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47 Cards in this Set
- Front
- Back
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Who discovered x-rays?
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Wilhelm Conrad Rontgen, 1895
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How are x-rays produced?
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X-rays are produced when high speed electrons strike a metal target
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What are some key requirements?
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Cathode source, method to accelerate electrons, anode target
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What is the function of the filament in the cathode?
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- Filament is the source of electrons
- Filament becomes hot and releases electrons in a surrounding cloud |
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What type(s) of filaments are there?
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Large & small
- larger & small focal spot - focusing cup tightens cloud |
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What does mA control do?
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Controls the amount of currnet passing through the filament
- higher mA ~ highger wattage lightbulb |
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What is the anode?
How does it affect the electron cloud? |
- Positively charged Tungsten target opposite the cathode
- Cloud of electons at cathode attracted to anode |
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How is the anode regulated?
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kVp regulates the voltage difference
- higher difference = higher velocity e- = higher energy x-rays |
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Will the machine catch on fire while I use it?
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Hopefully not, the anode roatates to help dissipate heat made
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Describe how x-rays are gnerated
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- e- of cathode are accelerated to anode
- at anode the e- interact with Tungsten - interaction occurs (different types) |
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What types of interactions occur when x-rays are generated?
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- characteristic x-ray generation (5% of x-rays in DI)
- Bremsstrahlung radiation (95% of x-rays in DI) |
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What are characteristic x-rays?
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x-ray created when an e- from the cathode collides with e- of Tungsten in anode
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What typically happens during a "Characteristic" x-ray?
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- Typically e- ejected from K shell of Tungsten
- transition of e- from outer to inner shell releases an x-ray |
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How does a material affect an x-ray?
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Every material has different values:
- x-rays of specific energy are released - difference of binding energies |
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What is Bremsstrahlung radiation?
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Fast e- are slowed as they approach the nucleus = loss of energy = x-rays
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What is the diagnostic x-ray energy spectrum?
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Bremsstrahlung results in broad, continuous range of x-ray energies
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Whi is there a range of energies?
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- Depends on how close e- was to the nucleus
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What is the maximum energy an e- will reach?
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Maximum energy = kVp
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What is kVp?
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kVp
- accelerates the e- fro the cathode to the anode - max energy of x-rays |
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What is mAs?
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mA x s
mA = number of e- generated by cathode s = time the current in on |
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What happens when mAs is increased?
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- bigger cloud of e- at cathode
- more x-rays - same energy spectrum |
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What happens when kVp is increased?
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- higher energy x-rays
- more e- from cathode accelerated to anode - more x-rays |
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What types of interactions can x-rays have with matter?
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- Coherent scatter
- Photoelectric effect - Compton scatter - none |
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What is coherent scatter?
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very low energy x-rays
- interaction causes whole atom to vibrate - ~5% of interactions above 70 kVp |
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What happens during coherent scatter?
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- no absorption of the photon
- no ionization - x-ray looses no energy - changes direction slightly |
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What is photoelectric effect?
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- when the x-ray energy is completely absorbed
- biggest contribution to radiographic contrast |
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What happens to the e- during photoelectic effect?
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Photoelectron is ejected from inner shell of atom
- ionization of target atom -low energy charcteristic x-rays produced (don't reach film/absorbed by patient) |
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What is the probability of a Photoelectron interaction?
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Proportional to Z cubed
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How do differences in atomic number affect x-rays?
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Differences in the atomic number of patient tissues are magnified
- small differences in atomic composition lead to big differences in number of x-rays absorbed. -radiographic contrast |
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How does the x-ray energy effect Photoelectric interactions?
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Inversely proportional to cube of x-ray energy
**Much less likely with high energy x-rays |
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What is compton scatter?
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x-ray interact with outer shell e- in atom of patient's tissues
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What does the atom interaction in compton scatter cause?
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- x-rays eject outer shell e-
- ionization of the target atom - change in the x-ray direction ("scatter") - reduction in x-ray energy |
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What form of x-rays are responsible for the most occupational radiation?
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Compton scatter
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What is the probability of compton scatter?
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proportional to number of e- in patient
- Physical density - e- /g |
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What types of radiography are there?
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Conventional radiographs
- film viewed with light box Digital radiographs - radiograph exist as DICOM - displayed on monitor - computed radiography (CR) - Direct digital rad. (DR) |
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What is radiographic x-ray film?
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Silver halide crystals bound to polyester base
- single or double emulsion, usually double |
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What happens when x-rays expose the film?
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Silver halide crystal convert to metallic silver after exposure to ligh/x-rays & development
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What is formed?
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Latent image, revealed with development
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What is x-ray film most sensitive to?
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Light > x-rays
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what color is developed and exposed silver?
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Black
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What affects x-ray film blackness?
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- Number of x-rays hitting the film
- energy of the x-rays - distance from the x-ray tube to the film - film development conditions - film & screen speed |
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What affects the number of x-rays hitting a film?
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- mAs
- Patient attenuation |
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What is the distance from the x-ray tube to the film called?
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Focal spot-film distance
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What are 3 conditions for film development.
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- Temperature
- Time - Concentration of chemicals |
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What is the function of an intensifying screen?
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Intensifying screens contain a fluorescent layer
- converts x-ray energy to light |
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What type of light is emitted when an x-ray strikes an intensifying screen?
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Colored light is emitted
- match color to sensitivity of film - blue & green |
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With an intensifying screen where is the light emitted?
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inside the cassette, adjacent to the film
- screen-film contact ensure optimum exposure - minimize light diffusion |
