Fluke Biomedical 76-025 - Manual (Page 8)

2-2
2.2 Phantom Image Evaluation
1. Insert one packet of the facility's film into the film holder, which is a “U”-shaped area located in the phantom
bottom. The film holder is in close proximity to the wire mesh components of the phantom. Make sure that
the tube side or flat side of the film packet is facing down in the direction of the wire mesh. (This is critical,
since there is lead foil on the opposite side of the dental film. If the film is positioned incorrectly, the film
density will be too light.)
2. After the film packet has been inserted, the phantom should be placed on the phantom cradle, so that the film
packet is at the opposite end from the cone.
3. Move the phantom and cone into contact with each other. The cone should be aligned with the phantom and
phantom cradle, and not be angled.
4. Utilizing the facility's standard technique settings for the facility's film, make an exposure.
5. Remove the film packet from the phantom, and develop the film. Measure the optical density. The optical
density should be measured at the area adjacent to the low contrast object. Record the measurement.
6. Measure the densities of the three low contrast objects, and record those measurements.
7. Count the number of different gauge wire meshes that you can see, and record this number. You should not
count a wire mesh pattern if you cannot see the tiny spaces that result from the mesh running both vertically
and horizontally.
The results of these evaluation procedures should not deviate when re-evaluating the dental x-ray equipment in the
future.
2.3 Technique Evaluation
1. Make an exposure, using the facility's standard technique, and record this reading.
2. Process the film.
3. Measure/compare the density against the reference/base value.
2.4 HVL Exposures
1. Slide the end of the cone away from the probe in the phantom cradle so that it is aligned to the edge of the
filter slot. The cone tip should make contact with the aluminum.
2. In order to position the dental cone, first insert a thickness of aluminum into the slot, and bring the cone tip as
close to the aluminum as possible.
3. Remove the aluminum, and make an exposure. Record the output for 0.0 mm added aluminum.
4. Insert 1.0 mm of aluminum in the slot of the phantom cradle. Be sure the filter is aligned with the probe so that
the probe is completely within the filtered x-ray beam. Make a second exposure. Record the total thickness of
added aluminum in mm and the output in mR.
5. Repeat Step 4 until the last exposure is less than half of the 0.0 mm added aluminum measurement. Record all
of the exposures and added aluminum (filter thicknesses).
6. Determine the HVL to the nearest tenth of a millimeter of aluminum by drawing the best straight line fit to all
but the first (0.0 mm Al) data points. By plotting the exposure versus the aluminum thickness used, find the
point on the line where the exposure is half that of the 0.0 mm Al exposure. The thickness of Al corresponding
to this point is the HVL.