Term
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Definition
The filament is heated by a separate filament current.
increase in temperature=increase in the rate of electron emission |
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Term
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Definition
| electron cloud: electrons sitting---no kVp |
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Term
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Definition
space charge electrons are driven over to the anode at high speed by the large potential difference
(lots of electrons-->repel each other) |
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Term
| What percentage of x-rays are produced? |
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Definition
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Term
| The glass envelope is made of what and why? |
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Definition
Pyrex: can withstand large amounts of heat without melting
surrounds cathode and anode |
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Term
| Why is the glass envelope made into a vacuum? |
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Definition
| So electrons don't interact with air molecules |
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Term
| What is the purpose of the window in the glass envelope? |
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Definition
the x-rays emerge from here
(thinner portion of glass envelope) |
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Term
| What is the filament (cathode) made of? |
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Definition
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Term
| What is the function of the filament (cathode)? |
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Definition
Provides a source of electrons: boils off electrons:thermionic emission
heats/excites the electrons |
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Term
| the 2 properties of Tungsten that make it a suitable filament material... |
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Definition
high melting point
its ability to conduct heat |
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Term
Purpose of the focusing cup
What is it made of? |
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Definition
confines the elecrons to a narrow beam and focuses them as the focal spot on the tungsten target.
Mo: Molybdenum |
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Term
|
Definition
1. filament
2. supporting wires
3. focusing cup |
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Term
| Double focus cup tubes are: |
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Definition
| double filament tubes with 2 different sized focal spots on the target |
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Term
short filament=
and a disadvantage |
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Definition
small focal spot=good detail
can only used limited technique bc only so many electrons can be burnt off |
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Term
long filament=
and an advantage |
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Definition
large focal spot=poor detail
reduces motion, can use larger technique |
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Term
| What is the most common cause of tube failure? |
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Definition
tungsten deposits
the vaporized tungsten deposits on wall of glass tube, which tends to attract electrons, eventually puncturing the tube. |
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Term
| What is the function of the anode? |
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Definition
Stop the electrons
electrons convert kinetic energy into x-rays and heat |
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Term
| Focal spot is dependent on 2 factors: |
|
Definition
1. filament size
2. anode angle |
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Term
What is the focal spot?
the size of the focal spot determines what? |
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Definition
where the electron stream bombards a limited area on the target
size of focal spot determines the detail (sharpness on the image) |
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Term
|
Definition
Due to the angle of the anode, the effective focal spot will be smaller than the actual focal spot
Allows you to dissipate heat and gain detail |
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Term
|
Definition
| where the electrons actually hit the anode |
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Term
| Define effective focal spot |
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Definition
projected towards the film
much smaller than actual focal spot b/c of the inclinein the anode angle |
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Term
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Definition
| smaller effective focal spot=more detailed image |
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Term
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Definition
decreased density on anode side of image--the diverging beam of the x-rays is absorbed into heel of anode
less evident on smaller films bc we collimate it off |
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Term
| Reason for rotating the anode |
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Definition
| can use a higher technique because the anode doesn't heat up as fast |
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Term
| What is the anode made of? |
|
Definition
Molybdenum base
Tungsten coats Mo
Rhenium is top coat |
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Term
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Definition
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Term
|
Definition
| the large area the heating of the beam spreads across |
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Term
| factors which reduce anode life |
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Definition
overheating of the anode
serial exposure:continuous exposures
pitting and cracking occurs |
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Term
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Definition
| gives the maximum "safe" exposure time for any selected combo of kVp and mA for a single exposure |
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Term
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Definition
Tells us when another exposure can be made
:how long we have to wait to make another exposure |
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Term
| Methods used to cool anode |
|
Definition
- mounting a small fan outside tube housing
- forced oil circulating
- rotating anodes
- temp. of housing kept below 90 degrees
- heat exchanger: tube system
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Term
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Definition
device that displays the amount of heat in percentage of total capacity
at 80% it will lock out any exposures being made |
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Term
| Space Charge Compensation |
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Definition
| automatically lowers mA with an increase in kV in order to maintain the tube mA |
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