CPI Canada Inc
Reproducibility, Linearity, & HVL Testing
X-Ray Generator Service Manual Supplement 740917-00 Rev. A
Page 9
5.0 H.V.L.
EVALUATION
1.
Be sure the X-ray source assembly (X-ray tube and beam limiting device) is fully assembled and
functional.
2.
Use the test setup as per figure 1.
3.
Set the generator as follows: 3 point generators, 80 kV, 200 mA, 50 ms, large focus. For 2 point
generators use 80 kV, 200 mA if this can be set, and 10 mAs.
4.
Take a series of three exposures and record the mR values in table 10. Calculate and record the
average of the three exposures.
5.
Place 2 mm of Al on top of the lead diaphragm (total of 2 mm added), repeat the exposure and
record the mR value in table 10.
6.
Place an additional 1 mm of Al on top of the lead diaphragm (total of 3 mm added), repeat the
exposure; and record the mR value in table 10.
7.
Place an additional 3 mm of Al on top of the lead diaphragm (total of 6 mm added), repeat the
exposure; and record the mR value in table 10.
8.
The relative transmission for the average of the three mR values where no Al was added is
assigned a value of 1.00. Using that base, assign relative transmission values to the remaining
mR values. For example, if the average mR value was 247 and has a relative transmission factor
of 1.00, then 162 mR will have a relative transmission of 162 / 247 = 0.66.
9.
Plot the relative transmission values in figure 1. This should produce a straight line on the graph
since the X-axis is logarithmic.
10.
Interpolate to determine the HVL. The Al thickness at a relative transmission of 0.5 will be the
required HVL value.
11.
Repeat steps 4 to 10: 3 point generators, 100 kV, 200 mA, 50 ms, large focus. For 2 point
generators use 100 kV, 200 mA if this can be set, and 10 mAs. Use table 11 to record the values
and figure 2 to plot the results
12.
Table 12 and figure 3 show example HVL determination.
