Film Processing

Dr. Hussein Ahmed Hassan

Processing CycleThe complete processing cycle comprises:

Manual Processing• Development• Rinse • Fixing• Washing &• Drying

Automatic Processing• Development • Fixing• Washing &• Drying

The object of the cycle is to produce a dry radiograph carrying a high quality image which can be stored for a number of years without deterioration.

The formation of the latent image• It is the first stage of photochemical process• All information eventually seen in radiograph

is recorded as minute changes in silver bromide crystal.

• These changes are so small that even electron microscope reveal no difference between an exposed and an unexposed crystal.

• Only developer will show which is which.

Cubic crystal lattice: silver bromide

The silver bromide crystals of photographic emulsion consists of positive silver and negative bromide ions arranged in a geometric pattern known as a crystal.

• Diagram of one plane of a silver halide crystal. The structure of a silver halide crystal is simple cubic, with alternating lattice points occupied by either a positively charged silver ion or a negatively charged halide ion. In a three-dimensional view, each negatively charged halide ion has six nearest neighbors along orthogonal directions that are positively charged silver ions.

Similarly, each positively charged silver ion has six nearest neighbors along orthogonal directions that are negatively charged halide ions. The diagram also illustrates the Frenkel defect, which consists of a silver ion vacancy and an interstitial silver ion. Such defects are created by thermal excitation of a silver ion from its lattice site into an interstitial position, and the equilibrium concentration of such defects is a function of temperature

Diagram of one plane of a silver halide crystal.

It is well known that exposure of any substance to a source containing the correct wavelengths and energy produces three effects;

1.Compton effect.

2.Photoelectric effect.

3.Pair production.

In the x-ray to the blue range used to expose conventional unsensitised film the first two effects occur in the silver halide crystal (96% of the electrons produced are from the photoelectric effect .

• An electron-trap is a region in the crystal of low energy called a sensitivity speck is produced during manufacturing.

Diagram illustrates the Mott-Gurney model for the photographic process.

1. The process starts with the absorption of a photon of light (hv). The energy absorbed liberates an electron (e), which is hence called a photoelectron.

2. The net result of this process is a photoelectron and a neutral bromine atom or a photohole.

3. Both the photoelectron and photohobe can move through the silver halide lattice by thermally activated transport processes.

4. The photoelectron is readily trapped at a sensitivity’ center in the silver halide grain, making this center negatively charged.

5. A positively charged interstitial silver ion is then attracted to the now negative by charged sensitivity center, where the photoelectron and the interstitial silver ion combine to form a neutral silver atom.

6. This sensitivity center will now attract another photoelectron, and the process repeats until this site is populated by at least four silver atoms; this site forms a developable latent image center.

7. In an optimally exposed film, the number of silver atoms per latent image center will range from four to about 30, with experiments suggesting that the most common population is four or five .

1

1. When silver bromide grain is exposed to light (or x-ray), some of the bromine ions in the lattice emit electrons.2. These electrons are able to travel through the crystal, and their rapid movement carried them into what are known as electron-traps existing in the crystals.3. Not all silver ions in the crystal are held in the lattice (interstitial- ions). Those that are able to travel are attracted to the negatively charged electrons in sensitivity speck.4. The negative charged on electrons neutralizes the positive charge on the silver ions, and when this happens silver atoms are formed.

5. The sequences repeats its and the sensitivity speck has a number of atoms of silver ( Latent image).

6.This cycle of events takes place extremely quickly (10 ms)

Processing Chemistry Overview

• Developer – converts latent image into manifest image

• Fixer – clear the film of unexposed, undeveloped silver bromide crystals, promotes archival quality

• Wash – rid the film of residual chemicals

Film Processing

The latent image is invisible because only few silver ions have been changed to metallic silver and deposited at sensitivity centre.

Processing the film magnifies thus action many millions of time.

Thus latent image is converted to visible image.

The production of latent image and the conversion of the latent image into manifest image follow several steps. A, radiation interaction releases electrons.B, these electrons migrate to sensitivity center.C, at the sensitivity center, atomic silver is formed by attracting an interstitial silver ion.D, this process is repeated many times, resulting in buildup of silver atoms.E, the remaining silver halide is converted to silver during processing. F, the resulting silver grain.

The nature of development

• Development is the first stage in processing cycle . This is the production of a visible metallic silver image from the latent one which exists in sensitive material after exposure to light or x-radiation.

• Exposed silver halide grains + Development = Metallic Silver (black color).

• Unexposed silver halide grains + Development = remain largely unchanged (light color).

Chemical action of the developer

The Action of the Developer

• Conversion of silver halide = metallic silver

• Developer ---- gives electrons to silver ions.

• Electrons + silver ions = silver atoms.

Radiography recorded by x-ray

• Imaging = exposure + processing

Exposure latent image

Processing permanent image

Schematic distribution of silver halide grains on the film emulsion.The gray areas indicate latent image produced by exposure.

Partial development begins to produce metallic silver (black) in exposed grains.

Development completed.

Unexposed silver halide grains have been removed by fixing.

A developer is chemical solution that converts the invisible (latent) image on the a film into a visible one composed of minute masses of metallic silver.

An alkali chemical solution

• Converts exposed silver bromide crystals (latent image) to black metallic silver (visible image).

Production Permanent image

• This involves the action of a chemical agent to make the hidden image visible. This stage is known as development, and it is followed by further chemical processes which fix the image and make it into permanent record.

Developer Solution(8 compounds)

1. Reducing Agent: reduce exposed silver halide to black metallic silver

-Hydroquinone (Blacks)-Metol or Elon-Phenidone (Grays)

Constitution of Developing Solutions;

• Developer agents - Reducing agent

(Metol, hydroquinone MQ. Phenidone,Hydroquinone PQ

Hydroquinone slowly action

Metol & Phenidone quickly action

Manual Processing \ MQ

Automatic Processing \PQ

Activity of Reducing Agent

• High or low reduction potential.

Susceptibility to bromine ions concentration released into solution.

• High or low selectivity ratio.

• The PH scale:

• The PH scale is used to express the degree of acidity or alkalinity of a solution. Its based on measure of concentration of positively charged hydrogen ions in the a solution.

• In water the H2O molecule dissociates into H+ & -OH-. In water these ions are equal in numbers, at concentration of 10-7mol/l. addition of substances result increase of H+ >10 -7. The solution said to b acidic.When the added substances reduce to<10-7,the solution said to be alkaline.

•The logarithm of H+ concentration provides a convenient figure on which to base a scale of acidity and alkalinity.

•For gastric juice, for example: log10 (H + concentration) =log10 10 -1.7 = -1.7 the pH of gastric juice is then said to be 1.7.

•For blood plasma, log10 (H + concentration) =log10 10-7.4 = -7.4 the pH of blood plasma is then said to be 7.4.

The pH scale. A pH greater than 7 is alkali, less than 7 is acid. Note that even unpolluted rain water is acidic, due to the effects of dissolved carbon dioxide.

pH scale

The nature of development

• Development is the first stage in processing cycle . This is the production of a visible metallic silver image from the latent one which exists in sensitive material after exposure to light or x-radiation.

Developing Agents• Is a substance able to change silver halide

into metallic silver.• Chemical reducing agents.• Neutralize silver ions in silver bromide by

donating electrons to them.• Has ability to differentiate between exposed

and unexposed grain of silver halide.• Lack of this ability would make a reducing

agent totally unsuitable for use in a developing solution.

• Exposed silver halide grains + Development = Metallic Silver (black color).

• Unexposed silver halide grains + Development = remain largely unchanged (light color).

Must exhibit certain characteristics:1- Must be selective and distinguish effectively

between exposed and unexposed grains.2- Must very active to allow complete

development in short time e.g 20-30 seconds, giving a total processing tie of 11/2 –2 minutes (selectivity and activity tend to be antagonistic properties).

3- Must be as resistant as possible to the presence of bromide ions in solution.

Developer agents

The Action of the Developer

• Conversion of silver halide = metallic silver

• Developer ---- gives electrons to silver ions.

• Electrons + silver ions = silver atoms.

• By-products of developer:• The developer becomes depleted of electrons; it

said to oxidized.• Reaction with atmospheric oxygen, causing

aerial oxidation of developer.• Thus the supply of reducing agent in developer

is gradually exhausted.• pH fall due to formation of hydrotropic acid as

combination of positive hydrogen ions and bromide ions release by developed silver halide grain.

• If not corrected, these chemical changes will cause the developer to become progressively less effective.

Chemical action of the developer

Unexposed crystal protected from attack by electrons because of the presence of a complete negative barrier around the crystal. Exposed crystal has break in the barrier, due to presence of neutral silver atoms at sensitivity speck,constitutes a development center which enables electrons from developer to penetrate the crystal and reduce it completely to silver.

Underdevelopment results in a dull radiograph overdevelopment produced too dark radiograph. Proper development in maximum contrast.

Superadditivity effect obtained with a PQ or MQ developer. The effect obtained from the phenidone-hydroquinone mixture is far greater than the simple arithmetic sum of their separate effect.

هلوجينات وجود يعني هذا التظهير قل اذا ( سوداء ( تصبح لم تظهر تنمي لم معرضة

والعكس.

PQ compared with MQ1. High contrast than MQ2. High speed than MQ3. Low auto oxidation than MQ4. The activity not dependent on Br-

concentration5. Temperature dependent6. Liquids concentration7. Less likely to cause dermatitis8. Cause less stain (color) than MQ9. Long shelf life time

Phenidone (P) characteristics High speed Low selectivity low contrast Liquids concentration5. Only 10-15% compared with Q give

similar activity( more active)

Metol (M) characteristics slow speed High selectivity High contrast Ability to auto oxidation by O2 The activity not dependent on tem- and

PH .

Metol (M) characteristics = Hydroquinone (Q) characteristics

Development time

• The time for reducing all exposed Ag Br only ,do not cause changes in unexposed one.

Factors determining development time; the development time required to produce optimum image quality is determined by :

Developer activity.Type of film.Agitation of developer solution.

Factors affecting development

The production of optical density and radiographic contrast can be used as a measure of the efficacy of development. The following factors influence the quantity and quality of development;

1. Constitution of developing solution.

2. Developer temperature.

3. Development time.

Control of developing

1. Time temperature control.

2. Inspection.

Most chemical activity is temperature-dependent, and photographic development is no exception. In general, developer activity increases with temperature.

temperature control therefore essential to development.

15º C 7 min16º C 6 min18º C 5 min20º C 4 min22º C 3 min24º C 2 min26º C 1 min28º C 30 sec

Replenishment;

Adding of fresh developer to the used developer (exhausted) to maintain activity and volume .

Without replenishment the activity of a developing solution inevitably falls and image quality suffers.

Activity of developer can only be maintained if the lost chemicals are replaced by adding developer replenished at the correct rate

Maintenance of developer volumeCarry over

1.Developer solution which has been absorbed in the emulsion.

2.Developer solution adhering to the surface of the film.

Evaporation a small amount of solution volume will be loss due evaporation.

Factors affecting developer replenishment rate

• Area of processed film. (35x43 cm film uses more developer than 18x24 cm).

• Type of emulsion. (direct exposure film consumes more developer agent than a screen –type).

• Type of image. (radiograph for the which the has been collimated,

uses less developing agent than a similar radiograph with collimation)

• Aerial oxidation. ( the rate of aerial oxidation and thus the need for replenishment are reduced if the area of the surface od developer solution exposed to the air can be minimized).

Developer Solution

2. Activator: (Accelerators) an alkali, PH

softens gelatin, maintains alkaline pH (increase pH)

-Sodium Carbonate

• sodium carbonate NaCo3& NaoH

• soften and swells film emulsion

Development

• The stage convert invisible latent image into visible image

• Development is a process of chemical reduction oxidized.

•A good developer is highly selectivity act on exposed grains

•A poor developer is low selectivity act on exposed grains

Developer Solution

3. Hardener: prevents damage to the film from over swelling of gelatin in automatic processors.

-Gluteraldehyde

• Hardener Glutaraldehyde)

• prevent swelling;

Developer Solution

4. Preservative: Antioxidant that prevents oxidation of developer

-Sodium Sulfite

• (antioxidant; sodium sulphite)• Slow oxidation of the reducing agent

by room air

Developer Solution

5. Restrainer: prevents chemical fog in new developer

-Potassium Bromide

6. Solvent: dissolves & ionizes the developer chemicals

-Water

Developer Solution

5. Restrainer: prevents chemical fog in new developer

-Potassium Bromide

• (potassium bromide KBr , potassium iodide).

• Reduce the action of the reducing agents

Developer Solution

6. Solvent: dissolves & ionizes the developer chemicals

-Water

• Solvent (water)

• Medium in which chemicals are dissolved

• Developer Solution

• 7 Buffers

• maintaining the pH;carbonates {accelerators, and sulphite acting as preservative}.

• 8.Sequestering agents (prevent precipitation of insoluble mineral salts EDTA (Ethylene-diamine-tetra-acetic –acid}).

Rinsing : Stop bath or water rinse

Between developing and fixing stages to avoid carry of the developer to fixer and this cause:

1. Dichotic fog ( Pink greenish color if view reflective light and yellow brown when viewe by transmitted light.)

2. Increase fixer alkalinity.

3. Require about 30 sec

Rinsing stage

• Manually by

1. Static water

2. Continually renewed water

More effect water + acid to stop developer action.

• Different between silver halide and metallic silver

1. Silver halide can be converted into soluble compound by action of chemicals known as fixing agent

Metallic silver Ag un affected and remains in soluble.

2. Metallic silver is opaque to light the black parts of radiographic image are formed from metallic silver.

3. Silver halides are sensitive to light, metallic silver is not

Fixer Solution(7 compounds)

1. Clearing (Fixing) Agent: dissolves undeveloped silver halide

Sodium thiosulphate Na2 S2 O3 in manual

Ammonium thiosulphate (NH4)2 S2 O3.

Ag Br + Na2 S2 O3 Argento thiosulphate complexes

Ag S2 O3 (NH4 ) or Ag S2 O3 Na2 white Solvent ( milky appearance)

Clearing time • The clearing time” is defined as the time for the milky

appearance of film that receiving fixation, to just disappear, leaving the expected transparent image.

• The clearing times and fixing times for the two common agent used are:

• Ammonium thiosulphate;

Fixing time = 1.3 x clearing time, clearing time = 8-10 sec (approx.).

• Sodium thiosulphate;

Fixing time = 2 x clearing time, clearing time = 4-5 min.

Fixation• Fixing agent; It has four majors 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.

4. To complete the process of hardening the emulsion.

Fixer Solution

2. Hardener (Tanning) Agent: shrinks, hardens, preserves emulsion

-Aluminum Salt

Aluminum chloride Shrink and hardens emulsion

Fixer Solution

3. Activator: neutralizes developer, maintains acidic pH (decrease pH)

-Acetic Acid

• Acidifier

Acetic acid provides acid medium in which fixing agent operates

stop the action of the alkaline developer solution on contact.

Fixer Solution

• 4.Buffer (acetic acid + sodium sulphate or potasium sulphate)

Is a solution whose acidity or alkalinity is practically unchanged by dilution and which resists a change in pH on adition of acid or alkali.

Fixer Solution

5. Preservative: prevents oxidation, prolongs solution life

-Sodium Sulfite6. Sequestering agent; to remove aluminum

ions - Boric acid 7. Solvent: dissolves other ingredients

-Water

Factors control fixation rate

1. Agitation

2. fixer Agent type

3. Temperature

4. Solution concentration.

Wash

• Rid the film of residual chemicals• Residual chemicals on the film will discolor

radiograph over time.• Cold water processors are less efficient in

removing chemicals – Warm water processors much better.

• Agitation during wash process is essential

Washing • Water is as washing solution.• Function of washing is to remove from the emulsion of the

film fixer and silver complex salts.• Silver complex deteriorates with time to form silver sulphide

which produces an overall yellow/brown fog. • Residual thiosulphate if not completely removed it

decomposes to produce acid which attacks the silver image and converts it to silver sulphide. This result in yellow/brown staining and image fade.

• The level of fixer residual in the film determines the archival performance.

Factors affecting wash rate

1. Steepness of concentration gradient.

2. Rate of water flow.

3. Degree of agitation.

4. Temperature.

5. Degree of hardening.

6. Time in wash tank.

7. pH of wash water.

•

Fixer Retention(Not Washed Off)

Drying Is to remove all of the surface water from the film’s emulsion.

Factors affecting drying time the time required to dry a radiograph adequately by evaporation depends on two major factors; (1) The wetness of the emulsion (volume of water retained in the emulsion). It depends on hardness of emulsion and emulsion thickness. (2) The drying conditions. The medium is air, the speed with which it can evaporate moisture from the emulsion depends on: air humidity, air temperature and circulation.

MQManual Processing

Whichever way they are produced, processing chemicals must be mixed and handled according to manufacture’s published instructions. This includes careful control of cleanliness of receptacles, contamination, temperture, and volume of chemical and water used .

Automatic Processing PQ

Whichever way they are produced, processing chemicals must be mixed and handled according to manufacture’s published instructions. This includes careful control of cleanliness of receptacles, contamination, temperture, and volume of chemical and water used .

Manual processing

• Before the introduction of automatic film processing films were processed manually.

• The film was first immersed in tank containing developer

• Immersed in a stop bath.• Fixer solution.• Water for washing.• Hung to drip dry.

Processing Sequence• Developing Developing is the stage during which

latent image is converted to a manifest image.• Rinsing stop bath• Fixing Is the stage of processing during which unexposed

silver halide dissolved & removed from the emulsion.• WashingIs the stage during which any remaining chemicals are

removed from the film

Processing Equipment Materials

Film hanger and film tanks made from material

• Do not cause change by action of processing solutions

• with low cost

Processing tank

Two types of tanks

1) Vertically (deep tank)2) Horizontally (shallow tank)

Manual processing tanks. The tank labeled A, is developerB, is the rinse and wash tank and C is fixer tank

Water jacket to control processing chemical temperature and keep site clean

Film hanger

1. Channel hangers

2. Tension hangers

3. Dental hanger

4. Hanger bar sand clips

Made from steel resistant to solutions reaction

A clip hanger (left) versus a channel film hanger

Horizontally (shallow tank)

• Can not develop number of films

• Can not control processing

• Can not control temperature

• Cause air oxidization

Processing• Amplifies latent image by 100,000,000!• forms visible silver• reduces silver ions into neutral black

metallic silver atoms which remain on the film after processingAg+ + electron Ag

• processing initiated at latent image speck– grain either develops entirely or not at all

Processing

• Silver atoms at latent image center act as catalyst

• Grains with no latent image also develop much more slowly– Developer time is fundamental in

development– processing should stop when maximum

difference between exposed & unexposed crystals

Processing Developing Solution

• developing agent– hydroquinone– phenidone or metol– combination yields development rate greater than sum of each

• alkali– adjusts pH

• preservative (and oxidation preventative)– sodium sulfite

• restrainers– antifoggants (reduces development of unexposed grains)

Developing Time• Controlled by

– Speed of transport– Film path in develop rack

• System of rollers & chains which direct film through developer tank

• “90 second” processor– 90 seconds from film in to film out– Time in developer ~ 20 second– Time in fixer & wash tanks controlled by

size of fixer & wash racks• Transport speed does not change because at any

time films may be in any or all tanks

Developing• Temperaturecontrolled to ~0.5 degrees90 - 95 degrees for 90 second processor100+ degrees for 60 second processor

• Replenishment– automatic addition of fresh chemistry to

replace chemistry depleted in development– even with replenishment, chemistry must

be completely replaced periodically

Fixing

• Function– removes remaining silver halide / silver ions without

damaging metallic silver

– hardens gelatin

• composition– cyanides (poisonous & not usually used)

– thiosulfates• sodium or ammonium salt

– hypohypo

– buffers to maintain pH

Washing

• Removes fixer chemicals

• Fixing leaves milky appearance on film– unwashed film turns brown with age

CONCLUSIONS• Understanding the basic physics and chemistry’

involved in the photographic process and the various steps involved in recording and interpreting a radiographic image is an important prerequisite to producing consistently’ good diagnostic image quality.

• Because the technologist is ultimately responsible for the production quality image that he or she makes, it is appropriate that student radiographers are provided with the information needed to achieve such an understanding.