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41 Cards in this Set
- Front
- Back
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Required parts to produce a controlled x-ray beam |
source of electrons a way to accelerate the electrons vacuum target envelope to maintain vacuum |
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What is a cathode |
negative end of the tube has a filament made of tungsten heated by a low energy circuit directs x-rays to target |
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Focusing cup |
cathode sits in this "focuses" electron beam on the target |
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Anode |
positive end of the tube aids in heat dissipation contains target |
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Stationary anodes |
small portable machines |
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Rotating anodes |
dissipates heat over a larger surface area |
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Focal spot |
effects detail |
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Detail |
sharpness of the edge of the image |
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Target |
Is a focal spot can be small or large |
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Small focal spot |
yields sharper image |
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Large focal spot |
less sharp image penumbra |
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penumbra |
fuzzy border lack of sharpness on edge of image |
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Line focus principal |
effective focal spot vs actual focal spot effect of making the actual focal spot size appear smaller when viewed from the position of the film because the angle of the target to the electron stream |
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Vacuum |
contained by envelope if oxygen is present electrons won't hit target |
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Ma |
controls # of electrons increase Ma, increase the density of the film |
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Time |
longer the time, the more dense the film becomes |
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KvP |
acceleration of electrons determines penetrating power of the x-ray beam non-linear 70 to 80KvP doubles film density |
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What is the heel effect? |
an unequal distribution of radiation emitted from the target, due to the angle of the target
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Does the cathode had stronger x-rays than the anode? |
yes |
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SID |
Source image distance |
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When is the heel effect most noticeable? |
when large films, short SID and low KvP are used |
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Contrast |
visual difference between two densities low KvP= high contrast High KvP= low contrast |
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low contrast or long scale contrast |
Shades of gray |
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High contrast |
white, black |
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What causes tube failure |
cathode or filament failure anode bearing malfunction target failure arcing due to deposits on the envelope |
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Arcing |
a phenomenon in which metal deposits on the inner wall of the envelope act as a secondary anode, thereby attracting electrons from the cathode |
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Cathode failure |
caused by thermal overload film is unexposed no movement of the Ma meter needle during exposure |
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Prevention of cathode failure |
turn off when not in use do not hold the pre-exposure button excessively avoid thermal overload |
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Anode failure |
rotor noise becomes very loud target can become damaged uneven production of x-radiation |
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What happens when there is a leak in the glass envelope |
x-rays bounce off air molecules reduce amount of x-rays produced |
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High voltage circuit |
creates KvP provides the electrical potential to accerlerate the electrons to the target |
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Step-up transformer |
increases the incoming voltage of 110-220V to thousands of volts |
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Step-down transformer |
reduces x-ray machine input voltage from 110 or 220V to 10V to prevent burnout of the cathode filament |
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Autotransformer |
kilovoltage selector |
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Full wave rectification |
increase efficiency resulting in twice the x-ray production |
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Rectifier |
changes alternating current (AC) to direct current (DC) assures the flow of electrons occurs in one direction only |
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Half wave rectification |
loses on half of the current increases amount of heat generated at the anode |
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Collimator |
controls the size of the primary beam reduces scatter reduces radiation exposure to personnel |
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Actual focal spot |
the area of the focal spot consisting of a coiled wire that perpendicular to the surface of the target |
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Focal spot |
the small area of the target with which electrons collide on the anode |
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Do x-rays have a higher frequency and shorter wavelength than radio or TV waves? |
Yes |
