66 Image Quality
MAMMOMAT Novation DR SPB7-250.815.06.02.02 Siemens AG
12.05 CS SD 24
Page 66 of 116
Medical Solutions
4. Make a new rectangle on a grid line according to (Y/Fig. 43 / p. 65). The rectangle
should be approximately 5 cm long.
5. Note the mean value result in column Y in (Tab. 15 / p. 66).
6. The mean pixel value difference should be calculated as (X-Y)/X where Y is the mean
value in the grid line and X is the mean value in the background as seen in
(Tab. 23 / p. 104).
Note the result in the (Tab. 15 / p. 66).
7. Choose the next image that had visible grid lines in the list and start over with step 3 un-
til all images are evaluated.
Test Protocol
Tab. 15 Measuring Grid Lines
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 (Eliminating grid lines / p. 66).
Otherwise
P - Record the measured value in the "Start-up Protocol" on (Start-up Protocol / p. 97)
and
- continue with "Checking Image Quality" on (Checking Image Quality / p. 71).
Eliminating grid lines 0
There are various adjustments for eliminating grid line problems:
• Adjusting the grid switch
• Adjusting the "wheel" that is mounted on the grid motor.
• Adjusting the grid location
• Adjusting the grid speed
Expo-
sure
Exp Mode mAs
PMMA/m
m
Tube
Angle
visible
grid lines
(yes/no)
XY
Mean pixel
value differ-
ence [%]
1mAs32 30 0
o
2mAs 56 40 0
o
3mAs 200 60 0
o
4 AEC "H" - 40 0
o
5 AEC "H" - 40 + 60
o
6 AEC "H" - 40 - 60
o
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