DARK ROOM AND FILM PROCESSING TECHNIQUES

BY ROS HA N VA LEN T I NE

Dark roomIt is a facility where handling and processing of films can be carried out without the hazard of producing fog by accidental exposure to light or x-rays.

It must exclude all outside light and provide “SAFE” artificial light

It should be in close proximity to the place where the work of radiographer is carried out.

It should serve as many imaging rooms as geographically possible.

LocationIt should be centrally sited and served by hatches(passboxes) from the adjacent imaging rooms.Away from damp and hot areasPower and water accessibilityAdjoining viewing area where processed films can be checked or sorted out

Dark room SIZEMinimum floor area of 10m2

Ceiling height 2.5-3mRADIATION PROTECTIONCoating the walls with barium plaster or increase the thicknessLining the doors with LEAD ply-sheetShielding any gaps around the door

Dark Room FLOORSDurable and easy to maintain(Eg: Plastic tiles)Non porous non slip flooring materialWALLS/CEILINGLight in colorEasy to wipe over and keep clean

Dark room VENTILATION AND HEATINGSatisfactory working condition for staff Good film handling and storage conditionsThis can be ensured by Relative humidity : 40-60%Min of 10 air changes per hourRoom temperature 18-200C

DARKROOM ENTRANCE:SINGLE DOOR

DARKROOM ENTRANCE:DOUBLE DOOR

DARKROOM ENTRANCE:MAZE

DARKROOM ENTRANCE: REVOLVING DOOR

DARK ROOM ILLUMINATION 2 modes of lighting :Ordinary white lighting

Safe lighting

WHITE LIGHTING It is necessary forInspection and maintenance of cassettes and screensCleaning of work surfaces and floorsServicing of equipmentWhite light should beClose to the ceiling to avoid shadowsModerate in intensity (60W tungsten /30Wfluorescent) Centrally placed

SAFELIGHTINGNeed: Working in compete darkness all day long is not a pleasant condition to work on.

White light cannot be used as it causes fogging of film.

Hence DIM COLORED LIGHTING sufficient enough to work at is used

BUT THERE IS NO TOTALLY SAFE “SAFE”LIGHTING

How does a safelight filter work

Its about choosing a filter which will transmit a color to which the film is relatively unresponsive while stopping all light to which the film is most sensitive.

WHY SAFELIGHTING IS NOT 100% SAFENo Filter completely absorbs the undesirable wavelengths

All films have SOME sensitivity to all wavelengths

HOW TO MAKE IT MORE SAFER?Reduce the film handling time and intensity of illuminationRecommended Standard : 25w lamp sited at a minimum of 1.2m from the film

CONSTRUCTIONColored gelatin filter is sandwiched b/w plane glassFitted in a metal lantern box

SAFELIGHTING Areas where safe light is required

Film loading / unloading areas.

Processor film feed-in points.

Path b/w above two.

At developer tank.

SAFELIGHTING Type/prop Direct Indirect Mixed Construction Filter forms the undersurface Filter forms the upper surface Filters on both its upper and lower surfaces Working Directs light towards the floor Directs light towards the ceiling Directs light towards both floor and ceiling Function For film loading and unloading areas For general illumination of the darkroom For both the purposes

SAFELIGHTING Safelight handling timeMaximum time a film can be exposed to safelight during the procedure without causing any appreciable degree of fogging.

Average time : 20-45secs

Faster films need shorter time

DARK ROOM Equipment and arrangementAn automatic processorCassette hatchesFilm storage hopperLoading bench/cupboards

Film processing techniques

PROCESSING CYCLE

Washing

PROCESSING CYCLEStage 1: DEVELOPMENT The primary function of development is to convert the latent

image into a manifest or visible image

Secondary purposes of development. To amplify the amount of metallic silver To reduce the exposed silver halide crystal into metallic silver.

CONSTITUENTS OF DEVELOPINGSOLUTION

Developing Agent

Accelerator

Restrainers

Preservative

Hardener

Solvent

DEVELOPING SOLUTIONDEVELOPING AGENTPrincipal component is hydroquinone (produces black tones slowly).Secondary constituent is phenidone or metol (produces shades of grey rapidly).

Advantage of PQ developer: adequate activity high selectivity super-additivity (oxidised phenidone is reduced by hydroquinone)

DEVELOPING SOLUTION ACCELERATOR/ACTIVATOR/BUFFERING AGENTAlkaline medium for the action of PQ-accelerates the developing processKCO3 or KOHIdeal range of pH: 9.8-11.4RESTRAINER/Anti-foggantIt reduces converting unexposed AgX to Ag and thus prevent chemical fogging.KBr, benzotriazole(used with PQ developer)

DEVELOPING SOLUTION PRESERVATIVE It reduces the oxidation of developing agents. Eg: Potassium sulphite

HARDENERIt controls gelatin swelling to minimize risk of physical damage. Eg:Glutaraldehyde

DEVELOPING SOLUTIONSEQUESTERING AGENTPrevents the precipitation of insoluble mineral salts which occur in hard water areasEDTA containing compounds are used

SOLVENTCarrying medium for dissolving the developer constituentsSoftens the film emulsion gelatinMC used : Tap water

FACTORS AFFECTING DEVELOPMENTTemperature of the developing solutionTotal time of the development

An adequate combination of both is important for complete development

TEMPERATURE FOR DEVELOPMENTOptimum temperature is 20-22oCBelow 16oC, action of hydroquinone ceases

◦ Radiograph lacks contrast and density◦ Can be compensated by increasing the developing time.

Above 24oC (too warm) emulsion softens.◦ Chemical fog results

DEVELOPMENT TIMETime interval which elapses between the entry of a specified part of a film into the developing solution and its exit.

Short processing times reduce waiting times.

FACTORS DETERMINING DEVELOPMENT TIME Developer activity- Active developer achieves given image density more rapidly.

Type of film emulsion- Thick emulsion film > thinner ones(non screen type>screen type film)

Agitation- Proper agitation fasten the development process.

STAGE 2:FIXINGDuring development not all the silver halides are reduced. Only 40% get reduced

The remaining silver halides greatly impairs the usefulness and permanence of the developed radiograph and hence have to be removed.

FIXATIONIt has four major functionsStop any further development

Makes the solution more acidic

Remove the unexposed AgX from the emulsionConvert it to soluble compounds and remove it

Makes the image chemically stable and no longer photosensitiveCompletes the process of hardening of emulsion

Minimizes water absorption and reduces drying time

FIXER SOLUTION FIXING AGENTThe fixing agents by forming water soluble complexes

tightly binds the silver ions and removes them from

the solution.Eg: sodium thiosulphate(HYPO) Silver bromide +sodium thiosulphate

Silver thiosulphate complex +Sodium bromide

FIXER SOULTION ACIDIFIER

To stop the development process. Create an acidic pH environment for fixing agent.Eg-Acetic acid

PRESERVATIVE To protect the fixing agent from oxidation and to maintain its activity, - Sodium Sulfite

HARDENERTo further harden the emulsion to make the resultant image permanent. Al salt such as Al sulphate, Al chloride.

SOLVENTThe purpose is to dilute the chemicals in the fixer solution – so that the chemicals can function at their desired level of activity. Water

STAGE 3 : WASHINGPurpose of washing is to remove fixing solution from the surface of the film.

If the film is not properly washed, it will show a brown staining caused by thiosulfate (fixing agent that remains in the emulsions).

The process by which washing works is diffusion.

Tap Water is mainly used

STAGE 4 : DRYINGPurpose is to remove 85-90% of the moisture from the film.

If film is dried excessively, emulsion can crack which decrease the diagnostic quality.

TYPES OF FILM PROCESSINGAUTOMATIC

1- Unloading the film2- Inserting into processor

MANUAL

1-Unloading the film2-Loading the film onto a hanger 3-Development4-Rinsing or stop bath5-Fixing6-Washing7-Immersion in a wetting agent8-Drying

AUTOMATIC PROCESSOR

AUTOMATIC PROCESSORConsists of chemical tanks, a roller transport system and a dryer system for the processing of radiographic film.

Processing time -amount of time taken to process a single piece of film-90-115s.

Processor capacity – No.of film that can be processed per hour based on which its divided into high and low.

AUTOMATIC PROCESSOR Tanks

1. For Developer solution

2. Fixer solution

3. Wash tank for water

During a 90s processing cycle Developer------ 26s Fixer ----- 15s Wash ----- 15s Drier ------ 24s Travel time----- 10s

SUBSYSTEMS OF AN AUTOMATIC PROCESSORTransportTemperature controlReplenishmentRecirculationWashDrying

TRANSPORT SYSTEM It ensures that the film moves through developer , fixer , wash and dryer at a controlled and consistent speed without damage

Mainly 3 roller assemblies1)Entrance roller2)Transport roller3)Turn around roller

CYCLE OF EVENTS Drive motor energized(to turn the rollers)Safelight above the feed tray extinguishedDeveloper and fixer replenisher pumped into tanksDrier heater energizedWash water flow rate boostedFilm signal delay time activated

But how does it get triggered ?

ENTRY ROLLER DETECTION SYSTEM

INFRARED DETECTOR

MOTOR DRIVE An electrical motor provides power for the roller assemblies to transport the film through the processor.REPLENISHMENT SYSTEMFunction of replenishment system is replacement of fresh chemicals after the loss of chemicals during processing - specifically developer and fixer solution.

OVER REPLENISHMENT Of developer solution causes an increase in radiographic density and decrease in radiographic contrast.Of fixer solution – no effect on radiographic quality.

UNDER REPLENISHMENT Of developer can cause decreased density. Of fixer – result in poor archival quality of finished radiograph

RECIRCULATION SYSTEMTo maintain solution activity and the required agitation. Also, to maintain proper temperature of the developer solution.Temperature controlIf the temperature in developer tank Raises increases the density. DropDecreases the density.

WASHINGSPRAY WASH By the help of processors situated in between the transport

roller. Water flow rate could be as high as 10 L/min

TANK IMMERSION Water fed in to the tank by developer/heat exchanger. Water flow rate is between 4-7L/min

DRYING SECTIONInitial drying happens when the film moves through the squeegee rollers between the wash and drying sectionWhile in drying section , it is commonly dried by 1 Hot air drying 2 Infrared drying.

Dichroic Fog

MANUAL PROCESSING1-Unloading the film2-Loading the film onto a hanger3-Development4-Rinsing or stop bath5-Fixing6-Washing7-Immersion in a wetting agent8-DryingFour Compartment tank – Developing, rinsing, fixing, and washing.

MANUALPROCESSING

MANUAL PROCESSING TANKS

DARK ROOM

MANUAL PROCESSING

DEVELOPINGIt is done by time – temperature techniqueHere film is immersed in developer for 4 minutesTemperature is maintained at 20 CAt intervals with in 4 minutes film is examined under safelightsIf image seems to lack expected density at 4 minutes, development is continued

MANUAL PROCESSING RINSINGPurpose is to slow the action of developer and to remove it from the surfaces of the film, done by a plain rinse bath.To stop the action of developer, done by acid stop bath. FIXING After rinsing, the film is immersed in fixer solutionFixing time can be up to 5 minutes

MANUAL PROCESSING WASHINGImmerse the film in large tank or in a series of tanks through which water is kept flowing.Time duration:- 20 – 30 minutes DRYINGHot air drying cupboards or by rapid drier machines.Temperature may vary from 40-50 C

COMPARISONMANUAL

• DEVELOPING TEMP 200 c

• FIXING TEMP 200 C

• WASHING TEMP 200 C

• DRYING TEMP 430 C

• DEVELOPING TIME 3-5 MIN

• FIXING TIME 2-10MIN

• WASHING TIME 15-30MIN

• DRYING TIME 15-20MIN

• SURFACE CHANGE- MANUAL

• REPLENISHMENT - MANUAL

AUTOMATIC

• 350 C

• 350 C

• 350 C

• 570 C

• 25s

• 21s

• 9s

• 20s

• TRANSPORT ROLLER

• AUTOMATIC

THANK YOU