GE CT-9800 - Alignment Light Visualization; Tomographic Plane Indication and Alignment Check

GE MEDICAL SYSTEMS CT 9800 QUICK SYSTEM
Rev. 1 Direction 18000
4-9-4
9-4 Alignment Light Visualization
H.H.S. Requirements state that if a light is used to define the tomographic plane, it must be visible under ambient
light conditions up to 500 lux. This procedure assumes that the alignment lights are aligned and that the final
Table-Gantry alignment has been performed.
1. Turn on the scan room lights to their brightest normal level. Do not add localized spot lights to increase
the brightness level.
2. Raise the table to its highest position, advance the cradle into the gantry, and turn on the alignment
lights.
3. Use the back of your hand centered over the cradle and held normal to the alignment light as a viewing
surface to visualize the external axial alignment lights. It is only necessary to see the axial lights, not the
sagittal or coronal light.
4. Repeat step 3. using the back of your hand to visualize the internal axial lights.
5. If the external or internal axial lights cannot be visualized under the above conditions, obtain a
DIGAPHOT model #3300 or 3303 light meter and measure the ambient light intensity at the cradle
surface for the external and internal alignment light locations. Note: Footcandles x 10.76 = lux.
6. If the light reading(s) are greater than 500 lux reduce the room lighting to that level and repeat steps 3
and 4. If the light meter readings are 500 lux or less, replace the laser light(s) and/or their power
supplies.
9-5 Tomographic Plane Indication and Alignment Check
H.H.S. requirements state that the distance between the indicated location of the tomographic plane and its
actual location may not exceed 5 millimeters. This procedure requires that the system be calibrated and fully
functional to perform scans and reconstruct images.
1. Use the QA Phantom and follow the procedure “Laser Light Accuracy” given in OM B9801, page 11.
Align the circumferential line on the QA Phantom to the external axial light. Perform a 1.5mm scan from
the external landmark, and examine the hole pattern of the reconstructed image. Record the scan
location as determined by the hole patterns on both sides of the resolution block. The actual scan
location shall be within +/- 3.0mm of the external alignment light reference.
2. Repeat the procedure of step 1 using the internal axial alignment lights, and performing a scan from the
internal landmark. Verify that the actual scan location is within +/- 2.0mm of the internal alignment light
position reference.