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162 Cards in this Set
- Front
- Back
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Beyond what proton number are nuclei unstable?
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82
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What two quantities are conserved when nuclei decay?
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Mass number and electric charge
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What are emitted when excited states transform to lower energy levels?
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Gamma rays and internal conversion electrons
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What is an internal conversion electron?
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Nuclear energy that is transferred to orbital electron, which is emitted from the atom
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How long must a isomeric state live for it to be called metastable?
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> 10 ^ -9
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What is an isomer (vs isotope)?
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An excited state of a nucleus (vs same atomic number)
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What type of decay is most common in atoms with high atomic number (Z > 82)?
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Alpha decay
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What does 226 Ra decay to?
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222 Rn
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What are typical energies of alpha particles?
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4 to 7 MeV
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How far do alpha particles travel in tissue?
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< 0.1 mm
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What is the main risk of Radon?
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lung cancer
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What happens in the nucleus with beta minus decay?
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Neutron converted to proton
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What other particle does beta - decay emit?
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Antineutrino
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What is the rest mass and charge of antineutrino?
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zero and zero
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What happens with the atomic number in beta - decay?
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Increases by 1
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What is the average beta partical energy?
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Emax / 3
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What carries away the energy difference between Emax and the beta particle energy?
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the antineutrino
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What is the mean beta particle energy of 32-P (Emax = 1.71 MeV)
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0.570 MeV
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What are the Emax of tritium H-3 and carbon C-14
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18 keV, 156 keV
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What happens in the nucleus with beta plus decay?
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Proton converted to neutron
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In what type of nuclei is beta plus decay occurring in?
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Too man protons
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What other particle does beta plus decay emit?
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Neutrino
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What happens to atomic and mass number in beta plus decay?
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atomic number decreases by 1, mass number stays the same
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What is the half life of C-11?
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20 minutes
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What is the half life of O-15?
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2 minutes
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What is the half life of F-18?
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110 minutes
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What is the maximum energy of the F-18 positron?
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0.63 MeV
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What is the distance range of F-18?
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0.4 mm
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What happens in electron capture?
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A proton captures an orbital electron
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Electrons from which shell are usually captured in electron capture?
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K-shell
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What type of nucleus is electron capture most likely to occur?
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Too many protons
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What occurs with atomic number and mass number with electron capture?
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Atomic number decreases by 1, mass number stays the same
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What happens to the excess energy when a K-shell vacancy is filled in electron capture?
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Emitted as characteristic x-ray or Auger electron
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What are four important electron capture electrons in nuclear medicine?
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67-Ga, 111-In, 123-I, 201-Tl
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What is the decay process of 57-Co
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Electron capture
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What process produces radionucleotides in a nuclear reactor?
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Adding neutrons (neutron activation)
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What process produces radionucleotides in a cyclotron?
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Charged particles added to stable nuclides
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How do cyclotron produced radionucleotides normally decay?
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Beta plus process, 15-O is a positron emitter and 123-I decays via electron capture
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What is the decay process of 99m-Tc?
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Isomeric transition
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What is the decay process of 82-Sr
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positron emission
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What is the definition of 1 Bq?
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1 transformation per seconde
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What is the equivalient of 1 mCi?
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37 MBq
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How many transformations per second is 1 Curie?
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37 x 10^10
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What is the defining formula for activity?
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A = N x lambda
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What is the formula for the fractional activity of a source remaining at time t?
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exp (-lamda x t)
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What is the relationship between T/12 and lamda?
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T1/2 = 0.693/lamda
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What is the parent compound of Tc?
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99-Mo
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What is the half life of 99-Mo?
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66 hours
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How many half lives does it normally take to reach equilibrium in a generator between 99m-Tc and 99-Mo?
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4 daughter half lives (24 hours for 99m-Tc)
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What is the equilibrium name given to short lived parent nucleotides?
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Transient equilibrium
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What is the equilibrium given to long lived parent radionucleotides?
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Secular equilibrium
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What percent of gamma ray energy is converted to light?
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10%
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How many PMT tubes do scintillation cameras usually use?
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55
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How many counts are acquired for a typical scintillation camera image?
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500,000
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Converging collimators produce a _____ image
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magnified
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Diverging collimators produce a ____ image
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smaller
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What is the term used to designate the fraction of gamma rays reaching it from all directions?
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Collimator sensitivity
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What happens with resolution with increasing distance from the collimator?
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Degraded
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Low energy collimators are used for which radionucleotides?
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99m-Tc and 201-Tl
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Medium energy collimators are used with which radionucleotides?
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67-Ga and 111-In
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High energy collimators are used for which radionucleotides?
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131-I
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How thick are the NaI scintillators?
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10 mm
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Does the iodine escape peak occur below the the photopeak or above the photopeak?
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Below
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How many bytes are used to store NM images?
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2 bytes
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What type of collimators are used in SPECT imaging?
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Parallel hole collimators
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How long does each projection take in SPECT?
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30 seconds
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What is the matrix size in cardiac SPECT?
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64 x 64
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What is the typical NM matrix size?
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128 x 128
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What is the whole body matrix size?
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1024 x 1024
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What are modern PET scanner detectors made from?
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lutetium oxyorthosilicate (LSO) or gadolinium oxyorthosilicate (GSO). Also lutetium yttrium oxyorthosilicate (LYSO)
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What is the disadvantage of GSO as a PET detector?
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poorer absorber of 511 keV gamma rays
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What are the advantages of LSO and GSO over BGO?
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Emit more light
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What is the advantage of organic scintillators?
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Faster light emission
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Is attenuation in PET depth dependent?
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No, it only depends on total thickness of tissue traveled.
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What is used for attenuation correction in PET?
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CT images
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What is ordered-subset expectation maximization (OSEM)?
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PET reconstruction algorithm
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What is the FWHM uncertatinty of TOF PET?
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~7.5 cm
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What is the usefulness of TOF information?
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improved spatial resolution and enhanced lesion contrast
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How many counts are typical in PET images?
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Several million
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What is the half life of 18-F?
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110 minutes
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What is the half life of 82-Rb?
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75 s
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What is the half lifle of 68-Ga?
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68 minutes
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What is the axial length of PET systems?
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22 cm
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What is used to rebin data for reconstruction between 3D and 2D data sets?
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Fourier rebinning (FORE)
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What is the scanner sensitivity of 3D PET compared to 2D PET?
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6 times higher
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Are scattered coincidences higher in 3D or 2D PET?
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3D
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Modern PET scanners operate in 2D or 3D mode?
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3D
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What is the 18-F activity in PET?
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555 MBq (15 mCi)
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How many minutes is 18-F administered prior to scanning?
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60 to 90
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What is the mAS of low-dose CT?
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40-80 mAs
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How many detector positions are used in current clinical PET scans to cover the body?
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5
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How long do typical PET scans taek at each detector position?
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2 to 3 minutes
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How many detector positions are requried for typcial head to toe PET imaging for melanoma patients?
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11
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What are the gamma ray energies of 99-Mo?
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181, 740, 780
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Why does 99-Mo contamination degrade image quality?
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Septal penetration
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What instrument is used to determine content of 99-Mo each time the generator is eluted?
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Dose calibrator
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What is the legal limit of Mo breakthrough?
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5.5 kBq / 37 MBq 99-Tc
0.15 uCi / mCi 99m-Tc |
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What can breakthrough into saline that can interference with 99m-Tc kits?
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Alumina
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What is used to test for alumina breakthrough?
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Color indicator paper
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How are contaminant radionucleotides identified?
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Gamma ray spectroscopy
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What is a potential contaminant in 201-Tl?
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202-Tl
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Who checks radionucleotide purity?
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Manufacturer
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How is radiochemical purity checked?
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Thin-layer chromatography
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What kind of contaminant is pertechnate in 99m-Tc DTPA?
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Radiochemical contaminant
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How often is the photopeak window checked?
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Daily
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How is the photopeak window evaluated?
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With a sheet source or point source
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What is the typical uniformity between adjacent areas in modern cameras?
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2%
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What is the energy of 57-Co?
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122 keV
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What is the half life of 57-Co?
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270 days
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What is the difference between extrinsic and intrinsic flood images?
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Extrinsic - with collimator
Intrinsic - without collimator |
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What are typical dimensions of the quadrant bar phantom?
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3.5, 3.0, 2.5, 2.0 mm
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What is used for measuring dose calibrator constancy?
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Cs-137
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What is the half life of Cs-137?
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30 years
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What should day to day measurements of dose calibrator constancy be below?
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5%
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How often is dose calibrator accuracy checked?
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Annually
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How often is dose calibrator linearity checked?
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Quarterly
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What is used to check dose calibrator linearity?
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99m-Tc over 72 hours
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What is the typical intrinsic resolution of a scintillation camera?
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3 and 5 mm
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What dose system resolution depend on?
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Intrinsic resolution and camera resolution
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What is the formula for system resolution?
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(Ri ^2 + Rc ^2) ^ 0.5
Ri intrinsic resolution of camera Rc resolution of collimator |
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What is the typical FWHM of the low-energy high-resolution collimator in clinical imaging?
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8 mm
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What is the limiting spatial resolution for a FWHM of 8 mm?
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1 / ( 2 x 8 ) lp/mm
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Does SPECT or planar imaging have better resolution?
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Planar is better
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What is the spatial resolution of comercial PET systems?
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5 mm FWHM
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What is statistical variation in pixel counts?
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Quantum mottle
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What are two classification of noise?
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Random noise and structured noise
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What is increased brightness at the edge of the crystal called?
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Edge packing
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What causes edge packing?
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Internal reflection of light at the edge of the crystal
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What design decision was made to minimize edge packing?
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Crystals are made larger than the imaged field of view
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Off-peak images on the low side of the photopeak contain excessive _____ scatter.
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Compton
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What can cause "hot" artifacts in CT attenuation-corrected PET images?
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Contrast material
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What is the relationship between T-1/2 and radionucleotide decay constant (lambda)?
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T-1/2 = 0.693/lambda
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How can biological clearance be modeled?
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Exponential decay
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What is the relation between effective half life and biological and physical half lives?
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1/Te = 1/Tb + 1/Tp
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What is the total number of nuclear transformations called?
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Cumulative activity
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What two numbers are required to generate organ dose in NM?
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Cumulative activity and S factor
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What is the cumulative activity formula for exponential decay?
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1.44 x A x Te where A is initial activity and Te is effective half life
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What is the whole body to whole body S factor?
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1
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What is the liver to liver S factor?
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23
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What is the thyroid to thyroid S factor?
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2300
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What is the thyroid to liver S factor?
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0.08
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What 3 factors does energy absorbed in a target organ depend on?
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Number of emissions per transformation
Energy associated with each emission Fraction of emitted energy deposited in the target organ |
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How is the S factor determined?
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Absorbed energy / organ mass
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What is the S factor?
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Absorbed energy in a target organ by per unit cumulative activity in a source organ
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What is the unit of S factor?
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mGy / uCi-hr
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Uniform distribution of 99m-Tc in the whole body gives what average whole-body dose?
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1.6 x 10 ^ (-13) mGy/Bq-s
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What happens to S factor as the size of organ decreases?
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Increases
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How to calculate the dose to a target organ from activity in a source organ?
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D = A x S
A - cumulative activity S - source to target S factor |
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What is the highest organ dose from diagnostic nuclear medicine?
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~50 mGy
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What is the average effective dose for NM exams?
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5 mSv
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Effective doses in PET scans is how much?
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~10 mSv
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Disgnostic CT in a PET/CT scan amounts to how much effective dose?
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~15 mSv
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Attenuation correction CT in a PET/CT scan amounts to how much effective dose?
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~5 mSv
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Calculate the thyroid dose for a 10 mCi administration, 50% uptake, physical and biological half lives of 8 days, S (thyroid->thyroid) of 1.7 x 10 ^ (-9) mGy/Bq-s
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160,000 mGy
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What are NM operator doses during injection?
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0.01 to 0.02 mSv/hour
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How are extremity doses monitored in NM?
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Ring dosimeters
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What precaution is required for volatile radionucleotides?
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Fume hoods
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What is used to measure wipe tests?
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Well counter
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How long is radioactive waste stored before being surveyed and being disposed of as regular waste?
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10 half lives
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What are annual effective doses for NM technologists?
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1 and 5 mSv
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What safety precautions are taken to protect staff in PET?
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Very thick vial shields, syringe shields, and shadow shields
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Do x-ray rooms or PET rooms have thicker lead shielding?
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PET rooms
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