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Natural background radiation
radiation contained in the unpolluted environment
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Artificially produced radiaition
also called man-made radiation
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Primary radiation
radiation exiting the x-ray tube
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Exit radiation (remenent radiation; image-producing radiation)
x-rays that emerge from the patient and strike the image receptor
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Attenuation
absorption and scatter (loss of intensity) of hte x-ray beam as it passed through the patient
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Hetrogenous beam
x-ray beam that contains photons of many different energies
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Photoeletric Effect
absorption of x-ray photons in the atoms of the body
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Compton effect
scatter of x-ray photons from the atoms of the body
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Roentgen (R)
traditional unit of in-air exposure
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Coulombs per kilogram (C/kg)
SI unit of in-air exposure
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Rad
traditional unit of absorbed dose
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Gray
SI unit of absorbed dose
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Rem
traditional unit of eequivalent dose and effective dose
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Sievart
SI unit of equivalent dose and effective dose
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Curie
traditional unit of activity
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Becquerel
SI unit of activity
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National Academy of Sciences/National Researche Councile Committee on the Biological Effects of Ionizing Radiation (NAS/NRC-BEIR)
Study biologic effects of ionizing radiation protection guidelines
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Internation Commission of Radiological Protection
Publishes internation radiation protection guidelines
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National Council on Radiation Protection and Measurements (NCRP)
Published radiation protection guidelines for the United States
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Nuclear Regulatory Commission (NRC)
Enforces radiation protection standards at the federal level related to use of radioactive material
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NCRP Report # 102
Makes recommendations on equipment design and protection regarding lead shielding and fluoroscopic and mobile exposure rates
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NCRP Report # 116
Makes recommendations pertaining to risk-benefit analysis of radiation exposure; states that somatic and genetic effects should be kept to a minimum when radiation is used for diagnostic imaging; defines annual exposure limits
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Effective dose limit
The upper boundary dose that can be absorbed, either in a single exposure or annually, with a negligible risk of somatic or genetic damage to the individual; effective dose implies whole body radiation exposure
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Cumulative effective dose (CED)
limit lifetime occupational exposure must not exceed the radiographer's age multiplied by 1 rem
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Equivalent dose
equal to the absorbed dose multiplied by the radiation weighting factor; formerly known as dose equivalent
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Equivalent dose limit
Upper boundary dose that can be absorbed, either in a singler exposure or annually, with a negligible risk of a deterministic levels
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ALARA (As Low As Reasonably Achievable)
A concept of radiologic practice that encourages radiation users to adopt measures that keep the dose to the patient and themselves at minimal levels
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Dose-Response Curve
graphs taht illustrate the relationship between radiation dose and the response of hte organisim to exposure; may be linear or nonlinear, threshold or nonthreshold
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Stochastic Effects
radomly occurring effects of radiation; the probabitlity of such effects id proportional to the dose (increased dose equal increased probability, not severity, of effects)
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Deterministic Effects
Effects of radiation that become more severe at high levels of radiation exposure and do not occur below a certain threshold dose
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Genetically significan dose (GSD)
Average annual gonadal dose of radiation to the individuals of childbearing age; addresses the relationship of gonadal doses to individuals versus and entire population and overall effects
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Linear Energy Transfer (LET)
amount of energy deposited by radiation per unit length of tissue
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Relative biolgic effectiveness (RBE)
Ability t oproduce biolgoic damage; varies with the LET
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Direct Effect
occurs when raidaiton directly strikes DNA in the cellular nucleus
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Indirect Effect
Occurs when radiaiton strikes the water molecules in the cytoplasm of the cell
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Radiolysis of water
Occurs as radiation energy is deposited in the wate rof the cell; the result of radiolysis is an ion pair in the cell: a positively charged water molecule (HOH+) and a free electron
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Mutation
Erroneous information passed to subsequent generation via cell division
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Law of Bergonie and Tribondeau
Cells are most sensitive to radiation when they are immature, undifferentiated, and rapidly dividing
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Early Somatic Effects of Radiation
hemopoetic syndrome, gastrointestional syndrome; central nervous system syndrome
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Late Somatic Effects of Radiation
Carcinogenesis, cataractogenesis, embryologic effects, thyroid dysfunction, life span shortening
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Cardinal principles of Radiation Protection
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Distance
Best protection against radiation exposure
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Personnel Monitoring Devices
- Optically stimulated luminescence (OSL) badge
- Film Badge
- Thermoluminescent dosimeter (TLD)
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Mean Marrow Dose
average dose of radiation to the bone marrow
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Ionization may cause
unstable atoms, free elctrons , or formation of new molecules harmful to the cell
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What 2 types of damage can occur to the cell?
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What is the greatest source of natural radiation present in the environment?
Radon
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Where does 82% of human exposure come from?
Natural Background Radiation
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Photelectric Interaction
- Incoming x-ray photon strikes a K-shell electron
- Energy of x-ray photon is transferred to electron
- Electron is ejected from the K-shell and is now called a photoelectron
- X-ray photon has depsoited all of its energy and ceases to exist
- Photon has been completely absorbed
- Photoelectron may ionize or excite other atoms until it has deposited all of its energy
- Characteristic cascade happens to fill hole in K-shell
- Produces contrast in image because of differential absorption of incoming x-ray photons
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Compton Interaction
- Incoming x-ray photon stikes a loosely, bound outer-shell electron
- Photon transfers part of it's energy to the electron
- Electron is removed from orbit as a scattered electron, referred to as a recoil electron
- Ejected electrons may ionize other atoms or recombine with an ion needing an electron
- Scattered photon may interact with other electrons, causing more ioniziation, addition scattering events, or photoeletric absorption, or it may exit the patient
- Scattered photons emerging from the patient travel in very divergent paths in random directions
- Scattered photons may also be present in the room and expose the radiographer or radiologist
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Coherent Scatter (Classical Scattering or Thompson's Scattering)
- Produced by low energy photons
- Electrons are not removed but vibrate from deposition of energy from photon
- As electrons vibrate they emit energy equal to original photon
- Does not affect image under 70 kVp
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Pair Production
- does not occur in radiography
- produced a photon energies above 1.02 mEv
- involves interacton between incoming photon and atomic nucleus
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Photodisintegration
does not occur in radiography
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