Fluke Biomedical 76-810 - Manual (Page 8)

Nuclear Associates 76-810,76-814,76-815, &76-818
Operators Manual
2-2
2.2 System Resolution
1. Put on the desired collimator and invert the detector.
2. Place the test pattern on top of the collimator.
3. Place the filled Flood Phantom or Co-57 Flood Source on top of the bar phantom (Figure 2-2). The
Flood Phantom is filled with the desired isotope, using an activity that will produce less than 10,000
cps.
4. Accumulate an image consisting of 1 million counts for standard-field cameras, and 2 million counts
for large-field cameras.
5. Process the data or develop the film, and inspect the final image.
6. Place 10 cm of the suitable attenuating and scattering material, such as Masonite or Lucite,
between the bar test pattern and collimator (Figure 2-3),
7. Repeat steps 4 and 5.
2.2 Evaluating Of Results
Inspect each of the films to determine the smallest bar spacing that can be visualized. This is an
indication of the resolution under the conditions of measurement. Note that the intrinsic resolution is better
than the system resolution, due to the addition of the collimator. The addition of 10 cm of scattering
material further reduces the resolution.
Inspect the images for linearity by observing how straight the images of the bars are. Check for barrel or
pincushion distortion near the edges of the image.
The evaluation is somewhat subjective. However, if the images are kept in a logbook and compared with
images taken when the camera is properly adjusted, it will be possible to detect any changes or
deterioration of the images. Service can then be initiated immediately.
2.3 Additional Tests
Since each quadrant of the detector face sees a different size pattern when using the Quadrant Bar Test
Pattern, it is desirable to make 3 additional images at 90-degree rotational increments. For the Hine-Duley
Test Patterns, make an additional image at 90-degree rotation.
The resolution obtainable, as well as the overall quality of the image, will be a function of all of the
parameters listed. It is desirable to repeat the procedure and vary each of these parameters in order to
study how the image is affected by changes in window width, very high count rates, distance from the
collimator, or information density.