Stacy Kopso, M.E.d. RT(R)(M) Film-Screen Stacy Kopso, M.E.d. RT(R)(M)

Density/Contrast/Patient dose As film speed increases density, As film speed increases contrast, As film speed increases patient dose, decreases As film speed increases detail,

Film Characteristics Emulsion layer Film base Silver halide crystals suspended in gelatin Radiation sensitive (silver halide) and light sensitive Film base Polyester layer Gives the film physical stability for handling and processing Blue tint to decrease eye strain when viewed on illuminator

Double emulsion film

Screen Film Used with one or two intensifying screens More sensitive to light and less sensitive to x-rays Single-emulsion screen film Emulsion layer on only one side/used with single intensifying screen Require higher exposure factors/yield greater detail Used for duplication,subtraction, CT, MRI, sonography, mammography, nuclear medicine and laser printing Double-emulsion screen film Emulsion coating on both sides of the base/used with two intensifying screens Most common x-ray film

Latent Image Formation Image that exists on film after that film has been exposed Before its is chemically processed Film processing Changes the latent image into a manifest image Manifest image Image that exists on film after exposure and processing Radiographic image

Latent Image Latent image centers appear as radiographic density on the manifest image after processing After enough silver is neutralized, the sensitivity specks in the silver halide crystals are converted to black metallic silver after chemical processing

Film Speed Degree to which the emulsion is sensitive to x-rays or light ↑ speed = ↑ sensitivity = less exposure needed to produce a specific density Primary factor in speed of film Silver halide crystals (in emulsion layer) # of crystals present ( #↑ = speed↑) Size of crystals (size ↑= speed ↑) Manufacturers manipulates both of these factors in the production of specific speeds of film Lower speed film= small crystal size and fewer number of crystals/ low sensitivity, more exposure is needed High speed(faster) film- large crystal size and increase in number of them/ high sensitivity, less exposure needed

Film Contrast Ability of film to provide a certain level of image contrast High-contrast= more black and white areas Low-contrast = shades of gray Film latitude Affects the range of radiation exposures that can provide diagnostic optical densities Higher contrast= narrow exposure latitude Low contrast= wider exposure latitude

Spectral Sensitivity The color of light to which a particular film is most sensitive Blue sensitive Green sensitive Film and screen need to match Film will be underexposed if it does not

Spectral Emission The color of light produced by a intensifying screen Blue light Green light Spectral matching Correctly matching the color sensitivity of film to color emission of intensifying screen

Intensifying screen

Intensifying Screen A device found in cassettes that contains phosphors that convert x-ray energy into light This light exposes the radiographic film Screens purpose is to intensify the action of the x-rays and thus permit much lower x-ray exposures compared with film alone Generally included two screens (front/back) Film is exposed to twice as much light Single screen is used for single emulsion film Screen is mounted on the backs side of the cassette (opposite side from the xray tube) Emulsion side of film is placed against the screen

Intensifying Screens Film is much more sensitive to visible light than to x-rays When screens are used, 90-99% of the total energy to which the film is exposed is light x-rays account for the remaining 1% to 10% of the energy Luminescence Emission of light from the screen when stimulated by radiation Fluorescence Ability of phosphors to emit visible light only while exposed to x-rays

Intensifying layer Phosphor layer Active layer Absorbs the x-rays(High absorption coefficiency) and converts them to visible light(High conversion efficiency). Transmits light to the radiographic film (High transmission rate) Phosphor materials are rare earth elements Relatively difficult and expensive to extract from earth

Screen Speed The capability of a screen to produce visible light Purpose Decrease the radiation dose to the patient Intensity the action of the x-rays by converting them to visible light Allows radiographer to use lower mAs Disadvantage Reduction in recorded detail Faster screen produces more light than a slower screen given the same exposure Faster screen reduces pt exposure but it degrades image resolution and increases quantum noise (too few photons reaching image receptor to form the image/ grainy appearance) find a balance Slower screen speed produces less light so more technique is needed/ better detail

Factors that affect Screen Speed Absorption efficiency Screens ability to absorb the incident xray photons Rare earth phosphor screen absorbs 60% of incident photons Conversion efficiency How well the screen phosphor takes these xray photons and converts them to visible light Thickness of phosphor layer Thicker layer contains more phosphor material(more light is produced/intensifying the screen speed) Size of phosphor crystals Larger crystals produce more light= faster screen Increased absorption and conversion efficiency mean that rare earth have increased speed compared to previous used phosphor calcium tungstate

Factors that affect Screen Speed (cont’d) Reflective layer Increases screen speed by reflecting light back toward the film Absorbing layer or dye in phosphor layer Decreases screen speed by absorbing light that would otherwise reach and expose the film Fast sppeds (400) is a good balance of decrease dosage while still maintaining detail Slower speed (100) labeled detail or extremity (tabletop exams only/low technique)

Screen Speed Par speed screen is given a numerical speed value equal to 100. A screen that requires one half the amount of radiation to produce a desired density is considered to have twice the speed of the par speed screen and would have a numerical value of 200. New mAs/Old mAs= Old screen speed/New screen speed

An acceptable radiographic image is obtained using exposure factors of 75kVp and 25 mAs with a 200 speed inmaging system. If the imaging system speed is increased to 400, what new mAs is required to produce an image of similar density? 12.5 mAs

Reflective layer increases screen speed by reflecting light back towards film Protective layer is above the phosphor layer

Screen Maintenance Daily cleaning of screen Film screen contact test Wire mesh tool/ placed on screen and exposed Screen B shows poor film-screen contact/local area of unsharpness (poor recorded detail)

Film Processing

Manifest Image The image that exists on the film after processing/radiographic image Exposure of the silver bromide crystal in the film emulsion by light or x-ray photons initiates the conversion Chemical processing of the exposed film completes the conversion of latent to manifest

Automatic Film Processor Chemical tanks, roller transport system, dryer system

Stages in Processing of a Radiograph Developing Fixing Washing Drying 90 second process Temperature of processor must be between 90-95°F

Developing Reducing agents Purpose Chemicals used (work together) Reduce exposed silver halide to metallic silver and to add electrons to exposed silver halide Chemicals used (work together) Phenidone Fast reducer, producing gray(lower) densities Hydroquinone Slow reducer, producing black(higher) densities Alkaline pH environment Needs an alkaline PH environment

Fixing Remove unexposed silver halide from the film Makes the remaining image permanent Secondary functions Stop the development process Further harden emulsions Fixing agent Ammonium thiosulfate Acidic pH environment Silver recovery unit

Washing Remove fixing solution from the surface of film If not properly washed, film shows a brown staining of the image fixing agent thiossulfate remained Process of washing Diffusion- exposes the film to water that contains less thiosulfate than film Wash water must be replaced frequently

Drying Remove 85 to 90% of the moisture from the film If films are dried excessively, the emulsion layers can crack (10-15% of water must be retained)

Systems Automatic processor Vertical transport system of rollers The film enters the feed tray Transport and crossover rollers ensure the film is moved into and through the tanks at a constant speed Electric motor/ on off power and standby control (shuts off when processor is not in use for awhile/reactivates when button is pushed)

Systems Replenishment Developer Fixer Replacement of fresh chemicals after the loss of chemicals during processing (developer/fixer) Developer Use and exposure to air, reducing chemical strength Fixer Silver halide removed as it is used during fixing process Developer solution remains in the film, decreases strength and activity of fixer Chemicals eventually become exhausted or inactive and their ability to perform their functions decrease Replenishment is preset in the processor/ bases on size of film or timed intervals

Systems Recirculation system Advantages Dryer Circulates the solutions in the developer and fixer In developer and fixer tanks Keeps the chemicals mixed Advantages Facilitates fast processing Helps to maintain proper temperature of developer solution 90 sec processor (93-95 degree) Immersion heater at the bottom of developer & fixer tan Dryer by pumping solution out of one portion of the tank and returning it to a different location within the same tank Temperature an increase or decrease in developer temp can adversely affect the quality of the radiographic image Most processors are controlled to heat the solution to its proper temp an maintain that temp for as long as the processor is turned on

Radiographic Appearance Processing Problem Decrease in density Developer exhausted Developer under replenishment Processor running too fast Low developer temp Developer improperly mixed Increase in density Developer over replenishment High developer temp Light leak in processor Pinkish stain Contamination of developer by fixer Developer or fixer under replenishment Brown stain Inadequate washing Emulsion removed by developer Insufficient hardener in developer Milky appearance Fixer exhausted Streaks Dirty processor rollers Inadequate drying Water spots Minus-density scratches Scratches from guide plates caused by roller or plate misalignment

Stacy Kopso, M.Ed., RT(R)(M) Quality Control Stacy Kopso, M.Ed., RT(R)(M)

Quality Control Film storage Vertically/ prevent pressure artifacts Away from white light, heat sources and radiation Shelf life of 18months Stored at 55-75° temperature Humidity of 30-60% Safelight that use filters for the type of film(blue or green light) and wattage matched with film (7.5-15W) Heat and radiation casue silver halide in film emulsion to break down/ results in fogged film Low humidity(no moisture) static charges can expose film Countertops and feed tray should be clean Film bin and walls lined with lead if wall backs up to xray room

Bending or kinking the film( plus density) Scratching with fingernails (plus density)

C- static discharge from sliding the film over a flat surface if there is to low humidity(plus density) D- moisture on techs finger (minus density) E- dirty screen (minus density)

Silver Recovery Fixer solution Used to remove unexposed silver halide from film Used fixer solution contains high concentration of accumulated silver Silver recovery(large volume facilities) Removal of silver from used fixer solution Connected to drain system of fixer tank Two methods Metallic replacement Steel wool Silver-extraction filter Electrolytic method Electrically charge drum or disk that attracts silver Steel wool silver replaces iron in steel wool and can them be removed easily after accumulation in a canister or replacement cartridge occurs Silver extraction foam filter that contains steel wool/ does the same as above Electrolytic once the drum is full/ remove it Silver is toxic to environment (follow local and stage agency rules for disposal)

Sensitometric Curve OD can range from 0-4 Useful range of optical density is .5-2.0 Straight line region is a properly exposed radiograph The radiation exposure to the film screen receptor determines the amount of OD created on the film after processing The intensity of the radiation exposure is a measurement of the amount and energy of the xrays reaching an area of the film When all other factors remain the same , increasing the exposure intensity, increases the optical density

Speed Point Closer to the y axis Determines the speed of the radiographic film

Slope and Film Contrast The steeper the slope, the higher the film contrast An increase in contrast= decrease in latitude

Exposure Latitude The range of exposures that produce optical densities within the straight-line region of the sensitometric curve Exposure latitude and Film contrast have an inverse relationship Wide-latitude film is a lower contrast film(cxr) Narrow-latitude film is a higher contrast film(skeletal)