Slope Calibration - GE CT-9800 Technical Publications

GE MEDICAL SYSTEMS CT 9800 QUICK SYSTEM
Direction 18000
Rev. 19
SECTION 13

SLOPE CALIBRATION

13-1 Slope Calibration Theory
Slope Calibration is a software processing step in the image reconstruction cycle to identify and correct slope
artifacts that may be created by changes in the HiLight Detector over time. A slope artifact may appear as a spot,
smudge, band or ring artifact centered around iso-center. The slope calibration is safety related. Therefore this
additional processing is applied to all patient scans that are taken for 5 & 10mm slice thicknesses. It is not
necessary for 1.5 & 3 mm aperture scans.
ILLUSTRATION
The illustration above shows how the determination is made to apply slope calibration and how the calibration is
applied to the image. The artifact levels calculated for Area 1 are used to determine whether or not to apply the
slope calibration. This 1 cm radius area represents approximately 30 channels at the center of the detector.
When the slope calibration is needed, it will be applied fully (100%) in Areas 1 and 2, to a radius of 5cm from iso-
center. The amount of slope calibration then tapers off, from 100% applied at 5 cm radius, to 0% applied at 10
cm radius (Area 3).
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