Fluke Biomedical 76-025 - Manual (Page 7)

2-1
Section 2
Operation
2.1 Darkroom Fog Measurement
The following procedure is used to sensitize a film for determining darkroom fog levels. You will need to use the
darkroom fog test tool for this procedure. A 1.0 optical density of one of the fog test tool steps is needed, in order to
evaluate fog. Because of this, two films may need to be taken.
1. Take the fog test tool, and invert it. A depression lies underneath the steps of the test tool. Place a packet of
film in this depression, making sure that the tube side or flat side of the film packet is in contact with the test
tool. Take the test tool, and turn it back over. The steps of the test tool should be facing upright toward the x-
ray tube. Place the cone from the intra-oral unit down, so that it makes contact with the test tool. The cone
should cover the steps of the test tool.
2. For the first film: Make an exposure using the facility's standard technique. Remove the film from the fog test
tool, mark the film and place it in a shielded area.
3. For the second film: If needed, insert a new packet of film into the depression area of the fog test tool, and set
up as you did previously. Use the same kVp but divide the mAs by ten, and take an exposure. Take this film,
and place it with the other fog film.
4. In the darkroom, or the film-processing compartment, unwrap the previously exposed films from their
packaging, and insert the films into the top slots of the test tool. The long side of the films should be inserted
into the slots located on the left and right sides of the top of the test tool. The slots are located in the flat part
of the test tool and not the step portion. Be sure that you are bisecting the latent image.
5. Position the films and test tool in an area of the darkroom, usually on the workbench, closest to a safelight. This
should represent, in your opinion, an area where film is routinely handled and has the highest probability of
safelight exposure.
6. Expose the uncovered half of the films to normal safelight conditions for two minutes. Make sure that you are
not accidentally shielding the films from other potential fog sources, such as light leaks or digital light sources.
7. After two minutes have elapsed, quickly remove the films from the stepwedge, and feed them into the
processor.
8. If a visible line appears down the center of the film, then you have a fogging problem. Using the densitometer,
measure the densities of both the left and right sides of the film at various steps. Record the greatest density
difference. Fog levels with a difference of less than 0.05 density units between unshielded and shielded film
should be considered satisfactory for normal film handling times. Fog levels in excess of 0.05 can usually be
reduced with minimal effort.
Fogging can either be attributed to improper bulb wattage, close safelight positioning, too many safelights, wrong
safelight filters for the film processed, aged/damaged safelights, or any combination of these factors.