Topic 15: nuclear medicine Flashcards
(49 cards)
1
Q
Describe the use of radioisotopes in nuclear medicine
A
- Gamma rays = diagnostic = penetrate tissue + be detected outside body = distribution in body can be determined
- Beta particle= measuring samples taken from patient
2
Q
Why are β particles desirable in therapeutic work?
A
- Short range in tissue = don’t travel far from target
- Deliver high radiation dose to location of radioisotope
3
Q
Name scientists responsible for nuclear physics
A
- Henri Becquerel = discovered radioactivity
- Marie Curie
- Pierre Curie
- Ernest Rutherford
- Frederick Soddy
4
Q
Describe radioactive nuclides
A
- Natural/man-made
- Unstable = try reach stable configuration
- Via spontaneous radioactive decay
5
Q
Give 6 types of radioactive decay
A
1) α decay
2) β decay
3) γ decay + internal conversion
4) Spontaneous fission
5) Proton emission decay
6) Neutron emission decay
6
Q
Give types of particles emitted in decay modes
A
α DECAY:
- α particles
β− DECAY:
- e-
- Antineutrinos
β+ DECAY:
- Positrons
- Neutrinos
γ DECAY:
- γ rays
INTERNAL CONVERSION:
- Atomic orbital electron
SPONTANEOUS FISSION:
- Neurons
- Heavier nuclei
NE DECAY:
- Neurons
PE DECAY:
- Protons
7
Q
Give the qualities conserved during nuclear transformation
A
- Total energy
- Momentum
- Charge
- Atomic number
- Atomic mass number
8
Q
Explain the stability of atom depending on N/Z ratio
A
- N = number of protons
- Z = number of neurons
- Small atoms = low atomic number = stability when neutrons ≈ protons
- Larger atoms = need neurons > protons for stability = N/Z increases from 1 > 1.5
9
Q
Explain how stability is gained in high N/Z
A
- Neutron-rich nucleus
- Gets rid of neurons = stability
- Converts neuron > proton = emits e- + anti-neutrino
- Called β− decay
- Extreme high ratio = neuron directly emitted
10
Q
Explain how stability is gained in low N/Z
A
- Proton-rich nucleus
- For stability = proton > neutron = emits positron + neutrino
- β+ decay
- Electron capture = nucleus takes e- from own atom = causes proton > neutron + emit neutrino
- Very high imbalance = proton directly emitted
11
Q
Define α-particle
A
- Helium 4 nucleus = 2 protons + 2 neutrons
- Very stable configuration
12
Q
Describe alpha decay
A
- 1st mode of radioactive decay
- Nuclear transformation = unstable parent nucleus > more stable nuclear configuration > eject α-particle
- Number of protons + neutrons conserved = produce He nucleus = reduce parent A+Z by 4+2
13
Q
What happens to unstable parent nucleus when α-particle emitted?
A
- Atomic number of parent = Z = decreases by 2
- Sheds 2 orbital e- from outer shell
- Energetic α-particle slows down = captures 2 e- from surrounding = becomes neutral He atom
14
Q
Give the range of α-particle
A
- Air = 1-10 cm
- Tissue = 10⁻³/10⁻²
15
Q
What is the most important α decay?
A
- Decay of radium-226→radon-222
- Half life 1602 years →3.8 days
16
Q
Define β particle
A
17
Q
Describe β decay
A
- Parent nucleide atomic number Z = changes by ±1unit
- Mass number A = constant
- Neuron/proton + total charge = conserved
- Daughter AKA = isobar
18
Q
Give the 3 categories of β decay
A
1) β− decay
2) β+ decay
3) Electron capture
19
Q
Describe β− decay
A
n → p + e⁻ + ν̅ₑ
A/Z P → A/Z+1 D + e⁻ + ν̅ₑ
- Gains a proton → becomes a different element (D) with +1 atomic number
20
Q
Describe β+ decay
A
p → n + e⁺ + νₑ
A/Z P → A/Z−1 D + e⁺ + νₑ
- Atom loses a proton → atomic number goes down by 1 = becomes a new element
21
Q
Describe electron capture
A
p + e⁻ → n + νₑ
A/Z P + e⁻ → A/Z−1 D + νₑ
- Atomic number drops by 1 = Z−1 because you’ve turned a proton into a neutron
22
Q
In what case does β decay only take place?
A
- When binding energy of daughter nucleus > binding energy of parent nucleus
- β decay of parent not directly = ground state daughter nucleus
- Parent > unstable excited daughter = de-excites via transmission of γ-rays/internal conversion e-
23
Q
What is the excited state of daughter nucleus called when not immediately decaying?
A
- Metastable state
- De-excitation = isomeric transition
- Nucleus in metastable state = ‘m’ next to atomic mass number = barium-137m /¹³⁷ᵐBa
24
Q
Give use of β− decay in medicine
A
- External beam radiotherapy
- Brachytherapy
25
Describe how β− decay is used in medicine
- Parent nuclide > excited daughter nuclide
- Decay process to ground state = emits excited energy = γ-ray photon
- Photon used for radiotherapy
26
How many radionucleotides are known?
- 3000 = natural/artificial
- Only few suitable for radiotherapy
- Mainly cobalt 60
27
Describe the use of cobalt 60
²⁷₆₀Co → ²⁸₆₀Ni + e⁻ + ν̄ₑ + Qβ⁻ (2.82 MeV)
- Half-life = 5.26 years
- Decays = excited nickel 60 = decay instantly to ground state = 2 γ-rays
28
Define the characterization of β+ decay
- Production of positrons
- Radionuclides undergoing β+ decay = positron emitters
29
Describe the use of β+ decay in medicine?
- Functional imaging = positron emission tomography = PET
FLOURINE 18:
- Labeled FDG = injected IV
- Based on areas of increased glucose metabolism FDG PET =
> Detect malignant disease
> Distinguish benign/malignant
> Determining stage of malignant disease
> Monitor response to therapy for disease
NITROGEN 13:
- labeled ammonia = injected IV
> Cardiac imaging = CAD diagnosis + myocardial infraction
> Liver imaging
> Brain imaging
30
Describe the use of nitrogen 13
⁷₁₃N → ⁶₁₃C + e⁺ + νₑ + Qβ⁺ (1.2 MeV)
- Half-life = 10 mins
- Decays = carbon 13
- Nitrogen 13 = proton rich = produced in cyclotron
31
Describe the use of fluorine 18
- Half-life 110 min
- Decays = oxygen 18
- Sugar compound
32
Describe gamma decay
-Isomer = nucleus that has the same number of protons (Z) + neutrons (A) = BUT in a differing energy state
- γ decay = excited nucleus releases its extra energy in the form of γ radiation
- In gamma decay = no protons/neutrons emitted = only energy in form of γ rays
- Energy of γ ray = energy level structure = how much energy the nucleus getting rid
33
Describe the γ decay process
A*_Z X → A_Z X + γ + Q_γ
- A*_Z X = excited nucleus
- A_Z X = change to a stable nucleus = gives off a photon γ + some energy = Q_γ
34
Define spontaneous fission
- Decay process = nuclei with large atomic mass = disintegrate splits into 2 equal fission fragments
- Simultaneously emits 2-4 neutrons + energy
35
Describe how SF occurs
- Not self-sustaining
- Only occur = thorium + protactinium + uranium + transuranic elements
- Transuranic elements = manmade + synthesized in nuclear reactions
- Competing process to α decay
- Higher atomic mass = > uranium-238 =more prominent SF = shorter half-life
36
Why is SF a limiting factor in creating new elements?
- SF = limiting factor of how high atomic number/mass can go to produce new element
- As the atomic number + mass number increase = nucleus becomes too unstable = limits how heavy an element can be before it becomes impossible to create = it decays too quickly
37
Define proton emission
- Proton rich nuclide = normally reach stability via β+ decay/α decay
- Extreme cases large excess = gain stability via emitting 1/2 protons
- Competing with β+ decay/α decay = BUT less common than them + not observed naturally
38
Describe how PE occurs
ZᴀP → Z₋₁A₋₁D + p
- Atomic number Z + atomic mass A = decreases by 1
- Proton ejected from parent = sheds orbital e- from outer shell = neutral daughter
- Energetic proton slows down = captures e- = neutral hydrogen atom
- Number of neutrons = no change = parent + daughter = isotones
39
What is the likelihood of PE depending on proton number?
- Lighter + proton rich + odd number of protons = PE likely
- Lighter + proton rich + even number of protons = simultaneous 2 proton emission
40
Give an example of PE
₃⁵Li → ₂⁴He + p
- Lithium 5 = helium 4
- Half life = 10⁻²¹ secs
41
Define neutron emission
- Neutron-rich nucleus = normally β− decay
- Competing with β− decay = BUT less common + not naturally occuring
42
Describe how NE occurs
Z A X → Z A−1 X + n
- Atomc number Z = same
- Atomic number A = decrease by 1
- Parent + daughter nucleus = isotopes
43
Give example of NE
⁵₂He → ⁴₂He + n
- Helium 5 = helium 4
- Half life 8x10⁻²² sec
44
Describe the use of radiopharmaceuticals in tomographic imaging
- Radioactive compound = radiation source
- Tomographic techniques used to reconstruct based on concentration of radiopharmaceutical in body
2 TYPES:
1) SPECT = gamma emitter for single photon emission computed tomography
2) PET = positron emitters for positron emission tomography
45
Give examples of gamma emitters
- 81mKr = krypton = directly = can be inhaled for lung ventilation studies
- 99mTc = technetium
46
Give examples of positron emitters
- 18F = fluoride
- 15O = oxygen
- 13N = nitrogen
- 11C = carbon
- 82Rb = rubidium
47
Explain the use of 18F
- Not used directly = relevant compound labeled with radioactive atom
- FDG = metabolized at site of high glucose demand = brain/tumors
- Spatial distribution of FDG refects = glucose uptake
- Substitite stable F > 18F = glucose concentrations imaged by PET
48
Describe the decay of 18F
- Fast decay desirable = reduce patient exposure
- Half-life = 2 hrs = only 1.6% left after 12hrs
- Fraction less = gets excreted via urine
49
Give the qualities of an ideal radiopharmaceutical
- Short physical half-life
- Eliminated from body rate = effective half-life equal to examination time
- Emit pure γ rays = no other change to nucleus
- Emit mono-energetic γ rays
- High activity per unit mass
- Localise largely + quickly at target site
- Deacy to more stable daughter nucleus
- Easily + effectively attach to chemical compound at room temp
- Easily produced + found at hospital site
