Processing

Objectives:

Although digital imaging and CR PACS is becoming more popular and the common knowledge seems to be that the processor is growing to be extinct; we, the technologist on the floor where the action takes place still are responsible for the care and feeding of more processors than PACS systems. Until we are all basking in the cool light of the film-less Mammography suite here is some help.

Emulsion wet, streaky, milky, sticky or crinkled films; what to do? Who to call? It is so-o-o-o frustrating to start having processor problems in the middle of a busy day. If we know a little about what our chemistry is doing to our films it can help us identify the problem and eliminate the mess.

We may still need ‘the man’ but if we can direct him straight to the problem we can get him in and out of the department in record time.

We are not service engineers or photo chemists; it is not essential for us to know how to repair the processor or how to restore our chemistry. It is, however, our mandate to produce the best images in the most economical, efficient way possible. The more we know about how our images are produced and maintained the better we can accomplish our ultimate goal.

Development:

What is it?

Our developer turns the silver halide crystals in the emulsion that have been exposed to radiation to black metallic silver. The silver halide crystals that have not been exposed are not affected.

What are the most important factors affecting development?

1. immersion time
2. temperature
3. activity (type, concentration, replenishment, agitation)

What is in developer and what does it do?

CHEMICAL	COMPONENT	FUNCTION
Phenidone + Hydroquinone	The reducing agent	This chemical reduces (turns) the exposed silver halide crystals into back metallic silver.
Sodium Carbonate + Potassium Hydroxide	The activator or accelerator	This chemical swells and softens the emulsion and produces an alkaline environment.
Sodium Bromide or Potassium Bromide	The restrainer(starter)	This chemical restrains or stops the reduction of the unexposed silver halide crystals.
Sodium Carbonate/Bicarbonate or Sodium Hydroxide + Boric Acid	The buffer	This chemical maintains the base or alkaline nature of the solution. The pH of the developer should be maintained at 10.5.
Sodium Sulfate or Potassium Sulfate	The preservative	This chemical reduces oxidation and maintains the freshness of the chemicals.
Gluteraldehyde	The hardener	This chemical controls the softening and swelling of the emulsion.
Water	The solvent	Water holds the developer chemicals in solution.

Fixation:

What is it?

The effect of the fixer is twofold. First it stops or arrests the development action of the exposed silver halide crystals. Secondly it loosens and removes the remaining unexposed silver halide crystals leaving differing shades of gray on the film base.

What are the most important factors affecting fixation?

1. immersion time
2. temperature
3. activity(type, concentration, replenishment, agitation, exhaustion)

What is in fixer and what does it do?

CHEMICAL	COMPONENT	FUNCTION
Ammonium Thiosulphate	The clearing agent	This chemical clears the undeveloped silver halide crystals from film base.
Sulfuric acid	The activator	This chemical stops the development action and produces an acid environment.
Sodium sulfite	The preservative	This chemical reduces exhaustion and maintains the freshness of the solution.
Aluminum Chloride	The hardener	This chemical shrinks and hardens the emulsion.
Sodium Acetate + Acetic Sodium Bisulfate	The buffer	This chemical maintains a stable acid environment of pH 4.5.
Water	The solvent	The water holds the fixer chemicals in solution.

Wash Cycle:

What is it?

The wash cycle removes the chemical residue left behind by the process of development and fixation.

What are the most important factors affecting the wash?

1. The water temperature (must be significantly cooler than the development temperature)
2. The length of time the films are washed.
3. The circulation of the wash water (at least 2 to 3 gallons per minute)

Drying Cycle:

What is it?

The drying process squeegees the water from the film base and dries and hardens the gelatin base for storage.

What are the most important factors affecting the drying cycle?

1. The temperature of the air used to dry the films has to adequate to dry thoroughly but gentle enough not to burn the delicate emulsion.
2. The air used for film drying must be the correct humidity.
3. There must be adequate airflow over and around the films.

A Little Troubleshooting advice:

Ten Really Easy Things to Do at the First Sign of Trouble:

1. Check your water supply is: on, hot water OK, cold water OK, pressure OK, not contaminated.
2. Check the wash tank drain is closed.
3. Check the temperature of both the developer and fixer (by hand).
4. Check the levels of all the chemicals in your processor.
5. Check your replenishment rates.
6. Check the setting on your sensitometer.
7. Check the setting on your densitometer.
8. Check the pH level of the developer (10.5) and fixer (4.5) with litmus paper.
9. Run a second strip from the QC film box and recheck parameters.
10. Run a strip from a fresh box of film and recheck parameters.

What’s the Problem & Where to Look?

• Low-density films or poor penetration – MR/mAs, AEC, kVp.
• Decreased resolution — focal spot, phantom image, screen contact.
• Decreased contrast – kVp, HVL, mR/mAs, compression.
• Recurring artifact – screens, cassettes, film bin, processor rollers, compression.
• Grid lines – grid motion, defective grid mechanics.

Troubleshoot Your Phantom Image:

Resolution (clusters):

1. Is the contrast stable? If not, see #2.
2. Is the optical density stable? If not, check processor and place AEC on middle position, reverse your phantom so target is near film, if no improvement, check film/screen contact, screen speed and processor artifacts
3. If contact film improves resolution check focal spot.

Contrast (masses):

1. Check processor
2. Trend charts,
3. Optical density (processor, AEC)
4. Grid
5. kVp
6. HVL

Artifacts on image:

1. Retake image with same screen; feed film into processor OPPOSITE to the first film
2. If artifacts turn 90 degrees your problem is with a processing roller
3. If the marks remain the same they are either, on the screen (clean) or with the unit (service)

Troubleshoot Your Processor:

Temperature fluctuations

1. Check developer temperature with calibrated thermometer
2. Check rinse water temperature ( should be about 5 degrees lower than your developer temperature)
3. Check that hot air fans stop when no film is running
4. Check developer thermostat

Speed decrease (too light):

1. Chemistry? Too dilute, expired, ammonia smell
2. Replenishment? Not sufficient, blocked line
3. Developer? Agitating, still, temperature too low

Speed, contrast and/or base + fog increase (too dark):

1. over replenishment
2. Chemistry? Too concentrated, no starter, temperature too high

Contrast poor:

1. Chemistry? Brand change, environment change etc.
2. Temperature? Too low or too high
3. Extended processing? OK
4. Chemistry? Expired, diluted, contaminated

Conclusions:

Good, clean, sharp, high contrast images are consistently possible if we pay attention to a few details. This sometimes feels like a never ending, thankless job, however, our patients very lives might depend on it so I guess its just grit our teeth and get on with it. I hope the preceding charts will make the task a little faster, a little easier, a little more cost and time efficient.