問題一覧
1
Have several causes, most of which are related to the thermal characteristics of the x-ray tube
X-Ray Tube Failure
2
must be dissipated for the x-ray tube to continue to function.
Heat
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Three Methods of Heat Dissipation
Radiation - transfer of heat by emission of infrared radiation. Convection - transfer of heat by the movement of a heated substance from one place to another Conduction - transfer of heat from one area of an object to another.
4
results in reduced tube life (also the first reason for tube failure)
Excessive heat
5
caused by excessive temperature of the anode
Localized Surface Melting & Pitting
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what may result to cracking of the anode.
Too rapid increase in temperature of the anode
7
should not be applied to a cold cathode.
Maximum radiographic technique
8
results from maintaining the anode at elevated temperatures for prolonged times.
Second type of tube failure
9
what’s the final cause of tube failure?
Tube Arcing
10
caused when vaporized tungsten coats the inside of the glass or metal enclosure is interacted with electrons.
Tube Arcing
11
- causes disturbed electrical balance on the x-ray tube, - causing abrupt, intermittent changes in tube current
Tube Arcing
12
guides the the radiologic technologists in using the x-ray tube
Rating Chart
13
Three types of Rating charts
- Radiographic Rating Chart - Anode Cooling Chart - Housing Cooling Chart
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most important of the three types of rating charts
Radiographic Rating Chart
15
shows scales of mA and kVp
X and Y
16
- contains the thermal capacity of the anode and its heat dissipation characteristics. - has a limited capacity in storing heat.
Anode Cooling Chart
17
- has a shape similar to that of the anode cooling chart and is used precisely the same way. - complete cooling after maximum heat capacity requires from 1 to 2 hours
Housing Cooling Chart
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- describes the energy deposition of a particular type of radiation, which largely determine the biological consequence of radiation
Linear Energy Transfer
19
- proportional to the square of the charge of the particle. - inversely proportional to the particle's kinetic energy.
Linear Energy Transfer
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what is the unit of LET
keV/um
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High Linear Energy Transfer Radiation range
3-200 keV/um
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Low Linear Energy Transfer Radiation
0.2-3 keV/um
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High Linear Energy Transfer is mediated by what?
alpha particles, proton, neutrons
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- Greater density of interactions at cellular level - produce biological damage in a given volume of tissue
High Linear Energy Transfer
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Low Linear Energy Transfer is mediated by what?
Electrons, Positrons, Gamma rays, X-rays
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less likely to produce tissue damage in the same volume of tissue
Low Linear Energy Transfer
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conveys which radiographic techniques are safe and unsafe for x-ray tube operation
Radiographic Rating Charts
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average energy deposited per unit path length along the track of an ionizing particle
Linear Energy Transfer
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LET of Linac X-rays (6-15 MeV)
0.3 keV/um
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LET of Beta Particle (1 MeV)
0.3 keV/um
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LET of Cobalt-60 Y-rays
0.2 keV/um
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LET of 250 kVp x-rays (standard)
2 keV/um
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LET of 150 MeV protons
0.5 keV/um
34
LET of Neutrons
0.5-100 keV/um
35
LET of Alpha Particles
50-200 keV/um
36
LET of Carbon ions
40-90 keV/um