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27 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What does the x-ray tube consist of? |
A cathode, an anode enclosed within an envelope and then encased in a protective housing |
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Is the cathode the positive or negative side of the x-ray tube?
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Negative |
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What is the function of the cathode? |
Produce a thermoionic cloud, conduct the high voltage to the gap between cathode and anode, and focus the electron stream as it heads for the anode |
3 Things |
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What composes the cathode assembly? |
Filament, focusing cup, and associated wiring |
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What is the purpose of the focusing cup? |
It is a shallow depression in the cathode assembly designed to house the filament |
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What is the space charge effect? |
As more and more electrons build up in the area of the filament, their negative charges begin to oppose the emission of additional electrons |
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What is saturation current? |
As kVp increases, a greater percentage of the thermionically emitted electrons are driven toward the anode |
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Is the anode the positive or negative side of the x-ray tube? |
Positive |
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What are the three functions of the anode? |
- Serves as a target surface for high voltage electrons from the filament - Conducts the high voltage from the cathode back into the x-ray generator circuitry - Primary thermal conductor |
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What os the anode assembly made up of? |
Anode, stator, and rotor |
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Why is Tungstem the metal of choice for the source of x-ray photons? |
It has a high atomic number (74), high melting point, and good heat conducting ability |
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What is the anode warm-up procedure? |
To bring the anode heat from room temperature to near the range of operation. Also permits the heat from the hot anode to serve as a "vacuum pump" to maintain a strong vacuum inside the envelope |
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What happens if you don't follow the anode warm up procedure? |
Can cause the entire anode to crack if the molybdenum absorbs the heat too rapidly and exceeds its expansion capability |
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What is the target area? |
The portion of the anode where the high voltage electron stream will impact. Also known as the "target", "focus", "focal point", "focal spot", "focal track". This is where the photons are created! |
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What is the "actual focal spot"? |
The physical area of the focal track that is impacted
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What is the "effective focal spot"? |
The area of the focal spot that is projected out of the tube toward the object being radiographed |
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What is the "Line Focus Principle"? |
Used to reduce the effective area of the focal spot. Permits the best resolution of detail while permitting as large an actual area as possible. |
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What is a fractional focal spot? |
Used to refer to a very small focal spot, one that is a fraction of a millimeter in size |
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What is the anode heel effect? |
Due to the geometry of an angled anode target, the radiation intensity is greater on the cathode side. Because the cathode end of the x-ray tube has a more intense beam, it should be positioned towards the denser side of the body |
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In which direction should the cathode be placed for an AP exam of the thoracic vertebral column? |
The inferior thoracic region is more dense, the cathode's more intense beam should be positioned inferiorly to help increase the exposure in that region. |
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What is the stator? |
Only part of the cathode/anode assemblies that is located outside the vacuum of the envelope. The induction-motor electromagnets comprise the stator that turns the anode. |
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What is the primary function of the envelope? |
To maintain the vacuum between the cathode and anode |
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Why is there a vacuum between the cathode and anode? |
The removal of the air permits electrons to flow from cathode to anode without encountering the gas atoms of air |
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What does the protective housing do? |
Controls leakage and scatter radiation, isolates the high voltages, and provides a means to cool the tube |
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What is leakage radiation? |
Any photons that escape from the housing except at the port |
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What is off-focus radiation? |
Composed of photons that were not produced that the focal spot. Occurs when the high voltage electrons striking the focal spot produce scattered electrons or photons |
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What are the three types of rating charts? |
Radiographic tube rating charts, anode cooling charts, and housing coolings charts |
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