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MED-107 Medical Physics II: Medical Imaging and Radiotherapy > 7.1 intro to nuclear medicine > Flashcards

7.1 intro to nuclear medicine Flashcards

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1
Q

what do we use in nuclear medicine?

A

radiopharmaceuticals - radioactive substances/agents used to diagnose certain medical problems or treat certain diseases

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2
Q

what is the main difference in the source of radiation of nuclear imaging compared to other types of imaging?

A
  • in nuclear imaging, the source of radiation is the patient
  • rather than the X-ray tube used in other types of imaging
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3
Q

describe this mechanism

A

the patient breathes in/or is injected with the radiopharmaceutical, and the gamma camera detects the photons from the patient

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4
Q

what are the modes of radioactive decay?

A

(1) alpha decay
(2) beta decay
(3) gamma decay

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5
Q

what are the two purposes of nuclear medicine?

A

nuclear medicine can be used for BOTH diagnostic and therapeutic procedures that use radioisotopes

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6
Q

in nuclear medicine, (1) what do we use for therapeutic purposes and (2) what do we use for diagnostic/imaging purposes?

A

(1) beta-emitters
(2) gamma radiation

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7
Q

why is it necessary for the radioisotope to emit gamma rays in diagnostic work?

A
  • gamma radiation has greater penetrability so it can exit the patient & reach the gamma camera
  • it can penetrate tissue and be detected outside the body
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8
Q

why is it more desirable for the radioisotope to emit β particles for therapeutic work?

A
  • β particles have lower penetrability, so they can pass through shorter distances inside the patient
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9
Q

explain why we would use β-emitters for treatments such as tumor cleaning?

A
  • because they have a short range in tissue
  • can deliver a high radiation dose to the location of the radioisotope (localize the radiation)
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10
Q

what is used for thyroid gland treatments?

A

radioiodine (i131)

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11
Q

who discovered natural radioactivity and when?

A
  • Henry Becquerel
  • 1896
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12
Q

radioactivity is characterized by an unstable nucleus; what is an unstable nucleus?

A

a nucleus in which the number of protons and neutrons are NOT equal

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13
Q

what are radioactive nuclides?

A
  • a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable
  • since they’re unstable, they try to reach more stable nuclear configurations
  • either occur in nature or are man-made
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14
Q

what is the process that allows radioactive nuclides to reach more stable nuclear configurations?

A

radioactive decay

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15
Q

radioactive decay processes are divided into six main categories:

A

(1) alpha (α) decay
(2) beta (β) decay
(3) gamma (γ) decay and internal conversion (IC)
(4) spontaneous fission (SF)
(5) proton emission (PE) decay
(6) neutron emission (NE) decay

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16
Q

what are nuclear transformations usually accompanied by?

A

emission of energetic particles

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17
Q

what are the particles released in the various decay modes:
(1) α decay
(2) β- decay
(3) β+ decay
(4) γ decay
(5) internal conversion (IC)
(6) neutron emission (NE) decay
(7) spontaneous fission (SF)
(8) proton emission (PE) decay

SOS

A

(1) α particles (helium particles)
(2) electrons or antineutrinos
(3) positrons or neutrinos
(4) γ-rays
(5) atomic orbital electrons
(6) neutrons in spontaneous fission
(7) heavier nuclei
(8) protons

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18
Q

what are neutrinos and antineutrinos?

A

subatomic particles with no electric charge

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19
Q

why do we use them?

A
  • because they carry energies and angular momentum during the process of the decay
  • in all transformations, the energy, atomic and mass numbers, and the angular momentum are conserved
  • so these subatomic particles remove some energy from the system to reach this configuration
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20
Q

what is an alpha particle?

A
  • high-energy helium nuclei consisting of 2 protons and 2 neutrons
  • atomic number: 2
  • mass number: 4
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21
Q

what is a beta particle?

A
  • high-energy electron
  • charge: -1
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22
Q

what is a positron?

A
  • particles with the same mass as an electron but with 1 unit of positive charge
  • charge: +1
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23
Q

what is a proton?

A
  • nuclei of hydrogen atoms
  • atomic number: 1
  • mass number: 1
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24
Q

what is a neutron?

A
  • particles with a mass approximately equal to that of a proton but with no change
  • no protons, so atomic number: 0
  • mass number: 1
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25
Q

what is a gamma ray?

A

very high-energy electromagnetic radiation

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26
Q

in each nuclear transformation, several physical quantities must be conserved:

A
  • total energy
  • momentum
  • charge
  • atomic number
  • atomic mass number (number of nucleons)
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27
Q

how is nuclear stability achieved in elements with a low atomic number (Z)?

A

when the number of neutrons (N) is approximately equal to the number of protons (Z)

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28
Q

what happens as the atomic number Z increases?

A
  • N/Z increases from 1 to about 1.5
  • N/Z: ratio of # of neutrons/# of protons
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29
Q

compare a light nucleus (low atomic number) to a nucleus with high atomic number

A
  • light nucleus = more stable
  • high atomic number nucleus = more UNSTABLE
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30
Q

what are the 3 possible cases of N/Z in radioactive nuclei

A
  1. N/Z is too high for nuclear stability, nucleus is neutron-rich
  2. N/Z is extremely high
  3. N/Z is too low for nuclear stability, nucleus is proton-rich
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31
Q

what happens when a nucleus has N/Z too high for nuclear stability?

A

(1) it has an excess number of neutrons and is called NEUTRON-RICH
(2) it decays through conversion of a neutron into a proton and emits an electron and anti-neutrino

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32
Q

what happens when a nucleus has N/Z extremely high for nuclear stability?

A

a direct emission of a neutron is possible

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33
Q

what happens when a nucleus has N/Z that is too low for nuclear stability?

A

(1) it has an excess number of protons and is called PROTON-RICH
(2) it decays through conversion of a proton into a neutron and emits a positron and a neutrino

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34
Q

‘nucleus decays through conversion of a neutron into a proton, and emits an electron and anti-neutrino’
what is this process known as?

A

β- decay

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35
Q

what is β- decay in practice?

A

we have more neutrons, so they’re converted into protons in order to achieve stability (equal protons & neutrons)

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36
Q

‘nucleus decays through conversion of a proton into a neutron, and emits a positron and neutrino’
what is this process known as?

A

β+ decay

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37
Q

what is another process we can emit a neutrino?

A
  • a process known as electron capture
  • this occurs when the nucleus may capture an orbital electron
  • then transform a proton into a neutron and finally, emit a neutrino
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38
Q

what process is electron capture the inverse of?

A
  • electron capture is the inverse of β- (minus) decay
  • β- decay: we have the emission of an electron
  • electron capture: the nucleus captures an electron from the orbital, and emits a neutrino
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39
Q

what was the first mode of radioactive decay detected?

A

alpha (α) decay

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40
Q

what is alpha decay characterized by?

A

a nuclear transformation

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41
Q

what is an alpha particle?

A

a helium-4 nucleus that has a VERY stable configuration

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42
Q

describe alpha decay

A
  • we have a parent nucleus, which is unstable
  • it attains a more stable nuclear configuration (daughter D) through the ejection of an α-particle (Helium)
  • because the atomic and mass numbers must be conserved, the daughter nucleus has to have a mass number lower by 4 and an atomic number lower by 2
  • therefore, in α-decay the number of protons & neutrons is conserved by producing a helium nucleus
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43
Q

what happens when an α-particle is emitted by the radioactive parent (Z, A) nucleus?

A
  • the atomic number Z of the parent decreases by 2
  • the mass number A decreases by 4
  • it sheds two orbital electrons from its outermost shell
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44
Q

describe what happens to an emitted α-particle

A
  • the energetic α-article slows down through the absorber
  • this allows it to capture 2 electrons from its surroundings to become a neutral He atom again
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45
Q

why can α-particles be dangerous?

A
  • since they are relatively heavy & slow particles, they can only travel short distances before losing their energy and being absorbed
  • this can be dangerous if absorbed by the human body
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46
Q

α-particles have what range (1) in air and (2) in tissue

A

(1) air: about 1cm - 10cm
(2) tissue: about 10^-3 cm - 10^-2cm

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47
Q

what is the most important example of radioactive decay in α-decay?

A

the decay of radium-226 into radon-222

48
Q

what occurs in β decay modes of radioactive decay?

A
  • the atomic number Z of the parent nuclide changes by one unit (+1)
  • the mass number A remains constant
49
Q

what are other characteristics of β-decay processes?

A
  • the number of nucleons (protons & neutrons) and total charge are both conserved in the process
  • the daughter D can be referred to an isobar of the parent P
50
Q

what 3 processes fall into the category of β-decay?

A

(1) β minus decay - emission of an electron of negative charge (therefore, β-)
(2) β plus decay - emission of a positron of positive charge
(3) electron capture

51
Q

what occurs in β minus decay?

A
  • # of neutrons > # of protons
  • neutron is converted into a proton by the emission of an electron and an anti-neutrino
  • mass number: same
  • atomic number: +1
52
Q

what occurs in β plus decay?

A
  • # of protons > # of neutrons
  • proton is converted into a neutron by emission of neutrino and positron
  • mass number: same
  • atomic number: -1
53
Q

what occurs in electron capture?

A

nucleus captures an electron from the orbital and converts it into a neutrino

54
Q

β decay of a parent nucleus sometimes does not lead directly to the ground state of the daughter nucleus, this leads to?

A

an unstable or metastable excited state of the daughter nucleus

55
Q

what is the condition under which β decay requires to take place?

A

β decay can only occur when the binding energy of the daughter nucleus exceeds the binding energy of the parent nucleus

56
Q

several radionuclides decaying by β(-) decay are used in medicine for:

A
  • external beam radiotherapy
  • brachytherapy
57
Q

what is brachytherapy?

A
  • a type of radiotherapy where we insert the radioactive source inside the patient
  • ex: in prostate cancer, the radioactive source is placed near the prostate so the the radiation can kill the tumors
58
Q

a parent nuclide decays into an excited daughter nuclide through?

A

β(-) decay

59
Q

describe the decay of a parent nuclide into an excited daughter nuclide

A
  • the nuclide decays either instantaneously or through a metastable decay process into its ground state
  • by doing so it emits the excitation energy in the form of γ-ray photons
  • these photons are then used for radiotherapy
60
Q

which radionuclide is practically suitable for use in radiotherapy?

A

cobalt 60

61
Q

what is β(+) decay characterized by?

A

the production of positrons

62
Q

what are radionuclides undergoing β(+) decay called? what are they used for?

A
  • called positron emitters
  • they are used in medicine for functional imagine with positron emission tomography (PET)
63
Q

what is an example of a β(+) decay?

A

the decay of nitrogen-13 into carbon-13 with a half-life of 10 min

64
Q

what is nitrogen-13 labelled ammonia, which is injected intravenously, mainly used in?

A
  • cardiac imaging for diagnosis of coronary artery disease and myocardial infarction
  • liver imaging
  • brain imaging
65
Q

what is one desirable characteristic of a radiopharmaceutical? give an example

A
  • having a short half-life
  • ex: fluorine-18 decays into oxygen-18 with a half-life of 110 min, which protects the patient as it is short
  • a drug with a half-life of 5 years means the patient will be radioactive & receive radiation for 5 years
66
Q

what is a sugar compound that can be injected intravenously into a patient for use in PET functional imaging?

A

fluorodeoxyglucose (FDG) labeled with radionuclide fluorine-18

67
Q

what are some functions of the FDG PET scan?

A
  • can detect malignant disease
  • can distinguish benign from malignant disease
  • can be used for staging of malignant disease
  • can be used for monitoring response to therapy of malignant disease
68
Q

how does gamma decay differ from both alpha and beta decay?

A
  • gamma decay only occurs after alpha and beta decay in a sample
  • gamma decay doesn’t change the mass or any other properties of the atom, they are simply high energy photons, electromagnetic radiation
69
Q

what do we need to have in order for gamma decay to take place?

A
  • an EXCITED PARENT NUCLEUS through β decay
  • which de-excites through the emission of gamma photons
  • gamma photons are electromagnetic radiation
  • so excess of energy on this excited nucleus is released as E.M. radiation in order for the daughter nuclei to reach a stable configuration
70
Q

what are the two processes in which a daughter nucleus reaches its ground state?

A

(1) emit the excitation energy in the form of a γ photon in a decay process called γ-decay
(2) transfer the excitation energy to one of its associated atomic orbital electrons in a process called internal conversion (IC)

71
Q

compare X-rays to γ-rays

A
  • characteristic X-rays are produced when we have a vacancy, and an electron from a higher orbital drops down to fill that vacancy & the excess in energy is released in form of radiation
  • gamma radiation is when we have an excited nucleus (this is why gamma energies are higher in energy compared to X-rays because this nucleus reaches a stable configuration by the release of gamma photons)
72
Q

why do we refer to the emitted γ-rays as if they were produced by the parent nucleus?

A

because in most radioactive α or β decays the daughter nucleus de-excitation occurs instantaneously

73
Q

give an example of γ-rays being referred to as from the parent nucleus (gamma decay)?

A
  • the cobalt-60 β decays into nickel-60 after the release of 2 γ photons
  • the γ-rays following the β decay originate from nuclear de-excitations of nickel-60 (daughter nucleus)
  • we refer to these γ-rays as the cobalt-60 γ-rays for convenience
74
Q

describe the 99.88% path of cobalt-60 decay into stable nickel-60

A
  • first part of the transformation we have the Co-60 which decays into the EXCITED nickel by β decay, and we have the emission of 1 electron (so β(-) decay)
  • then the excited nickel reaches the stable configuration by the release of 1 γ photon and then another γ photon
75
Q

describe the other 0.12% path of cobalt-60 decay into stable nickel-60

A

here we have the excitation of Co-60 into Ni-60 by β(-) emission where we have the emission of 1 electron followed by the emission of only one γ photon

76
Q

what do BOTH paths have in common?

A

(1) to first excite the nucleus by β emission
(2) nucleus reaches stability by release of γ photons

77
Q

in some α or β decays, the excited daughter nucleus does not immediately decay into its ground state; what is this state referred to as?

A
  • the excited state of the daughter is then referred to as a metastable state
  • a nucleus in a metastable state is identified with a letter “m” next to the mass number
78
Q

what is the process of de-excitation of a metastable daughter nucleus called?

A

an isomeric transition

79
Q

what is the term isomer used for?

A

designation of nuclei that have the same atomic number Z and same atomic mass number A but differ in energy states

80
Q

γ decay stands for nuclear de-excitation by? it only implies emission of what?

A

(1) emission of γ-ray photons
(2) internal conversion
- only implies emission of γ photons

81
Q

the γ decay process can be represented as:

A
  • check ppt
  • star - means daughter nucleus is excited
  • Q - symbol indicating heat or energy
  • nucleus de-excites through the release of a γ photon
82
Q

what is the process of internal conversion (IC)?

A

nuclear de-excitation in which the de-excitation energy is transferred from the parent nucleus almost in full to an orbital electron of the same atom

83
Q

describe spontaneous fission

A
  • type of radioactive decay found in only very heavy chemical elements (nuclei with large atomic mass numbers A)
  • occurs when an unstable nucleus spontaneously & randomly splits into smaller parts
  • this simultaneously emit 2-4 neutrons
  • accompanied by the release of a significant amount of energy
84
Q

what does ALL fission release?

A

neutrons

85
Q

spontaneous fission follows the same process neutron-induced nuclear fission; what is the only difference between them?

A

SF is not self-sustaining

86
Q

where does SF only occur?

A

in thorium, protactinium, uranium, and transuranic elements (Z>92)

87
Q

spontaneous fission is a competing process to?

A

α decay

88
Q

the higher the atomic mass number above uranium, what happens to (1) spontaneous fission and (2) half-life

A

(1) the more prominent the spontaneous fission
(2) the shorter the half-life

89
Q

what is SF a limiting factor of?

A

how high in atomic number Z and mass number A one can go in producing new elements

90
Q

describe proton emission

A
  • also known as proton radioactivity
  • occurs when a proton is ejected from the nucleus
  • proton-rich nuclides normally approach stability through β(+) or α decay, so in extreme cases of a large proton excess, a nucleus may move toward stability through emission of one or two protons
91
Q

proton emission is a competing process to?

A

β(+) and α decay

92
Q

what effect does proton emission have on atomic number and mass number?

A

both atomic number Z and mass number A decrease by 1

93
Q

what happens when a proton is ejected from a radionuclide P?

A
  • the parent nucleus P sheds an orbital electron from its outermost shell to become a neutral daughter atom
  • the energetic proton slows down in moving through the absorber medium and captures an electron from its surrounding to become a neutral hydrogen atom
94
Q

what are isotones?

A

atoms that have the same neutron number, but different proton number

95
Q

why are the parent P and daughter D nuclides in proton emission considered isotones?

A

because the number of neutrons does not change in proton emission decay (we only have the release of a proton)

96
Q

for lighter, very proton-rich nuclides (A≈50), what is more likely to occur when they (1) have an odd number of protons Z and (2) have an even number of protons Z

A

(1) odd number of protons - proton emission decay is likely
(2) even number of protons - a simultaneous two-proton emission is likely

97
Q

describe neutron emission

A
  • mode of decay where one or more neutrons are ejected from the nucleus
  • the atomic number Z remains the same
  • the mass number A decreases by 1
98
Q

regarding atomic number Z, neutron emission is the inverse of?

A

spontaneous fission

99
Q

in neutron emission, the parent and daughter nuclei are thus?

A

isotopes
(of the same nuclear species)

100
Q

why do we not use spontaneous fission, proton and neutron emissions for imaging?

A

the half-lives in these types of decay are too short, therefore time is not enough to obtain an image

101
Q
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103
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107
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108
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109
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113
Q

(1) process competing with β(-) decay, not observed in naturally occurring radionuclides
(2) process competing with/ less common than β(+) and α decays, not observed in naturally occurring radionuclides
(3) process competing with α decay

A

(1) neutron emission
(2) proton emission
(3) spontaneous fission

114
Q

what is the type of decay in each of the following:
(1) atomic number of parent nucleus changes by +1, mass number stays constant
(2) atomic number of parent nucleus decreases by 2, mass number decreases by 4
(3) atomic and mass numbers are not affected
(4) both atomic and mass numbers decrease by 1
(5) atomic number remains the same, mass number decreases by 1
(6) atomic number decreases, mass number decreases

A

(1) beta decay
(2) alpha decay
(3) gamma decay
(4) proton emission
(5) neutron emission
(6) spontaneous fission

115
Q

what does an ideal radiopharmaceutical need?

A
  • to have a short physical half-life
  • to be eliminated from the body with an effective half-life approximately equal to the examination time
  • to emit pure gamma rays with no subsequent change in the nucleus
  • to emit mono-energetic gamma rays
  • to have a high activity per unit mass (specific activity)
  • to be able to localize largely and quickly at the target site (ex: iodine is captured by the thyroid)
  • to decay into a more stable daughter nucleus
  • to. easily and effectively be attached to the chemical compound at room temperature
  • to be easily produced or found at the hospital site

MED-107 Medical Physics II: Medical Imaging and Radiotherapy (16 decks)

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