Processing of Radiographic Films
Following exposure to radiation, the latent image formed on the film is converted to a visible image by a technique referred to as film processing. Radiographic films have been traditionally processed in a darkroom. However, over the years, techniques such as daylight processing, automatic processing and self-developing films have eliminated the need to use a darkroom for processing films.
Traditionally radiographic films are processed in a darkroom. Before one learns the art of radiographic film processing, it is essential to be familiar with the designing of the darkroom and its contents.
Radiographic films are sensitive to X-rays and visible light. In order to prevent exposure of the films to visible light it is necessary to process the exposed radiograph in a room specially designed to keep away visible light.
2. An ideal darkroom should have a doorless maze pattern (Figure 2A) or a conch shell design (Figure 2B) to prevent entry of light into working area.
3. In the event of having a door it should be light tight and should have provisions for locking to prevent accidental opening of the door, which might unnecessarily expose the image receptors to visible light (Figure 3).
The film processing tank is commercially available and made of inert plastic (RinnTM) or can be made custom-made out of stainless steel or bricks and mortar (to prevent reaction with the chemicals of the processing solutions). The processing tank should be placed at a convenient height and away from the working area where films are unwrapped or loaded into cassettes.
Commercially available tanks comprise of a large master tank and two smaller removable inserts (for the developer and fixer solution) which are placed within the master tank that contains water (Figure 5A). Many of the commercially available master tanks measure 8 X 10 inches and the smaller tanks hold about 9 liters of the fixer and developer solution.
The master tank holds either running water or water stored at room temperature. The temperature of the water in the master tank will help regulate the temperature of the developer and fixer. The water contained in the master tank is also used for rinsing the film during processing. A lid should always be placed over the tank to minimize the oxidation of the processing solutions by atmospheric oxygen and evaporation (Figure 5B).
Visible light illumination can be in the form of ceiling or wall mounted light source (Figure 6A). However, care should be taken to ensure that these tube lights are switched off during loading the films into cassettes or while processing the films. However, the visible lights may be switched on once the films are placed in the fixer tank.
The safe light should ideally be 15 W bulb in the orange-red-yellow spectrum of light (Figure 5B) as these colors have the longest wavelength and low penetrating power (X-rays are highly sensitive to blue and green colors). A red GBX-2 filter may be placed over the safe light.
One or two safe lights may be used based on the size of the darkroom. One safe light over the processing tanks (ideally on the right hand side or the fixer solution side of the tank) and one over the working area (place where the films are loaded). The safe lights should ideally be placed 4 feet above the working area and processing tanks (Figure 6B).
A floating thermometer (Figure 7A) and stop clock are used for the time-temperature method of processing films. The thermometer helps to assess the temperature of the processing solutions so that the duration for which the film should be developed is known. The thermometer is left floating in the water in the master tank prior to the processing (Figure 7B). Alcohol containing thermometer is preferred as mercury containing thermometers may contaminate the processing solutions in the event of a breakage. The stop clock helps to set the exact time for the developing procedure.
Drying racks should strategically be located above the washing area in the darkroom. Once the films are removed from film hangers after drying, the empty hangers should be thoroughly rinsed and left to hang dry over the drying racks (Figure 8).
Presence of any remnant fixer solution remaining on the hangers may result in faulty radiographs in the form of light spots. Water droplets on the hangers may produce watermarks on the films, which might obscure diagnostic details in the radiographic image.