The hot item of the decade in radiology may be the picture archiving and communication system (PACS) which is making inroads at major medical facilities to produce X-ray images—from image acquisition to storage, retrieval, reading, and review—totally electronically. One drawback with this advanced technology is its expense. Yes, PACS, by any measure of cost, is an expensive proposition, one that requires a substantial capital investment. Many smaller hospitals—particularly cash-strapped rural facilities and those in developing nations—physician group practices, stand-alone physicians, dentists, and veterinary offices simply cannot afford to make such a substantial investment in these economic times. Instead, they continue using the “wet film” systems that we biomeds have maintained for decades. With the retirement of senior biomeds and their replacement with young, inexperienced technicians, the basic fundamentals of film-based X-ray imaging and automated X-ray film processors must be understood by the new biomeds who will maintain them in the future.

X-ray film processors subject the film to essentially the same chemicals and processes as manually processed film. They automate the manual “dip-and-dunk” system—eliminating the need for a technician to repeatedly place the film into a chemical tank, constantly agitate the film, time the process, move it to the next chemical tank, etc.—freeing the technician for other duties, such as taking X-rays of the next patient. Automated processors perform all the necessary steps in the proper sequence to develop, fix, wash, dry, and deliver the dried film into the hands of the X-ray technician. Additionally, they automatically replenish the chemicals in the processing tanks when their potency diminishes and their volume levels decrease. Most of the time, replenishment is from bulk tanks of developer and fixer (traditionally linking the colors red with developer and blue with the fixer by color-coded package printing, tank-lid colors, etc.) in which concentrated solutions have been either manually or automatically diluted. However, by design, some processors are able to utilize concentrate solutions directly, without bulk tanks, diluting the concentrate as it is used for replenishment.

With the retirement of senior biomeds and their replacement with young, inexperienced technicians, the basic fundamentals of film-based X-ray imaging and automated X-ray film processors must be understood by the new biomeds who will maintain them in the future.

X-ray film processors typically are designed with a straight-through film path, beginning with the point-of-film entry—typically inside a darkroom—and ending in a bin, rack, or other dry film receptacle outside the darkroom. In between the film entrance and exit are, typically, three chemical tanks. The first contains developer; the second, fixer; and the third, plain water. The film goes through a heated drying blower before exiting into a receptacle. Within each tank is a removable film-transport rack mechanism containing a number of mechanically linked rollers that accepts the film, snakes it down to the bottom of the tank, brings it back up the other side and out of the tank to the next rack and tank in the process. Some rack designs pass the film directly to the next rack, while other designs employ external crossover racks that bridge the small gap and allow the film to pass from one tank to the next. The racks are either individually driven by a long worm gear revolving at a constant speed or by coupling the mechanical motion from one rack to the next. In either case, the speed of the rack-and-roller movement controls the development, fixing, washing, and drying time so that all film-transport components move at the same speed throughout the film processor.

Figure 1.

Drawing of a Typical Large X-Ray Film Processor

Figure 1.

Drawing of a Typical Large X-Ray Film Processor

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In addition to the racks, the tanks also contain several other important features. The chemical tanks contain a method of maintaining a constant, usually elevated, temperature and a method of replenishing both chemicals. Although some use a heated water bath, most processors use a thermostatically controlled immersion heating element to maintain a constant processing temperature. Depending on the processor and brand of chemicals used, temperatures are set between 100oF and 135oF to speed the chemical action and reduce processing time. At the processor's operating temperature, which is generally at or near the maximum temperature recommended by the chemical manufacturer, the reaction of the chemicals upon the film is substantially increased while still yielding controlled and consistent results. Partially because of the elevated temperature, but also due to the nature of film processing, both chemicals eventually become exhausted and unable to effectively reveal the latent image on the film. To remediate this, the processor automatically performs two critical functions. First, there is a circulation pump (or pumps in some designs) for each chemical that ensures fresh solution is always in contact with the film as it passes through the tank. Second, an additional pump replenishes both the developer and fixer in small quantities as the film is processed. Early designs, and even now some small volume processors, simply run replenishment pumps (one each for developer and fixer) for a predetermined duration each time a film passes through the processor. Later designs of high-volume, so called “workhorse” units, actually compute the size of the film and replenish chemicals at rates more closely related to their actual use.

The fixer contains dissolved silver removed from the film's coating, and special handling is required, as this silver is valuable, a heavy metal, and considered hazardous waste by the Environmental Protection Agency (EPA).

Typically, the overflow developer runs down the waste line, eventually going down the sanitary sewer with the rest of the building's effluent. However, the overflow fixer is drawn off for special processing. The fixer contains dissolved silver removed from the film's coating, and special handling is required, as this silver is valuable, a heavy metal, and considered a hazardous waste product by the Environmental Protection Agency (EPA). In the United States, the overflow fixer is captured and sent to a recovery unit to reclaim the dissolved silver. This both reduces pollution and produces additional income for the facility.

The last tank the film passes through is a plain water bath to remove most traces of the processing chemicals. Rather than using a wasteful running stream to wash the film, it is washed in a tank similar to those containing developer and fixer, but is replenished with only a trickle of water to refresh and replenish the water used for cleaning. It relies upon a water-level overflow-type drain to remove contaminated water. Additionally, the agitation provided by the wash-rack assembly prevents chemistry-laden water from settling at the bottom of the tank.

Drying and delivery to a film bin is the last step in processing the film. This is accomplished by a relatively low-tech system consisting of a fan blowing air over electric heating elements and through a shroud system to blow the hot air over both sides of the film. The last set of rollers passes the film through this shroud to the holding device awaiting pickup by the X-ray technician. Again, the film moves at the same speed as elsewhere in the processor, so drying is primarily a function of dryer temperature.

As is the case with so many large, expensive, and operation-critical medical devices, maintenance should be uniquely scheduled by device, using the serial number or some other local, item-unique coding system. Unfortunately, X-ray film processors are preventive maintenance (PM) intensive, which is necessary to minimize operational failures, and it must be scheduled and performed on a regular basis. X-ray film processors do not benefit by postponing scheduled services to achieve short-term savings. Performing preventive maintenance on X-ray film processors is a nasty, messy business which can only be performed on site, many times shutting down the entire darkroom during the procedure. If the biomed manager is lucky, routine preventive maintenance will be performed for free or at a reduced cost as part of a film/chemical purchase plan. While this is good for the in-house biomed, sloppy or “pencil-whipped” preventive maintenance can lead to an increase in catastrophic failures. Remedial maintenance costs should be closely tracked since they impact replacement. Lastly, if a facility maintains several of the same brand and model processors, they would be well-advised to invest in a “float” set of film racks. This will allow the maintainer to swap out a malfunctioning rack with a serviceable rack and return the processor to service, while the unserviceable rack is repaired or rebuilt.

State laws and environmental requirements notwithstanding, and except for units used in conjunction with mammography, there are no specific federal regulations pertaining to X-ray film processors. For mammography operations, the X-ray film processors are included in the annual equipment evaluation of the overall mammography program. The Mammography Quality Standards Act and Program applies to units used in conjunction with mammography and requires that newly installed processors, those that have been disassembled and reassembled, or have undergone major repairs, be evaluated by a medical physicist. This evaluation verifies that all functions that may have been affected by the change or repair have been successfully restored. The Food and Drug Administration (FDA) uses the example of a total overhaul to illustrate a major repair and further states that maintenance functions such as routine PM, pump replacement, replacement of the racks, and replacement of the control board do not constitute “major repairs.” Individual states may have more stringent requirements.

Performing preventive maintenance on X-ray film processors is a nasty, messy business which can only be performed on site, many times shutting down the entire darkroom during the procedure.

Risk falls into three general categories: misdiagnosis, worker, and environmental. The first pertains to the film and image quality. Assuming the film was perfectly exposed (mA, kVp, and time were precisely correct), the developed image can be compromised by old and contaminated chemicals, crud on the film-transport rack rollers, and incorrect processing temperature, all of which can result in poor quality images. Poor quality images on the film can mislead the physician to an incorrect diagnosis due to underdeveloping or overdeveloping. Film artifacts (left by the dirty rollers) may be misinterpreted as a false positive, such as a small tumor, resulting in unnecessary anguish on the patient's part and surgery on the practitioners' part. On the other extreme, poor quality may not reveal a bone fracture, thus causing additional pain for the patient and a delay of the appropriate treatment.

The second category falls under the purview of the Occupational Health and Safety Administration (OSHA). X-ray technicians and others working in and around the darkroom, are potentially exposed to the processing chemicals and their fumes. The fixer fumes typically contain both ammonium bisulfite and sodium bisulfite, which are both a respiratory tract irritant and harmful if swallowed. Additionally, the most noticeable trait of fixer fumes, the potent vinegary smell, comes from the high concentration of acetic acid, which is corrosive and also a respiratory tract irritant. This risk is managed by power-venting the fumes from the interior of the film processor and the dark room. Another risk, also under the purview of the OSHA, is to the X-ray technicians as they perform their operator maintenance and routine cleaning tasks. The interior of the film processor contains several exposed moving parts (such as the worm gear that drives the film-transport rack mechanisms) that can trap clothing and crush fingers. While the manufacturers attempt to protect workers by providing shrouds to cover these “pinch points,” many of these are removed during routine servicing. This risk can only be truly mitigated by attention to detail, not allowing oneself to become distracted when near the moving components.

Origin and Evolution

Like many other items in the medical field, X-ray film processors are representative of the adoption of another technology into the medical field. In this case, X-ray film processors were adopted from the larger photographic film industry. In reality, medical X-ray film is specific-sized photographic film, exposed in a special way, but developed using the same chemistry and procedures used for other photographic film. The automated film processors that were developed to process movie film and still photos were simply right-sized to handle medical X-ray film.

The third category attracts the attention of the EPA. The used fixer contains a high percentage of dissolved silver. By federal and state law, most of this dissolved silver must be removed before the used fixer enters the sanitary sewer. This is typically handled by a silver recovery system either at the point of generation (the film processor) or the used fixer from several film processors is piped to a silver recovery system in a central location within the treatment facility. Sometimes, small-volume generators, those who regularly process only a few films, pay a hazardous waste hauler to ship the used fixer to their facility for processing. In no event is unprocessed fixer allowed to enter the sanitary sewer.

The majority of problems with X-ray film processors are mechanical and center on the film-transport rack. A single broken gear, for example, can cause a major film jam, ruining several films and requiring retakes. Likewise, failure to perform operator maintenance can result in slippery rollers, again causing a major film jam. To remediate rack problems, many hospitals maintain a “float” set of racks. In conjunction with regularly scheduled maintenance and based upon empirical data, the biomed exchanges the float racks with those in a processor and rebuilds the old racks. They become the new float racks. Then, at the next scheduled service interval, the float racks are exchanged and the whole process occurs again. This may seem like a waste of time and money (replacing rollers, gears, and bearings which are apparently still usable), but in the long run it eliminates unscheduled downtime and lost revenue when the rack actually fails, films are ruined, and retakes are required.

Another problem area in film processors is temperature control. Underheating the chemicals slows the reactive process and results in underdeveloped film, while overheating speeds the reactive process, resulting in overdeveloped film. It can be difficult even for experienced eyes to differentiate between an underdeveloped film and an underexposed film. The opposite holds true as well: It is difficult to tell whether the film is overdeveloped or overexposed. Therefore, the biomed must ensure the processor is actually at fault, troubleshooting it when the actual problem is with the phototimer of the X-ray unit. If the problem occurs only with films taken in one room or shot by one technician, then the film processor is probably not the culprit..

Another problem area in film processors is temperature control. Underheating the chemicals slows the reactive process and results in underdeveloped film, while overheating speeds the reactive process, resulting in overdeveloped film.

Eventually, the recirculation and replenishment pump will fail. No matter the processor, pumps moving corrosive chemicals of the type used in X-ray film processing will eventually fail. Even when the motor shaft is magnetically coupled to the pump impeller, the pump will fail. Many biomeds believe most pump failures occur because the pump motor, especially the bearings, is exposed to the erosive chemical fumes (particularly the acetic acid fumes from the fixer) within the processor housing. Although a ventilation system removes these fumes from the processing area, the internal components of the processor are initially exposed to them due to chemical evaporation exacerbated by the elevated operating temperature.

Sometimes, despite color coding, X-ray technicians will confuse developer and fixer concentrates, putting the one in the other's tank. When this happens, the usual complaint is sticky film, since one of the functions of the developer is to soften the film's emulsion, and the film passes through the developer last before the wash. When this happens, the entire processor and replenishment tank system and plumbing must be drained, flushed, and new chemistry mixed. This problem seems to occur more often in teaching institutions because of student errors; unfortunately, this is part of the learning process.

Physics and Chemistry

Before one can really understand and appreciate what automated X-ray film processors do and how they function, one must have a basic understanding of the physics and chemistry of exposing and developing photographic film. This process is the same whether the film is exposed by X-rays, visible light, or a combination of both. The only thing “special” about X-ray film are the sizes (for example, 14″ X 17″ flat sheets instead of 35mm roll film) available in the marketplace.

The Physics: Exposing the Film. Briefly, when X-rays pass through the body, dense parts such as bone and metal implants absorb or block some of the rays, while less dense parts such as muscle and skin block or absorb less. The X-rays that exit the body then strike the X-ray film cassette, the image intensifier screen, and sheet of film inside it. There, the screen releases visible light which strikes the X-ray film that is in intimate contact with the screen. (While the film can be exposed by X-rays alone, it is more responsive to visible light. Therefore, a phosphorescent screen is placed next to the film to expose the film quicker, allowing lower exposure levels which reduces radiation exposure to the patient.) Areas of the film corresponding to areas of the body that are dense receive less exposure because more X-rays are blocked. (This is called “radiopaque” or “radio-opaque.”) Conversely, areas of the film corresponding to soft tissue receive more exposure since these tissues block fewer X-rays (termed “radiolucent”). Thus, a latent image is placed on the X-ray film that the action of film processing makes visible.

At the molecular level, the physics of creating a latent (hidden) image are both simple and complex. The simple act of exposing film to X-rays and/or visible light creates the image, but it occurs because of a plethora of activity occurring within the crystalline structures. X-ray film consists of a blue-tinted, transparent plastic substrate—typically polyester or cellulose triacetate—thinly coated with gelatin mixed with silver halide (comprised of a proprietary mixture consisting of mostly silver bromide and silver iodide in the form of grains), dispersed as an emulsion on one or both sides, depending on the film's intended use. When the visible light from the image intensifying screen strikes the emulsion, bromide ions are freed and captured by the silver ions. It is this action of the visible light upon the crystals that creates the latent image which development of the film makes visible to the naked eye.

The Chemistry: Developing the Film. Once the latent image has been placed on the X-ray film, processing the film makes it visible. Film processing involves five basic steps, accomplished manually in small facilities (such as stand-alone dental practices and veterinary clinics) and by automatic film processors in large facilities. The basic steps are developing, stopping, fixing, washing, and drying—all of which are easy to automate. By convention, the packaging of chemicals used for developing contains red printing, while the chemicals used for fixing the film contains blue printing. This convention extends, by some manufacturers of film processors, to the mechanical components immersed in the respective chemical baths.

Developing consists of immersing the film in a solution that converts the exposed silver halide to metallic silver. Although there is an optimum temperature and time for development, if the chemical process occurs at too high a temperature or for too long, eventually even the unexposed silver halide will be converted to metallic silver.

Stopping, as the term implies, terminates the development process to prevent overdeveloping the film. The fixing solution will also stop the film, but using fixer as a stop bath depletes the fixer rapidly, so a separate stop bath is sometimes employed. Fixing, which is often combined with stopping, performs several tasks with one chemical solution. First and foremost, fixing removes the unexposed silver halide grains, which stay suspended in the fixer solution, leaving the silver metal behind on the film. Second, it hardens the gelatin containing the exposed grains. Washing removes the fixer residue from the film and prepares the film for the last step. The last step is drying the film so that it may be safely handled, read, and archived for later reference.

Basic biomed training, a good general toolkit, an understanding of the theory of operation, and good observational skills are required for servicing X-ray film processors. Manufacturer's literature is a plus, but not absolutely necessary for many basic repairs. Observational skills are necessary to quickly detect missing teeth on rack gears and residue on rack rollers causing film artifacts, and to track chemical residue to the source of the leak. Most electronic troubleshooting of X-ray film processors can be performed with a good multimeter. One word of advice: Because of the chemicals involved and the general area of processor use, one should always ensure parts such as optical film sensors are clean before considering replacing them; chemical residue will block the sensor while remaining invisible to the naked eye, imitating a component failure. Other problems, like failed pump bearings, will be readily apparent.

X-ray film processors are becoming obsolete with the advent of digital imaging systems. However, a large installed base of automated X-ray film processors still exists that require regular maintenance.

X-ray film processors are becoming obsolete with the advent of digital imaging systems. However, a large installed base of automated X-ray film processors still exists that require regular maintenance.

Eastman Kodak Company
Material Safety Data Sheet: Kodak GBX Fixer and Replenisher.
Available at https://www2.itap.purdue.edu/msds/docs/9727.pdf. Accessed January 2011
.
ECRI Institute
Healthcare Product Comparison System for X-Ray Film Processors, Automatic.
Available at: www.ecri.org/Products/Pages/hpcs.aspx. Accessed January 2011
.
eHow Health
History of Radiographic Film Processing.
.
NDT Resource Center
Film Processing.
.
xRay2000
The Photographic Latent Image.
Available at: www.e-radiography.net/radtech/l/latent_image.htm. Accessed January 2011
.

About the Author

Robert Dondelinger, CBET-E, MS, is the senior medical logistician at the U.S. Military Entrance Processing Command in North Chicago, IL. E-mail: robert.dondelinger@mepcom.army.mil