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AEC Limitation Messages
The AEC feature optimizes patient images and helps you to obtain precise exposures. Many default
techniques are AEC based in order to optimize image processing. The exposure time and mAs are
automatically selected when you are in AEC mode, producing uniform quality images. The system
displays messages to inform you when the AEC feature reaches its limit.
When acquiring AEC images, the AEC Back-up time is displayed below the mSec area. After the exposure
is taken, the current mSec is displayed (Figure 7-5).
Figure 7-5 mSec and AEC back-up time on Acquisition screen
When an AEC exposure reaches the back-up time limit, a message appears on screen: "The AEC back-up
time has been reached." Click [OK] to close the message. The system will not allow you to continue taking
exposures for the current protocol. To resume image acquisition, select another protocol and continue
the exam.
The backup time is calculated from the following three conditions:
•
A 2000 millisecond limit
•
A 500 mAs limit or 512 mAs limit (based on the nearest Renard step)
•
An X-ray tube protection 'formula' limit
In this instance, the maximum exposure time reached may cause the digital image to be lighter than
desired. You may wish to change the mA selected to avoid reaching one of these limitations in a
subsequent exposure.
In addition to the limits provided by the Applications software, the system also has a maximum mAs limit
for AEC operation.
•
The maximum mAs limit ensures that if an AEC exposure exceeds 512 mAs, the maximum mAs limit
terminates the exposure at values less than 600 mAs.
•
Whenever the maximum mAs integrator limit (550 mAs ± 10 mAs) is reached during an AEC exposure,
a message appears: "The AEC back-up time has been reached."
NOTE: The regular occurrence of this message may be evidence of a malfunction in your system. Call your
service engineer to assess the situation.
Definium 5000 X-Ray System
Operator Manual
Chapter 7: Automatic Exposure Control (AEC)
5197809-1EN
Rev. 4 (13 February 2008)
© 2008 General Electric Company. All rights reserved.
7-7
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