1. FILM CASSETTES & INTENSIFYING SCREENS WEEK 9
RTEC A SPRING 2010
FILM
CASSETTES
& INTENSIFYING SCREENS
WEEK 9

2. ALWAYS KEEP THE COLLIMATED AREA SMALLER THAN THE SIZE OF THE CASSETTE
You should always see a 4 sided borders.

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
Cellulose acetate is a base that was highly flammable.

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

6. Film Sizes 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
There are problems with film and cassettes. If you have a metric film and a standard cassette, they are not compatible.
IF you user a smaller film inside a larger cassette, it can be used but often times people will clip.

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
The light from the screen and emulsion creates the actual image on the film.

9. X-ray Film cont’d Radiographic film was most common image receptor
Two parts:
1. Base
2. Emulsion
Base is like the bread and emulsion is like the peanut butter
Emulsion is the active layer of the film.

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
Single emulsion you can get better detail but you must use more radiation.
Double emulsion you use less radiation but you get less detail
With single emulsion you place the active layer closest to the intensifying screen.
There is protective coat on top of the emulsion to protect the 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
There is a protective coat on the emulsion to protect from handling damage
Gelatin is filled with silver halide 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
They used to be round but now they are more flat.

13. FILM COMPOSTION SINGLE OR DOUBLE EMULSION EMULSION : GELATIN
COATED ON A BASE
EMULSION : GELATIN
WITH SILVER HALIDE CRYSTALS
BASE: SUPPORT
POLYESTER
When the silver halide crystals are exposed to xrays and processed the silver turns to black metallic silver.
The fixer washes away all the unexposed silver halides.

14. Some film is manufactured to give me more shades of gray or black and white. This is part of the film construction.
More detailed- slower speed.

15. X-Ray Film Cross Section
Supercoat is like a top coat on nail polish. Or the waxing on a car to protect the car.
This document is on the web page for your review.

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
The light blurring from the screen only comes from one side.

18. PARALLAX – each emulsion has an image single 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
We rate film by its speed, the thicker the film the faster the film, but we get less detail.

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)
Slower cassettes are called extremity cassettes.

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

24. Some film have a lot of silver in the films and others have few.
Xrays are so expensive because we have to have silver in the film.
Right side is a faster speed of film because it has more crystals.
Left side is slower.

26. The right side is faster film because it has bigger crystals.

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
You have to store it upright because they will warp.

31. X-ray Film Sensitivity
Light
X-rays
Gamma Rays
Gases
Fumes
Heat
Moisture
Pressure
Static Electricity
Age
This is what xray film is sensitive to.
It gets fogged if it is exposed to these things.
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
These do not have screens, we get great detail. But it takes 25 to 400 times the radiation.
200 mas with 50 kvp.
2 mas with intensifying screens.

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.
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.

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

39. Right side has better detail but takes more image to the patient to see the resolution better.

40. FILM CONSTRUCTION
MUST BE MATCHED WITH 1 OR 2 SIDED INTENSIFYING SCREENS
Single emulsion film is used with single intensifying screen.
Emulsion must be towards the light (intensifying screen) on a single emulsion.
If you have two films the image will be too light.

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
Calcium tungstate was a slower film.

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

46. Reduce patient exposure Increase x-ray tube life
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 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

48. Intensifying Screen & Film Cross Section
Now we have an image of the film with the intensifying screen.

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.
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

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

56. Screen Speed Greater efficiency Speeds for routine work: 200 – 800
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:
The 50 speed you have to use double the exposure. Because it is a slower film.

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

58. Low contrast detailed cassette on left.
On right used a regular cassette.

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

60. Film on bottom does not have good film screnn contact
Film on bottom does not have good film screnn contact. So the image is blurry and it dereases the detail.

61. 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

63. QUESTIONS ?