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Radiology
Chapter Three
Term | Definition |
---|---|
Alternating Current (AC) | A flow of electrons in one direction, followed by a flow in the opposite direction. |
Anode | The positive electrode (terminal) in the x-ray tube. Tungsten block, normallyset at a 20-degree angle facing the cathode, imbedded in the copper portion of the terminal. |
Cathode | The negative electrode (terminal) in the x-ray tube. The cathode consists of a tungstun filament wire that is set in a molybdenum focusing cup that directs the cathode stream toward the target on the anode. |
Central Ray | The central portion of the primary beam of radiation. |
Collimator | A diaphragm, ususally lead, designed to restrict the dimensions of the useful beam. |
"Dead -Man" Exposure Switch | A switch so constructed that acircuit-closing contact can only be maintained by continous pressure by the operator. |
Direct Current (DC) | Elctric current that flows continuously in one direction. Similar to current produced in batteries. Ideal for use with digital imaging. |
Electron Cloud | A mass of free electrons that hovers around the filament wire of the cathode when it is heated to incandescence. The number of free electrons increases as the milliamperage is increased. |
Exposure Button | Keypad or switch that activates the x-ray production process. |
Filament | The spiral tungsten coil in the focusing cup of the cathode of the x-ray tube. |
Filter | Absorbing material, usually aluminum, placed in the path of the beam of radiation to remove a high percentage of the low energy (longer wavelength) x-rays. |
Focal Spot | Small area on the target on the anode toward which the electrons from the focusing cup of the cathode are directed. X-rays originate at the focal spot. |
Focusing Cup | A curved device around the cathode wire filament that is designed to focus the free electrons toward the tungsten target of the anode. |
Impulse | Measure of exposure time. There are 60 impulses per second. |
Intensity | The total energy of the x-ray beam. The product of the number of x-rays (quantity) and energy of each x-ray (quality) per unit of area per time of exposure. |
Kilovolt Peak (kVp) | The crest value in kilovolts of the potential differnece of a pulsatng generator. |
Milliampere (mA) | One thousandth of an ampere. Milliamperage determines the number of electrons available at the filament. See Ampere. |
Primary Beam (primary radiation of useful beam) | The original undeflected useful beam of radiation that emanates at the foacal spot of the a-ray tube and emerges through the aperture of the tube head. |
Quality | Term used when describing the intensity of the x-ray beam. Refers to the number of x-rays in the beam. |
Quantity | Term used when describing the intensity of the x-ray beam. Refers to the penetrating ability of the beam. |
Target | Small block of tungsten imbedded in the face of the anode, bombarded by the electrons streaming from the cathode. The focal spot is located on teh target. |
Thermionic Emission | The release of electrons when a material such as tungsten is heated to incandescence. Electrons are boiled off from the cathode filament in the x-ray tube when electric current is passed through it. |
Tube Head (tube housing) | Protective metal covering that contains the x-ray tube, the high-voltage and low-voltage transformers, and insulating oil. Attached to the flexible extension arm by a yoke. The PID attaches to the tube head at the port. |
Tungsten (Wolfram) | Element with an atomic numver of 74. High melting point makes this metal ideal for use as the cathode filament and as the anode target. |
X-Ray Tube | Electronic tube located in the tube head that generates x-rays. |