Automatic exposure control (AEC) Flashcards
What is the function of AEC?
Measures the quantity of x-rays that reach the IR and terminates exposure when radiation intensity has been recieved
How does AEC compensate for pt. size
By adjusting time
When using AEC the technologist chooses __, __, __, _ on the operating console
- kVP
- mA
- Back up time
- Photocells
Back up time should be __-__ times the expected mAs for the patinet
2-3 times
Name the two types of AEC?
- Ionization chamber
2. Photodiode
Which AEC is
most common ?
Ionization chamber
Describe the Ionization chamber AEC
- It is a flat placed between the pt. and IR
- // to IR
- Must be radiolucent
- Ionization causes a charge in the chamber , when enough charge has been reached, system terminates the beam
Describe the Photodiode AEC
- It is a solid state detector that converts light into electric current
- Current flows in 1 direction that is opposite of the electrons
- AKA: Rectifiers
Why are photodiodes rectifiers?
because they conduct current in 1 direction
What is the purpose of calibrating the AEC circuit
to produce the proper image density regardless of pt. size
Phototimer is another name for?
Photocells
When more than 1 cell is activated , which cell will contribute the greatest electrical signal and have the most influence on density
The cell receiving the most radiation
Why is proper positioning important when using AEC?
- Because the cell is selected for anatomical location of the part of interest. If the parts not completely over the cell, the image could be too light or too dark
Which cells would be chosen for KUB
All cells
What is APR
Anatomically Programmed Radiography
Describe APR
Anatomically Programmed Radiography
* IT is an electronic technique for pt. exposure control
-RT selects part to be imaged and Body habitus, OD
Microprocessor pre-selects kVp and mAs automatically
___ acts as a timer for the x-ray circuit
AEC circuit
Why are back up timers normally set?
In case the AEC fails to terminate
- Prevents damage to x-ray tube
- Prevents overexposure
Regulations require that AEC have a __ mAs or ____ sec. safety override
- 600 mAs
2. 6 second safety override
What are advantages of AEC?
- Reproducability
- Less chance of repeats
- Nearly flawless images
- Less chance of over / underexposure
What are the 2 most important things to remember when using AEC?
- Choose the correct photocells
2. Proper positioning
an electronic technique for pt. exposure control
APR ( anatomically programmed radiography)
