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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
. The rectangle
should be approximately
5 cm
long.
5. Note the mean value result in column
Y
in
.
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
.
Note the result in the
.
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
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)
X
Y
Mean pixel
value differ-
ence [%]
1
mAs
32
30
0
o
2
mAs
56
40
0
o
3
mAs
200
60
0
o
4
AEC "H"
-
40
0
o
5
AEC "H"
-
40
+ 60
o
6
AEC "H"
-
40
- 60
o