Nuclear medicine Flashcards by Darin Kepler

Define activity

of radioactive atoms undergoing nuclear transformation per unit time

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What is a Curie? (math)

Ci = 3.7 x 10^10 disintegrations per second

Amount of distingetrations of 1gm of Radium

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What is a Bequerel? (math)

1 Bequerel = 1 disintegration per second

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How do you convert Curie to Bequerel?

1mCi = 37MBq

multiply mCi by 37 to get MBq

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What is equation for activity?

A = -dN/dt

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What is the decay constant?

of atoms decaying per unit time is constant and unique to each element.

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What is short equation for decay constant?

Decay constant = 0.693/ T 1/2 life

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How does activity relate to the decay constant (equation)

A = λ (decay constant) x N (# of radioactive atoms)

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What is the physical half-life?

Time required to decrease # of radioactive atoms by 50%

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How do you calculate how many radioactive atoms remain after n half-lives?

N = No / 2^n
n = # of half lives that have occurred

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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

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What are the 5 types of nuclear transformation?

Alpha decay, Positron, Negatron, electron capture, isomeric transition

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What occurs in alpha decay?

The nuclide will lose 2 neutrons and 2 protons (1 helium atom)

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When does Negatron decay occur?

In Neutron rich nuclides (high N/Z ratio)

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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

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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)

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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)

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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

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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

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When does isomeric transition occur?

When molecules remain in excited (unstable) state for longer than 10^-12s

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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)

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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