Siemens MAMMOMAT Novation DR - Eliminating Grid Lines

MAMMOMAT Novation
DR
SPB7-250.815.02 Page 4 of 20 Siemens AG
System Rev. 02 09.04 CS SD 24 Medical Solutions
9 - 4 Image Quality
Test Protocol
Test Criteria
If the mean pixel value difference is less than 1%, for the images with visible grid lines,
the test has passed.
If the "mean pixel value difference" does not meet the criteria,
- continue with "Eliminating Grid lines" on Page 9 - 4 .
Otherwise
- Record the measured value in the "Startup Protocol" on Page 11 - 1 and
- continue with "Checking Image Quality" on Page 9 - 8.
Eliminating Grid lines 9
There are various adjustments for eliminating grid line problems:
• Adjust the grid switch
• Adjust the "wheel" that is mounted on the grid motor
• Adjust the grid location
Adjust the grid switch
The switch S1, see Fig. 4, on the detector table disables the high voltage when the grid is
in the turning point. The switch must be correctly adjusted otherwise the high voltage will
be active when the grid is standing still.
To minimize the risk that the high voltage is active when the grid is standing still, the time
that the high voltage is disabled should be as long as possible.
1. Move the grid to the left end position.
Expo-
sure
Exp Mode mAs
PMMA /
mm
Tube
Angle
visible
grid lines
(yes/no)
X Y
Mean pixel
value differ-
ence [%]
1 mAs 32 30 0
o
2 mAs 56 40 0
o
3mAs200600
o
4AEC "H"- 40 0
o
5 AEC "H" - 40 + 60
o
6AEC "H"- 40 - 60
o
Tab. 2 Measuring Grid Lines
"