An Assignment on

Dark Room Procedure

For

Quality Radiography

Submitted toDr. Manoj Kumar Shah

LecturerDepartment of surgery and pharmacology

IAAS, Rampur campus, Chitwan

Submitted bySuraj Subedi

B.V.Sc & A.H 7th semesterRoll no 29

IAAS, Rampur campus, chitwan

September, 2010

Introduction 

The most common errors made in radiography of animals are related to the processing of exposed radiographic film. The area used as a darkroom must be clean, lightproof, and uncluttered. If film should accidentally come into contact with spilled processing chemicals, specific artifacts will appear on the radiograph. Pressure, creasing, buckling or static electricity can also cause artifacts, dictating the need for great care in the handling of film. Because of the variety of errors possible in the darkroom and the frequency of these errors, it is not difficult to explain the trend toward purchase of automatic processors. These units are costly and the cost of maintenance and replenishing of solutions is high. Still, in the practice using radiography frequently, the automatic process may save time and money by decreasing the number of repeat examinations required because of technical problems.

It is difficult to encourage a technician to perform a radiographic examination carefully if the quality of the study is to be lowered by damaging the film in the darkroom. There are basic considerations in construction and layout of a darkroom that can assist in lowering the chances of film damage. Nothing is more discouraging than to work long minutes to achieve proper positioning of the patient and then have the study ruined by careless acts in the darkroom. 

General Dark room proceduresa. Layoutb. Light traps and entrancec. Wet and dry benchesd. Film pass hatchese. Processing unitsf. Safe-lights and ancillary equipmentg. Storage, handling and loadingh. Film processing (automatic and manual)i. Temperature control

Darkroom Configuration

Work flow is more important than is room size and shape. The physical layout of the darkroom should consider the following items.

If manual processing is performed with wet tanks, there must be dry and wet sections of the room. This enables you to handle film, unload and reload cassettes, and store film in the dry section while the wet section is used only for processing of the film. If used, the pass box should be next to the loading bench. Film hangers can be stored either under or over the loading bench. The bench must be far enough from the wet tanks to prevent solutions from splashing on the film.

Film storage bins are a convenient method of storing the open film boxes currently in use. If the number of radiographic examinations performed is low, it may be easier to replace the lid on the film box to keep the remaining film protected from the light. A box opened and reclosed in this manner can be stored on a shelf without risk of light exposure of the remaining film.

Location of the wet film examining area is important. This is a wet, messy, area at the best. The film viewer should be near the fixer tank since most films to be evaluated are taken from the fixer tank, viewed, and then are replaced in the fixer tank for completion of the fixation process. Place a tray of some sort under the view box so that some of the splashing of fixer can be controlled. An absorbent towel hanging near this area is of use in assisting in controlling dripping of solutions.

Since film is stored in the darkroom and is handled without a protective cover in this room, problems of film fogging or undesirable background exposure covering the film, often center around the darkroom.

Fogging can be due to:

improper use of the darkroom safelight accidental illumination of the film by visible light radiation exposure. 

  

Schematic drawing of a darkroom using wet-tank processing.

Flow of films from left to right. The cassette is opened on the counter top.

(a) Where the film is placed on a hanger. The film is placed in a series of tanks

(b) containing developer, rinse, fixer and wash. Note the separation of dry and wet portions of the darkroom. Safelights are mounted on the wall

(c) A viewbox

(d)With drip sink is available for wet film viewing.

FEATURES IN A DARKROOM USING WET TANK PROCESSING

1. access door

2. lightlock entrance

3. cassette storage*

4. cassette pass box*

5. loading bench

6. film storage

7. film bin

8. waste basket

9. processing tanks

10. safe lights

11. exterior warning

12. view box

13.floating thermo-cabinets meter

14. water temperature regulator

15. film hangers

16. hanger storage rack

17. drying rack or film dryer

18. towel light indicating use*

19. clock

Safelight illumination is of critical importance in the operation of a darkroom. The function of the safelight is to provide sufficient illumination to enable you to work quickly and efficiently but must be of such a type that does not add fog to the radiographic film. X-ray film is sensitive to light in several regions of the spectrum; therefore, safelights must be covered with the correct filters ___________________________________________________

*may be desirable in certain circumstances

Safelights must:

1) be used with the correct filter,

2) be of the correct wattage (standard frosted, 6 1/2 watt to 10 watt, and

3) be the correct distance from film on the counter top.

Even following these rules, film can still be fogged if left exposed to the light for a long enough period of time. It is possible that the safelight is satisfactory but outside light is entering the darkroom around a door or through cracks and causing fogging of the film

The film should be sensitive to a light energy emitted by the screen but should not be sensitive to the light energy emitted by the safelight in the darkroom.

The following technique is recommended to evaluate the level of illumination in the room and its effect on the film. place a film on the counter top in a location where you normally unload the cassette and cover it with a heavy cardboard, the film box, or other light opaque material. Position the cardboard so that 1/4 of the film is exposed to the normal illumination of the room under that 1/2 of the film is now exposed for an additional 1 minute. shift the cardboard once more so that 3/4 of the film is now exposed for an additional minute. Finally, remove the cardboard and permit the entire film to be exposed to darkroom light for an additional minute. Process the film in the routine manner and examine it. If the darkroom illumination is safe, none of the film will have any fogging which appears as a darker portion on the film. If there is evidence of fogging, examination of the film will tell you the extent of the exposure and how long you can safely leave a film exposed to the darkroom light before fogging occurs. This same Test can be performed with the safelight off to evaluate leakage of light into the darkroom.

X-ray film is highly sensitive to radiation and therefore must be protected from any accidental exposure. If fogging of film occurs, the possibility of the fogging occurring within the darkroom must be considered especially if the room is adjacent to the examination room. A simple test for the possibility of stray radiation reaching the film bin or box is to tape a dental x-ray film packet with a coin placed to the outside of the film packet on the inside and outside of the door of the film bin. After several weeks, develop the film. If an image of the coin is seen on the film it will be due to radiation reaching the film but being absorbed by the more dense metal coin.

DARKROOM LIGHT FILTER

Light Sensitivity

Filter

blue Wratten series 6Bgreen Wratten series GS-

1Red Wratten series GS-

1

Direct and indirect illuminating types of Darkroom Lights

Cleanliness of the room is important since this is the one place where both intensifying screens and films are exposed to the air. If the counter tops are dirty or contaminated with

chemicals, it is easy for the dust to be blown into the cassette and result in damage to the intensifying screens. Counter tops should be of a material that can be easily cleaned. It is also important to prevent contamination or oxidation of the processing solutions. This is most easily done by use of plastic or wooden covers for the processing tanks.

Surfaces above the working area should be finished with a white or light-tinted paint in a semi-gloss or flat finish. A gloss finish sometimes reflects light in an objectionable manner. Surfaces at and below the working area should be finished with a gloss paint for ease of cleaning.

Ventilation is important in keeping the darkroom dry and removing objectionable odors. Film stores best at 30% to 50% humidity. 

Film Processing

Despite the increase use of automatic processors, most radiographs in veterinary radiography

are still processed in wet tanks. The discussion on film processing is divided into a section on

the use of wet tanks and a section on use of an automatic processor. 

Developing The primary function of the developer is to reduce exposed silver halide crystals to

metallic silver. This is done by supplying electrons to the positively charged silver ions that exist

in the exposed film. Developer consists of:

1) reducing agents

2) activator

3) restrainer

4) preservative

5) solvent

The reducing agents or developing agents most commonly used are hydroquinone and metol in

various combinations. The reducing agents convert the exposed silver halide crystals into black

metallic silver. The activator is sodium carbonate and provides a pH range of 9.8 to 11.4. It also

swells and softens the emulsion so that the reducing agent can work more effectively. The

restrainer is potassium bromide which limits the activity of the reducing agents so that it does

not reduce unexposed silver halide crystals. The preservative is sodium sulfite which prevents

rapid oxidation of the reducing agents. The solvent is water and dissolves the chemicals.

Five minute developing time is recommended for film processing because it permits a reduction

of required exposure factors. This could permit use of a shorter exposure time. Use of five

minute developing time allows for almost all of the exposed crystals to be converted to metallic

silver. Because the chemical reaction has gone to completeness, the time of developing is not

as critical and the film may be in the developer solution 4 1/2 to 6 minutes with little difference

in film density or blackness. The advantage of this greater degree of freedom in removing the

film from the developer solution is obvious. 

DEVELOPER TEMPERATURE - TIME RELATIONSHIP

Temperature C0

Temperature F0

Time Minutes

15.5 60 8 ½18.5 65 6*20 *68 *521 70 4 ½24 75 31/2

*(Optimal temperature-time combination) 

The process of film developing is a chemical process and is therefore dependent on both time and temperature. Because of this, a constant developer temperature is important in obtaining consistent film density or blackness. Manufacturers recommend a specific temperature for the developer solution they produce. Generally, this is 20°C (68°F). The temperature should not exceed that given in above table.

DEVELOPER CHEMISTRY FOR MANUAL PROCESSING

GENERAL FUNCTION

CHEMICAL SPECIAL FUNCTION

Reducing Agents

Metal -- Quickly builds up gray tones in the image.

Hydroquinone---Slowly builds up black tones and contrast in the image.

Developing agents convert exposed silver bromide crystals into black metallic silver.

 

Activator Sodium Carbonate Swells and softens emulsion so that reducing agents may work more effectively. Provides required alkalinity for reducing agents

Restrainer Potassium Bromide Restrains reducing agents from causing fog.

Preservative Sodium Sulfite Prevents rapid oxidation of developing

agents

Solvent Water Liquid for dissolving chemicals

High developer temperature causes swelling of the gelatin as well as an increase in chemical activity. The gelatin thickens unevenly and "slips" causing a film artifact called "reticulation".

Care must be taken in the placement and removal of the radiograph from the developer solution. That tank is usually small and the film holder can scratch other films in the tank. Gentle film agitation immediately after immersion ensures good mixture of the solution and prevents accumulation of air bubbles on the surface of the film that would prevent good contact of solution with the surface of the film.

When the film is removed from the developer bath, there should be a deliberate attempt made to early developer solution over into the rinse bath. This depletes the developer bath of exhausted solution and enables you to replenish the solution. 

Rinse Bath The rinse bath removes developer from the film and diminishes the carry-over of this solution to the fixer tank. Agitation of the film for 30 seconds is adequate to accomplish this. If the bath uses running water, the rinse will be more complete and can be done in a shorter time. It is possible to use an acid bath or stop bath between developer and fixer solutions. This solution is 1.5% acetic acid and it neutralizes the alkali of the developer and protects the acidity of the fixing bath. In addition, it immediately stops the reduction of silver halide crystals. The pH of the stop bath will be altered by the basic pH of the developer and will require changing to remain effective.

 Fixing The purpose of the fixer is to convert undeveloped silver bromide crystals left on the film into a soluble compound and dissolve them away. This leaves the silver image as a permanent record. Fixer solution is composed of:

1) a fixing agent

2) an acidifier

3) a hardener

4) a preservative

5) a solvent

The fixing agent is sodium thiosulfate (hypo), if the fixer is prepared from a powder, or ammonium thiosulfate if the fixer is prepared from a liquid solution. It acts to clear away the unexposed and undeveloped silver bromide crystals. Sodium thiosulfate forms water soluble complexes in which silver ions are tightly bound

(AgBr + Na2S203 ~ AgS203 + NaBr).

FIXER CHEMISTRY FOR MANUAL PROCESSING.

GENERAL FUNCTION

CHEMICAL SPECIAL FUNCTION

Fixing Agent Sodium or silver bromide Clears away unexposed Ammonium Thiosulfate crystals.

Acidifier Acetic or Sulfuric Acid Stops development by neutralizing developer.

Hardener Aluminium Chloride or Sulfide emulsion

Shrinks and hardens

Preservative Sodium Sulfite Maintains chemical balance of fixerSolvent Water Liquid for dissolving chemicals

The acidifier is acetic or sulfuric acid, and its purpose is to stop development by providing the required acidity to neutralize the developer. The hardener is aluminum chloride or aluminum

sulfide and it shrinks and hardens the emulsion. The preservative is sodium sulfite and it maintains chemical balance of the fixers and suppresses sulfur deposition. The solvent is water and serves to dissolve the chemicals. Agitation of the film for 15 seconds after being placed in the fixer bath helps to insure equal chemical action and avoid streaks and stains on the film.

Washing The purpose of the final washing bath is to wash away the remaining silver complexes and the excess fixing agent. Inadequate washing causes film artifacts that appear later when the image becomes discolored due to residual fixer. The length of washing time depends on the frequency with which the water is changing and the number of films being processed. If the water changes completely ten times each hour, the washing time can be 20 minutes. Films can be left in the wash tank overnight without permanent damage. However, the emulsion swells and a longer drying period is required. A longer wash time is required for non-screen film because of the increased thickness of the film emulsion.

Drying Film drying should be performed in a clean cabinet or room. If a fan is used to circulate air, ensure that a steady stream of air blows over the films. Any dust stirred by the fan will settle on the films and make them feel like sandpaper after they dry. Other problems in film drying are manifested by "water spots" or other drying streaks or marks. It is possible to hasten film drying and avoid some artifacts by use of a wetting agent bath (a surface tension reducer such as a detergent). The film is briefly dipped into a tank of this solution prior to placing in a dryer. These wetting agents are commercially available.

Film hangers create a sharp point in the corner of each film that cuts badly into the film emulsion when a film is slid over the surface of another film. Therefore, it is important to cut the corners of the radiographs either with scissors or a film corner cutter. 

Processing Temperature Too often, consideration is given only to the temperature of the developing solution. It is equally important to maintain all of the processing baths in manual processing at about the same temperature to insure the best quality of film processing.

Reloading Cassettes During the time the film processing cycle is occurring, the cassettes are usually reloaded with film. This is somewhat hazardous when performing wet tank processing since you are working back and forth from the wet section of the room to the dry section. It is, therefore, important that you have towels available so you may dry your hands. Cassettes should not be left open on the counter top since it is easy to drop objects and damage the intensifying screens. Load and close the cassettes as quickly as possible.

Use caution when drawing film from the storage box since it is easy to create electricity as the films rub together. Avoid bending the film as it is placed in the cassette. Some film is packed with interleafing paper. This must be removed before placing the film in a cassette. The paper may be left around the film if it is nonscreen film. After the cassettes are reloaded, they should be placed in a specific location in the darkroom. Following completion of the processing of the films, the cassettes can be returned to the radiographic examination room.

Hot Weather Processing It is frequently difficult to lower the temperature of freshly prepared solutions being used. Ice may be used as a part of the solvent to lower the temperature of solutions as they are being prepared. Permit the ice to melt completely to determine the temperature of the solution before adding the final solvent.

It is not possible to use ice in the developer or fixer solutions to lower their temperature on a daily basis because of the dilution factor. It is a standard practice of those working in warm climates to place artificial camper's ice such as "Blue Ice" into the solutions to achieve a lower temperature. Do not use artificial cooling agents that are in a metal container that would react chemically with the developer or fixer. Another method of lowering solution temperature is to fill a plastic container with water and freeze. This type of closed carton will not react chemically with the solutions and will not leak water as it melts. It can be reused on a daily basis.

Overnight cooling can be used in clinics where three or five gallon solution tanks are used. Remove a gallon of developer and a gallon of fixer and place them in separate glass containers in a refrigerator overnight. In the morning add the chilled solutions to the warm solutions to bring the working temperatures closer to normal.

Satisfactory radiographs can be obtained at developer temperatures between 24° and 27°C ( 75° and 80°F) by adding additional restrainer to the developer. Dissolve 71 gms (2.5 ounces) of sodium bicarbonate in 177 cc (6 ounces) of warm water at 27°C (80°F). Add this solution of sodium bicarbonate to each 3.8 liters (gallon) of diluted developer.

Rinsing times should be longer in hot weather because the swollen gelatin holds more alkali. An acetic acid stop bath is also helpful. The fixer may be helped in hot weatherby adding concentrated acetic acid to restore the hardening action of the solution. Keep washing times to a minimum if the wash water temperatures are high. This will avoid damage to the emulsion.

 Processing Solutions Developer and developer replenishers are available in both powdered and liquid concentrated forms. The liquids are easier to work with since they eliminate the problem of powder settling on counter tops in the darkroom.

Solution Replacement Determination of developer and fixer replacement is dependent on the number of films processed and the care exerted in avoiding contamination of the solutions. As a rule, a change in color of developer solution to green or brown suggests aging developer and a need for changing the solution. This change in color is associated with processed film having less density than expected and a tendency for the film to have less contrast because of chemical fogging. Usually developer solutions require changing less often than fixer solutions. This is because the film is dry when first placed into the developer and, therefore, no dilution of the solution occurs. When the film is removed from the developer, a certain amount of developer is carried out with the film, lowering the solution level. This makes it possible to add replenisher solution to maintain a satisfactory level and strength of developer solution.

Activity of the fixer is easier to ascertain because of your ability to evaluate the length of clearing time. The fixer is changed when the clearing time is as long as two to three minutes. It is more difficult to keep the fixer solution at an acceptable strength. This is because each film placed in the fixer brings with it a certain amount of water from the wash tank. The amount of dilution depends on how rapidly you move the film to the fixer tank. Because of this continual addition of water, the level of the fixer solution does not drop at the same rate as the developer and a continual dilution and subsequent weakening of the fixer solution occurs.

Combating Algae Filtration of incoming water is basic in eliminating algae from the film processing system. Partial specifications for such a filter are as follows:

l) a mean pore opening of not more than 35 microns, 2) a water flow capacity of at least 19 liters (5 gallons) per minute, and 3) a line-pressure drop of less than 0.227 kg (0.5 lb) per 6.45 cm2 (2.6 in2).

Algae can be removed from the walls of the water compartment through repeated scrubbing with a neutral algicide. Diluted acid or laundry bleaches also can be used to clean the tanks and retard algae growth. With each of these procedures the tanks must be washed thoroughly prior to use. A simple method of minimizing the growth of algae is to let the wash tanks dry over a weekend. 

14.3 Operating Procedure for Manual X-ray Film Processing

In order for manual processing of films to be done correctly a scheme must be followed. The major part of the scheme describes the processing technique for individual films. Monthly duties are also included.

 Daily

l) stir solutions thoroughly 2) check temperature of solutions (20°C [68°F]) 3) visually check for light leak in darkroom 4) check for dry towel 5) clean counter tops 6) check level of solutions

7) check first film carefully for a rough quality control study 

Individual film

1 ) turn off all white lights 2) turn on darkroom safety light 3) unload cassette and close cassette lid 4) load film on hanger 5) set timer to 5 minutes 6) immerse film in developer, brief agitation (avoid scratching adjacent film) 7) cover developer tank if possible 8) dry hands 9) reload cassette 10) remove film from developer quickly when alarm sounds preventing dripping into developer tank 11) drain film into rinse tank 12) agitate film in rinse water for 30 seconds 13) lift out of rinse water and let drip into rinse tank 14) immerse film in fixer bath, agitate briefly (avoid scratching adjacent film) 15) remove film from fixer quickly after 10 to 20 minutes 16) immerse film in wash tank 17) remove film from wash tank after 20-30 minutes (depending on level of water replenishing) 18) immerse in quick drying solution (if used) 19) place in drying oven or drying area 20) remove from hanger when dry 21 ) cut corners 22) place in film filling envelope 23) write technique and patient identification on film filing envelope 

A Radiograph film developed by dark room procedure