Nuclear medicine Flashcards
Define activity
of radioactive atoms undergoing nuclear transformation per unit time
What is a Curie? (math)
Ci = 3.7 x 10^10 disintegrations per second
Amount of distingetrations of 1gm of Radium
What is a Bequerel? (math)
1 Bequerel = 1 disintegration per second
How do you convert Curie to Bequerel?
1mCi = 37MBq
multiply mCi by 37 to get MBq
What is equation for activity?
A = -dN/dt
What is the decay constant?
of atoms decaying per unit time is constant and unique to each element.
What is short equation for decay constant?
Decay constant = 0.693/ T 1/2 life
How does activity relate to the decay constant (equation)
A = λ (decay constant) x N (# of radioactive atoms)
What is the physical half-life?
Time required to decrease # of radioactive atoms by 50%
How do you calculate how many radioactive atoms remain after n half-lives?
N = No / 2^n n = # of half lives that have occurred
What is the decay equation? What other physics equation is it similar too?
Nt = No e ^ (λ x t)
Linear attenuation coefficient and the half value layer
What are the 5 types of nuclear transformation?
Alpha decay, Positron, Negatron, electron capture, isomeric transition
What occurs in alpha decay?
The nuclide will lose 2 neutrons and 2 protons (1 helium atom)
When does Negatron decay occur?
In Neutron rich nuclides (high N/Z ratio)
What occurs in negatron decay?
Neutron –> Protron (Z+1)
Betatron and anti-neutrino are emitted
Betron acts as an electron - will cause excitation or ionization
When does Positron decay occur?
Neutron poor nuclides (low N/Z ratio)
Parent must exceed daughter by energy greater than 1.02 MeV (otherwise electron capture will occur instead)
What occurs in positron decay?
Proton –> Neutron (Z-1)
Positron and neutrino are emitted
Positron will interact with anti-particle (Electron) and cause annihilation photons (511keV)
When does electron capture occur?
Neutron poor nuclides (Low N/Z ratio)
Will occur in place of positron decay when energy between parent and daughter is less than 1.02 MeV
What occurs in electron capture?
Nucleus will capture an orbital electron (K/L shell) –> Proton is converted into neutron (Z-1) –> gamma ray
electron cascade occurs and characteristic radiation occurs
When does isomeric transition occur?
When molecules remain in excited (unstable) state for longer than 10^-12s
What occurs in isomeric transition?
Metastable –> stable state resulting in production of gamma radiation without changing the mass, proton or neutron number (isobaric and isotonic)
What do the different lines in a decay scheme represent?
Horizontal lines (top - parent, middle - excited, bottom - daughter)
Vertical line = gamma ray emission, including isomeric transition
Diagonal (to the left = electron capture, vertical and to the left = positron, to the right = negatron)
What is half-life, energy and mode of decay of Technetium 99?
Half life - 6 hours
Energy - 140keV
Isomeric transformation
What is half-life, energies, and mode of decay of Iodine-131
Half life - 8d
Energy - 364 (81%) keV
Decay - Beta negative/Negatron
In a feline. What is considered normal thyroid:salivary gland and thyroid:background?
Does this ratio change with time?
Thyroid:salivary: 0.8:1
Thyroid:background: 2.75:1
Ratio does not change over time
In a dog, what is considered a normal thyroid:salivary gland ratio?
Does this ratio change with time?
1:1 - d
This ratio changes after 60 min (will start to decrease)
What percentage of feline thyroid hyperplasia are unilateral vs bilateral?
What happens to the other thyroid gland in unilateral cases?
Unilateral: 30%
Bilateral: 70%
Other thyroid gland will have reduced uptake - nearly complete
What is the most common form of feline thyorid disease?
feline thyroid hyperplasia
feline thyroid adenoma
feline thyroid carcinoma
Adenoma
What percentage of dogs will have extra-thyroidal tissue?
50% - will have around the base of the aorta
Where is technetium-99 taken up, and how is it excreted?
Taken up: thyroid, salivary gland, GI,
Excretion: mainly renal, but some GI
Where is Iodine-131 taken up, and how is it excreted?
Taken up: thyroid, salivary glands, stomach, bladder
Excretion: mainly renal, breast tissue, and will cross the placenta
What percentages represent each pattern of thyroid uptake in cats?
Unilateral
Bilateral-asymmetric
Bilateral-symmetric
Multifocal
Thyroid scintigraphy findings in 2096 cats with hyperthyroidism. VRU 56.1.
Unilateral - 30%
Bilateral asymmetric - 50%
Bilateral symmetric - 10%
Multifocal -
What was prevalence of ectopic thyroid tissue and thyroid carcinoma in Thyroid scintigraphy findings in 2096 cats with hyperthyroidism. VRU 56.1.?
Ectopic thyroid - 4%
Carcinoma - 2%
What was considered a normal thyroid:salivary and thyroid:background in Thyroid scintigraphy findings in 2096 cats with hyperthyroidism. VRU 56.1.?
Thyroid:salivary
What was sensitivity for thyroid:salivary ratio and thyroid:background in
Thyroid scintigraphy findings in 2096 cats with hyperthyroidism. VRU 56.1.?
Thyroid:salivary >1.5 was 0.987
Thyroid:background >6.4 was 0.961
What is the difference between physical and biologic half-life?
Physical - time it takes for radioactive atoms to decrease by half - sitting in a syringe doing nothing
Biologic - time it takes for radionuclide to lose half of its radiologic activity in the body with interactions with bodily tissues etc
What is the effective half life
Combination of physical and biologic half-lives
How do you calculate the effective half life?
T 1/2 effective = (T 1/2 physical x T 1/2 biologic ) (T 1/2 physical + T 1/2 biologic)
Describe the line of stability and the chart associated with it?
Line of stability is where the N/Z ratio is approximately 1 (neutrons/protons) for low Z elements, and 1.5 for higher elements
Left of the line of stability - Neutron excess –> beta minus decay
Right of the line of stability - proton excess –> positron or electron capture
Further from the line of stability, the more unstable an agent is.
Z > 85 (above bismuth) - are all unstable
If a radionuclide is to the left of the line of stability -w hat does this indicate? the right?
If to the left of the line of stability will undergo beta-minus decay (neutron rich)
If to the right of the line of stability - will undergo electron capture or positron (proton rich)
Further from the line of stability - more unstable the radionuclide.
What are half lives: Tc99 F18 Io131 Co57
Tc - 6.0h
F18 - 110min
I131 - 8.0d
Co57 - 271.8d
How do you calculate the decay constant?
0.693 (which is the natural log of 2) / half life
Label will remain the same!! (Tc will be hr-1, and I will be d-1)
What type of decay will occur if the N:Z ratio is high?
Negatron decay (beta minus)
What type of decay will occur if the N:Z ratio is low?
Alpha
Positron
Electron capture
Only one form of decay will result in a change in atomic mass… which is it?
Alpha decay (A - 4, Z-2)
What needs to be present in order for positron decay to occur?
1.02MeV of energy for annihilation
Tc99 Z? Mode of decay Principle energy Physical half life
43
Isomeric transition
140keV
6 hours
I-131 Z? Mode of decay Principle nergy physical half life
53
B- (neutron excess) –> Xe-131
364keV
8d
Mo-99 Z? Mode of decay Principle energy Physical half life
42
B- (neutron excess) - Tc-99m
740keV
67h
F-18 Z? Mode of decay principle energu physical half life
9
B+ (neutron poor) - O18
635keV
110min
O-15 Z? Mode of decay principle energu physical half life
8
B+ (neutron poor) - N15
173keV
2 minutes
in case we don’t have natural exponential button on our calculators… how can you adjust the decay equation?
N = No * 2.78^ (- gamma * t)
Str-89 Normal A? Mode of decay principle energu physical half life
38
Beta - Yttrium 89
None
50d
I-123 Normal A? Mode of decay principle energu physical half life
53
Electron capture
159keV
13.2h
