GE CT-9800 Technical Publications page 266

GE MEDICAL SYSTEMS
Rev. 13
NOTE: A positive tube shift moves the tube toward the table, a negative shift towards the gantry.
In the example of Illustration 6-9A-10A, the X-Ray tube should be moved toward the table to shift the
wide beam to be better centered over the narrow beam. The X-Ray tube should be shifted 0.26
[0.23 - 0.07 + 0.02] = 0.047".
Refer to Section 9A-2 for details of Tube Z shift adjustment.
8. After adjustment, repeat the procedure starting at Step 2. Wait 5 minutes after the last scan before
repeating the exposure series of Step 4.
•
After the scan for the 10mm aperture, do not remove the film. Advance the cradle out 25mm, wait 5
minutes and repeat the scan of Step 4 using the 1.5mm aperture. This should be CTDS default scan
#2; "POR 1.5MM". Then proceed to Steps 5 through 7.
•
Measure the 10mm exposure; XF = XR - 0.01" ±0.001" or XF = XR - 0.25mm ±0.25mm.
•
Examine the 1.5mm. Check that edges of the wide beam can be seen on either side of the narrow
beam.
•
Date and save the final film when adjustment is to specification.
9. If an additional tube shift is required following Step 8, repeat that step after a 5 minute wait to allow the
tube to cool.
9A-5 Beam on Window (detector Z-axis) -
This procedure checks and adjusts the position of the detector window so that it intercepts the entire width of the
X-Ray fan beam under worst case conditions. This procedure offsets the beam to account for the fan beam shift
toward the table that occurs with heating of the X-Ray tube. Therefore, beam centering at the detector is set for
-0.020" (-0.5mm) with the bias towards the gantry.
NOTE: Verify that the Tube Unit is "cold"; i.e., that it has had
[KV•mA•Sec/1000] within the last 30 minutes. Wait a minimum of 90 minutes from the completion of a
generator cal or other high technic exposures. Each exposure in this procedure adds 12.8 kj of heat to
the tube, exposures should be made no faster than one every 5 minutes.
recommended prior to this procedure.
1) Using option 3 in DC, move the tube the 0°.
2) Turn OFF the azimuth drive switch, and open the gantry front cover. Position the detector at the 6:00
o'clock position.
3) If this is a newly installed detector, check that the detector is plumb at its three mount locations. It is
very important that the detector window be perfectly parallel to the gantry mounting surface before
continuing.
4) The detector at the 6:00 o'clock position, place three pieces of Polaroid film on the detector as shown in
Illustration 6-9A-12. Orient the film with the side marked "This side toward lens" toward the detector.
5) Butt the metal strip on the film up tightly against the rotating base of the gantry.
6) Make a small pencil mark on both sides of the film at the edge of the detector window closest to the
table.
no more than 25 kilojoules exposure
6-9A-12
CT 9800 QUICK SYSTEM
Direction 18000
Tube warm-up is NOT