NORMI 13 (T42023)
Operating Manual - Constancy Test
D703.131.00/03 en
19
3 Constancy Test
3.1
Purpose of the Constancy
Test
The constancy test is intended to ensure con-
sistent image quality and achieving the required
image quality with the same radiation exposure.
The first constancy test is performed immediately
after the acceptance test of an X-ray system. Dur-
ing this test, the initial state is documented and
the reference values are defined.
In subsequent constancy tests, the measured val-
ues of the various performance characteristics are
compared with these reference values.
The following performance characteristics are to
be verified:
– dose
– exposure index
– optical density / luminance or pixel value
– spatial resolution
– contrast resolution
– coincidence of light field and radiation field
– artifacts
3.2
Performing the
Constancy Test
In order to take the effects of the X-ray generator,
X-ray tube, application device, and image recep-
tor into account, images with manual exposure
setting and with automatic exposure control and
simultaneous dose measurement are required.
Proceed as follows to obtain the test image:
•
Adjust the same parameters, voltages, and
analysis programs as well as documentation
and display conditions as in the acceptance
test.
HINT
For constancy tests with voltages of 100 kV,
an additional 1.3 mm copper plate can
be attached to obtain adequate switching
times.
Ensure the correct orientation of the plate.
The cut-out must be positioned over the
dose measurement area. On test images
with the copper plate, two spots are visible
next to the X-ray test pattern towards the
center of the image.
•
Position the test object according to
section
