Increasing the developer temperature during automatic film processing results in
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chapter 7 Film Processing Three qualities constitute a good darkroom. A darkroom must be (1) clean, (2) organized, and (3) lightproof. Although individual darkrooms may vary in design, all should
possess the same qualities. A darkroom should be separate from the radiographic suite and should be used for only one purpose: processing exposed radiographs. Ideally, the room dimensions should be no less than 6 × 8 feet (2.6 × 2 m), and the layout should reduce the possibility of film damage. Most of the work in the darkroom is performed with minimal illumination. Therefore it is important that the darkroom be organized so that all of the equipment can be located quickly and easily. And, of
course, cleanliness is crucial. This is the only room where both the intensifying screens and the x-ray film are exposed to the air. If the countertops are dirty and soiled with chemicals, it is easy for both to be sucked into the cassette as it is opened, possibly causing damage to the intensifying screens. Another factor that is often overlooked in the darkroom is climate control. Because the film emulsion is extremely sensitive to heat and humidity, good ventilation
and temperature control are mandatory. A darkroom should be relatively cool and should have low humidity. The specific temperatures and humidity for proper film care are described in Chapter 6. Film processing, whether it is manual or automatic, comprises five basic steps: (1) developing, (2) rinsing or stop bath, (3) fixing, (4) washing, and (5) drying. The first
step in learning how to process a film is a basic understanding of the processing solutions. The chemical solutions can be purchased in a number of forms. Powders and liquid concentrates are those most commonly used in veterinary practice. Water is added to the concentrates according to the manufacturer’s instructions to produce the proper amount of solutions for the processing tanks. Preparing the chemicals correctly is important or the resulting solution may adversely affect the radiographic
product. Every effort should be made to keep the chemical solutions at a specified temperature—any variance may adversely affect the radiographic product. At temperatures below those recommended, some of the chemicals may become sluggish in action and may produce an underdeveloped or underfixed radiograph. At temperatures much above those recommended, the chemical activity is too high for manual control. Keep in mind also that all of the chemical
solutions should be the same temperature. If the chemicals vary greatly in temperature, film reticulation can result. Reticulation appears as a mottled density on a finished radiograph and is caused by irregular expansion and contraction of the film emulsion. A quality assurance program should be established and maintained in the veterinary practice. This program allows reproducibility, and it gives the radiographer confidence in the exposures
used on each radiograph (see Chapter 10). Premium Wordpress Themes by UFO Themes WordPress theme by UFO themes Section 12: Darkroom and Processing IntroductionIn most of the modalities discussed in this manual, film is used and the final link in the diagnostic imaging chain, photographic processing, is very important and often the one that is overlooked. All of the efforts by the technical staff aimed at maintaining quality imaging equipment will be futile, if the photographic processor is not maintained under a good quality control program. The photographic process controls not only the image quality (eg. contrast, density, base plus fog) but also the patient exposure. This chapter deals not only with the photographic processor and all of the associated aspects of film processing including darkroom, fog, daylight loading systems, darkroom conditions, film and chemical storage, but also with daily processor quality control. Definition Photographic quality control is a process that ensures the optimization of film processing in order to maintain high image quality and low radiation exposure to patients. In a photographic quality assurance program the following information should be logged as appropriate:
All of the above information should be included on the sensitometry charts in an effort to assess continuity in contrast and density. Processing TechniquesStandards Manual Processors Sight developing must never be done . The time-temperature method of manual processing must be followed according to the chemical manufacturer's specification. The accuracy of the timer and thermometer should be checked monthly.Manual developer containers must be opaque and must be covered to prevent deterioration or oxidation of the developer. A non-mercury thermometer and a minute timer are necessary for proper manual processing. A thermometer on the in-coming hot water line (mixing valve), or a thermometer external to the developer tank may not accurately measure the developer temperature. Renewal of chemistry depends on workload, original volume, replenishment (if any), on the appearance of the radiographs before a need to increase patient exposure is in order to obtain a good film quality. Quality control checks, ie. sensitometry, should be performed to ensure the activity level of the chemicals before processing clinical films. Automatic Processing Automatic processors should be cleaned regularly and the cross-over rollers should be cleaned each operational day. Digital readouts of developer temperature or temperature gauges that are part of the processor itself should not be used as the sole check on developer temperature as they have been seen to be inaccurate. A separate thermometer is required to monitor the developer's temperature. Dental Processors Not all processors are fully automatic. Some have automatic transportation systems, but use manual chemicals because they do not have a heater to warm the developer. Processors designed for use at room temperature do not contain a heating element. 21 As a result, special attention should be given to the location of such processors. A draft from a window may cause a fluctuation in the temperature of the chemicals. Overheated, small enclosures with improper air circulation may make the developer too warm. Both of these situations can result in poor quality images and increase the potential for repeat radiographs or exposures. 21 Some automatic processors without heating elements use manual chemicals. Evaluate as follows: Automatic Processors The developer temperature, processing chemistry, cycle time of the automatic processor, and radiographic exposure, are factors which influence the quality of the final image. In order to obtain high quality films, the manufacturer's recommendations concerning the operation of the processor should be closely followed. When measuring developer temperature a separate thermometer must be uses as it is not acceptable to rely solely on the integrated digital readouts of developer temperature or of the temperature gauges that are part of the processor, as these can be out of calibration by as much as 5 degrees Celsius. Equipment
22 A non-mercury thermometer (i.e. alcohol or metal) is recommended, in order to prevent contamination of the processor or chemicals by mercury in the event of thermometer breakage.
Procedure
In addition, it is important that you follow the manufacturer's recommendations for proper maintenance of your processor by: Manual Processing The time/temperature method of processing films must be followed, according to the chemical manufacturer's directions. Sight development must NEVER be done as it promotes the use of higher radiation exposure to patients and often results in poor quality radiographs.23 23 Proper photographic chemical tanks (opaque) should be used. The tanks should have a lid to cover the chemicals to minimize oxidation. Solutions should be changed at regular intervals as recommended by the manufacturer. Solutions should be topped up or replenished according to manufacturer's instructions. Equipment
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Sensitometry AnalysisOptional with dental equipment. Sensitometry is performed on a daily basis to ensure that all processors are operating at the same levels and producing consistent, high-quality films. Equipment
Procedure
Dental Step Wedge Analysis (Sensitometry)Frequency Weekly 24 24 Each x-ray machine should yield films of similar density and contrast. However, for photographic quality assurance and machine output reproducibility assessment, only compare the films taken for each x-ray machine. Equipment
Procedure
Note: A visible difference in corresponding step images indicates an output difference of approximately +/- 20 percent. It is possible that the patient may be receiving an overexposure. Safelights Standard A safelight must have the correct filter for the film type being used and the bulb must be of the correct wattage. A direct safelight cannot exceed 15 watts. An indirect safelight cannot exceed 25 watts. Safelights must be placed a minimum of 1 metre from the working area. The filter must not be cracked or scratched or otherwise permit unfiltered light (white light) to reach the film. The filter must be of a type specific to the film being used. Evaluation
Dental automatic processors are frequently fitted with a light-tight compartment covered by a filter screen which enables the dentist to use the processor in a location other than a darkroom. The operator slips his/her hands through a set of sleeves and views the unwrapping of the film and the insertion of it into the processor by looking through the filter screen.
Darkroom IntegrityStandard There must be no white light shining in the darkroom when film are being transferred to and from their protective holders. Evaluation Close the door to the darkroom. Turn out the lights, allow your eyes to adjust to the dark and check the darkroom for light leakage. In particular, check around the vertical edge of the door frame, window blinds and pass boxes. On automatic processors, which have daylight loading, check entry sleeves for tears or cracks that may cause film fogging. Also refer to darkroom testing in mammography section for more information. Procedure
Evaluate as follows The exposure should produce less than a 0.05 increase in the mid-density portion of the film. Ideally, less than 0.05 increase should also be obtained with a two minute exposure to the darkroom safelight. Unused Film StorageStandard If unused film is stored in the x-ray room, then it must be stored in a container which provides adequate protection against scatter radiation such as a lead container or something equivalent to 1.6 mm of lead. Film should be stored standing on its edge, not flat, as it is sensitive to pressure marks. Outdated film must not be used as it has an increased base fog. Photographic materials should be stored at temperatures less than 24 degrees C, preferably in the range of 15 to 21 o C. Open packages of film should be stored in an area with humidity ranging between 40 and 60 per cent. Many x-ray facilities provide lead shielding on the walls to the seven foot level. Care should be taken to ensure either that film is not stored above this level in darkrooms adjacent to exposure rooms or that the lead shielding is extended to the ceiling in such areas. Evaluation If in doubt about the safety of the film storage, take a scatter measurement at the storage position. Any reading will indicate the film is being exposed to scatter radiation. If there is no reading, but there is a possibility that the film could be fogged (tube near or pointed at film), a direction warranted. Film can be stored in a freezer to extend shelf life. The expiry date on the box must be changed, so that the duration the film remains in the freezer is not included in the shelf life. Table 12-1 Summary of Processor Maintenance
What effect does increased developer solution temperature have on the film?If the temperature of the developing solution is high, the films appear darker.
What is the likely result of excessively high developer temperature?An abnormally high temperature results in increased blackening. Abnormally long time in the developer. This will cause excessive blackening.
What is the temperature of the developer in an automatic processor?Check temperature of developer and fixer tanks. This is generally set at 27°C (81 °F).
What is the ideal temperature of processing solutions when the film is processed automatically?The temperature range for fixation should be the same as that for development, with 68° F optimum. The developing and fixing solutions should have the same temperatures to avoid unevenness of development and reticulation of the final radiograph.
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