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4.5 Backup Timer Indicator
The system has backup timers that terminate the X-ray if it remains on longer than the
prescribed scan time.
A warning message is posted when a scan is stopped by the backup timer.
WARNING
X-RAY EXPOSURE TERMINATED BY BACKUP TIMER INSTEAD OF NORMAL
CONTROL.
4.6 Starting Scans from the Scan Room
Start Scan buttons are located on the right and left panels of both the front and rear gantry.
Illustration 22: Start Scan Button
If you want to stand by the gantry and start the scan, you can press Start Scan after you have
confirmed the prescription and the table has been moved to the start location. Once the tube
has reached the exposure speed, the button flashes green for 30 seconds and then times out.
Press the solid green Start Scan button again to bring the system back to the ready to scan
state.
4.7 CTDI
vol
As you setup the scan parameters from the
Scan Settings
screen, the Dose Information area at
the bottom center of the scan monitor contains updated dose information. This dose information
is based on a measurement of the CTDI or CT Dose Index, which is the current standard for CT
dosimetry and performance. By using a measurement called CTDI
vol
, a single value is provided
to estimate the relative dose for an exam.
The CTDI
vol
is a weighted average measurement in a reference phantom. This dose is
expressed in milliGrays. For additional information on specific CTDI
vol
doses and their
calculations, refer to your Technical Reference manual.
The DLP or Dose Length Product is the product of the CTDI
vol
and the scan length for a group of
scans. This number can be summed over the entire exam to give an estimate of the total dose.
The value is expressed in milliGray centimeters.
The Projected DLP shows the DLP that would result from scanning the current group or groups.
Revolution CT User Manual
Direction 5480385-1EN, Revision 1
62
4 Radiation Safety