1. Radiographic Film & Intensifying Screens
Bushong Ch 11 & 13

2. Objectives Review Film Review Intensifying Screens
Technique Changes for Screen Speeds

3. What is the function of radiographic film?
What is exit radiation? What is another name for exit radiation?
What is an IR? Name some examples

4. 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

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

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

7. Early Film base Cellulose Triacetate
Highly Flammable
Emulsion would crack & peel away from base when chemicals were too hot
RETICULATION

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
Emulsion is the “active” layer of film

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

11. Film Emulsion
Made of mixture of gelatin & silver halide crystals (fluorine, chlorine, bromine, & iodine)
Most x-ray film emulsions made of :
silver bromide (98%) silver iodide (2%)
Photographically active layer – activated by light & radiation to create image

12. Silver halide crystals
Crystals are cubic
in structure
Crystal lattice
containing ions

13. Film construction
Film is manufactured to have specific characteristics of speed, contrast & resolution
Film is also manufactured to be sensitive to specific colors of light = spectral matching
Direct-exposure film = thicker emulsion with more silver halide crystals

14. X-Ray Film Cross Section

16. 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

17. Image formation X-ray photons converted to light photons
Image before processing = latent image
Made visible by chemical processing
After proper chemical processing = manifest image

18. 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

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

20. Radiation interacts releasing e-
Silver atoms buildup at the sensitivity center, building the latent image center
The group of silver atoms is called the latent image center

22. 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

23. Processing
The term applied to the chemical reactions that transform the latent image into a manifest image

24. FILM direct exposure & screen-film or film-screen
SIZES
14 X 17
14 X 14
11 X 14
10 X 12
8 X 10

25. 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

26. Screen-Film Most widely used IR ??
Many Types of Film Used in Medical Imaging Table 11-1
Screen-Film has several characteristics to consider: contrast, speed, spectral matching, anticrossover dyes, and safe light requirements

27. Contrast Manufactured in multiple levels
High-contrast (black-and-white image)
Low-contrast (more gray)
Exposure LATITUDE = the range of exposure techniques that produce an acceptable image (medium, high or higher)

28. So what is the difference?
Depends on the size and distribution of the silver halide crystals
High-contrast = smaller crystals, uniform grain size
Low-contrast = larger crystals, wider range of sizes

29. Film Speed Single vs Double emulsion Size of Crystals
Thickness of emulsion
Intensifying screen used

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

31. Film 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:

32. 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

33. Screen speed vs Spatial resolution

34. 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)

37. FILM SPEEDS FASTER SPEED – REDUCES PATIENT EXPOSURE
FASTER SPEED - REDUCES IMAGE DETAIL

39. IMAGE ON FILM
Crossover is when the exposure of the emulsion by light is from the opposite side of the intensifying screen
Causes increased blur on the image

40. CROSSOVER
Reducing crossover by adding a dye to the base

41. Reducing Crossover
Changing the shape of the crystal improved light absorption and reduced crossover

42. Loss of Detail

43. 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

44. Film is either blue-sensitive or green-sensitive
Rare earth-
green emitting
screens must
use a red filter

45. Direct-Exposure Film Thicker emulsion and more crystals
Not sensitive to light
Not commonly used because of increased patient dose
Very detailed images

46. Laser Film Uses the digital electronic signal
The intensity of the laser beam is varied in direct proportion to the strength of the image signal = LASER BEAM MODULATION
The more intense the signal the darker the image

47. Laser printers
Provide consistent image quality for multiple film sizes. Most lasers only print on 14 X 17 regardless of initial IR
Printers can be linked to multiple users (CT, MRI, US & Computed Radiology)

48. Laser Film
Is silver halide film sensitive to the red light emitted by the laser
Laser film is light sensitive
Laser film must be handled in the darkroom in total darkness… Why?

49. Blue or Green filter would work

50. Duplicating film
Single-emulsion film (active layer toward the initial radiograph)
Exposure to light reduces OD on duplicating film (short time = dark film)
Light is exposed through the initial radiograph

51. FILM BIN - STORAGE

52. Film Storage Clean, dry location, light tight location
40 – 60 % Humidity º Fahrenheit
Away from chemical fumes
Safe from radiation exposure
Standing on edge
Expiration date clearly visible. Film can be stored for about 45 days, use the first-in first-out rule

55. Film Handling Do not bend or crease Hands must be clean
Film is sensitive to pressure and scratches
What happens if any of these happen?

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

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

58. QUESTIONS ?

59. Intensifying Screens
Bushong Ch 13

60. 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.

61. 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

62. Cassette Features - Front
Exposure side of cassette is the “front”.
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.

63. 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
Has the ID blocker (patient identification)

64. 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

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

66. 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

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

68. 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

69. 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

70. 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

71. Intensifying screens

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

73. Screen Speed
A relative number that describes how efficiently x-rays are converted into usable light
Ranges from 100 (slow) to 1200 (fast)

74. 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
Increasing speed also increases image noise

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

76. Technique Changes Relative Speed = Film speed & Screen speed
mAs = RS 2
mAs RS 1
They are inversely related

77. Image Noise Speckled background on the image
Caused when fast screens and high kVp techniques are used. Noise reduces image contrast
The percentage of x-rays absorbed by the screen is the detective quantum efficiency (DQE)
The amount of light emitted for each x-ray absorbed is the conversion efficiency (CE)

78. SCREEN SPEEDS
Quantum Mottle causing a grainy, mottled or splotch image
Often results of using very fast-speed screen-film systems

79. 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.

86. Image Quality

87. Rare Earth Screens
Have higher DQE (detective quantum efficiency). Higher x-ray absorption abilities.
Have higher CE (conversion efficiency). More light emitted per x-ray absorbed by the screen.

88. Spatial resolution
The use of intensifying screens lowers spatial resolution compared with direct-exposure radiographs.
Spatial resolution
expressed by the
number of line pairs
per millimeter
(lp/mm)

89. The higher the lp/mm the smaller the object that can be imaged
Very fast screens = 7 lp/mm
Fine-detail screens= 15 lp/mm
Direct-exposure screens = 50 lp/mm

90. Screen speed vs Spatial resolution

92. Wire mesh test – check for screen-film contact. Good contact

93. Wire mesh test – check for screen-film contact.
Warped cassette –poor contact

95. Care of Screens Image artifacts can appear if screens are modified
Small scratches can leave artifacts
Dirty screens can leave artifacts
Screens should be cleaned once each month with manufacturer’s cleaner with antistatic compounds

96. Questions?