Siemens SOMATOM Emotion syngo CT 2007E Operator's Manual page 80

Information about Personal Safety
Calibration
Detector deviations
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syngo CT 2007E
02/2008
If the CT system is not properly setup (e.g., no check-up per-
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formed) CT scale displacements and inhomogeneities can
result. This may result just after switching on the unit, during
warm-up to operational temperature (calibration), or due to an
extended length of service of the X-ray tube. The same applies
to defects in the measurement system.
The daily quality checkup usually detects and reports such dis-
crepancies.
Additional calibrations may also be necessary if large changes in
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temperature occur in the room.
Other system defects or calibration deviations cause streaks or
(partial) rings to appear in the CT image.
In CT systems with a rotating combined tube-detector system
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even minimal deviations of individual detector channels from
the original calibration level may lead to rings or partial ring
artifact structures in the CT image. The closer such channels lie
to the detector center, the greater are these effects.
In an extreme case rings may appear concentrated as a blurred
spot in the center of the scan field (the scan field center appears
at the image center if the Center X and Y image parameters are
both zero). Such rings are easily recognizable, but a blurred spot
in the center of the scan field might lead to inaccurate diag-
noses.
Safety
Emotion Operator Manual
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