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ANUAL
4343W/4336W-G5/2530W-G5 X-ray Detectors
6
Once all frames are acquired, the X-ray detector is updated with the averaged offset
calibration frame for the current mode. The updated message will show on the progress
window and
calibration process is complete
.
7
Click
Close
.
Figure 34 Finish Offset Calibration
11.12.3 Gain Calibration
To compensate for non-uniformities in the X-ray detector, a gain reference image (flat field) is
used by the Corrections module to correct all images. The flat field image must be captured by
the VSP prior to acquiring images. The process of capturing the flat field image is known as gain
calibration.
Note
The gain calibration process will include automatically running an Offset
calibration to ensure that the detector is properly calibrated.
Gain calibration is based upon the linear response of the X-ray detector to dose. Normalization is
achieved by applying the flat field image acquired during the gain calibration to all images
corrected by the VSP. Gain calibration should be performed in the range where the detector is
linear.
Flat field images acquired near or exceeding the saturation point will cause normalization
failures with all images acquired until a gain calibration with the correct dose is performed.
Note
It is recommended that flat field images be acquired with a median count of
approximately
11000 - 15000
.
This range will ensure that gain calibration will meet both the upper and lower dose
requirements under all modes of operation. Dose requirements are determined by the settings of
the generator X-ray source.
