DMI 261DMI 261
Radiation BiologyRadiation Biology
AndAnd
ProtectionProtection
Unit 2 RADIATIONUnit 2 RADIATION
Electromagnetic SpectrumElectromagnetic Spectrum– The frequency range of electromagnetic radiation and The frequency range of electromagnetic radiation and
the photon wavelength associated with them.the photon wavelength associated with them.
Important to RadiographyImportant to Radiography
Visible lightVisible light– Smallest segment of the EM spectrumSmallest segment of the EM spectrum– Only part of the spectrum that we can directly Only part of the spectrum that we can directly
sensesense– Radiographs viewed on viewboxes (visible Radiographs viewed on viewboxes (visible
light)light)
Radio frequencyRadio frequency– Very low energy, very long wavelengthVery low energy, very long wavelength– Used for communication, TV and radioUsed for communication, TV and radio– Microwaves (shorter radiowaves), cell Microwaves (shorter radiowaves), cell
phones, highway radar, cookingphones, highway radar, cooking– MRI uses radiowaves.MRI uses radiowaves.
Ionizing radiation – gamma & x-raysIonizing radiation – gamma & x-rays– High energy, short wavelengthHigh energy, short wavelength– SourcesSources
X-rays – emitted from electron cloud in a man X-rays – emitted from electron cloud in a man made tubemade tube
Gamma – emitted from nucleus of a radioactive Gamma – emitted from nucleus of a radioactive atomatom
– Both have similar energy and travel at the Both have similar energy and travel at the speed of lightspeed of light
Characteristics of Ionizing Characteristics of Ionizing RadiationRadiation
Electromagnetic radiationElectromagnetic radiation
High energy, high frequency, short High energy, high frequency, short wavelengthwavelength
Travels at the speed of lightTravels at the speed of light
X and gamma are identical except for X and gamma are identical except for originorigin
No massNo mass
Electrically neutralElectrically neutral
Characteristics of Ionizing Characteristics of Ionizing RadiationRadiation
Interaction with matter causes electron Interaction with matter causes electron excitation or ionizationexcitation or ionization
Affects photographic film and fluorescent Affects photographic film and fluorescent crystalscrystals
Behaves as a wave and a particleBehaves as a wave and a particle
Travels in straight linesTravels in straight lines
Produces chemical & biological changesProduces chemical & biological changes
Produces secondary & scatter radiationProduces secondary & scatter radiation
Interactions of Radiation with Interactions of Radiation with MatterMatter
Coherent ScatteringCoherent Scattering– X-ray photon interacts X-ray photon interacts
with a target with a target atomatom causing it to vibrate.causing it to vibrate.
– Electrons emit Electrons emit electromagnetic waves electromagnetic waves with the same energy with the same energy as the incoming as the incoming photon.photon.
Coherent ScatteringCoherent Scattering(also called Rayleigh Scattering)(also called Rayleigh Scattering)
Occurs mostly below 30 kVpOccurs mostly below 30 kVp
Small change in direction occurs Small change in direction occurs (scattering of x-ray photon)(scattering of x-ray photon)
Diagnostic radiology – some x-ray are Diagnostic radiology – some x-ray are scattered by classical scattering and may scattered by classical scattering and may contribute to radiographic fog.contribute to radiographic fog.
Compton ScatteringCompton Scattering
Responsible for most Responsible for most scatter radiation scatter radiation produced during produced during radiographic radiographic proceduresprocedures– Forward scatterForward scatter– Small angle scatterSmall angle scatter– BackscatterBackscatter– Side scatterSide scatter
Compton ScatteringCompton Scattering
important
Compton ScatteringCompton Scattering
Probability in Diagnostic RadiologyProbability in Diagnostic Radiology– As photon energy increases, probability As photon energy increases, probability
increasesincreases– 100 kVp beam = significant interactions100 kVp beam = significant interactions– Occurs along with photoelectric absorptionOccurs along with photoelectric absorption– Can cause large amounts of scatterCan cause large amounts of scatter
Grids to absorb scatter (radiographic fog)Grids to absorb scatter (radiographic fog)
Lead aprons in fluoroscopyLead aprons in fluoroscopy
Compton Scattering is responsible for most Compton Scattering is responsible for most of the scatter radiation produced during a of the scatter radiation produced during a
radiologic procedureradiologic procedure..
Photoelectric AbsorptionPhotoelectric Absorption
X-ray absorption X-ray absorption interaction in which interaction in which the the photonphoton is not is not scattered, scattered, but totally but totally absorbed.absorbed.
important
Photoelectric AbsorptionPhotoelectric Absorption
Most important mode Most important mode of interaction between of interaction between x-ray photons and the x-ray photons and the atoms of the patient’s atoms of the patient’s body for producing body for producing useful images.useful images.
(photons #1 and 2)(photons #1 and 2)
Auger ElectronsAuger Electrons
Outer shell electronsOuter shell electrons that are released that are released (instead of characteristic radiation) when (instead of characteristic radiation) when an electron moves from an outer to an an electron moves from an outer to an inner shell during the photoelectric inner shell during the photoelectric absorption interaction.absorption interaction.
Photoelectric AbsorptionPhotoelectric Absorption
Probability in Diagnostic RadiologyProbability in Diagnostic Radiology
– Dominant interaction in diagnostic radiologyDominant interaction in diagnostic radiology
– Between Between 30 and 150 kVp30 and 150 kVp, it is the most , it is the most important interaction for producing useful important interaction for producing useful images.images.
Photoelectric AbsorptionPhotoelectric Absorption
Probability in Diagnostic RadiologyProbability in Diagnostic Radiology– Probability increases as the Probability increases as the effective atomic #effective atomic #
increases:increases:Air 7.6Air 7.6Compact bone 13.8Compact bone 13.8Barium 56Barium 56Iodine 53Iodine 53
– Because it has a higher Because it has a higher effective atomic #,effective atomic #, bone will undergo more PE absorption than bone will undergo more PE absorption than an equal amount of soft tissue or air.an equal amount of soft tissue or air.
Photoelectric AbsorptionPhotoelectric Absorption
Probability in Diagnostic RadiologyProbability in Diagnostic Radiology
– Probability increases as the energy of the x-Probability increases as the energy of the x-ray photon decreases (longer wavelength) ray photon decreases (longer wavelength) and the effective atomic # of the irradiated and the effective atomic # of the irradiated atoms (bone vs. soft tissue) increases.atoms (bone vs. soft tissue) increases.
Attenuation / Absorption / Contrast MediaAttenuation / Absorption / Contrast Media
Pair ProductionPair Production
Incoming photon Incoming photon interacts with the interacts with the nucleusnucleus of an atom of an atom and disappearsand disappears
Only occurs with Only occurs with photons greater than photons greater than 1.022 MeV1.022 MeV
Pair Production & PETPair Production & PET
Annihilation reaction photons are products Annihilation reaction photons are products of radioactive decay of an unstable of radioactive decay of an unstable isotope.isotope.
Scanner detects this reaction and Scanner detects this reaction and produces a cross-sectional image of the produces a cross-sectional image of the radioactivityradioactivity
Commonly used isotopes: fluorine-18, Commonly used isotopes: fluorine-18, carbon-11, nitrogen-13carbon-11, nitrogen-13
PET scan demonstration of epilepsy on the PET scan demonstration of epilepsy on the right side of the brainright side of the brain