X-Ray Production PDF

X-ray Production RADT 1010  How are x-rays produced? When fast moving electrons collide with matter in the tube Potential difference = kV -heating...

X-ray Production RADT 1010  How are x-rays produced? When fast moving electrons collide with matter in the tube Potential difference = kV -heating current  Loading… Produced  Tube Characteristics je needtoace Sealed glass or metal envelope to create a vacuum Anode and cathode + - Electrons produced at cathode (-) and attracted to anode (+) Electron target area on anode called focal spot Kinetic energy of electrons transformed into heat heat (99%) and X-rays (1%) (inifisunt) - make X-rays Most tubes are the rotating type – anode must step rotate during exposure 2 exposure I-anode spin 2 - I speed and interact Two step process for taking the exposure  higher mA # of X-ray more boiled off - 1 e intensity Exposure Factors - mA -# of E Current measured in milliamperes - mA Amount or # of electrons flowing Current causes thermionic emission Loading… Controls number of electrons boiled off, therefore number of x-rays produced I α mA Exposure Factors - mA lower mA lower contrast higher ma - whites -higher contrast - more detail Which image was taken with higher mA?  Increase KV = more energy - potentionene Exposure Factors - kV kilovoltage or kVp for kilovolts peak potential difference between the anode and cathode 1000’s of volts - Need high voltage controls kinetic energy of the electrons and therefore the energy of the x-rays and number of x-rays I α kV2  Contrast = # of greys Exposure Factors - kV LowKV-less grays/White high kV-more grays/white High Contrast Low Contrast low higher energy - more pass through lower energy- Absorbed this high High kV = low contrast  Exposure Factors - Time + O = MA intensity (mAs) seconds or milliseconds length of time the exposure lasts mA x time = mAs I α time Exposure Factors - Time Longer time High contrast low k more energy Which image was taken with a longer exposure time (all other factors the same)? Conditions Necessary to Produce X-rays 1. Source of electrons – cathode 2. Means to accelerate the electrons – kV 3. Way of stopping the electrons – anode Loading… 4. Vacuum to ensure electrons have no interference  Pie Piece Atom = neutral Neutrons in Nucleus Full Atom [not important Energy changes !  Can't lose create energy nor - or destroy E = mc2 energy mass speed of light The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another  Kinetic energy of electrons transformed into heat (99%) due to excitation & X-rays (1%) due to ionization transformed 99 % heat into is typical o 2 types of radiation: Anode Bremsstrahlung & Characteristic  Breaking Bremsstrahlung Radiation the Any energy up to max different All types of X-rays Produced Electrons interact with the nucleus of the target atom and “braking radiation” is produced %) (1 Wave length longer Shorter less wave energy X-ray more length energy - Photon - electron loses energy more energyfor a interacting represents Nucleus electron with - - slows down/change direction loss = X- r ay photon - energy  after Nucleus interact depends Nucleus 100kVp Energy on of 80% the kup is n ow zokup is Brems ! -90 % Bremsstrahlung Radiation out of turn 100 into only heat 1 ends up an X- r ay electrons With anode atom interact in the as KE converted to electromagnetic radiation Energy is dependent upon the distance between the electron and nucleus final KE of electron = initial KE of electron minus the energy of X-ray photon produced Wide distribution of energy produced Makes up 90% of the radiation beam X ray have different wave length (has to) become 2 energy interact Photons X- r ay with Nucleus  between difference shells creates X-rays specific to something Characteristic Radiation Atom Electrons interact with inner shell electrons, enough ejecting them energy to force-e out Vacancy filled by an electron dropping down from a higher energy state The transition is accompanied by an emission of an X-ray photon with energy = the difference in binding energies of the 2 electrons Characteristic of the element and shells involved 10% of radiation beam  set energies going in enough Pe energy to elect - e Don't memorize numbers !  Spectral Curves Represents the beam-90 % Brems 10 % characteristic A graphic representation of a beam of radiation amount of X- r ay photon per...? I = # of X-ray photons (amount of radiation) Quantity of radiation flowing per second through a unit area I = joules/m2sec, but not measured in these units R or C/kg I energy  Spectral Curves Continuous spectrum Intensity of radiation is distributed in a continuous fashion Contains all possible values higher energy more likely = for photon to pass through [think Punching wai] a Low more energy Photon = more absorbed radiation Jose (bad)  Spectral Curves Characteristic or line spectrum non-continuous, discrete without a filter [Spike] Set amount So it. Peeks at the set always line amount [urve] Approx. 1/3 of max. energy majority of X-rays - Brems Curve -characteristic - characteristic - Controls contrast  Set 100kV Set Gokv Can't go anymore than 60 30-40 % has most intensity  Test ! Increasing mA - To draw : Spectral curve Second exposure ma is directly proportional to the First exposure intensity /time - continuous - Non-continuous cuz break in line -characteristic Set aau Increasing kV To Draw : Spectral Curve # of more end at correct X-rays k  Factors that cause the heterogeneous -all different energies nature of the continuous spectrum: 1. incoming e- have different energies 1 electron can produce more interactions to Produce X- r ays like heat or Photon... 2. distance between e- and nucleus is variable Loading… 3. e- may undergo many interactions before coming to rest  Heterogeneous vs homogeneous X-ray beams are heterogeneous which is not ideal for imaging There are methods to try to decrease this: Make incoming voltage as consistent as possible Use filters to remove lower energy photons  Increase electrons - m o re likely for that 1% of X-ray photons to hit Quantity vs Quality Quantity = # of photons ↳ # We boil off Controlled primarily by: Directly proportional # of electrons hitting the anode (mA & time) # of interactions that each electron will make in the target (kV) Quality = penetrating power of the beam Determined by wavelength > - The quality of the image reguarding contrast Effects dose inversely Controlled primarily by kV low kV = more > energy high - kV = less energy  Next class… X-ray Attenuation Homework: Compose 2 T/F questions on Topic 2 to date. Use topic objectives (found in course outline) and the textbook to focus your questions. Please email to Stephanie ([email protected]) by 11:59 PM on Tuesday.