Radiology Film Processing.docx

8/11/2019 Radiology Film Processing.docx

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There are two sides of the darkroom:

1) Dry Side2) Wet side

1) Dry Side:

Flim processing consists of five basic steps:

1. Developing2. Rinsing3. Fixing4. Washing5. Drying

Chemicals:

Chemicals can be purchased in variety of ways. The chemicals may be in concentrated form andmay need to be diluted. Preparing thesolution correctly in important or it mayaffect the final radiographic film. Chemicalsshould be kept at specified room

temperature.

Variances may adversely affect the

radiographic product. Too low temps, some of the

chemicals may become sluggish in action and produce an under-developed or under-fixed radiograph.

Too high temperature may be too hot for manual control.

All chemicals should be kept at same temperature. Variances in temperature between the chemicalscan result in film reticulation. Reticulation refers to the darkroom artifact produced by variablechemical temperatures that cause irregularexpansion and contraction of the film emulsion,

resulting in a mottled density appearance.

1) Developer

Figure 1 Reticulation


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It is a chemical solution that converts the latent image to a visible image. Primary function is to convertthe exposed silver halide crystals to black metallic silver .Developing time is specified by chemicalmanufacturer. Developer temperatures affects the developing time.

The manual developer solution is composed of four basic agents: an activator,reducers, a restrainer, and a preservative. Each of the agents is mixed with water,

which acts as a solvent. Because each of the agents has its own specific function, eachone will be dealt with in a separate paragraph.

a. Activator. The activator (or alkali), sodium carbonate, softens the gelatin of theemulsion and provides the necessary alkaline medium to the solution so that thereducing agents can diffuse into the emulsion and attack the exposed silver bromidecrystals. In general, the more alkaline the developer, the more powerful and rapid is itsaction. A disadvantage of sodium carbonate is that when a film is processed in an x-raydeveloper containing it and then transferred to a warm acid-fixing bath, tiny bubbles ofcarbon dioxide gas may form in the soft gelatin. As the bubbles escape, they form tinycraters or pits in the emulsion, thereby breaking up the normal character of the silver

image. The finished film or radiograph is blistered. To overcome this effect, thetemperature of the developer, rinse, and fixer solutions should be approximately thesame.

b. Reducers.(1) Reduction process . As described previously, the latent image site is a speck of silvercapable of initiating development. The latent image site provides a place where thereducers accomplish the process of breaking down the silver bromide crystal to blackmetallic silver. The reducing agents act as electron donors to the latent image site,giving it a negative charge. Thus, the positively charged silver ions may move into theareas of the sensitivity speck and become attracted to it. As this process continues,

more silver ions are attracted and deposited as atoms of silver. The final result is thebreakdown of the entire crystal to black metallic silver.(2) Reducing agents. The agents commonly used are Elon (another trade name isMetol) and hydroquinone. The activity of these chemicals requires their presence inan alkaline solution. Chemical functions differently in attacking the emulsion. The Elonstarts development by attacking the exposed silver bromide crystals swiftly withresultant production of gr ay tones in the image. Elon is unpredictable above 75F andhydroquinone ceases its activity below 60F. The activity of the hydroquinone is slower,but it serves to build up the black tones required in the image. The reducers, acting as ateam, produce a good image with satisfactory contrast in a minimum of time, as long asthe temperature of the solution remains in the optimum range. Reducers are not too

stable in the presence of oxygen, which they can readily absorb from the air or from thewater.c. Restrainer. The restrainer (potassium bromide) limits the action of the reducingagents to the breaking up of the exposed silver bromide crystals only without attackingthe unexposed crystals in the emulsion during the normal development. If the restraineris omitted, the reducers are hyperactive and break down the unexposed crystals,fogging the film. If the film is left in the developer too long, the reducers will override therestrainer and chemical fog will result. Also, the bromide released from the crystals into


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the solution will gradually restrain the action of the reducing agents to a point wherethey no longer function efficiently. Therefore, when a replenisher solution is mixed, itshould not include the restrainer.

d. Preservative. The preservative (sodium sulfate) retards the activity of the reducing

agents to within controlled limits so that the life of the developing solution ismaintained over a reasonable period of time. Since the reducing agents react quicklywith oxygen, this reaction must be controlled or the developing solution will not last verylong. Sodium sulfate works very well as a preservative because it retards oxidation ofthe reducing agents and prevents the formation of stains on the film.

2) Rinsing

When the film is removed from the developer, the gelatin emulsion is swollen and like asponge, saturated with all the soluble chemicals of the developer solution. Also, thegelatin contains the black metallic silver image and unexposed, undeveloped silver

bromide crystals. The bulk of the soluble developer chemicals should be removed fromthe film before it is placed in the fixing bath and these chemicals replaced by eitherfresh or acidified water. Such treatment is necessary to stop the reaction ofdevelopment, to neutralize the alkalinity of the residual developer, and to remove theoxidation products of development. There are two methods of removing thesechemicals--rinsing the film in fresh water and rinsing the film in acidified water.3-25. WATER RINSE BATH

After development, the film should be rinsed for 30 seconds in circulating fresh waterand drained before being placed in the fixer. This rinse should remove the solubledeveloper chemicals form the surface of the film and the pores of the emulsion. Theemulsion on a 14 by 17-inch film holds at least three ounces of developer. To stop

development, the residual developer must be quickly diluted with water. If films areinsufficiently rinsed and repeatedly placed directly in the fixing bath, the chemicalbalance of the fixer is eventually upset and its useful life materially shortened. Poorrinsing causes the acidity of the fixer to be rapidly reduced, the hardening action to bedestroyed, and stains to appear on radiographs. Still, water should not ordinarily beused for rinsing. An accumulation of developing solution in the rinse bath eventuallyoxidizes and when it is carried over to the fixing solution, it streaks and stainsradiographs because of fixing solution contamination.3-26. ACID RINSE BATHa. Acid rinse baths prolong the life of the fixer and ensure maintenance of the hardeningaction. An acid rinse bath eliminates the need for running water (required by a waterrinse bath). The most efficient rinse (stop) bath is one consisting of a dilute solution ofacetic acid in water made according to the following procedure. Add two and one-halfquarts of 28-percent acetic acid to one gallon of water. Stir thoroughly. Add sufficientwater to make five gallons of solution. This bath can be made in a five-gallon tank andplaced between the developer and fixer tanks. The bath immediately stops developmentof the emulsion and neutralizes the alkali in the developer contained in the emulsion.b. Radiographs should be rinsed in the acid bath for 30 seconds but they may be left inthe bath for as long as one and one-half minutes. Do not overwork the acid rinse bath.


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When the activity of the solution is reduced, it will accentuate rather than prevent stainsand streaks. The acid rinse bath will operate satisfactorily within the normal range ofprocessing temperature when the rapid x-ray developer is used. During this useful life,the acid rinse bath will rinse about 200 14 by 17-inch films or their equivalent per fivegallons of solution. .

2) FixingWhen the film is placed in the fixing solution, it is milky in appearance because ofthe residual silver bromide crystals; but as it is moderately agitated and both filmsurfaces are completely bathed by the solution, the milkiness gradually disappears.The action of the acidifier immediately neutralizes the residual alkaline developerand any continuing development action ceases. Since the gelatin is still swollen andporous, the clearing agent dissolves out the unexposed and undeveloped silverbromide crystals, leaving untouched the developed silver image. This is the clearing

action.

As clearing abates, the hardening action begins, causing shrinking and hardening ofthe gelatin emulsion containing the silver image. This hardening action is mostimportant, since it prevents swelling of the emulsion to any marked degree in the laterwashing operation. Do not turn on the white light in the processing room until the film isentirely clear, as white light will streak and fog the film.

The duration of the fixing process is dependent upon several factors. These include thestrength and nature of the fixer; the temperature of the solution, the amount of filmagitation, the volume of fixing agitation is related to the number and surface area of

films being fixed, and the emulsion thickness. The minimum fixing time is that needed toclear and harden the film. For best results, the film should remain in the fixing bath threetimes as long as necessary to clear the film.

Although radiographs may be left in the fixer for a slightly longer period, it is not wise todo so, for it will only take longer to wash them free of residual silver and fixing bathsalts. The hardness of the emulsion in a given fixing solution decreases with solutionexhaustion and the initial fixing time must be extended as the solution is used tomaintain normal hardening.

Also, the higher the temperature, the greater the speed of fixation; however, the

optimum range of temperatures is from 60 to 75F. With higher temperatures, a fixingsolution tends to sulfurize, thereby shortening its life. Therefore, it must be specificallytreated when high temperatures prevail.

COMPOSITION OF FIXER SSOLUTION Clearing or fixing agents

Dissolve and remove unexposed silver halide crystals from the filmemulsion.


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Preservatives Prevent decomposition of the fixing agent.

Hardeners Prevent excessive swelling of gelatinous emulsion during fixation

procedure and softening during the wash procedure. Shorten drying time.

Acidifiers Compounds that accelerate action of other chemicals and neutralize anyalkaline developer possibly carried over into the acidic fix solution.

Buffers Chemical compounds added to the solution to maintain the desires pH.

Help to stabilize the acidity against the addition of alkaline developercarryover. Without buffer, developer would neutralize fix solution. Can alsoprevent sludge formation in the fix bath.

Solvent Consists of water. Purpose is to dissolve other ingredients and assist in the fixing agent to

diffuse into the emulsion layer of the film. Carried silver halide away from film.

3) WASHINGProper washing ensures the permanence of radiographs as records. Washing ofradiographs must be regarded as a chemical operation, the object being toremove residual chemicals and silver salts from the film. If these are notremoved, the image will discolor or fade, eventually stain (brown stain of silversulfide), and the entire film may deteriorate. This is especially true when theradiographs are stored under conditions of high temperature and humidity. Asthe fixing solution nears the exhaustion point, the concentration of silver saltsbecomes so high that the washing process should be more thorough at this time.

WATER FOR WASHINGa. Supply. Any drinkable water should be satisfactory for film washing. Normally x-rayfilms are washed in running water circulated so that the entire emulsion area and everyportion of the wash tank receive frequent changes. In tank processing, the bar of thehanger and the top clips should always be covered by the water. When fresh water is inshort supply, radiographs may be safely washed in seawater. There is also a specialprocedure (to be discussed in this sub course), which can be used when water is scarceand which will ensure the processed radiograph's permanence.b. Filtration. The bulk of microscopic and animal matter sometimes contained in tapwater or water from other sources should be removed by filtration. Several thicknessesof gauze placed over the outlet of the water supply will provide some degree of filtrationif some other is available. The gauze filter should be cleaned or changed daily.

Washing timea. General. The time required for adequate washing depends principally upon thetype of film, the rate of water flow through the tank, and the temperature of thewater. If circumstances demand, a shorter washing time may be used. As long as


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the film is not subjected to high heat and humidity conditions, it may be thoroughlywashed at a later time (within three to six months). Generally, if a radiograph is toremain in a temperate zone, less washing is necessary than for those kept in atropical or subtropical region. However, every effort should be made to wash the filmproperly during its initial processing, since it is unlikely that at this time the area of

ultimate storage can be determined.4) b. Washing in a Single Tank. If the hourly flow of water through a single tank isfour times the capacity of the tank, 30 to 40 minutes is required for washing x-rayfilm at a water temperature of about 70F. When the flow is eight times the tank'scapacity per hour, the washing time is 25 to 30 minutes. Shorter washing timesthan these should not be used no matter how frequently the water in the tank ischanged. If the flow of water through the tank is very slow, the films shouldremain in the water even longer than the above specified times. The washingtime should be measured from the immersion of the last film in the wash water,since washed and partly washed films fixing bath chemicals rinsed into waterfrom newly added films.

c. Washing in a Two-Compartment Tank. The total volume of water may bedivided into several small units, especially when flow is inadequate. In the two-stagecascade system of washing, the flow of water is from right to left while the flow offilms in normal processing is from left to right. The film laden with fixing bath isplaced in the first compartment of the tank and is bathed with a very dilute solutionof water and fixing bath salts. After remaining in the first compartment approximatelyfive minutes, the radiograph is placed in the second compartment. Here it is bathedwith uncontaminated fresh water for an additional five minutes--giving a total of 10minutes washing time. At no time should a film fresh from the fixing solution beplaced in the second compartment.

TEMPERATURE OF WASH WATERThe temperature of the wash water is important. It should range between 68 and 70F,if possible. This range is about 40 percent more efficient than 40 would be, forinstance, and temperatures above 75F tend to soften the emulsion, leaving it open todamage. In general, the temperature of the wash water should approximate that of theother processing solutions.

5) DryingThe success of any drying operation lies in the rapid removal of the water fromthe emulsion. The most common procedure is the use of a rapid flow of air (withor without the aid of heat) over the edges of the film surfaces. Drying often takesmore than all the other operations together, so it is often a bottleneck in the flowof radiographs through the processing room. The radiographs are wet andvulnerable to damage, so they should not be removed from their hangers. If theyare not handled carefully, dust may become embedded in the emulsion or thefilm may get scratched and abraded.

DRYING AIDS


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Prevention of Emulsion Swelling. The speed with which x-ray film dries is dependentupon the quantity of water that must be evaporated from the emulsion. This speed isproportional to the combined thickness of the emulsions. It is, therefore, necessary toprevent excessive emulsion swelling. The use of a good fixing bath will keep swelling toa minimum by shrinking and hardening the emulsion. The emulsion should be hardened

before excessive swelling can occur. Hardening of a swollen emulsion raises its meltingpoint but does not necessarily reduce its thickness. Consequently, developing and fixingsolutions should be within the optimum temperature range. These precautions shouldespecially be observed when processing is done in hot, humid climates where dryingalways tends to be prolonged. Washing of the film should be adequate but notexcessively long. When processing temperatures are above 75F, special treatmentkeeps the emulsion hard, provided that short washing times are used.b. Wetting Agent. A wetting agent is a detergent that reduces the surface tension ofwater so that the water can drain more rapidly from the radiograph after washing. Thisshortens the drying time and eliminates drying marks. There are a number of wettingagents (labeled under various trade names), which are safe for photographic purposes.

A separate tank of dilute wetting agent is to be used as a final rinse after washing isprepared by adding 2-1/2 ounces of the detergent to five gallons of water. Afterwashing, the radiograph is immersed in this solution for 30 seconds and then drained.The radiograph may then be placed in the dryer. When 400 14 by 17-inch films, or theirequivalent, have passed through the solution, it should be replaced with a fresh one.c. Alcohol. The use of alcohol for drying is recommended only where some emergencyrequires the use of a dried radiograph in a minimum of time after processing. Any goodgrade denatured alcohol may be used for drying films, provided that when diluted withwater it does not turn milky. The alcohol concentration should be no greater than 70percent by volume if opalescence of the emulsion or deformation of the base is to beavoided. After washing, the radiograph is thoroughly drained. Then, the film is immersedin a tray of alcohol for two minutes at temperatures under 70F. The tray should berocked to assure uniform bathing of both film surfaces and to prevent the film fromsticking to the bottom of the tray. This operation causes the water to diffuse from thepores of the emulsion, and the water is replaced by the alcohol. With the bulk of thewater removed, the film is immersed in a second and final tray of alcohol to remove anyresidual water. The film is then drained. The alcohol will evaporate rapidly to leave a dryemulsion.d. Dryers. X-ray departments are usually provided with cabinet dryers equipped with afan and heating elements. The dryer should always be vented to the outside of theprocessing room to prevent excessive humidity. Drawers are provided in which the filmsare hung in their hangers. Ordinarily, radiographs should be dried with air moderatelywarm. Heat should be used cautiously when drying films in hot, humid weather becausethe water-laden gelatin emulsion may soften and distort the radiographic image. Underthese conditions, it is safest to use only the dryer fan. Overheating of the dryer shouldbe avoided because very rapid drying is apt to cause distortion of the radiograph.e. Drying Rack. When a small number of films are to be dried each day and a cabinetdryer is not available, film hangers may be inserted in a wall drying rack. The rack maybe simply a board in which holes have been drilled into which one end of the hangercrossbar can be inserted while the film is drying.


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DRYING TIMEThe time required to dry a film is dependent upon the efficiency of the hardener in thefixing solution, the amount of water retained in the gelatin emulsion after washing, thevelocity and temperature of the drying absorption is reduced to a minimum by the use ofa reasonably fresh fixing solution which will assure proper hardening of the emulsion.

Ideally, the humidity should be below 50 percent and the temperature under 90F. Whenfilms are dried in cabinet dryers, they should be adjusted so that drying takes place in10 to 20 minutes. The use of infrared lamps is not recommended, since they causeunequal drying of the film surfaces.

DARKROOMa. C o n s t r u c t i o n . Since x-ray films are more sensitive to light than most photographic films, it isimportant to have a good darkroom. The room need not be large, but it must be constructed sothat no light can enter through cracks or crevices. An entrance built in the form of a maze tokeep out light is better than a door. If the darkroom has a door, it should have an inside lock sothat no one can accidentally enter while films are being processed. The walls of the darkroomand the maze should be painted black to absorb light. The ceiling may be painted white so thatenough illumination will be reflected when the correct type of safelight is used. The roomshould be supplied with both hot and cold water. The water pipes should lead to a mixing valveso the temperature of the flow can be regulated. Adequate ventilation must be provided. Thiscan be done by forcibly changing the air with a ventilator fan.b. Clean l iness . Because of the extreme sensitivity of x-ray films, rigid cleanliness must beobserved when processing films. Clean all equipment and only use for its intended purpose.The dental specialist must not spill chemicals. If chemicals are spilled, wipe up immediatelyand wash the area with clear water. Spilled chemicals that are not wiped up will evaporate andleave a precipitated concentrate that contaminates films. Wash the thermometers and filmholders thoroughly before transferring them to either the developing or fixing solutions. Filmhangers require particular attention after films have been removed from them. If a hanger is notwashed properly, the fixing solution dries on it. Then, when new films are placed on the hangerand immersed in the developing solution, the dried fixing solution runs down onto the films andcauses streaked or spotted radiographs. It also contaminates the developing solution.c. T h e r m o m e t e r. Since films must be processed at an exact and predetermined temperature, athermometer is needed to register the temperature of the solutions.d. Timer. Because of the direct relationship between temperature and time in processing, thedental specialist must know the exact time and any given film is to be left in each solution. Agood watch may be used for this purpose, but it is much better to use an interval timer. Theinterval timer is a small clock giving the time in minutes and fractions of minutes. When set forthe exact time required for development, it sounds an alarm at the expiration of that time.e. F i l m H o l d e r s . There are three types of film holders. The frame type is used for extraoral filmsand the clip and hinge types are used for intraoral films (see figure 3-2).f. I l l u m i n a t i o n . A photographically safe light must be used to illuminate the darkroom. Thestandard for a safelight is that it must be possible to permit underdeveloped film to be exposedto the light at a distance of 4 feet for 1 minute without the least evidence of fogging.g. Sink . A sink is useful in the darkroom for mixing solutions, washing hands, and disposing ofused chemicals. Remember that the fixing solution is not disposed of like other chemicals. It isretained for silver recovery.h. S o l u t i o n s . There are two types of processing solutions. One is used for the automatic

processor and another for the manual processor. They are not designed to workinterchangeably. Before changing the processing solutions, check the manufacturers'instructions to be sure that you have the proper chemicals for the processor you are using.

Also, follow manufacturers instruction when preparing them. Some will require severalchemicals mixed with water while others may be used directly from the container.

THE LOADING BENCH


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a. General. The loading bench is the primary component of the "dry" side (manual) and"dark side" (automatic) of the processing room. It contains an area for loading andunloading film holders, a cassette transfer cabinet, a film bin, compartmentsMD0954 2-8for cassettes and exposure holders, storage for hangers, a wastepaper receptacle, and

storage for processing materials. Generalized layouts for a loading bench are shown infigures 2-4 and 2-5. In figure 2-4, the racks for storing dry film hangers are above theloading bench and storage compartments are beneath the bench.b. Loading Area. The length of the loading bench depends on the volume of work andthe space available. The minimum length of the working surface should accommodatetwo 14 by 17-inch cassettes, side by side, to permit unloading and reloading of twocassettes. Preferably, it should be long enough to accommodate at least four 14 by 17-inch cassettes, side by side, to preclude piling of cassettes. The working surfacesshown in figures 2-4 and 2-5 require approximately 96 inches, exclusive of transfercabinet and dryer space. The bench should be about 36 inches high and 24 inchesdeep. A strip of one-half by one-inch molding placed lengthwise and six inches from the

back edge of the bench anchors the cassettes while they are being opened and closedand keeps them at the front of the bench within the working area of maximum efficiency.THE LOADING BENCHa. General. The loading bench is the primary component of the "dry" side (manual) and"dark side" (automatic) of the processing room. It contains an area for loading andunloading film holders, a cassette transfer cabinet, a film bin, compartmentsMD0954 2-8for cassettes and exposure holders, storage for hangers, a wastepaper receptacle, andstorage for processing materials. Generalized layouts for a loading bench are shown infigures 2-4 and 2-5. In figure 2-4, the racks for storing dry film hangers are above theloading bench and storage compartments are beneath the bench.b. Loading Area. The length of the loading bench depends on the volume of work andthe space available. The minimum length of the working surface should accommodatetwo 14 by 17-inch cassettes, side by side, to permit unloading and reloading of twocassettes. Preferably, it should be long enough to accommodate at least four 14 by 17-inch cassettes, side by side, to preclude piling of cassettes. The working surfacesshown in figures 2-4 and 2-5 require approximately 96 inches, exclusive of transfercabinet and dryer space. The bench should be about 36 inches high and 24 inchesdeep. A strip of one-half by one-inch molding placed lengthwise and six inches from theback edge of the bench anchors the cassettes while they are being opened and closedand keeps them at the front of the bench within the working area of maximum efficiency.

PROCESSING HANGERSa. Types. There are three general types of processing hangers:(1) Sheet film hanger. The sheet film hanger holds the x-ray film taut during processing.It consists of a crossbar and rigid frame to which are attached four clips, two of whichare mounted on a bow spring welded to the crossbar (figure 2-9).(2) Dental film hanger. The dental film hanger consists of a bar to which film clips areattached.


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(3) Roll film hanger. When it is necessary to process roll film and a special processingtank is not available, a special adjustable processing hanger may be used. It will accept35, 45, 50, 60, and 70 mm film widths and any length up to 11 feet. The outer frame isapproximately the size of a 14 by 17-inch hanger and can be used in the regularprocessing tanks. For four by 10-inch short film and 70 mm roll film, there are special

hangers, which will fit the same five-gallon tanks.Dry Bench The dry bench is where the cassette are unloaded and recharged with fresh film. It must be impossible

for splashes of developer to reach the dry bench surface. The top of the dry bench must be large enough to accommodate the largest cassette in use when

opened out. The top surface should be either of wood or linoleum. Plastic laminates are not recommended

because they hold static charges of electricity which can cause marks on films. It is usual to store film boxes, especially those in current use , beneath the dry bench , either in a

cupboard ( protected if near an X-ray set ) or in a film hopper. The processing frames should hang above the bench , cash size on its appropriate. There are two

designs of processing frame the channel type and the clip type.

Hanging x-ray film X- ray film should be grasped only at the corners and inserted into the clips of the film hangers and

locked in place. The upper corner of the film grasped and a Hached to the top clips. The film now

ready to be placed in the developing tank. The clips of the film hanger should be cleaned periodically to prevent an accumulation of chemicals

that may rundown on the film during processing and cause streaks.

Manufacturers specify the correct type. Two forms of safe-light can be used in the radiographic dark room. Direct: a diffused light shines directly over the work point, such as the dry and wet bench. Indirect: the filtered light is directed up to the ceiling where it is reflected over the room. Safe-light efficiency: Safe-lights should be placed so that the work of the dark room can be done

without fumbling . where the dry and wet benches are separate , a small direct wall light should be

provided for each reloading

Open the lid of the X-ray film box and extract a film in its folder by its edge . Film emulsion is

sensitive to pressure, so dont fold or buckle film by careless handling. Open the cassette. Pull back the top leaf of the protective holder, twist the wrest and drop the film into the well of the

cassette. Withdraws the folder. Run a finger around the edge of the well to make sure that the

film is not protruding over the edge. Close the cassette and replace the top on the film box.


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At the end of the developing period, left out the film and allow the solution to drain back into the

developer tank for a few seconds. Rinse in water for about 10 seconds. Place the film in the fixer and wait for 30 seconds.

The white light can now be switched on.

When the milky appearance caused by the dissolving silver halides had disappeared the film can

be viewed for technical quality and professional diagnosis. The film should be washed in running water for half an hour.

Loading the X-ray film

The X-ray film should be correctly positioned within the cassette by touching only the corners. The central portion should never be touched. Then the cassette should be closed and locked.

Storing x-ray cassettes

Loaded x-ray cassettes should be stored in an upright position in cool dry place within the dark

room.

Removing the x-ray film from the cassette

The processing room should be darkened except for the safe light. Great care must be taken in

removing the x-ray film from the cassette to prevent damage of the intensifying screens. The

workers fingers should not touch the screens of the cassette. Rubbing the film across the end of

the cassette must be avoided to avoided black pressure scratches on the developed radiograph.

DARKROOMa. Construction. Since x-ray films are more sensitive to light than most photographic

films, it is important to have a good darkroom. The room need not be large, but itmust be constructed so that no light can enter through cracks or crevices. Anentrance built in the form of a maze to keep out light is better than a door. If thedarkroom has a door, it should have an inside lock so that no one canaccidentally enter while films are being processed. The walls of the darkroomand the maze should be painted black to absorb light. The ceiling may be paintedwhite so that enough illumination will be reflected when the correct type ofsafelight is used. The room should be supplied with both hot and cold water. Thewater pipes should lead to a mixing valve so the temperature of the flow can beregulated. Adequate ventilation must be provided. This can be done by forciblychanging the air with a ventilator fan.

b. Cleanliness. Because of the extreme sensitivity of x-ray films, rigid cleanlinessmust be observed when processing films. Clean all equipment and only use forits intended purpose. The dental specialist must not spill chemicals. If chemicals


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are spilled, wipe up immediately and wash the area with clear water. Spilledchemicals that are not wiped up will evaporate and leave a precipitatedconcentrate that contaminates films. Wash the thermometers and film holdersthoroughly before transferring them to either the developing or fixing solutions.Film hangers require particular attention after films have been removed from

them. If a hanger is not washed properly, the fixing solution dries on it. Then,when new films are placed on the hanger and immersed in the developingsolution, the dried fixing solution runs down onto the films and causes streakedor spotted radiographs. It also contaminates the developing solution.

c. SAFELIGHT

The processing room must be provided with both white and safelight illumination. Whitelight for such work as cleaning tanks and preparing the solutions is done. Reliable safe-light lamps are indispensable - their function is to provide adequate light of quality thatis safe for exposed X -ray films during handling and processing. Always remember thatX-ray films are sensitive to light until after fixation.

d. Thermometer. Since films must be processed at an exact and predeterminedtemperature, a thermometer is needed to register the temperature of thesolutions

e. . Timer. Because of the direct relationship between temperature and time inprocessing, the dental specialist must know the exact time and any given film isto be left in each solution. A good watch may be used for this purpose, but it ismuch better to use an interval timer. The interval timer is a small clock giving thetime in minutes and fractions of minutes. When set for the exact time required fordevelopment, it sounds an alarm at the expiration of that time.

f. Illumination. A photographically safe light must be used to illuminate thedarkroom. The standard for a safelight is that it must be possible to permitunderdeveloped film to be exposed to the light at a distance of 4 feet for 1 minutewithout the least evidence of fogging.

g. Sink. A sink is useful in the darkroom for mixing solutions, washing hands, anddisposing of used chemicals. Remember that the fixing solution is not disposedof like other chemicals. It is retained for silver recovery.

MINIMUM REQUIREMENTS FOR A DARKROOM.a) Light-tight roomb) Both safe-light and white-light illuminationc) Processing tanks and / automatic processord) Hot and cold running watere) Accurate thermometer and interval timerf) Drying racks or dryer


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g) Adequate storage spaceh) A radiograph vieweri) Has a light-tight storage

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