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25 Cards in this Set
- Front
- Back
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What are x-rays?
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a form of electromagnetic radiation, similar to visible light with shorter wavelengths.
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what is the amount of x-ray absorption dependent on?
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atomic number
density of object energy of x-rays |
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The energy of the electrons interacting with the atoms of the target is converted to...
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99% heat and 1% x-radiation
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What does milliamperage (mA) control?
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mA controls the current to the cathode and thereby controls the amount of radiation that is produced.
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What is the site of x-ray production?
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The anode, which contains a tungsten metal plate on which the electrons are focused.
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What is the Anode heel affect?
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unequal distribution of the x-ray beam intensity emitted form the x-ray tube.. By placing the patients head toward the anode side, the part of the x-ray beam with the higher intensity (cathode side) is directed to the thickest area.
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When is heel affect most noticeable?
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When large films and short focal film distances are used
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What does kVp mainly control?
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the quality of the x-ray beam: the higher the kVp, the more penetrating the x-ray beam.
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What does mA and mAs produce?
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the mA and exposure time (mAs affect the quantity of x-rays produced.
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What is radiographic density
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the degree of blackness on a radiograph.
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How can you increase radiographic density?
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increase the mA setting (increase the number of x-rays produced)
Increase the mAs (increases the amount of time the electrons are allowed to travel) Increase the kVp (increases the penetrating power of the x-ray beam) |
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What is radiographic contrast?
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the differences in radiographic density between adjacent areas on a radiograpic image.
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What is a long scale of contrast?
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a few black and white shades with many shades of gray (usually desired)
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What is a short scale of contrast?
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black and white shades with only a few shades of gray in between.
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the amount of contrast depends on what factors?
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subject density
kVp level film contrast film fogging |
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tissues from least dense to most dense (low atomic # to high atomic #).
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1. air
2. fat 3. water or muscle 4. bone 5. metal |
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how can you change radiographic contrast?
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lengthen or shorten the kVp. The higher the kVp the longer the scale of contrast.
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what is focal-film distance? (FFD)
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the distance from the target to the film (usually 36-40 inches)
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What is object film distance (OFD)
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The distance from the object that is being imaged to the film.
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What causes foreshortening?
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when the object is not parallel to the recording surface ( use foam wedges)
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What is a collimator?
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consist of lead shutters installed in the tube of the x-ray to reduce the primary beam and reduce scatter radiation.
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what are grids
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a series of thin lead strips placed between the patient and the cassette to absorb scatter radiation
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What is a potter bucky diaphragm
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device that sets the grid in motion, blurring the white gridlines on the radiograph.
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What 4 variables control radiographic density
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mA
kVp FFD OFD |
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3 layers of an x-ray film
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thin protective layer of gelatin, emulsion layer of silver halide crystals, and polyester film base.
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