Chapter 13 Flashcards
(56 cards)
How do AEC detectors function?
Radiation is transmitted through the patient and converted into an electrical signal that terminates the exposure
A system that controls the duration of the exposure and the amount of radiation used
AEC
2 types of AEC systems
Phototimers
Ionization chambers
Phototimers used a fluorescent screen coupled with a:
Photomultiplier tube or a photodiode
What is the function of photomultiplier tubes and photodiodes?
Covert light into electric signal
Phototimer AECs are _____ devices
Exit-type
What is an exit-type device?
Radiation has to pass through the IR before it can be measured and used to terminate the exposure
Currently, most AEC devices use this type of detector:
Ionization chambers
What is an ionization chamber?
Hollow cell filled with air, connected to a timer circuit via electrical wire
Ion chamber devices are _______ devices:
Enterance-type
What are enterance-type devices?
Positioned in front of the IR
What do ion chambers measure?
DAP
How do ion chambers function?
Once the correct amount of DAP has been detected, an electric signal is sent from the chambers that is used to terminate the exposure
Why are ionization chambers the most common form of AEC?
Less sophisticated and accurate than phototimers but much less prone for failure
AEC controls only the _____ of radiation that reaches the IR
Quantity
Does AEC affect contrast?
No
Using higher kVp with AEC will result in a _______ exposure time
Shorter
Lower mA will result in a _____ exposure time
Longer
Minimum response time is the ________ exposure time a system can produce
Shortest
Minimum response time is usually _______ with AEC systems
Longer
Backup time is the ______ length of time an exposure can go when using AEC
Maximum
The backup timer should be set to terminate the exposure at ____%
150-200
Exposure adjustment is also known as
Density controls
What is the function of density controls?
Increase or decrease the preset exposure levels by a preset amount
