NORMI 13 (T42023)
Operating Manual - Constancy Test
22
D703.131.00/03 en
3.3.6 Coincidence of the light field
and the radiation field
Using a test image, determine the deviation
between the light field and the radiation field.
Compare the irradiated field with the field outlined
by the line marks of the test object (to which the
light field indicator has been adjusted). Add the
marks missing on the test image. Determine the
deviations in both horizontal and vertical direc-
tion. Use the measurement tools of the program
installed at the workplace. Only in exceptional sit-
uations should rulers be used for measurements.
HINT
This test cannot be performed on facilities with-
out a light field indicator.
3.3.7 Artifacts
Check the test image for artifacts that may affect
the quality of the diagnosis.
3.4
Assessing the Results
The evaluation of the results is based on the fol-
lowing maximum deviations from the reference
values determined in the initial state.
If the deviations exceed the permitted ranges,
measures must be taken to eliminate the causes,
i. e., to restore the initial state.
3.4.1 Dose
– Measurements with PMMA absorber:
With automatic exposure control, the dose val-
ues shall not deviate by more than ±30% at 70
kV (±25% at 100 kV), and with manual expo-
sure setting, by not more than ±30% at 70 kV
and 100 kV from the reference value.
– Measurements with aluminum absorber:
With automatic exposure control, the dose val-
ues shall not deviate by more than ±25% at 70
kV (±20% at 100 kV), and with manual expo-
sure setting, by not more than ±30% at 70 kV
and 100 kV from the reference value.
3.4.2 Exposure Index
The exposure index and the maximum permitted
deviations are manufacturer-specific parameters
and usually indicated in the test image data.
The maximum permitted deviation of the expo-
sure index from the image receptor dose is ±50%.
