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Factors that effect x-ray emission
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X-ray quantity
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Imaging Ch.9
X-Ray Emission
| Question | Answer |
|---|---|
| Factors that effect x-ray emission | Quantity & Quality. |
| X-ray quantity | The number of x-rays in the useful beam. |
| mAs | -Primary controlling factor for quantity. - is directly proportional to the x-ray quantity. |
| mAs is expressed mathematically as: | I1=mAs1 I2 mAs 2 |
| kVp | -Secondary factor. -Quantity is proportional to kVp2. |
| kVp is expressed mathematically as: | I1=(kVp 1)2 I2=(kVp 2)2 |
| 15% rule | A change in kVp by 15% will have the same effect on optical density as changing the mAs. |
| Increase kVp 15% = | Doubling mAs. -To maintain density half mAs when changing kVp. |
| Decrease kVp 15% = | Half mAs to maintain density double mAs when changing kVp. |
| Distance is expressed mathematically as: | -Quantity varies inversely with the square of the distance from the x-ray tube target. -Called Inverse Square Law. -Mathematically expressed. |
| Distance | I1 = (D1)2 I2 = (D2)2 |
| Filtration | -Filters out low energy x-ray beams and hardens the x-ray beam. -Reduces patient dose to low-energy, non informative x-rays. |
| X-ray Quality | Refers to the penetrating ability of the beam. |
| Hard x-rays | Have high penetrability and high quality. |
| Soft x-rays | Have low penetrability and low quality. |
| kVp | -Chief controlling factor of quality.-Chief controlling factor of quality. -Increasing kVp increases the quality of the x-ray beam. -Increasing kVp increases the quality of the x-ray beam. |
| Half-value Layer | -The thickness of absorbing material necessary to reduce the x-ray intensity to half of its original value. -The best method for specifying x-ray quality (measurement of quality). |
| Filtration | Adding filtration increases the quality of the x-ray beam by selectively removing low-energy x-rays. |
| Inherent Filtration | Due to the tube construction, the glass window provides a means of filtering out some low energy x-ray photons. |
| Added Filtration | Adding a thin sheet of aluminum or comparable material between the useful beam and the patient. |
| Compensating filtration | A type of added filtration in which the thickness of the compensating filter coincides with the body part to be radiographed. |
| Wedge Shaped | Used for body parts that are thick at one end and thin at the other. |
| Trough Shaped | Used mainly for the chest medistinum. |
| Bow Tie Shaped | Used in CT to compensate for head or body shape. |
| Conical Filters | Used in Digital fluoroscopy. |
| X-ray Quantity | Is proportional to mAs. |
| X-ray quantity | Is proportional to the kVp^2. |
| ______________ is inversely proportional to the square of the distance from the source. | X-ray quantity. |
| When SID is increased, _________ must be increased by SID^2 to maintain constant exposure to the image receptor. | mAs. |
| Adding filtration to the useful x-ray beam reduces _______________. | Patient dose. |
| ______________ is the reduction in x-ray intensity that results from absorption and scattering. | Attenuation. |
| HVL | Is the best method for specifying x-ray quality. |
| X-ray beam quality | Can be identified by kVp or filtration, but HVL is most appropriate. |
| Increasing ___________ filtration increases the quality of an x-ray beam. | kVp. |
| Increasing ___________ increases the quality of an x-ray beam. | Filtration |
| Added filtration | Results in increased HVL. |
Created by:
sassyrad
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