penetrated by x-rays, lightweight metal alloy or plastic material made of resin.
Intensifying screen mounted to inside of front.

13. 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

14. 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

15. Intensifying Screens
Flat surface coated with fluorescent crystals called phosphors
that glow, giving off light when exposed to x-rays.

18. Image creation 1% of xray photons that leave patient
Interact with phosphors of intensifying screens
100’s of light photons created to make image on film
Light photons expose silver halide crystals in the film emulsion –
Turn black metallic silver after procession

19. 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

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

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

23. 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

24. Intensifying screens

25. Phosphor Layer Active layer – x-ray photons converted to light photons
*Photoelectric Effect

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

27. 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:

28. SCREEN SPEEDS FASTER SPEED – REDUCES PATIENT EXPOSURE
FASTER SPEED - REDUCES IMAGE DETAIL (LIGHT BLURING AROUND IMAGE)

29. FILM Standard Sizes in Inches 14 X 17 11 X 14 10 X 12 8 X 10 Metric:
18cm x 24cm
24cm x 30cm
30cm x 35cm
35cm x 43cm

30. 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:

31. RADIOGRAPH PERMANENT RECORD MADE USING RADIATION
RADIO- RADIATION (usually x rays)
GRAPH PERMANENT RECORD

32. FIRST “FILM”
GLASS PLATES
WW 1
CELLULOSE ACETATE
HIGHLY FLAMMABLE
EASILY TORN
RESPONSIBLE FOR MANY FIRES IN HOSPITAL BASEMENTS

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

34. 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

35. 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

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

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

38. X-Ray Film Cross Section

39. FILM CONSTRUCTION BASE WITH EMULSION CAN BE ON 1 (SINGLE EMULSION)
OR 2 SIDES (DOUBLE EMULSION)
MUST BE MATCHED WITH 1 OR 2 SIDED INTENSIFYING SCREENS

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

41. PARALLAX – each emulsion has an image single image overlaped – edges less sharp

42. 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

43. 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)

46. 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

48. FILM BIN - STORAGE

49. 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

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

53. FILM FOG!!!!
Unintended uniform optical density on a radiograph because of x-rays, light, or chemical contamination that reduces contrast & affects density

55. POOR SCREEN CONTACT
FOAM BACKING HELSP TO PLACE INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM – NO GAPS
IF GAPS – MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAIL

56. Intensifying Screen & Film Cross Section

59. Spectral Sensitivity OR SPECTRAL MATCHING Film 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

60. The light photons generated in the intensifying screen are emitted by phosphor crystals.
These crystals are significantly larger than the silver halide crystals in the film
use of a screen reduces image sharpness somewhat
Some examinations requiring extremely fine detail use screens with small crystals.

63. Questions?