Presentation is loading. Please wait.

Presentation is loading. Please wait.

Radiographic Film & Intensifying Screens Bushong Ch 11 & 13.

Similar presentations


Presentation on theme: "Radiographic Film & Intensifying Screens Bushong Ch 11 & 13."— Presentation transcript:

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 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 in structure  Crystal lattice containing ions 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

15

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 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

21

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) High-contrast (black-and-white image) Low-contrast (more gray) 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: 50 - 100

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) less exposure (chest x-ray)  Finer crystals / thinner crystal layer =Slower response, greater detail, more exposure (extremity)

35

36

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

38

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 green emitting screens must screens must use a red filter 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 70 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

53

54

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: 1. Protect film from exposure to light 2. Protect film from bending and scratching during use. 3. 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 INTENSIFYING SCREENS DISADVANTAGES:  less detail than direct exposure  (detail better with rare earth than  calcuim tungstate screens) ADVANTAGES: 1. Reduce patient exposure 2. 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 1 = RS 2  mAs 2 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.

80

81

82

83

84

85

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

91

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

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

94

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?


Download ppt "Radiographic Film & Intensifying Screens Bushong Ch 11 & 13."

Similar presentations


Ads by Google