66 Questions
How many known radionuclides are there?
Around 2700
What happens when an additional neutron is forced into a stable nucleus?
A neutron excess occurs
What is the result of forcing an additional proton into a stable nucleus, knocking out a neutron?
A neutron deficit occurs
In which type of facility do radionuclides produced through neutron excess have a long half-life?
None of the above
Where are medical minicyclotrons usually located?
At a hospital site
What is the half-life range of radionuclides produced in a cyclotron?
From less than a minute to a couple of hours
What is the name of the imaging technique that uses positron emitters?
PET
What is the process of radioactive disintegration considered to be?
Stochastic
How is the quantity of radioactivity measured?
By the transformation rate
What is the SI unit of radioactivity?
Becquerel
What is the activity of a radioactive sample?
The rate of disintegration
What happens when gamma rays enter a detector?
They may be registered individually as counts
What is a cyclotron commonly used for in nuclear medicine?
Producing radioactive isotopes for diagnostic scans and therapy
What is the result of accelerating charged particles in a cyclotron?
Collisions with a target material to produce radionuclides
How can molybdenum-99 be obtained?
Through chemical separation from spent fuel rods
What is the purpose of a generator in producing radionuclides?
To obtain a daughter product from a longer-lived radioactive parent
What happens to radionuclides with a neutron excess during radioactive transformation?
They lose energy and become stable
What is the result of a neutron changing into a proton plus an electron?
A radionuclide with a neutron excess becomes stable
Why are alpha or beta particles not used in imaging?
They have a short range in tissue and deposit unnecessary dose in the patient
What is the ideal energy range for gamma rays in imaging?
50-300 keV
What is the advantage of monoenergetic gamma rays?
Scattered radiation can be eliminated by energy discrimination
What is a desirable property of a radionuclide for imaging?
Emission of gamma rays
Why is it important for a radionuclide to be easily attached to a pharmaceutical?
It has no affect on its metabolism
What is a desirable property of a radiopharmaceutical?
Localization in the target tissue
What is the main advantage of 123I over 125I in imaging?
Superior imaging properties
What is the primary use of 131I in medical applications?
Thyroid ablation
What is the mechanism of decay for 123I?
Electron capture
What is the primary use of Xenon-133 in medical applications?
Lung ventilation imaging
What is the mechanism of production for Krypton-81m?
Generator production
What is the challenge associated with the use of Rubidium-81?
Short half-life
What is the main use of Gallium-67 in medical applications?
To detect tumours and abscesses
What is the half-life of Indium-111?
67 h
What is the main use of Indium-111 in medical applications?
To label white blood cells and platelets
What is the energy of gamma rays emitted by Indium-113?
390 keV
What is the most common PET radionuclide?
18F
What is the main use of 18F in medical applications?
To measure brain and heart metabolism
What is the half-life of 123I?
13 hours
What is the energy of the gamma rays emitted by 123I?
159 keV
What is the primary use of 131I in medical applications?
Thyroid ablation
What is the primary use of Xenon-133 in medical applications?
Lung ventilation imaging
What is the half-life of Krypton-81m?
7.13 seconds
Why is it difficult to use Rubidium-81?
It has a short half-life and must be used the day it is delivered.
What is technetium-99m used for in gastric-emptying studies?
Mixed with bran porridge
What is the primary use of iodine-131 in medical applications?
Thyroid imaging and treatment
What is technetium-99m labelled with for bone imaging?
Methylene diphosphonate (MDP)
What is the half-life of iodine-131?
8 days
What is technetium-99m labelled with for cerebral imaging?
Hexamethyl propylene amine oxime (HMPAO)
What is the primary use of technetium-99m in medical applications?
Cerebral blood flow imaging and testicular imaging
What is the primary advantage of 123I over 125I in imaging?
It decays by electron capture emitting 159 keV gamma rays
What is technetium-99m labelled with for bone imaging?
methylene diphosphonate (MDP)
What type of radiation does Xenon-133 emit?
Low energy gamma rays
Which radionuclide can be blocked from the thyroid by administration of potassium perchlorate?
Technetium-99m
What is technetium-99m labelled with for cerebral imaging?
hexamethyl propylene amine oxime (HMPAO)
What is the primary use of Krypton-81m in medical applications?
Pulmonary ventilation studies
What is the half-life of Iodine-123?
13 hours
What is technetium-99m used for in gastric-emptying studies?
Mixed with bran porridge
What is the primary use of iodine-131 in medical applications?
Thyroid imaging
Why is Rubidium-81 difficult to use?
It has a short half-life
What is technetium-99m used for in testicular imaging?
SIS
What is the energy of the gamma rays emitted by Iodine-123?
159 keV
What is the advantage of technetium-99m for radionuclide imaging?
It has a pure gamma emission, allowing for better spatial resolution
What is the purpose of the generator in producing technetium-99m?
To supply the radionuclide with its longer-lived parent
Why is technetium-99m suitable for imaging?
It forms a stable product in vitro and in vivo
What is the advantage of using technetium-99m with a short half-life?
It reduces the dose to the patient
How is technetium-99m supplied?
It is supplied from a generator shielded with lead
What is the characteristic of technetium-99m that allows for reasonably large activity administration?
Its short half-life and pure gamma emission
Study Notes
Production of Radionuclides
- There are over 2700 known radionuclides, and some are used in medical imaging.
- Radionuclides are produced artificially in the following ways:
- A) Neutron excess: forcing an additional neutron into a stable nucleus, resulting in a neutron excess, in a nuclear reactor.
- B) Proton excess: forcing an additional proton into a stable nucleus, knocking out a neutron, in a cyclotron.
- C) Radioactive fission products: extracted from spent fuel rods of nuclear reactors.
- D) Daughter products: obtained from generators containing longer-lived radioactive parents.
Radionuclides in Medical Imaging
- Desirable properties of radionuclides for imaging:
- Emission of gamma rays (50-300 keV) for easy detection and spatial resolution.
- No alpha or beta particle emission to minimize unnecessary dose to the patient.
- Ideally, emission of monoenergetic gamma rays for easy energy discrimination.
- Easily attached to pharmaceuticals at room temperature.
- Readily available at the hospital site.
- High specific activity (high activity per unit volume).
Radioactive Decay
- Radioactive decay is a stochastic process, making it impossible to predict which nucleus will disintegrate next.
- The activity of a radioactive sample is measured by the rate of disintegration (number of disintegrations per second).
- The SI unit of activity is the Becquerel (Bq), with common units being megabecquerels (MBq) and gigabecquerels (GBq).
Cyclotrons
- Cyclotrons are powerful machines that accelerate charged particles to produce radioactive isotopes.
- They are commonly used in nuclear medicine to produce radionuclides for imaging and cancer treatment.
Other Radionuclides and Their Uses
- Xenon-133 (133Xe): used in lung ventilation imaging, produced in a nuclear reactor, and has a half-life of 5.2 days.
- Krypton-81m (81mKr): used in pulmonary ventilation studies, generator-produced, and has a half-life of 13 seconds.
- Gallium-67 (67Ga): used to detect tumors and abscesses, cyclotron-produced, and has a half-life of 67 hours.
- Indium-111 (111In): used to label white blood cells and platelets for locating abscesses and thrombosis, cyclotron-produced, and has a half-life of 67 hours.
- Positron emitters: used in PET (positron emission tomography) scans, with common examples being 18F, 11C, 13N, 15O, and 82Rb.
Technetium-99m
- 99mTc is used in 90% of radionuclide imaging, fulfilling many desirable criteria.
- It has a gamma energy of 141 keV, making it easily collimated and absorbed in a thin crystal.
- It has a short half-life (6 hours) and pure gamma emission, allowing for a reasonably large activity to be administered.
- 99mTc is supplied from a generator containing the parent 99Mo, which can be produced in a nuclear reactor and has a 67 hour half-life.
This quiz covers the production of radionuclides, including the process of adding neutrons to a stable nucleus, and the role of nuclear reactors in this process. Learn about the creation of radionuclides used in medical imaging.
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