Lecture 4 The Darkroom

8/7/2019 Lecture 4 The Darkroom

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The DarkroomInside the darkroom:

- It is imperative that the counter tops, floors, accessories and equipment bekept clean and uncluttered.

- Cassettes will be opened and screens exposed to debris during

processing if not clean- The room has low light (safelights) which makes it hard to see

o In some darkrooms I have been in, it has been scary how messy it

was when the white light was turned on

The room should only be used as a darkroom- Some people actually have the darkroom in the bathroom ugg- Individuals who are processing films should have clean dry hands which

are free of chemicalsProper ventilation is important as the smell of the chemicals can be over bearingin a small space

The humidity must also be controlled (30-50% best) and the temperaturemaintained. Unexposed film is often kept inside the darkroom in boxes. Staticcan be a problem if the humidity is not controlled.

Safelights:Safelights are used for illumination to allow individuals to see to process filmsthat cannot be exposed to white light during processing. If safelights are notused, it will be pitch-black working conditions to develop the films. Care must betaken to prevent unwanted fogging of the film from light exposure.So, we use safelights.

Remember how we talked about film being sensitive to certain wavelengths oflight (blue and green)?

- If the film used is sensitive to blue light only a Wratten GB(6B) filter can beused

o It produces an amber light

- If the film used is sensitive to green light, a Wratten GBX(GS1) filter mustbe used

o It produces a red light

- If you are uncertain of the films sensitivity to light a red will be safest- Filters can crack so it is important to check them often

The bulbs used are15 Watt so the likelihood of the safelights fogging the film isdecreased. The safelights are also located a minimum of 4 feet from theprocessing work space. When removing the exposed film from the cassette,reloading the cassette and developing the film, one should complete this processquickly. If films are exposed to the safelight for too long, safelight fogging canoccur.


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If films appear to have unwanted density after processing, a safelight test can bepreformed. A piece of film is unloaded from a cassette and covered leaving a 1inch strip on the end for 10 seconds, the move the cover back another inch for 10seconds and so on till the whole film has been exposed. In the end, one end willhave been exposed for the entire time and you can see what your safelight will

do to your films if you leave them exposed to the safelights for various times.

Manual film processing: not recommendedThe tanks: (should be away from the dry working area)

- Developero Reducing agents (hydroquinone and metol)

o Activator (sodium carbonate) swells and softens the emulsion

o Restrainer (potassium bromide) - protects unexposed silver

halide crystals from being developedo Preservative (sodium sulfite) prevents oxidation of reducing

agents

o Solvent (water) dissolves the chemicals- Rinse- Fixer

o Fixing agent (thiosulfate)

o Acidifier (acetic or sulfuric acid) stops development, neutralizes

the developero Hardener (ammonium chloride) shrinks and hardens

o Preservation (sodium sulfite) maintains chemical balance of fixer

o Solvent (water) dissolves the chemicals

- WashThe tank levels should all be checked to be sure they will completely cover the

films.The temperature in the tanks should be noted and adjusted as necessary.The tanks should also be stirred so that chemicals are mixed. Different sticksshould be used for stirring. Some people use paddles to stir.Films are removed carefully from the cassettes only opening the cassette wideenough to remove the film. This decreases the chance for debris entering thecassette. Films should be held only on the edges. They are then placed in theappropriate sized hanger. Small clips are found on the corners and these areconnected to the film pulling the film tight. The bottom clip is usually attachedfirst since the top clip is spring-loaded for final stretching.Then it is time to develop.

Developing:The principle function of the developer is to reduce the exposed silver halide tometallic silver.When placing the films into the tank be sure to allow an adequate space betweenthe films. If the films touch, this will be an area what will not develop (kissingartifact).The film should generally be developed for 5 minutes at 68 degrees F.


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- Often film and processing chemical manufacturers will make suggestionsfor use with their product.

- There are also time temperature charts available for use.o Increasing the temperature will decrease developing time but will

also decrease the margin for error and lead to film fogging

o Decreasing the temperature will increase developing timeo A timer (like an egg timer) should be used

Start the timer, put the film in and agitate it for 15 seconds to remove any airbubbles that might reside on the surface.After 5 minutes remove the film from the tank rapidly to prevent developer fromthe film surface from dripping back into the developer tank.

- Developer on the film surface is spent and will cause the remainingchemicals in the tank to become less active for use next time.

Rinsing:- This allows for removal of excess developer on the film.

The film is then moved to the rinse bath and agitated for 15-30 seconds.Remove and all to drain back into the rinse bath, not into the fixer as this willcause fixer dilution.

Fixer:- Stops the residual chemical reduction process of the developer- Sodium thiosulfate (hypo) coverts undeveloped silver bromide crystals into

soluble compound and then they are removed.- Preserves emulsion and allows for film storage

The film is then placed in the fixer solution for twice the development time(usually 10 minutes). Be sure to restart the timer. Agitate the film to remove air

bubbles again. At the end of the time, the film is again quickly removed so as notto allow dripping of the fixer and then placed into the wash bath.

Wash:- Must have at least 10 water changes per hour- Removes excess fixer

The film should stay in the wash bath for 15-20 minutes.

An easy way to remember it is multiply by 25 develop10 fix

20 wash

Dry:- The film can be dried at room temperature or in a drier for a quicker dry- They should not touch during drying as they will stick together- If the film is dried for too long, cracking of the emulsion can occur


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Cut off the nipples created by the clips. There are specific cutters made to dothis or one can just use scissors. If these are not removed they can causescratches on other films. Then the film is ready to store.

Why not to do manual processing: (As I see it)

Manual processing is very labor intensive. Technicians time in a veterinarypractice can be better spent in a more financial productive manner.It is also very time consuming waiting for the radiographs to be processed to treatthe animal.People cut corners and this leads to poorly developed radiographs with lots ofartifacts present.The maintenance of the chemical solutions, the tanks and the other equipment isoften poor thus leading to a very nasty, messy darkroom. This again leads to filmartifacts.

Daily duties:-

Stir chemicals- Check temperature- Visually check for light leak in darkroom- Check levels of chemicals- Clean counter space- Check first film of day as a quality control

Monthly duties:- Safelight check- Check clips to make sure no residue on them- Clean cassettes and make sure hinges close tightly-

Scrub processing tanks and change chemicals if needed

Automatic Processing:

This is the way to go. Granted anytime mechanical devices are used there is apossibility for breakdown. A back up plan needs to be in place. Hooking up withanother vet practice or a human hospital in cases of emergencies arepossibilities.

These machines are pretty simple and you or a service person can perform manyof the repairs.

Automatic film processors:- Require little floor space, darkroom can be smaller- Less film artifacts- Save considerable time in darkroom- Control temperature of solutions automatically- Controls chemical quality automatically- Produce a dry radiograph in 90 seconds to 7 minutes per film


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- Films are much more consistent- They are reasonably priced

A heating element is built in for temp control.A feed tray takes them film and sends it through a series of rollers. The transport

mechanism is what separates automatic from manual processing.The same type chemicals are used as the film is rolled through each of thetanks. A rinse is not present between the developer and fixer a squeegeeaction is used instead. The amount of time spent in each tank depends on thesettings of the ears and the speed of the motor. Tanks are replenished aftereach film is developed automatically.The dryer is composed of a blower motor, blower fan, heater and an adequateexhaust system.Can be connected to a normal 110-volt outlet.Maintenance must also be performed on these machines too daily, weekly andmonthly. Particularly the rollers must be maintained to decrease the likelihood of

roller artifacts.

Patient identification:Every radiograph should be marked in such a way a positive identification can bemade at a later date. The information should be in the film emulsion. The labelshould be put on before processing. It is not good enough to write the name onlater this will not hold up in court.

- Films are a legal document.- You are more likely to get your films returned if the film is labeled with your

name or the clinic name.- For follow up radiographs, it is nice to know the date that the last films

were made.

What is the minimum information that must be on the film?- Patient name- Doctor or hospital name- Date

Other information such as breed, sex, age, and owners name can also be addedbut is not necessary to make it legal.

How do we get the information on the film?- Lead impregnated tape

o The tape comes in rolls like duct tape and you cut off a small piece

and the write the name on the tape and then stick the tape on thecassette.

o Must be inside the collimated beam to be seen

- Lead identification markerso These are little numbers and letters and you spell out the

information for the patient and put it on white tape then stick that tothe cassette


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o Cracks in the safelight or improperly working safelight

- Scatter fogo Get by not using a grid when one should be used

o If the x-ray cassette is left in the room when another radiograph is

being made (even though it is not in the primary beam it will be

fogged- Storage fog

o If the humidity is too high it will fog films

o Out dated film

o Temperature in the darkroom too high

o Stray radiation

Increased film density (film too black)- Over exposure with incorrect machine settings

o kVp or mA setting too high

o Seconds too long

-Decreased FFD

- Overestimation of thickness or density of the part to be examined- Surge in incoming line voltage or voltage inconsistent- Primary x ray beam filter missing- Increased developer time- Developer temperature too high- Developer improperly mixed, or concentration too high- Safelight leak- Safelight bulb stronger than 25 watts- Safelight not compatible with film sensitivity- Use of grid technique without using a grid

o It is hard to tell over exposure from over development without suingthe photoprinter

Decreased film density (film to light)- Under exposure with incorrect machine settings

o kVp or mA setting to low

o Seconds too short

- Lengthened FFD- Use of improper film for the type of screen used- Underestimation of the thickness or density of the part to the examined- Drop in incoming line voltage

-X ray tube anode failure

- Decreased developer time- Developer temperature too low- Developer exhausted, improperly mixed or contaminated- Grid cutoff (lateral decentering)- Failure to hold the exposure switch closed for the length of the exposure- Use of a grid with a non grid technique


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- Loading 2 films into 1 cassette

Localized area of increased film density- Developer splashed on film splashes- Bending the film will see dark half moons crescent marks-

Pressure exposure due to mechanical abrasion before development (filmdropped on floor) will see dark lines- Static electricity due to rough film handling, friction or low humidity- Exposure of film edge to white light while film is stored in the film bin or

opening of door before film is in the processor- Exposure of film border to light while in the cassette due to improperly

positioned film film sticking out- Felt worn inside cassettes to white light leaks in black area on edge of

film

Localized area of decreased film density-

Fixer or water splashed on film before developing splashes- Foreign material on screen will be white artifacts with sharp margins- Radio opaque material on hair or skin or patient (mud, poultice) white

with irregular fuzzy margins- Film not developed because stuck to other film or wall of tank while being

developed there will be a clear area on 2 films if 2 are stuck together- Silver halide crystals not reduced because of air bubbles next to the film

while in the developer solution these are usually small and circular- Film emulsion scratches fine white scratches- Positive contrast agents spilled onto the table or cassette or absorbed into

the hair or into positioning trays-

Bullet fragments or shotgun pellets- Developer level not as high a fixer level upper edge of the film clear- Cracks in the intensifying screens fine white lines- White fingerprints

o Greasy finger marks prevent development

o Finger prints on screens

o Fixer contaminated fingers toughing film before development

Distorted, Magnified, or blurred radiographic images- Patient motion- Cassette motion or table motion

-X ray tube motion

- Unequal FFD- Decreased FFD- X ray beam not perpendicular to the cassette- Poor film screen contact- Double exposure of the film


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Grid artifacts- Heavy parallel lines across the radiograph due to improper position on the

grid- Use of a grid outside the focal range- Grid not perpendicular to the central x ray beam (off level grid)-

Central x ray beam not centered to midline of grid- Grid inverted (upside down)- Bent or otherwise damaged grid

Loss of film contrast or unacceptably gray films- Film exposed to light before or after exposure- Film exposed to scatter radiation due to grid failure- Film exposed to back scatter during exposure- Film not properly stored- Combination of developer time too short and temperature too high- Developer chemistry exhausted, contaminated or diluted-

Temperature of developer solution too high- Combination of over exposure and under developing

Uneven film density- Grid cut off

o Lateral decentering

o Distance decentering

o Off level grid

o Upside down focused grid

o Damaged grid

- Inadequate fixation white and black streaks

-Developer not stirred darker at bottom due to higher concentration

- Sight development

Film discoloration- Brownish yellowing on the film where wash of fix was incomplete

o Yellowing and browning of image after storage incomplete wash

leaving silver sulfide (brown)- Cloudy or sticky film due to inadequate wash- Cloudy appearance incomplete fixation- White spots on surface water spots will appear white in reflected light

and dark in transmitted light

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Lecture 4 The Darkroom