GE CT-9800

GE MEDICAL SYSTEMS CT 9800 QUICK SYSTEM
Rev. 12 ➤ Indicates Change Direction 18000
4-12-5
4. First, perform center ROI’s on the 3 sets of scans that were performed for the small cal in step 3, i.e.,:
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)
Center a 14 x 14cm ROI box at coordinates 256, 256 for all six slices. Record the mean CT number for each
slice. Compute the 2 slice average at each kV and verify that all 3 average values are within 0 ± 1.5. If true,
go to step 5. If not, determine the desired CT number for the water phantom as follows:
N
desired
= N
entered
Two Slice Average Mean CT Number of Water
Next, enter the REGEN program (at R-level) and enter the new CT number for the small cal at 80 kV. For
example to enter the new CT number for 80 kV, proceed as follows:
R
REGEN
***REGENERATION OF INSTALLATION INFORMATION***
[RETURN] INDICATES NO CHANGE
CURRENT EXAM NUMBER: 11020
NEW EXAM NUMBER (11000-32000):
[CR]
--CURRENT CT NUMBERS OF PHANTOMS--
PHANTOM: SMALL MEDIUM LARGE
------------------------------------------
➤ 80KV 0 -94 -94
➤ 120KV 0 -94 -94
➤ 140KV 0 -94 -94
ENTER KV(80,120,140): 80 [CR]
ENTER PHANTOM SIZE(S,M,L): S [CR]
ENTER CT NUMBER: 1 [CR]
--CURRENT CT NUMBER OF PHANTOMS--
PHANTOM: SMALL MEDIUM LARGE
--------------------------------------------
➤ 80KV 1 -94 -94
➤ 120KV 0 -94 -94
New N-number for large (120 kV)
➤ 140KV 0 -94 -94
ENTER KV(80,120,140):
Likewise, enter the new CT numbers at 120 and 140 kV (small cal.). Rescan the failing kV station, only,
until values are in spec. Go to next step (5) for generating the new CT numbers for the medium and large
cals.