GE MEDICAL SYSTEMS CT 9800 QUICK SYSTEM
Rev. 12 ➤ Indicates Change Direction 18000
4-12-4
12-4 Phantom Self Calibration
Phantom Self Cals for the 35cm and 48cm polys must be performed prior to image performance for new
installations. In addition, if you have doubt whether the phantom CT numbers are good, or not, redo the phantom
self cals. The purpose of this type of calibration is to modify the CT numbers of the 20cm (water and 35cm and
48cm cals until water has a CT number equal to zero. When this is achieved, any water based anatomy when
scanned against a small, medium or large cal will have a CT number equal to zero.
The 20cm water section of the QA phantom will be scanned against the small cal, medium cal and the large cal.
A total of 2 scans of the 20cm phantom will be taken against each cal (small, medium and large). The average
mean CT number for each run is obtained by centering a 14cm x 14cm ROI box at coordinates 256, 256 for all
slices. Next, the REGEN program (at R-level) is called up and new numbers for the 20cm (QA), 35cm and 48cm
phantoms are entered. The 20cm phantom is rescanned and center ROI’s are retaken until the mean CT number
for the 20cm phantom is within the range of 0 ± 1.5 Proceed as follows:
➤ For a new installation, the default CT number for the small cal will be set to 0 at 80, 120 and 140 kV. Default CT
numbers for the medium and large cals are set to -94 at 80, 120, and 140 kV.
NOTE: If a new phantom self cal has to be performed later in system life, use the old N-numbers as
starting values.
2. Perform the following cals:
• Air Body Cals: at 120 kV/40 mA/10mm/4S. and 140 kV/40 mA/10mm/4S. This cal may have
already been performed in Section 12-3.
➤ • Small Body Cals: (20cm water section of the QA Phantom) at 80 kV/300 mA/10mm/4S, 120
kV/200 mA/10mm/4S. Also 140 kV/170 mA/10mm/4S for Xenon systems and 140 kV/140
mA/10mm/4S for HiLight systems.
• Medium Body Cals: (35cm Phantom) at 120 kV/200 mA/10mm/4S and 140 kV/170 mA/10mm/4S.
• Large Body Cals: (48cm Phantom) at 120 kV/200 mA/10mm/4S and 140 kV/170 mA/10mm/4S.
3. Scan two slices of the 20cm section of the QA phantom against the small, medium and large cal as
follows. Use 512 x 512 pixel reconstruction:
20cm/S/80 kV/300 mA/10mm/4S (2 Scans)
20cm/S/120 kV/200 mA/10mm/4S (2 Scans)
➤ 20cm/S/140 kV/170 mA/10mm/4S (2 Scans) (for Xenon systems only)
➤ 20cm/S/140 kV/140 mA/10mm/4S (2 Scans) (for HiLight systems only)
20cm/M/120 kV/200 mA/10mm/4S (2 Scans)
➤ 20cm/M/140 kV/170 mA/10mm/4S (2 Scans) (for Xenon systems only)
➤ 20cm/M/140 kV/140 mA/10mm/4S (2 Scans) (for HiLight systems only)
20cm/L/120 kV/200 mA/10mm/4S (2 Scans)
➤ 20cm/L/140 kV/170 mA/10mm/4S (2 Scans) (for Xenon systems only)
➤ 20cm/L/140 kV/140 mA/10mm/4S (2 Scans) (for HiLight systems only)
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