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47 Cards in this Set

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