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