Phantom Calibation - GE CT-9800 Technical Publications

GE MEDICAL SYSTEMS
Rev. 12 Indicates Change
5. Next, perform center ROI's on the 2 sets of scans that were performed for the medium cal and large cal,
i.e.,:
20cm/M/120 kV/200 mA/10mm/4S
20cm/M/140 kV/170 mA/10mm/4S
20cm/M/140 kV/140 mA/10mm/4S
20cm/L/120 kV/200 mA/10mm/4S
20cm/L/140 kV/170 mA/10mm/4S
20cm/L/140 kV/140 mA/10mm/4S
Center a 14 x 14cm. ROI box at coordinates 256, 256 for all eight slices. Record the mean CT number.
Compute the 2 slice average at each kV and verify that all 4 average values are within 0 ± 1.5. If true, record
the new phantom CT numbers for the small, medium and large cals at each kV. If not, determine the desired
CT number for the medium and large as shown in step 4 (above). Enter the new CT numbers using REGEN
as depicted in step 4. Rescan the failing kV station, only, until values are in spec.
12-5 Phantom Calibration
The following phantoms are required for system calibration:
a) 20cm water section of the QA phantom
b) 35cm poly phantom
c) 48cm poly phantom
Complete the phantom calibrations shown in Table 4-12-2. Remember that the respective air and medium cals
must be less than 75 hours for Xenon systems and must be less than 27 hours old for HiLight systems. if a
phantom has to be recaled at any other time. Otherwise, both the air, medium and the particular phantom must
be recaled. Refer to Illustration 4-12-2 for the phantom cal procedure. Note that for HiLight systems, the air
calibration needs to be performed prior to the small calibration and after the medium callibration.
(2 Scans)
(2 Scans)
(2 Scans)
(2 Scans)
(2 Scans)
(2 Scans)
4-12-6
CT 9800 QUICK SYSTEM
Direction 18000