Card Set Information
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?
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
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?
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?
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.