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accelerating anode
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air kerma
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Equipment
Chapter 15: Fluoroscopic Imaging
| Term | Definition |
|---|---|
| accelerating anode | a positively charged electrode in the neck of the image intensifier that accelerates the electron stream to the output phosphor by maintaining a constant potential of approximately 25 kV in the tube |
| air kerma | specifies the intensity of x-rays at a given point in air at a known distance from the focal spot or source of x-rays |
| analog-to-digital converter (ADC) | a device that takes the analog signal and divides it into a series of bits (1s and 0s) that the computer "understands" |
| automatic brightness control (ABC) | function of the fluoroscopic unit that maintains the overall appearance of the fluoroscopic image by automatically adjusting the kVp, mA or both |
| automatic exposure rate control (AERC) | automatically adjusts the tube current (mA), voltage (kVp), filtration, and pulse width to maintain radiation exposure to the flat panel detector |
| brightness gain | an expression of the ability of an image intensifier tube to convert x-ray energy into light energy and increase the brightness of the image in the process |
| camera tube | one of the two common devices used in a fluoroscopic system to convert the light image from the output phosphor to an electronic signal for display on a television monitor |
| charge-coupled device (CCD) | a light-sensitive semiconducting device that generates an electrical charge when stimulated by light and stores this charge in a capacitor |
| continuous fluoroscopy | type of fluoroscopy that uses a continuous beam of radiation and could deliver larger doses of radiation to the patient than pulsed fluoroscopy |
| conversion factor | an expression of the luminance at the output phosphor divided by the the input exposure rate; its unit of measure is the candela per square meter per milliroentgen per second |
| dose area product (DAP) | a measurement of exposure in air, followed by a computation to estimate absorbed dose to the patient |
| electronic magnification | selection of a smaller FOV; when a smaller FOV is selected, an area smaller than the size of the detector is exposed by the x-ray beam, but the area is enlarged to fill the display monitor area magnifying the anatomic structures |
| electrostatic focusing lenses | negatively charged plates along the length of the image-intensifier tube that repel the electron stream, focusing it on the small output phosphor |
| fluoro loop save | saves single images or a fluoro sequence loop to memory and are maintained in the patient's permanent record |
| flux gain | an expression of the ratio of the number of light photons at the output phosphor to the number of light photons emitted in the input phosphor; represents the tube's conversion efficiency |
| frame averaging | reduces overall patient dose and image noise by averaging multiple image frames together |
| image intensifier | an electronic vacuum tube used in fluoroscopy that converts the remnant beam to light, then electrons, then back to light, increasing the light intensity in the process |
| input phosphor | a layer of the image intensifier made of cesium iodide and bonded to the curved surface of the tube itself; it absorbs the remnant x-ray photon energy and emits light in response |
| kerma area product (KAP) | the same as DAP; the product of the total air kerma and the area of the x-ray beam at the entrance of the patient |
| last image hold (LIH) | indicates the position of the collimator plates on the display monitor |
| magnification mode | a function of the fluoroscopic unit that increases the voltage to the electrostatic focusing lenses, resulting in only those electrons from the center area of the input phosphor interacting with the output phosphor and contributing to the image |
| minification gain | an expression of the degree to which the image is minified (made smaller) from input phosphor to output phosphor |
| output phosphor | a layer in the image intensifier that absorbs the electron stream and emits light in response |
| photocathode | a layer in the image intensifier made of cesium and antimony compounds; these metals emit electrons in response to light stimulus |
| pulse rate | number of pulses (exposures) that occur per second during fluoroscopic operation |
| pulse width | length of each pulse (length of exposure) during fluoroscopic operation |
| pulsed fluoroscopy | a design of the unit that rapidly turns the x-ray beam on and off during operation |
| spatial resolution | a term used to evaluate accuracy of the anatomic structural lines |
| virtual collimation | adjusting the collimator without exposing the patient to additional radiation |
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