Hologic QDR 4500 - Measure X-Ray Scatter from Phantom; Perform Qc; Run Reproducibility Test

Section 3 - Installation
3-27
and working properly. Finally, clean up the machine and remove any unwanted packing materials
from the room.
MEASURE X-RAY SCATTER FROM PHANTOM
A radiation scatter measurement must be performed at installation time. You must use a survey
type radiation meter (Victoreen 450P or equivalent).
Do the following:
1. Center the table and C-arm.
2. Place the spine phantom in the center of the table and align using the laser.
3. Start a normal AP scan.
4. Stop the scan (<Esc>) when it is between the two middle vertebrae.
5. Turn on the X-rays using SUSQ.
6. Using the survey meter, measure the scatter radiation at a distance of 2 meters from the
phantom on a horizontal plane all around the unit. Move the meter slowly (refer to the
Victoreen response table on page 3-25).
Note:
If you can not measure the scatter radiation at a distance of 2 meters because of space
restrictions, you can measure at 1 meter and divide the result by 4.
This reading must be less than 10
µ
Gy/h (1.0mrad/h) at 2 meters (approx. 80 in.) in
array AP scan mode.
7. Record the highest reading in the service report.
Note:
Enter this information into
The Radiation Measurement Report
(see page 3-28).
PERFORM QC
Once the machine has been fully assembled and calibrated, at least one QC scan should be
performed.
•
Perform the daily QC procedure and enter the scan into the QC database.
RUN REPRODUCIBILITY TEST
Reproducibility is the ability of the scanner unit to perform consecutive scans while keeping the
amount of radiation for each scan consistent. Reproducibility is checked by scanning the spine
phantom shipped with the unit 10 consecutive times. You must then plot the results of the High
Air and Low Air measurements for these scans and assure that coefficient of variation for
absolute radiation is less than 4%.
The plot screen does not readily display the coefficient of variation for absolute radiation. You
must use the formula:
coefficient of variation for absolute radiation = standard deviation (SD) x .0028.
So: