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What is a cathode?
(-), consists of the filament a large one and a small one encased by a focusing cup.
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What is AC current?
Milliamperage = mA
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What does AC current or mA cause?
"boiling off" of electrons or "thermionic emission"
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What does "thermionic emission" produce?
An electron cloud around the filament.
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If you increase mA what does this cause?
An increase in temperature of the filament = more electrons
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What is the purpose of a smaller filament?
better detail, sharper image, less penumbra
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What is the purpose of a larger filament?
Allows more x-rays produced and better dissipation of heat. Used for thicker objects.
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What is another name for DC current?
kVp
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What happens when kVp is applied across the tube?
Results in electrical potential or "pressure" which drives the electrons towads the anode.
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What happens if you increase kVp?
Result in faster electrons
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What happens when electrons interact with the focal spot of the anode?
Resulting in 99% heat and 1% xray
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What is Bremsstrahlung radiation or "braking"?
The projectile electron is deflected by the nucleus
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What is Characteristic radiation?
Electron ejects an inner shell.
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What happens when an electron drops into the inner shell?
High energy radiation is produced.
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When xrays exit the port, what is the port made out of?
Inherent filtration = .5 AL equiv.
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What is another name for the port?
Collimator or Positive Beam Limiting device and any added filtration (AL- aluminum)
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What is the purpose of a filter?
"harden the beam" by absorbing "sot" xrays and reduce skin dose
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What do filters NOT have an effect on?
Decreasing scatter radiation
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What are shield made of?
Pb- lead
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What is the purpose of a shield?
to absorb all xrays
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Where is a shield placed?
in front of, or on the patient
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What is "remnant radiation"?
Photons that reach the subject and pass through to the film.
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Why does remnant radiation have different densities on the film?
Different tissues have different absorption rates
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What is caused when photons are absorbed in the body?
inonization of tissue and scatter radiation
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What does ionization of tissue and scatter radiation produce?
Film fog
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What are 2 other names for Classic scattering?
"coherent" and "Thompson"
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What is Classic scattering?
A change in direction of a low energy photon produces film fog and DOES NOT contibute to the radiographic image.
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What is Compton scattering?
Medium energy photon. Ejects outer shell electron and scattered xray photon. This mainly results in scatter radiation that DOES NOTaffect the image.
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What is a Compton electron?
Medium energy photon ejects an outer shell electron.
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What is photoelectric?
Low energy photon absorbed by the subject.
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What does a photoelectric photon produce?
It produces a photoelectron.
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What is the main interaction of a photoelectron?
The main interaction involved in producing the latent image.
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What is the purpose of a grid?
Allows "remnant radiation" to pass through.
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What does a grid absorb?
Absorbs scatter radiation
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What does a grid reduce and increase?
Reducing film fog and increasing contrast.
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What is the purpose of the Potter-Bucky diaphragm?
It moves the grid to "blur" the grid lines.
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What is a grid composed of?
lead or aluminum strips
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What is "grid cleanup"?
The ability of grids to absorb scatter radiation and reduce film fog.
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What is "grid ratio"?
Based on height of the strips to the inter-space between. Higher the ratio (8:1, 10:1, 12:1) greater the "clean up".
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What is "grid cut-off"?
Grids require an increase in exposure to compensate for 1 degree of radition absorbed.
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What happens when xrays reach the cassette?
Cause the intensifying screens to flouresce resulting in the exposure of the film.
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What is the purpose of intensifying screens?
Reduce patient exposure but results in loss of detail.
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What is the purpose of faster screens?
They have larger crystals but result in less detail.
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