Film Processor
Auto film processors have changed little since their introduction in the 1960s. The
exposed film moves downward into the developer solution, and then back up to the
crossover rack that sends the film downward into the fixer bath, and then back up to
another crosser rack and down through the rinse bath, and then into the drying rack
before being dropped into the developed-film bin on the front of the processor. With
each film that passes through the processor, additional chemicals are added to keep the
system in balance. If the processor sits for long periods without films being processed,
the chemical balance can be affected. Most processors have a “stand-by” cycle, during
which developer and fixer are added to the processor every hour, replacing the evaporated
chemicals. This can cause problems with the quality control on films, as the concentrations
can get too high and thus cause very dark films. It is wise to discourage
placing film processors in low-use areas, as they require more care then those in highuse
areas.
The solutions used must be compatible with the film emulsions and must be monitored
for quality by performing “densitometry” tests at least ever other day (or, better yet, every
day). A film is exposed with a sensiotometer and run through the processor. On the edge
of the film is a 21-step exposure that ranges in density from 0.05–3.05 in steps of 0.15.
Using a densitometer, three points on the exposed film are measured.
The first point is the film outside of where the gray scale appears from the sensiotometer.
This is the base, or fog reading, that should remain constant. Next, two steps
on the gray scale are measured, such as 9 and 13; this can vary from hospital to hospital
and even within a single hospital. The selected steps are part of the quality assurance
(QA) program for the radiology department. The measurements from these points are
plotted, and any variations longer than two days generally will require either the cleaning
of the processor or adjusting the chemical mix or temperature. If all 21 steps are measured
and plotted, one would have a characteristic curve of density and exposure. This is
also call and “H & D curve” (developed by Hunter and Driffield). The QA chart for each
processor shows the four key points, the base fog of the film, the readings at each selected
step, and the temperature of the developer.
The crossover rollers, or rack, should be cleaned each morning to remove any build
up of dried chemicals. Rinsing under running warm water for a minute or less is sufficient
to remove any accumulation. If not cleaned, the dried chemicals can lead to “pick
off” on the film and could indicate the presence of an anatomical change in the patient
that is not there. This can be a serious problem, especially in mammography (mammo)
studies.
Most hospitals will have a silver recovery system connected to the processors to
capture the silver that washes the films as they are developed. These can cause problems
if not changed on a regular basis, and they can impede the flow of water from the
processor to the drain. Clogged drains, leaking tanks, temperature changes, and stuck
pumps are common problems with processors. If the processor rollers and racks are
cleaned on a regular basis, and the rollers are replaced as needed, they are not major
problem areas. However, they become problem areas if they are not cleaned. A good
QA program must be followed, to minimize problems with processors and to ensure
consistent results.
In most hospitals, there is a dedicated film processor for mammo films. These films are
single-emulsion films and require temperatures that are different from those of regular
radiographic study films.
When digital systems are in place for either fluoroscopic or radiographic studies, the
signals are transmitted to a device called a “laser camera” or “laser imager.” In this device,
the images are scanned onto film and transported into the film processor. These systems
are prone to failures and require regular servicing, as with any digital system. One must
be aware of light leaks between the laser camera and the processor because they can affect
the quality of the film.
A verification of this is called the “dry imaging system” or “dry laser camera.” This
device takes the digital images and “prints” them onto the acetate-base “film.” This is not
a true film; it is clear acetate that contains printed images. There is no film processor, no
cassettes, no film and no chemicals to mix. It is less expensive to operate, and environmentally
friendly, but capable of being used only with digital imaging systems. Some
radiologists are not comfortable with it. These units are found mostly in the CT and MRI
areas. These systems will become more common as PACS are installed in hospitals. PAC
systems are expensive and require major changes in department policies and procedures,
but pricing is coming down. As