12. AEC Flashcards
What is the defenition of AEC?
Terminates the exposure when the IR recieves the proper amount of radiation (mAs) and measures the RR.
When do we use AEC?
When doing bucky work and with larger body parts
Where is the detector located?
After the grid and before the IR
Why can’t we have the detector outlines on the table?
Because the table floats
What object will recieve the same amount of radiation regardless?
Detector
What things does AEC compensate for?
(To produce the same mAs and relatively same DI value)
- SID
- Body thickness
- Desired mA
- kVp
- Laterally decentering the tube
What techniques can we select for falling load generators with AEC?
Only kVp
What techniques can we select for most x ray generators with AEC?
- kVp
- mA
What does the central ray always line up with?
The center detector
What happens when we select more than one detector?
The system averages out the exposure
What are the two goals of the detector?
- Consistent exposure/I to IR
- Less repeats/patient expsosure
What are the 3 types of detectors?
- Ion chambers
- Solid state detectors
- Photomultiplier tubes (not ussually used)
What is the ion chamber made of?
Gas atoms
What happens to the detectors (ionization chambers) during an exposure?
- X rays ionize gas atoms which make free e-
- The e- strike a positive anode plate
- A current is created
- Once a certian change has been created with current, exposure is terminated
With larger objects, how would AEC compensate?
- Increase in time
More absorption would take place, so less RR
When would you use the center detector on its own?
For long bones and lateral chest
When would you use the lateral/outside detectors?
Chest (concerned with lungs)
When would we use all 3 detectors?
Abdominal work
For all of the x ray radiographs, describe what would happen to the mAs, DI, and mAs with centering given.
DO IT DO IT DO IT
What happens if your detector is sup. to the point where you should be centered using AEC?
- The IR would see more readiation per time, so AEC would shorten time
- mAs would be lower
- The DI value would be too low
What woudl happen if you have a larger field size than needed when using AEC?
- More scatter
- Detector sees more radiation so the time would be shortened
- The mAs would be too low
- The DI value would be too low
What is the minumum response time for the system?
5ms
Define MRT:
The shortest poosible exposure time we can get with any exposure using AEC
What would we do if MRT is an issue?
- Use a lower mA
- Use a fixed technique
What is the back up time used for?
- System faliure
- Technologist faliure
What is the purpose of the back up time?
two
- So we don’t overexpose our patient
- To prevent tube wear (overload)
What is the personal MRT?
2 seconds
What is the BT rule of thumb for AEC?
Choose a back up time of 1.5-2x the expected /fixed exposure time, or mAs
