LORAD AFFINITY Series, Руководство по обслуживанию

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Service Manual
Chapter 4: Calibrations and Performance Checks
Performance Checks
6.2 Reproducibility and Linearity in Manual Mode
The following test verifies that the x-ray system (including the controls and x-ray tube) is
operating consistently. Record the readings and mathematical calculations in the
Reproducibility & Linearity Worksheets.
1. Set the radiation probe mod-
ule to read exposure in mil-
liroentgens. Fixture the probe
to set it 4.5 cm above the
IRSD (as shown in Figure 4-
7). Position the probe 4.0 cm
from the chest wall edge,
and center it laterally with
respect to the left and right
edges of the IRSD.
2. Turn the system ON and illu-
minate the light field. Limit
the beam to approximately
the size of the probe head.
Reposition the probe head to
center its detector in the
beam. Align the surface of
the probe so that it stays per-
pendicular to the beam axis.
3. Set the unit for a Manual
Mode exposure at 25 kV, 60 mAs, large Focal Spot, Mo Filter. Conduct the exposure,
then record the milliroentgen reading on the Reproducibility Worksheet (Table 4-14).
4. Change the technique factors for both kV and mAs, then return them to 25 kV and 60
mAs. Conduct a second exposure and record the milliroentgen reading on the Work-
sheet.
5. Continue to randomly change the technique settings for kV and mAs, then return to 25
kV and 60 mAs and take an exposure. Record the milliroentgen reading on the work-
sheet until ten individual readings have been recorded.
6. Compute and record the average milliroentgen reading. Subtract each actual reading
from the average, and square each difference. Add the squares and divide the sum by
nine. Then take the square root of the result.
7. Divide the number calculated in Step 6 by the average milliroentgen reading to obtain
the coefficient of variation. The coefficient of variation must be less than 0.05.
8. Leave the configuration on the image receptor support the same. Change the technique
settings to 25 kV and 20 mAs. Make an exposure and record the milliroentgen reading
and the mAs value on the screen on the Linearity Worksheet (Table 4-15).
9. Repeat Step 8, changing the mAs to 60, 100, 150, 200, 250, 300, 400 and 500. Record
milliroentgens and mAs at each setting.
10. Divide each milliroentgen reading by its corresponding mAs value.
11. For each pair of successive tests, calculate the difference between each corresponding
Step 10 result.
12. For each pair of successive tests, calculate the sum of each Step 10 result.
Figure 4-7: Reproducibility & Linearity Check Setup