Darkroom procedures during Radiography

DARKROOM PROCEDURES DURING RADIOGRAPHY
Sudil Paudyal, RT
THE LOADING BENCH (Dry bench):
The dark room must always be kept clean and tidy. The chemicals used during processing can
damage the cassettes the films and even wood or concrete. On one side of the darkroom there
should be a dry workbench for films, clean film hangers, film boxes and cassettes. The hands
must be dry when working at this bench. It contains an area for loading and unloading film
holders, a cassette transfer cabinet, a film bin, compartments for cassettes and exposure holders,
storage for hangers, a wastepaper receptacle, and storage for processing materials.
Loading Area. The length of the loading bench depends
on the volume of work and the space available. The
minimum length of the working surface should
accommodate two 14 by 17-inch cassettes, side by side,
to permit unloading and reloading of two cassettes.
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 surfaces shown
in figure require approximately 96 inches, exclusive of
transfer cabinet and dryer space. The bench should be
about 36 inches high and 24 inches deep. 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 closed and
keeps them at the front of the bench within the working
area of maximum efficiency.
Unloading the cassette:
Under safelights, the cassette is placed face downwards on the bench and the locking clip is
released. The cassette is then turned over and the front of the cassette is tipped so that the film
falls from the cassette well. The film is removed with the dry hand and the cassette closed.
Loading the cassettes:
Under safelights the cassette is placed face downwards on the bench and as before opened from
the back. The unexposed film, lightly gripped at its edge is lowered gently into the cassette well.
The cassette is closed by bringing over the back and engaging the locking lip.
Darkroom illumination:
This may be considered under two headings:
1. Ordinary white lighting
White lighting is necessary for the following tasks:
 Inspection and maintenance of cassettes and screens
Darkroom loading bench

 Cleaning of work surfaces and floors
 Servicing of equipment
2. Safelighting
While all film materials would instantly be fogged if exposed to white light, safelighting which is
the use of dim colored lighting provides sufficient illumination by which one can handle,
manipulate and process film. Providing exposure to such lighting is brief, no significant fogging
will occur. But it is to be noted that no safelighting is completely safe; all films will become
significantly fogged if exposed to safelights for ling enough.
INTRODUCTION
Image forming x-rays exit the patient and expose the radiographic intensifying screen placed in
the protective cassette. The radiographic intensifying screen emits light, which exposes the
radiographic film placed between the two screens. The emulsion of x- ray films must be
chemically processed to render visible and permanent the information recorded in the latent
image. Processing causes the silver ions in the silver halide crystals that have been exposed to
light to be converted into microscopic black grains of silver. The processing sequence comprises
the following steps: wetting, developing, rinsing in stop bath, fixing, washing and drying. These
processing steps are completed in an automatic processor. Film processing involves a number of
complex chemical reactions whose activity and efficiency are influenced by various factors
including temperature and pH of the chemical environment in which the reactions take place.
Before the introduction of automatic film processing, x-ray films were processed manually. All
radiographic processing is automatic today. The chemicals involved in both are basically the
same. In automatic processing, the time for each step is shorter and the chemical concentration
and temperature is higher.
FILM PROCESSING
The latent image is invisible because only a few silver ions have been changed to metallic silver
and deposited at the sensitivity center. Processing the film magnifies this action many times until
all the silver ions in exposed crystals are converted to atomic silver, thus converting the latent
image into a visible radiographic image.
The exposed crystal becomes a black grain that is visible microscopically. Processing is as
important as technique and positioning in preparing a quality radiograph. A change in
recommended processing conditions should never be a substitute for a poor radiographic
exposure because the result is always a higher patient dose.
PROCESSING SEQUENCE
Radiographic film processing involves several steps which are summarized as:

(Bushong S.C., 2009)
The first step in the processing sequence involves wetting the film to swell the emulsion so that
subsequent chemical baths can reach all parts of the emulsion uniformly. In automatic
processing, this step is omitted and the wetting agent is incorporated into second step,
developing.
The developing stage is very short and highly critical. After developing, the film is rinsed in an
acid solution designed to stop the developing process and remove excess developer chemicals
from the emulsion. Photographers call this step the stop bath. In radiographic processing, the
stop bath is included in the next step, fixing. The gelatin portion of the emulsion is hardened at
the same time to increase its structural soundness. Fixing is followed by vigorous washing of the
film to remove any remaining chemicals from the previous processing steps.
Finally the film is dried to remove the water used to wash it and to make the film acceptable for
handling and viewing. Developing, fixing and washing are important steps in the processing of
radiographic film. The precise chemical reactions involved in these steps are not completely
understood. However a review of the general action is in order because of the importance of
processing in a high quality radiograph.
PRECAUTIONS
the chemicals used to process films are designed to penetrate an emulsion and cause an effect.
those used in automatic processors do this very efficiently in hte very short time the film is
immersed. thus when one is mixing solutions cleaning a processor aor participating in any
activity with or near processing solutions these steps should be followed:
• wear a proper mask that reduces inhalation of fumes – not the standard surgical mask that
only guard against particles and bugs.
• wear nitrite gloves. do not use surgical gloves; they only protect aganst biologic matter.
remember that photographic chemicals are designed to penetrate and thin rubber gloves
provide no guarantee of safety.
• wear protective glasses. chemical splashes in the eyes are painful.
Event Purpose Approximate time
Manual automatic
Wetting Swells the emulsion to permit subsequent
chemical penetration
15s ----
Development Produces a visible image from the latent image 5 min 22s
Rinsing in stop
bath
Terminates development and removes excess
chemical from the emulsion
30s ---
Fixing Removes remaining silver halide from
emulsion and hardens gelatin
15 min 22s
Washing Removes excess chemicals 20 min 20s
Drying Removes water and prepares radiograph for
viewing
30 min 26s

LITERATURE REVIEW
The objective of whole processing cycle is to produce a dry radiograph carrying a high quality
image which can be stored for a number of years without deterioration.
WETTING:
For the chemicals to penetrate the emulsion the radiograph must be first treated with a wetting
agent. The wetting agent is water and it penetrates the gelatin of the emulsion causing it to swell.
In automatic processing the wetting agent is in the developer.
DEVELOPMENT:
It is the first stage in processing. Its primary purpose is to convert into visible form, the invisible
latent image produced when the film was exposed. During development the silver halide grains
in the emulsion which were affected by exposure are reduced to metallic silver while those
which were unaffected remain largely unchanged.
Chemical action of developer:
Development is a process of chemical reduction. The reduction is achieved by the developer
donating electrons to the silver ions in the exposed silver bromide grains, converting them to
atoms of metallic silver. Chemically the reaction is Ag+
+ e-
Ag
Constituents of developing solution:
The developing solutions used in automatic processors are different in several important aspects
from those used for manual processing.
Component Chemical Functions
Developing agent Phenidone
Hydroquinone
Reducing agent; produces shades of gray
rapidly
Reducing agent; produces black tones
slowly
Activator Sodium carbonate Helps swell gelatin; produces alkalinity;
controls pH
Restrainer Potassium bromide Antifog agent; protects unexposed
crystals
Preservative Sodium sulfite Controls oxidation

Hardener Glutaraldehyde Controls emulsion swelling and
enhances archival quality
Sequestering agent Chelates Removes metallic impurities; stabilizes
developing agent
Solvent Water Dissolves chemical for use
(Bushong, S.C., 2009)
Replenisher solutions:
The solution which is fed into the developing section of a processor when it is actively
processing films is known as developer replenisher. It is the developing solution used in greatest
quantities in x-ray departments today.
Developer replenisher consists of:
1. Solvent: water is the solvent used in radiographic processing. It acts as carrying medium
in which the developer constituents are dissolved. It has a softening effect on the film
emulsion gelatin, thus allowing the chemicals tio penetrate the emulsion and act on silver
halides. The water used for the developer solutions should be clean and free from
insoluble deposits which could scratch the delicate film emulsion or damage the
processing equipment.
2. Developing agents: developing agents are the educing agents which carry out the primary
function of supplying electrons that convert the exposed silver halide grain to silver.
Modern x- ray developers use a combination of two developing agents: phenidone and
hydroquinone. A developer based on this formulation is known as a PQ developer.
Phenidone is trade name of 1-phenyl-3-pyrazolidone. It is a quick acting reducing agent,
capable of developing all exposed silver halide grains but its selectivity is low and if used
alone may result in high fog levels.
Hydroquinone requires a strongly alkaline medium to act. It is more selective than
phenidone but it does not begin development quickly. It tends to produce a high contrast
result.
Advantages of PQ developers:
 Tolerant of increases in bromine ion concentration
 High selectivity and therefore low chemical fog
 Adequate activity even in low concentrations

 Fast acting, permitting complete development in 20-30 seconds
 Super additive effect: the reducing effect of the combination of phenidone and
hydroquinone is much greater than the sum of the effects they produce when used
separately. This effect is known as super additivity or synergistic effect and is a
major advantage of PQ developers.
3. Accelerators: PQ developers need an alkaline medium to operate. The alkalinity of the
solution is established by the inclusion of a strong alkali such as potassium carbonate or
potassium hydroxide. The alkali is known is known as accelerator since its effect is to
accelerate the developing process.
4. Buffers: A buffer is chemical compound which has the effect if maintaining the pH of a
solution within close limits. The presence of buffering agents in developing solution
prevents the undesirable effects of changes in pH due to aerial oxidation of developer and
the acidic by-products of the development process. Normally adequate buffering action is
provided by the carbonates used as accelerators and the sulphides acting as preservatives.
Thus no additional buffering chemicals are necessary in most developing solutions.
5. Restrainers: the action of a restrainer is to modify the behaviour of the developing agents
so that they become more selective in their action. The effect is to reduce the tendency to
convert the unexposed silver halide grains to silver and prevent the chemical fogging.
The development process itself produces as by product potassium bromide, which is a
very effective restrainer.
6. Preservatives: potassium sulphite is a commonly used developer preservative.
Developing agents are easily oxidized and readily combine with atmospheric oxygen.
The function of a preservative is to reduce the oxidation of developing agents.
7. Hardeners: the gelatin in a film emulsion swells and softens when it absorbs water. In
automatic processor, excessive swelling must be prevented in order the film can be
transported successfully without jamming or being damaged by the roller mechanism of
processor. To minimize the swelling, powerful organic hardeners such as gluteraldehyde
is employed because they are effective in alkaline developer.
8. Sequestering agents: these are chemicals which prevent the precipitation of insoluble
mineral salts which tends to occur in hard water areas. Compounds based on EDTA
(ethylene diamine tetra acetic acid) are commonly included in developer for this purpose.
Starter solution
The manufacturer supplies developer replenisher for automatic processor in a concentrated liquid
form which requires dilution before it can be used in a processor. When the developer tank has
been refilled, the developer replenisher will be overactive and the first few films will be
overdeveloped. To prevent these undesirable effects, a starter solution is added to fresh
replenisher.
Developer replenisher + developer starter = working developer

In 90s processing cycle time, 26s is allowed for development.
Factors affecting development:
The production of optical decsity and radiograpihic coantrast can be used as a measure if the
efficacy of the development process. The factiors which influence the quantity and quality of
development can be described as:
1. Constitution of developing solution: the image density produces depiends on the amount
of metallic silver formed in the film emulsion.for a particular exposuter this depends on
the emulsion characteristicas and developer activity. Developer activity is influenced by:
• Choice of developing agents and their relative proportions
• Concentration of developing agents in solution
• pH of developer solution: The byproducts of development are acidic and the pH
of developer solution tends to fall. Developer activity is heavily dependent on
solution pH and development is inhibited if pH decreases. Buffers can stabilize
pH upto an extent but rreplenishnemt of alkaline acceleratior is essentioal if
developer activity is to be maintained. The addition of roo much releninsher will
result in too much alkalination and cause chemical fog. The absence of developer
starter from a newly filled developing tank has a similar effect because the pH of
fresh replenisher solution is too high for it to be used as a working developer.
2. Developer temperature: in general developer activity increases with temperature.the
image density and contrast produced when a film is processed can only be standardized if
developer temperature can be maintained constant. Temperature control is therefore an
essentioal featuter of processor design.
In the early days, developr tempratur of upto 42c were necessary to permit 90s processing
cycle time. However low temperature developers for auto preocessor are also acailable
which operate around 30c and can still produce very rapid results. But must moderm
developers operate within a mid range of temperatures between 37 and 33c offering dry
to dry processing cycle times of 90 to 160 seconds, depending on the particular processor
model concermed.
Effect of increased developer temperature:
A slightly raised temperature without a compensating reduction in devleopmnt time
results in increased image density, slightly increased chemical fog and increased image
contrast. A more sever rise in temperature leads to gross increase in density, unacceptable
increase in chemical fog and reduction in contrast. If the temperature is left uncorrected
the developer becomes exhausred resulting in low density, low contrast images.
Effect of reduced developer temperature:

A slightly lowered temperature results in decreased image density for the same exposure,
slightly reduced chemical fog, reduced image contrast. But a more severe fall in
temperature leads to gross overall reduction in density and loss of contrast.
3. Development time: this time may be defined as the time interval which elapses between
the entry of a specified part of a film into the developing solution and the exit from the
developing solution of the same part of the film. The table below shows, development
time varies according to the full cycle time of the processor. In radiography the cycle
time is designed to be as short as possible, consistent with achieving a satisfactory quality
image.
Cycle time Developing time in sec
7 min 130
3.5 min 68
110 s 30
90 s 26
Factors determining development time:
• Developer temperature:
• Type of film emulsion
• Agitation of developer solution
FIXING:

Fixing is the second stage in automatic processing. It has four main functions:
1. To stop any further development
2. To clear the image by removing the remaining silver halide from the emulsion
3. To fix the image i.e. to render it chemically stable so that it undergoes no further changes
and is no longer photosensitive
4. To complete the process of hardening the film emulsion
Constituents of fixing solution: table
Fixing solution consists of:
1. Solvent: Water is the solvent and diluents used in fixing solution. It provides a means of
controlling the activity of fixer by diluting its effects.
2. Fixing agent: It is a chemical which combines with the largely insoluble silver halide in
the film emulsion to form soluble compounds which can diffuse and be washed out of the
emulsion. The fixing agent used in radiographic auto processor is ammonium
thiosulphate. The terms clearing agent, hypo and thiosulphate often are used to the fixing
agent.
3. Activator acid: To ensure that development ceases when a film enters the fixer and to
provide a suitable environment for the hardening agents in fixer, the fixer solution is
made acidic. The weak acid acetic acid is included to provide a pH between 4.0 and 4.5
Component Chemical Function
Activator Acetic acid Neutralizes the developer and
stops its function
Fixing agent Ammonium thiosulfate Removes undeveloped silver
bromide from emulsion
Hardener Potassium alum Stiffens and shrinks emulsion
Preservative Sodium sulfite Maintains chemical balance
Buffer Acetate Maintains proper pH
Sequestering agent Boric acid Removes aluminum ions
Solvent Water Dissolves other components

4. Hardening: Emulsion hardening is essential in automatic processing because it reduces
drying time and prevents physical damage to emulsion surface. Potassium alum,
aluminum chloride are commonly used hardening agent in fixing solutions.
5. Buffer: Precise control of pH of fixer is important in order to prevent sulpharizaton,
ensure neutralization of developer, and maintain optimum hardener activity. Sodium
acetate is commonly included to act as a buffer in conjunction with the acetic acid.
6. Preservative: The preservative in fixer delays the onset if sulpharization. Sodium sulphite
is commonly used as preservative.
7. Anti sludging agent: The aluminum salts used as hardeners have a tendency to produce
insoluble aluminum compounds which may precipitate and form sludge. To reduce the
formation of sludge, boric acid is used as anti sludging or sequestering agent.
In a 90s processing cycle, about 15s is available for the fixing stage.
WASHING:
When a film leaves the fixing tank its emulsion is saturated with fixing solution contaminated
with silver complexes and ammonium halides. To avoid the consequences the film is passed
through a washing stage in which these soluble chemicals diffuse out of the emulsion. Water is
satisfactory washing medium for automatic processing. The temperature of the wash water
should be maintained at approximately 3°C (5°F) below the developer temperature. But the
washing process is 100% efficient. In a 90s cycle processor about 15s is allowed for the washing
stage.
DRYING:
The final stage in the processing of a radiograph is to remove all of the surface water and most of
that retained in its emulsion. Some moisture must remain in the emulsion to prevent it from
becoming too brittle. In automatic processing surface water is removed by squeegee rollers,
while evaporation removes the water from within the emulsion. A 90s processing cycle allows
about 25s from the drying stage.
Automatic processor:
The processing of radiographic films is almost entirely done nowadays by machine with the film
being fed in at one end and received, processed and dried at the other end. While the size, design
and capacity may vary from one manufacturer to other the basic steps involved in processing by
machine remain the same.
TRANSPORT SYSTEM
The transport system functions to convey the film through the different processor sections by
means of a series of rollers driven by gears, chains, and sprockets. This is accomplished without
damage to the film and at a prescribed speed, which determines the length of time film spends in
each solution. The roller system also provides constant, vigorous agitation of the solution at the
film surface. The entire conveyance system consists of the feed tray, crossover rollers, deep
racks, turnaround assemblies, and receiving bin.

Film is aligned against one side of the feed tray as it is introduced into the processor. A sensor
initiates solution replenishment as the film enters, and replenishment continues as the length of
the film passes the sensor. Films should be fed into the processor along their short edge; feeding
the film in “the long way” leads to overreplenishment and increased radiographic density.
Crossover racks are out of solution and bridge the gaps between developer and fixer, fixer and
wash, and wash and dry sections of the processor. Crossover rollers must be kept free of
crystallized solutions that can cause film artifacts as the soft emulsion passes by. The last set of
rollers in each solution section has a squeegee action on film emulsion, thus removing excess
solution before film enters the
next tank. When the processor is not in use for a period of time, it is advisable to leave the lid
open so that moisture can escape. Because the crossover rollers are out of solution, chemicals
carried onto them by film can crystallize and should be cleaned off before the processor is used
again.
Turnaround assemblies are located at the bottom of the deep racks and serve to change the film
direction as it changes from downward to upward motion. Guide shoes, or deflector plates, are
also located where film must change direction. They will occasionally scratch film, leaving
characteristic guide-shoe marks, when they require adjustment.
When returning rollers to the processor after cleaning, care must be taken to seat them securely
in their proper position. Transport problems (processor jam-up) will result if racks are
misaligned.
REPLENISHMENT SYSTEM
As films travel from one processor solution section to another, chemical solution is carried away
in the swollen film emulsion. It is the function of the processor replenishment system to keep
solution tanks full. If solution level is allowed to lower, film immersion time decreases and
radiographic density and contrast changes will occur. Transport problems can also arise from
inadequate replenishment; that is, if insufficient developer replenisher, the inadequate addition of
hardener will result in excessive emulsion swelling. The essentially “thicker” film has difficulty
transporting between the closely distanced rollers.
As film travels through the fixer, it accumulates residual developer solution; fixer solution also
accumulates unexposed silver cleared from the emulsion. Wash water accumulates fixer. In these
ways, the activity of each solution is depleted through continual use. Diminished solution
activity can have the same effects as low solution levels. The replenishment system assures that
proper solution concentration
is maintained.
TEMPERATURE REGULATION
The temperature regulation system functions to control the temperature of each section of the
automatic processor. Developer is the most important solution temperature to regulate; in a 90-
second processor, developer temperature is usually maintained at 92◦F to 95◦ F. Once the correct
developer temperature is established, it must be constantly maintained. Even a minor fluctuation

(i.e., 0.5◦F) in developer temperature can cause a visible change in radiographic density and
contrast.
Developer temperature is thermostatically controlled and developer solution is circulated through
a heat exchanger under the fixer tank. Thus, the fixer temperature is regulated (in cold-water
processors) by heat conducted from the developer solution. In older processors having stainless
steel tanks, fixer temperature is regulated by heat convection from the neighboring developer
solution.
RECIRCULATION SYSTEM
As replenishment chemicals are added to solution, the recirculation system provides agitation
necessary for uniform solution concentration. As temperature adjustments are made, the
recirculation system agitates solution to promote temperature uniformity. Agitation provided by
the system also functions to keep fresh solution in contact with film emulsion. The recirculation
system also functions to filter debris, such as gelatin particles, from the solutions.
WASH AND DRYER SYSTEMS
Thorough removal of chemical solutions from the film emulsion is required for good archival
film quality and is provided by the wash section of the automatic processor. Agitation of the
water makes the process more efficient. Any residual chemicals will eventually result in film
stain. Residual fixer will eventually stain the film a yellowish brown that ultimately obscures the
image and diminishes the archival quality. Films can be tested (usually by the film manufacturer
or distributor) to determine their degree of fixer retention.
The dryer section functions to remove water from the film by blowing warm, dry air over the
film surface. Dryer temperature is usually 120◦F to 130◦F, sufficient to shrink and dry the
emulsion without being excessive. Excessive heat and overdrying can cause film damage. If
films emerging from a properly heated dryer are damp, the problem may be excessive emulsion
swelling and water retention as a result of inadequate developer or fixer replenisher (hardener).
SILVER RECOVERY
X-ray film is expensive and can represent a large part of a radiology department annual budget.
Approximately half of the film’s silver remains in the emulsion after exposure and processing.
The other half (unexposed silver) is removed from the film during the fixing process, and most
of it is recoverable through silver recovery methods. A drain is connected to the fixer tank, and
fixer is allowed to flow directly into a silver recovery unit or to a large centrally located
receptacle.
Silver recovery is desirable for financial and ecological reasons.
Fixer silver is toxic to the public water supply and environmental legislation makes persons
responsible for its direct passage into sewer lines, or other means of improper disposal, subject to
severe fines and penalties.
There are three types of silver recovery methods. Used fixer enters a metallic displacement (or
metallic replacement) cartridge and metallic silver is precipitated onto the steel wool within. This
method of silver recovery is most useful for low-volume locations.

Electrolytic silver recovery units (cells) pass an electric current through the fixer solution,
causing silver to be plated onto the cathode cylinder of the unit. The silver is periodically
removed by scraping it from the stainless steel cathode. Electrolytic cells are best used in
locations having medium-to-high volume.
There are a number of chemicals that will precipitate metallic silver. In the presence of one of
these chemicals (e.g., sodium borohydride), metallic silver falls to the bottom of the tank and
forms a sludge. This method of silver recovery is generally used only by large institutions having
large, centralized receptacles or by professional silver dealers, who employ special techniques
for separating the sludge or removing the entire tank.
PROCESSOR MAINTENANCE
The biggest advantage of automatic processors is their contribution to radiographic consistency.
Testing and monitoring procedures serve to indicate potential problems before they arise.
Developer, fixer, and wash temperature should be checked twice a day. Preventive maintenance
is frequently provided for by a commercial cleaning and parts replacement service.
Sensitometry is the measure of film response to exposure and processing and is used to monitor
quality control. A particular box of film is designated for testing purposes only, and a special
device (sensitometer) is used to precisely and consistently expose the film. Once the film is
processed and its densities are read (with a densitometer) and compared to known correct
readings, any variation in film density must be owing to processor variation. If solution levels in
processor and replenisher tanks are frequently low, a bigger problem may exist and should be
brought to the attention of the processor service company. Preprocessed films should not be used
to clean rollers, because they may contain residual fixer that will contaminate the developer
solution. The more effective the processor quality control program, the less troubleshooting will
be required. Nevertheless, it is important that the radiographer be able to recognize and resolve
some common processor problems.
TROUBLESHOOTING: COMMON PROCESSOR PROBLEMS
AND THEIR CAUSES:
Transport problems (jam-ups)
• Inadequately maintained (dirty) rollers
• Too rapid film feeding, overlapping
• Misaligned crossover or other racks
• Inadequate developer replenisher (hardener)
Excessive density (processor related)
• Developer temperature elevated
• Insufficient dilution of developer
Inadequate density (processor related)
• Developer temperature too low
• Excessive dilution of developer
Damp films

• Dryer temperature too low
• Faulty dryer blower
• Inadequate fixing
• Inadequate developer replenisher (hardener)
Fog (darkroom related)
• Unsafe safelight
• Contaminated developer
• Outdated film
• Improper film storage conditions
• Darkroom light leak
Ball J. and P.Tony,2009, Chesney’s radiographic imaging, 6th
edition. Blackwell publishing.
Bushong S.C., 2008. radiologic science for technologists, 9th
edition. mosby elsevier inc.
Misssouri, usa.
Palmer P.E.S,1978. WHO basic radiological systems, Manual of darkroom technique. WHO,
Geneva.
Saia D.A., 2009, radiography prepration ,5th
edition. Mc graw hill ,

Darkroom procedures during Radiography

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