Term
| radiation burden depends on what 3 things? |
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Definition
| medical applications (therapy vs. diagnosis), the amount of radioactive material injected (injected dose), type of radiation and energy (high or low) |
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Term
| excitation of alpha particles |
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Definition
| electrostatic attraction raises an electron to a higher energy state... when they drop back to normal state, they may emit electromagnetic radiation such as light or fluorescence |
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Term
| ionization of alpha particles |
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Definition
| kinetic energy is lost from the alpha particle, the velocity of the particle is reduced... when it loses all its energy, it combines wtih 2 free electrons to form helium and the radiation no longer exists |
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Term
| rank the 4 types of particles from lowest to highest penetrating distance |
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Definition
| goes in alphabetical order: alpha < beta < gamma and xrays < neutron |
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Term
| due to their small/large size and fast/slow motion, alpha particles lose their energy quickly/slowly |
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Definition
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Term
| what kind of beta particle loses excess kinetic energy by ionization and excitation to become an ordinary electron? |
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Definition
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Term
| what kind of beta particle loses excess kinetic energy by ionization and excitation and then reacts with an electron by annihilation? |
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Definition
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Term
| ___ is the combo of a positron with an electron, resulting in the production of 2 511 keV gamma rays going in the opposite direction. |
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Definition
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Term
| how do the velocities of alpha and beta particles compare? |
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Definition
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Term
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Definition
| something about transferring energy from beta particles |
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Term
| the energy of what particle follows a typical Guassian distribution |
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Definition
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Term
| Bremsstrahlung increases/decreases with higher atomic number absorbers |
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Definition
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Term
| "braking radiation" or "deceleration radiation"), is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. |
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Definition
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Term
| Specific Ionization (SI) for beta particles. how does this compare to alpha? |
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Definition
| 50-300 ip/cm in air -- much lower than alpha |
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Term
| What is the fate of positrons? what is this useful in? |
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Definition
| they combine with electrons to form 2 gamma photons, traveling in opposite directions. this is useful in PET (positron emission tomography) imaging |
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Term
| lower energy = higher/lower penetrating range and higher/lower SI |
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Definition
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Term
| higher energy B rays produce more/less Bremsstrahlung |
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Definition
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Term
| 3 interaction mechanisms for gamma spectroscopy |
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Definition
| photoelectric absorption (for low energy gammas), compton scattering, and pair production (for high energy) |
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Term
| __ is the ideal interaction process for measuring the energy of the original gamma ray. How does it work? |
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Definition
| photoelectric absorption -- incident gamma ray photon disappears and a photoelectron is produced in its place -- the effect is the liberation of a photoelectron, which carries off mos the the gamma ray nergy |
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Term
| result of compton scattering |
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Definition
| a recoil electron and scattered gamma-ray photon |
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Term
| result of pair production |
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Definition
| incident gamma ray photon completely disappears -- occurs near intense electron field near protons and creates an electron-positron pair |
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Term
| how are gamma photons detected? |
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Definition
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Term
| medical applications of SPECT |
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Definition
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Term
| Coincidences of PET detectors |
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Definition
| real (useful), scatter, and random |
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Term
| beta particle emitters in medicine |
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Definition
| can deposit and tumor cells and kill them, Y-90 (a pure beta-emitter) used to target other cancer cells |
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Term
| why are beta particle emitters useful in medicine? |
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Definition
| they penetrate deep enough to get into large, heterogeneous tumors, they yield a homogeneous dose even when heterogeneously distributed in a tissue |
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Term
| How do beta particles work to kill cancer cells? |
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Definition
| produce free radicals that are able to react wtih the DNA of the tumor and kill it |
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Term
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Definition
| used to kill liver tumors via a process called "SIRT" or selective external radiation therapy |
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Term
| Who is in charge of radiation safety? |
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Definition
| Nuclear Regulatory Commission (NRC), nuclear practitioners, and Health Physicists |
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Term
| 4 factors influencing external hazards of radiation |
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Definition
| exposure level, exposure rate, type of radiation (alpha, beta, gamma), energy level, and amount of activity (more activity = more exposure) |
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Term
| factors affecting internal radiation hazard |
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Definition
| amount of activity (more = more expsure), chemical form, type of radiation, half life, effective half life |
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Term
| combination fo the rate of excretion (biological half life) with the physical half liffe |
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Definition
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Term
| when must personnel monitoring equipment be used? |
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Definition
| when working in areas where there is likely exposure in excess of 10% of the maximum permissible exposure |
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Term
| Spin-Echo (SE) pulse sequences flips the magnetic moment of the proton completely into the ___ plane. Due to ____ interactions, the Mxy decays with time T2 |
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Definition
| transverse (xy), spin-spin |
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Term
| T2 relaxivity is a ____ interaction |
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Definition
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Term
| T1 relaxivity is a ____ interaction |
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Definition
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Term
| when a magnetic moment (a proton) is placed within an external magnetic field, a force or torque acts on it causing it to precess (spin like a top) |
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Definition
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Term
| transverse plane is the __ plane, external magnetic field is in the __ direction |
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Definition
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Term
| I = nuclear spin quantum number. if I=0, then? If I=1,2,3, then? If I=1/2,3/2,5/2, then? |
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Definition
| I=0 - even atomic number, no MR potential :: I=1,2,3 - odd atomic number, even atomic weight :: I=1/2, 3/2, 5/2 - odd atomic wieght (odd number of portons and even number of neutrons or vice versa) |
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Term
| scatter coincidences are dependent on? |
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Definition
| object size and attenuation coefficient (compton scattering) of the object |
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Term
| 3 categories of coincidences in PET sensitivity |
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Definition
| true, scattered, and random |
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Term
| spatial resolution of PET scanning can be blurred by what 3 things? |
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Definition
| geometry, non-collinearity, positron range |
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Term
| a filter on a CT scanner does what? |
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Definition
| make the image more clear |
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Term
| to minimize the effects of T2 to our signal in MRI, what 2 things do we do? |
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Definition
| choose small TE, maximal TR |
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Term
| to minimize the effects of TI in MRI, what 2 things do we do? |
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Definition
| choose very long TR, maximal TE |
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Term
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Definition
| magnetic resonance spectroscopy |
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Term
| 3 cardinal rules to radiation exposure and dose |
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Definition
| time, distance, shielding |
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Term
| distance radiation can travel |
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Definition
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Term
| radiation exposure will decrease as the distance increases... this is defined by what law? |
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Definition
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Term
| what types of shielding materials are needed for each type of radiation? |
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Definition
| increase with greater distance... alpha only needs paper or skin, beta needs plastic in combo with lead, gamma and x rays need high density lead |
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Term
| the ____ is characteristic of a given material in terms of radiological shielding. it is proportional to the density and atomic number of the substance. the ____, on the other hand, is often used to compensate for density. |
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Definition
| linear attenuation coefficient (u).. mass attenuation coefficient (um) |
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Term
| ice, water, and steam have the same/different linear attenuation coefficient and the same/different mass attentuation coefficient? |
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Definition
| different linear, same mass |
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Term
| are natural or man-made sources of radiation exposure to humans greater? |
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Definition
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Term
| of the natural sources of radiation exposure, which has the most effect on man? of the man-made sources? |
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Definition
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Term
| ___ and ____ radiation are particles. ___ radiation is electromagnetic waves. |
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Definition
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Term
| long periods of exposure to alpha and beta radiation can cause _____. short term exposure usually does not have a significant effect except when ___, ____, or ______. |
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Definition
| heat burns ... ingested, inhaled, or through an open wound |
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Term
| the ___ is used to express the amount of gamma radiation exposure. why isn't this entirely helpful for humans? |
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Definition
| Roentgen (R) - it only states the amount of exposure, not the dose absorbed |
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Term
| a ___ relates the different types of radiation to the energy they impart. it is the basic unit of absorbed dose of radiation. |
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Definition
| RAD (radiation absorbed dose) |
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Term
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Definition
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Term
| ____ relates the does of any radiation to the biological effect of that dose. |
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Definition
| REM - roetgen equivalent man |
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Term
| for gamma and beta radiation, 1 rad = __ rem. for alpha, 1 rad = ___ rem |
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Definition
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Term
| radiation exposure rate is expressed in what units? |
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Definition
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Term
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Definition
| Gray (Gy) = 100 rad, sievert (SV) = 100 rem |
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Term
| general public radiation dose limit and occupational dose limit |
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Definition
| public = 100 mrem/yr ... occupational = 5000 mrem/yr |
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Term
| removal of electrons is called ____. when this happens in the body as a result of collision of radiation with cells, the result is human sickness |
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Definition
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Term
| each person differs in their biological response to a given radiation dose due to what 5 factors? |
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Definition
| age, sex, diet, body temp, overall medical health |
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Term
| ____ occurs when an individual is exposued to a large dose of radiation in a short amount of time. doses greater than ___ rem/rad for gamma rays |
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Definition
| acute radiation sickness, 100 rem/rad |
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Term
| symptoms of acute radiation sickness |
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Definition
| changes in blood cells, vascular changes, skin irritation, gi effects, fever, flu-like symptoms, hair loss |
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Term
| 4 stages of acute radiation sickness |
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Definition
| prodromal phase (48 hrs), latent phase (days to weeks), manifest illness (weeks to months), recovery or death |
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