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Physics ch 37
AEC's
| Question | Answer |
|---|---|
| what is the proper name for the ionization chamber | Automatic Exposure Control |
| the AEC eliminates the need for the radiographer to set this | time |
| the art of using AEC's is the art of | positioning |
| how can you determine the configuration of the ionization chambers | produce an image without a body part, exposed at a very low kVp for maximum contrast |
| how many different combinations of ionization chambers can be made | 7 |
| when the boltages are summed and then divided by the number of cells that are activated | averaging |
| cell selection is determined by the radiographer based on the knowledge of ___ & ___ | anatomy and positioning |
| what are density controls used for | when machines have line voltage fluctuations or for pt. pathology |
| density controls should not be used to compensate for this | pt. thickness or kvp changes |
| the AEC will produce a diagnotic exposure for whatever tissue is placed ___ | directly over the chamber |
| when do problems with subject density and contrast occur with AEC? | when an unexpected density is present or lacking |
| what happens if fluid is in the lungs and you use AEC | unexptected density, causes AEC to stay on longer, causing an overexposure |
| what happens if a pt has emphysema and you use AEC | unexpected lacking of density, causes AEC to shut off faster, causing an underexposure |
| what happens if you collimate too tightly over an ionization chamber | chamber acts as if it is dense tissue, causing an overexposed image |
| what happens if your collimation is too wide over the ionization chamber | it causes the full primary beam to scatter and causes the AEC to terminate the exposure while some areas are underexposed |
| this is the length of time necessary for the AEC to respond to the ionization and send a signal to terminate the exposure | minimum response time |
| what is the minimum response time of modern AEC's | 0.001 second |
| what should the backup time be set at | 150% |
| generators must shut off at ____ mAs above 50 kVp | 600 mAs |
| generators must shut off at ____ mAs below 50 kVp | 2,000 mAs |
| these units combine an AEC system with a technique chart that is computerized to correspond to anatomical procedures | Anatomically Programmed Radiography (APR) |
| this will always provide a precisely repeatable exposure | manual technique |
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