Term
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Definition
- difference in potential/electrical charge between cathode (-) and anode (+)
- draws electrons across tube
- varies continuously due to alternating current power supply |
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Term
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Definition
| - highest value of kilovoltage |
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Term
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Definition
- 60/sec
- voltage continuously changing
- anode not always positive w/respect to cathode
- electrons move across tube in half cycles when anode is (+) |
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Term
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Definition
- only half the voltage cycle is useful
- aka self-rectified
- most dental x-ray machines use this |
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Term
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Definition
| - use both halves of voltage cycle by adding rectifiers to circuit |
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Term
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Definition
- electrons move fast
- have lots of kinetic energy
- make high energy x-rays
- cause more penetration = darker image |
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Term
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Definition
- electrons move slowly
- less kinetic energy
- make low energy x-rays
- less penetration = lighter image |
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Term
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Definition
| as ___ increases, number of photons and average energy level of photons increases. this results in darker image. |
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Term
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Definition
- current of electrons passing from cathode to anode
- determined number of x-rays, not energy level |
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Term
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Definition
- more electrons hit target
- make more x-rays
= darker image |
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Term
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Definition
- fewer electrons hit target
- make fewer x-rays
= lighter image |
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Term
| mA doubled = number of x-rays doubled |
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Definition
| linear relationship between mA and number of x-rays |
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Term
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Definition
| as ___ increases, he number of photons increases, but there is not change in energy distribution of photons. |
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Term
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Definition
- time during which electrons cross tube from cathode to anode
- time you expose the patient
- measured in impulses (1/60 sec) or seconds
- determines number of x-rays, but not energy level |
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Term
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Definition
- more e- hit target
- more x-rays
= darker image |
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Term
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Definition
- fewer e- hit target
- fewer x-rays
= lighter images |
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Term
| exposure time double = number of x-rays double |
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Definition
| linear relationship of exposure time and number of x-rays |
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Term
- number
- energy distribution of photons |
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Definition
| as time increases, the ____ of protons increases, but there is not change in the _______. |
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Term
impulses = seconds x 60
(always 1 or more) |
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Definition
| conversion of seconds --> impulses |
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Term
seconds = impulses/60
(almost always less than 1) |
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Definition
| conversion of impulses --> seconds |
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Term
| mA-s (milliampere-second) Law |
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Definition
| - since mA and exposure time control the same thing (quantity of x-rays, not energy), these settings can be multiplied to indicate number of photons in beam |
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Term
| mA-s (milliampere-second) Law |
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Definition
- to keep number of photons constant, if mA is increased, time must decrease.
- if mA is decreased, time must increase. |
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Term
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Definition
| - x-rays are absorbed by tube by this process |
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Term
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Definition
- x-rays exit tube head through window to become this...
- have wide range of energy |
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Term
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Definition
| - weak/low energy photons are absorbed before hitting the patient |
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Term
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Definition
- undesirable
- absorbed in tissue and cause ionization
- cause biological damage
- are filtered out of primary beam |
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Term
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Definition
- measures filtration
- usually 0.5-2.0 |
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Term
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Definition
- increases average energy of x-ray photons, but decreases number of photons
- has greater proportion of high energy photons |
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Term
| increased kVp and increased added filtration |
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Definition
| - Energy of primary beam photons increased with: |
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Term
| increased mA, increased exposure time and increased kVp |
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Definition
| - Number of primary beam photons increased with: |
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Term
| Position Indicating Device |
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Definition
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Term
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Definition
- limits size of beam at patient's tissue
- reduces area exposed |
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Term
| circular, rectangular, pointed |
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Definition
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Term
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Definition
- short: 8in
- medium: 12in
- long: 16in |
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Term
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Definition
| best shape and length for PID |
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Term
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Definition
- reduces radiation dose
- best shape for PID |
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Term
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Definition
- reduces radiation dose
- best length for PID
- more absorption of x-rays by PID |
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Term
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Definition
- affect exposure time
- intensity of radiation varies inversely with the aquare of the distance btwn source and absorbing material |
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Term
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Definition
| - produce more intense radiation on film |
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Term
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Definition
| - new exp time/old exp time = (new PID length)2/(old PID length)2 |
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Term
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Definition
____ PID needs short exposure time
____ PID needs long exposure time
And the difference in time varies with the ____ of the difference in distance. |
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Term
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Definition
- too high kVp, mA and/or exposure time
- too short PID |
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Term
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Definition
- Too low kVp, mA, and/or exposure time
- too long PID |
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