Ch15Beam Restriction Word Scramble
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| Question | Answer |
| Negative effects of scatter radiation | Not part of useful beam, unwanted density on the radiograph, overall graying effect (fog), contributes to patient and operator dose |
| Factors contributing to Compton scatter | High kVp values, tissue volume, field size, and patient thickness |
| Increase kVp | Decreases patient dose (less photoelectric interactions, more Comptons), longer scale of contrast, gray haze of entire image (scatter_ |
| Decrease in kVp | Decreased transmission through patient, increased photoelectric absorption, decreased Compton scatter |
| Decrease in kVp | Increases patient dose, increased photoelectric absorption, to maintain image density/exposure a decrease in kVp is accompanied by an increase in mAs |
| Decrease in kVp | Shorter scale of contrast, fewer grays |
| Field Size = Collimation | increased field size increases the volume of tissue irradiated, resulting in increased scatter, longer scale of contrast in image |
| Field Size | Use the smallest field size possible, decreases scatter production |
| The Trade Off | By decreasing the field size fewer photons reach the IR so the exposure is decreased, you must increase mAs to maintain exposure |
| Patient Thickness | Thicker body parts produce more scatter, more atoms, more photon interactions, resulting in an increase scatter production |
| Decreasing Part Thickness | Compression devices can be used to improve spatial resolution and contrast. Results in lower patient dose, brings tissue closer to field, mammography primarily |
| Beam Restricting Devices | 1. Reduce patient dose 2. Limits scatter produced 3. Enhances contrast 4. Visibility of detail |
| Variable Aperture Collimator | Function-reduces field size and controls shape of field (automatically) |
| Upper Stage | (1st) reduces off focus radiation |
| Lower Stage | (2nd) decreases penumbra |
| Positive Beam Limitating Device | PBL- Automatically collimates when a cassette is placed in the bucky |
| Beam Filtration | Removes low energy radiation, placed between tube part and collimator, above 70 kVp--- 2.5mm Al required (federal regulation) |
Created by:
lorperkins
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