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A measure of the number of ion pairs produced in air by a quantity of x-rays
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the number of x-rays in the useful beam
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Xray Emission
Bushong (9th; Ch 9)
| Question | Answer |
|---|---|
| A measure of the number of ion pairs produced in air by a quantity of x-rays | roentgen (R) or milliGray [subscript a] (mGya) |
| the number of x-rays in the useful beam | x-ray quantity |
| X-ray intensity of most general purpose radiographic tubes, when operated at approx. 70 kVp | 5 mR/mAs (50 μGya) at 100cm SID |
| Units of x-ray intensity | roentgens (R), mGya, mR/s, mR/min, or mR/mAs |
| X-ray quantity or intensity; measured in roentgens (R) | radiation exposure |
| radiation ________ = x-ray _________ = _____ quantity | exposure; intensity; x-ray |
| x-ray ________ is ________ proportional to the mAs | quantity; directly |
| a measure of the total number of electrons that travel from cathode to anode to produce x-rays | milliampere seconds (mAs) |
| a measure of the electrostatic charges; 6.25 x 10¹⁸ electrons | Coulomb (C) |
| Formula for x-ray quantity & mAs | I₁/I₂ = mAs₁/mAs₂ |
| Formula for x-ray quality & kVp | I₁/I₂ = (kVp₁/kVp₂)² |
| X-ray ________ is ____________ to the kVp² | quantity; proportional |
| mC = ___ | mAs |
| For optical density to remain constant, if kVp is increased by ___ then mAs should be _______ by ½ | 15%; reduced |
| X-ray quantity is _________ proportional to the square of the ________ from the ______ | inversely; distance; source |
| X-ray intensity varies _________ with the ______ of the ________ from the x-ray tube ______ | inversely; square; distance; target |
| Formula for x-ray quantity & distance | I₁/I₂ = (d₂/d₁)² |
| Square Law | mAs₁/mAs₂ = (SID₁)²/(SID₂)² |
| When SID is increased, ___ must be increased by ____ to maintain constant exposure to the IR | mAs; SID² |
| Purpose of filters | reduce number of low-energy x-rays |
| Commonly used metal filter | 1-5mm Al |
| Adding __________ to the useful x-ray beam reduces _______ ____. | filtration; patient dose |
| Disadvantage of ↑ kVp & ↓ mAs for OD to remain constant | ↓ image contrast |
| Disadvantage of added filtration | ↓ image contrast |
| increases the number of high energy x-rays in the beam by removing the lower-energy nonpenetrating x-rays | beam hardening |
| one description of the ability of x-rays to penetrate deeper in tissue | penetrability |
| the penetrability of an x-ray beam | x-ray quality |
| X-rays of any given energy are more penetrating in material of ____ atomic number than in material of ____ atomic number | low; high |
| the reduction in x-ray intensity that results from absorption & scattering | attenuation |
| the thickness of absorbing material necessary to ↓ reduce the x-ray intensity to ½ of its original value | Half-value layer (HVL) of an x-ray beam |
| HVL of diagnostic x-ray beam | 3-5mm Al, or 3-6cm soft tissue |
| the best method for specifying x-ray quality | HVL |
| X-ray beam quality can be identified by _______ or __________, but ___ is most appropriate | voltage; filtration; HVL |
| Atomic number of aluminum (AL) | 13 |
| Atomic number of gadolinium | 64 |
| Atomic number of holmium | 67 |
| Atomic number of copper (Cu) | 29 |
| Atomic number of tin | 50 |
| Increasing the ___ peak _________ the quality of an x-ray beam | kVp; increases |
| Amount of total filtration | 2.5mm Al |
| Increasing filtration increases the _______ of an x-ray beam | quality |
| Atomic number of Beryllium | 4 |
| ↑ filtration = ↑ beam _______ = ↓ beam ________ | quality; quantity |
| part of the glass or metal enclosure of an x-ray tube through which x-rays are emitted | window |
| reason why window is thin | provides for low inherent filtration |
| type of filtration provided by the glass or metal enclosure of an x-ray tube; filters emitted x-ray beam | inherent filtration |
| inherent filtration of a general purpose x-ray tube | 0.5mm Al equivalent |
| type of special purpose tube with very thin window | mammography |
| inherent filtration of mammography unit | 0.1mm Al; sometimes made of Beryllium rather than glass |
| Added filtration results in ↑ ___ | HVL |
| Added filtration resulting from the silver surface of the mirror in the collimator | 1mm Al equivalent |
| material inserted between an x-ray source & a patient to shape the intensity of the x-ray beam; an x-ray beam filter designed to make the remnant beam more uniform in intensity | compensating filter |
| special filters used with CT imaging systems to compensate for the shape of the head or body | "bow-tie"-shaped filters |
| type of filter sometimes used in chest radiography; thin region over mediastinum & thick portions lateral over lung fields | bilateral wedge filter; trough filter |
| type of filter applicable to digital fluoroscopy, where the IR, the image intensifier tube, is round; can be concave or convex | conic filters |
| type of filter that compensates for OD variation of body parts that vary considerably in thickness | wedge filter |
| type of filter used in special procedures involving long sections of anatomy on 2 or 3 separate IRs | step-wedge filter |
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GWCCRad12
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