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 FilmFilm 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. Base2. Emulsion
6 FIRST “FILM”GLASS PLATESWW 1CELLULOSE NITRATEHIGHLY FLAMMABLEEASILY TORNRESPONSIBLE FOR MANY FIRES IN HOSPITAL BASEMENTSCELLULOSE TRIACETATE
7 Early Film base Cellulose Triacetate Highly FlammableEmulsion would crack & peel away from base when chemicals were too hotRETICULATION
8 Film Construction - BASE Made of a polyester plasticMust be clear, strong, consistent thicknessTinted 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 emulsionEmulsion is a gelatin containing the film crystalsEmulsion is the “active” layer of film
10 FILM COMPOSTION SINGLE OR DOUBLE EMULSION EMULSION : GELATIN COATED ON A BASEEMULSION : GELATINWITH SILVER HALIDE CRYSTALSBASE: SUPPORT (POLYESTER)
11 Film EmulsionMade 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 cubicin structureCrystal latticecontaining ions
13 Film constructionFilm is manufactured to have specific characteristics of speed, contrast & resolutionFilm is also manufactured to be sensitive to specific colors of light = spectral matchingDirect-exposure film = thicker emulsion with more silver halide crystals
22 LIGHT VS DARK AREAS ON FILM DARK SPOTS – SILVER HALIDE CRYSTALS THAT HAVE BEEN EXPOSED TO PHOTONS – TURN TO BLACK METALLIC SILVER AFTER PROCESSINGLIGHT AREAS – NO CRYSTALS EXPOSED – SILVER HALIDE IS WASHED AWAY WITH PROCESSING
23 ProcessingThe term applied to the chemical reactions that transform the latent image into a manifest image
24 FILM direct exposure & screen-film or film-screen SIZES14 X 1714 X 1411 X 1410 X 128 X 10
25 Film Sizes Standard “inches”: 8” x 10” 10” x 12” 11” x 14” 14” x 17” Metric:18cm x 24cm24cm x 30cm30cm x 35cm35cm x 43cm
26 Screen-Film Most widely used IR ?? Many Types of Film Used in Medical Imaging Table 11-1Screen-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 crystalsHigh-contrast = smaller crystals, uniform grain sizeLow-contrast = larger crystals, wider range of sizes
29 Film Speed Single vs Double emulsion Size of Crystals Thickness of emulsionIntensifying screen used
30 Screen SpeedEfficiency 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 fastSpeeds for routine work: 200 – 800Speeds for high detail:
32 Film CharacteristicsSize of silver halide crystals & emulsion thickness determine speed of film and degree of resolutionSpeed – the response to photonsResolution – the detail seen
43 Spectral Sensitivity OR SPECTRAL MATCHING Film is designed to be sensitive to the color of light emitted by the intensifying screensBlue – UV light sensitive film – CALCIUM TUNGSTATE screensGreen, Yellow-Green light sensitive film -RARE EARTH screens
44 Film is either blue-sensitive or green-sensitive Rare earth-green emittingscreens mustuse a red filter
45 Direct-Exposure Film Thicker emulsion and more crystals Not sensitive to lightNot commonly used because of increased patient doseVery 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 MODULATIONThe more intense the signal the darker the image
47 Laser printersProvide consistent image quality for multiple film sizes. Most lasers only print on 14 X 17 regardless of initial IRPrinters can be linked to multiple users (CT, MRI, US & Computed Radiology)
48 Laser FilmIs silver halide film sensitive to the red light emitted by the laserLaser film is light sensitiveLaser film must be handled in the darkroom in total darkness… Why?
50 Duplicating filmSingle-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
52 Film Storage Clean, dry location, light tight location 40 – 60 % Humidity º FahrenheitAway from chemical fumesSafe from radiation exposureStanding on edgeExpiration date clearly visible. Film can be stored for about 45 days, use the first-in first-out rule
60 Cassettes Cassettes serve 3 important functions: Protect film from exposure to lightProtect 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 plasticInside back is a layer of lead foil – prevents backscatter that could fog the filmInside foil layer is a layer of padding – maintains good film/screen contactBack intensifying screen mounted on paddingHas the ID blocker (patient identification)
64 Image creation 1% of xray photons that leave patient Interact with phosphors of intensifying screens100’s of light photons created to make image on filmLight photons expose silver halide crystals in the film emulsionTurn black metallic silver after procession
65 Intensifying ScreensFlat surface coated with fluorescent crystals called phosphorsthat glow, giving off light when exposed to x-rays.
66 Intensifying Screens Phosphors RARE EARTH – (emits green light)Developed in 1980’sMost efficient – most common in use todayCALCIUM 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 filmBETTER DETAIL THAN FILM SCREEN (NO BLURRING OF IMAGE FROM LIGHT)ALL EXPOSURE MADE FROM X-RAY PHOTONSBIG DOSE TO THE PATEINT
69 Reduce patient exposure Increase x-ray tube life INTENSIFYING SCREENSDISADVANTAGES:less detail than direct exposure(detail better with rare earth thancalcuim tungstate screens)ADVANTAGES:Reduce patient exposureIncrease x-ray tube life
70 Screen Construction Polyester plastic base – support layer Phosphor layer – active layerReflective layer – increases screen efficiency by redirecting light headed in other directionsProtective coating
72 Phosphor Layer Active layer – x-ray photons converted to light photons *Photoelectric Effect
73 Screen SpeedA relative number that describes how efficiently x-rays are converted into usable lightRanges 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 fastSpeeds for routine work: 200 – 800Speeds for high detail: 50 – 100Increasing speed also increases image noise
76 Technique Changes Relative Speed = Film speed & Screen speed mAs = RS 2mAs RS 1They are inversely related
77 Image Noise Speckled background on the image Caused when fast screens and high kVp techniques are used. Noise reduces image contrastThe 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 SPEEDSQuantum Mottle causing a grainy, mottled or splotch imageOften 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 filmuse of a screen reduces image sharpness somewhatSome examinations requiring extremely fine detail use screens with small crystals.
95 Care of Screens Image artifacts can appear if screens are modified Small scratches can leave artifactsDirty screens can leave artifactsScreens should be cleaned once each month with manufacturer’s cleaner with antistatic compounds
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