MOD 2 - Xray Production

ELECTROMAGNETIC RADIATION

  • two parts in electromagnetic radiation

    • electric field

    • magnetic field

  • considered a transverse wave → both fields oscillate sinusoidally

WAVES

  • two important properties of waves

    • wavelength: longer wavelength = decreased wave energy = decreased x-ray photon energy

    • frequency: higher frequencies = higher energies

X-RAYS

  • form of electromagnetic energy

    • categorized as ionizing radiation = photons (have no mass nor charge)

  • ionization = the acquisition or loss of an electron by an atom, occurs as x-rays have sufficient energy to eject those orbiting -e

X-RAY PRODUCTION = look MOD 1 Notes

TYPE OF X-RAYS

  • CHARACTERISTIC:

    • interact with orbital electron

    • only the inner shell (K-shell orbital) -e loss creates diagnostic level x-rays

    1. projectile -e knocks an inner shell -e out of orbit

    2. which creates an -e vacancy in the atom → atom is unstable

    3. to balance this instability, an -e from an outer/higher energy state/valence will drop down into the vacant space

    4. now to stabilize the atoms energy changes, atom releases the differential energy as a x-ray photon

    5. x-ray photon = (-electron energy) + (-electron energy) THEREFORE the energy is back in balance

  • BREMS:

    • interact with the atom’s nucleus

    • most common

    • the direction change causes a release of energy in the form of an x-ray photon

    1. a projectile -e passes near to the positive nucleus as it’s attracted to it

    2. this course alternation slows down the -e

    3. this KE potential is released in the x-ray photon form

    4. this -e is either fully stopped (absorbed) or slowed and diverted

    5. resulting in a wide variety of x-ray photon energies

THE 0.5% OF PROJECTED -E

  • only ~0.5% of the energy deposited by the -e into the anode is converted to x-rays

THE 99.5% OF PROJECTED -E

  • projectile electrons are absorbed by atoms at the anode which LEADS to the production of infrared radiation or heat

    • quantity vs. quality and influenced by the following factors

FACTORS AFFECTING X-RAY BEAM

  • KVP

    • increasing kVp = increasing penetration quality of x-ray beam

    • affects how -e will interact with atoms

    • affects x-ray beam energy and higher kVp = higher energy = travels thru body more easily

    • kV only needs a 15% increase to double the amount of photons

  • MAS

    • double mAs = double the number of x-rays

    • impacts beam quantity ONLY

  • TARGET MATERIAL

    • higher the atomic number = better x-ray beam quality

    • tungsten and gold

  • FILTRATION

    • located between the x-ray tube housing and collimator

    • improves the overall penetration of the x-ray beam/ beam quality BY filtering out the low energy x-rays

    • high energy photons move thru easily while low energy photons don’t

    • important as it filters out x-rays which don’t contribute to beam quality but just increases PT dose

  • GENERATOR (SURFACE LEVEL)

    • increasing amount of voltage ripple = decreases the consistency of high voltage current reaching the cathode = lower shift in avg energy AND decrease in quantity of x-ray photons

    • hence, common machines run high frequency generators

X-RAY INTERACTION WITHIN PT

  • photoelectric effect = interaction at an inner shell -e and has no photon release (does ionize the atom)

  • coherent scattering = energy is absorbed then released as a x-ray photon (does NOT ionize the atom)

  • compton scatter = interaction with outer shell -e (atom ionized and photon released)