Chapter 7
Page no. 700
JC-ELE-A-032.fm
GE Healthcare
Senographe DS
Revision 1
Service Information and Procedures Class A 2385072-16-8EN
Job Card ELE A032 – IQ Tools Flat Field Test
7-2
Method
The flatfield image is analyzed by measuring the mean
signal level, the noise, and the number of new bad pix-
els in a moving analysis box (a 20 mm x 20 mm region
of interest scanning the flatfield image with a 10 mm
overlap). The total number of new bad pixels is
summed over the whole image.
The following checks are performed:
-
Brightness Non uniformity (BNU)
: compute maximum deviation of the mean signals measured
in each ROI.
-
High frequency modulation (HFM)
: measure the minimum signal–to–noise from all ROIs
-
New bad pixels:
detect and count all bad pixels in the whole image
-
New bad ROIs
: count number of regions of interest containing more than 2 bad pixels
-
Signal–to–noise ratio (SNR) Non uniformity
: compute maximum deviation of the SNR mea-
sured in each ROI.
8
PROCEDURE
1. From the Browser, click on the
QAP
button, then selec
t Flat Field Test.
2. Follow the on-screen instructions. You are asked to:
a. Remove the bucky and the compression paddle, and to place the flatfield phantom on the image
receptor.
b. Verify using the light beam that the collimator is in full field of view.
c. Verify that the tube arm angle is 0 degrees.
d. Make two exposures using the parameters set automatically (Large focal spot; Mo/Mo; 26 kV;
200 mAs).
3. Use the middle-button mouse function to adjust the image for optimum viewing conditions. Sug-
gested starting values are WW = 3000 and WL = 4500.
4. The system calculates and displays test results in a format similar to that shown below. The LSL and
USL columns show the minimum acceptable values (Lower Specification Limit) and the maximum
acceptable values (Upper Specification Limit) for each test.
Test
Measurement
LSL
USL
Pass/Fail
Brightness Non Uniformity
n/a
10.00
High Frequency Modulation
n/a
0.80
Bad Pixel
n/a
100.0
Bad ROI
n/a
0.00
SNR
n/a
40.00
Measurements made i
a moving analysis box
