-
What is AEC?
- Automatic Exposure Control.
- It stops exposure automatically at the right time so that you get a good density on your radiograph.
-
What part of AEC actually stops the exposure at the right time to get your xray?
Photocell
-
What does photocells actually do?
It determines length of exposure.
-
How does photocells work?
When x-ray hits it, a current is produced corresponding to the amount of radiation.
-
What is the preset amount for density?
The preset amount for density should fall around .25 and 2.5
-
What does having bigger patients do to how length of AEC?
If its a large patient, it would take a longer time for enough exit radiation to get through the patient and into photocell to charge the x-ray timer.
Hence, bigger patient = longer exposure.
-
When using AEC, what selectiosn must you consider that will influence radiographic quality?
- Back up time
- KVP
- mA
- Photocell Arrangement
- AEC density control setting
-
What is a back up timer?
Ordinary timer used without AEC and MUST be set above the length of expected exposure time.
-
How do you use the back up timer if AEC is set to stop at .20 seconds?
Set above AEC time.
-
Some radiographers set the back up time very high so taht is always will be above the expected exposure time. Is it good or bad?
BADDDD
-
Is the back up timer primarily used to protect a patient or the tube?
Screwww the patient. It's for the tube home boy.
-
How should you set the back up timer?
150% above anticipated manual exposure.
-
What does US public law 90-602 state for back up timer?
Generators must terminate at 600 mAS for exposures above 50 kvp, and 2000 mAs below 50 kvp.
-
Does hange of kvp in AEC affect density, contrast, or both?
Affects contrast.
-
If low mA is seleceted, what happenens to exposure time?
- Low mA = increased exposure time.
- High mA = decreased exposure time
-
When should you use the two outer photocells?
When density of the body part that is over the 2 cells are almost the same density.
-
When should you use the center cell?
When center section of the body part is being demonstrated ( lateral chest, AP or lateral spine, etc )
-
What may happen if use the wrong cell?
Your radiograph may come out too dark or too light.
-
How does a photocell determine length of exposure?
- Averages tissue densities it detects.
-
Why is centering important for AEC?
- If you center wrong, photocells will average the wrong tissue density and in turn gives you a lighter/darker film.
-
Why shouldn't you collimate too tight near the photocells?
Dont collimate over cells because cells will keep looking for exposure and it wont turn off.
-
What is the only way to adjust density with AEC?
- Change density control -2, -1, +1 , +2
-
What is minimum reaction time?
Shortest amount of time needed for photocells to stop.
-
What is APR?
Anatomically programmed radiography and corresponds to the anatomical structure with preset techniques for that structure.
|
|