RNI Flashcards
What are radionuclides, and how do they differ from radioisotopes?
- Radionuclides are radioactive elements with unstable nuclei that release radiation through nuclear decay.
- the correct term in nuclear medicine is radionuclides because:
- Radionuclides encompass all radioactive atoms, whether they are isotopes of the same element or not.
What are the key characteristics of radionuclides?
- Unstable Nucleus: An imbalance of protons and neutrons causes instability.
-Radioactive Decay: Emit alpha (α), beta (β), or gamma (γ) radiation to become stable.
-Energy Emission: The emitted radiation can be detected and used for imaging or therapy.
How are radionuclides named and identified using standard notation?
Element Name: Specifies the chemical element (e.g., Technetium, Iodine).
Mass Number: The sum of protons and neutrons in the nucleus.
For example, Technetium-99m (99mTc) is a radionuclide where 99 is the mass number, and “m” indicates a metastable state.
What is radioactive decay, and how does it work?
Radioactive Decay: A natural process where an unstable nucleus releases energy to become stable.
How it works:
1 -The unstable nucleus has an imbalance of protons and neutrons.
2- It emits particles (alpha or beta) or energy (gamma rays) to achieve stability.
3- This transformation may result in a new element or isotope (daughter nuclide).
Explain the differences between alpha, beta and gamma decay?
Alpha decay:
- Emits an alpha particle (2 protons + 2 neutrons, like a helium nucleus).
- Results in a decrease in the atomic number by 2 and the mass number by 4.
Beta decay:
-A neutron transforms into a proton and emits a beta particle (electron or positron).
-Increases or decreases the atomic number by 1 but keeps the mass number unchanged.
Gamma decay:
Releases gamma rays (high-energy electromagnetic radiation) without changing atomic or mass numbers.
What are the parent nuclide and daughter nuclide in radioactive decay?
Parent nuclide: The original unstable nucleus before decay.
Daughter nuclide: The resulting nucleus after decay, which may or may not be stable.
Radionuclides are produced through three primary methods, what are they?
1- Cyclotron:
Accelerates charged particles (e.g., protons, deuterons) to bombard stable materials.
Produces radionuclides like 18F and 11C for PET imaging.
2- Nuclear Reactor:
Uses fission reactions or neutron activation to produce radionuclides.
Produces commonly used radionuclides like 99Mo and 131I.
3- Radionuclide Generator:
Contains a long-lived parent radionuclide that decays into a short-lived daughter radionuclide.
Example: 99Mo/99mTc generator for SPECT imaging.
What factors influence the choice of radionuclides for diagnostic and therapeutic applications?
1 -Type of Application:
Diagnostic: Requires radionuclides with short half-lives to minimize radiation exposure while providing clear images (e.g., 99mTc, 18F).
Therapeutic: Uses radionuclides with longer half-lives for sustained radiation targeting specific tissues (e.g., 131I for thyroid cancer).
2- Imaging Modality:
- Gamma emitters for SPECT (e.g., 99mTc).
- Positron emitters for PET (e.g., 18F).
3- Half-Life Matching:
The radionuclide’s half-life should align with:
- The biological process being imaged.
- The duration of therapeutic efficacy.
4 - Energy Level:
Gamma rays must have energies suitable for clear imaging without excessive radiation dose.
How does half-life affect the suitability of a radionuclide for imaging or therapy?
- Short Half-Life:
Suitable for rapid imaging of biological processes.
Example: 15O (2 minutes) for brain perfusion. - Intermediate Half-Life:
Ideal for diagnostic imaging, balancing imaging time and radiation exposure.
Example: 99mTc (6 hours). - Long Half-Life:
Suitable for therapeutic applications, providing sustained radiation to target tissues.
Example: 131I (8 days).
How are radionuclides attached to biological molecules for imaging and therapy?
1- Labelling Process:
- The radionuclide is chemically bonded to a biologically active molecule (e.g., peptides, antibodies).
- This molecule targets specific tissues or processes in the body (e.g., glucose metabolism, cancer cells).
2- Controlled Conditions:
- Solvents, temperature, and purification methods are carefully managed to ensure the radiopharmaceutical is safe and effective.
Examples:
18F is attached to glucose molecules (FDG) for PET scans to track metabolism.
What is a radiopharmaceutical, and how is it administered?
Radiopharmaceutical: A compound consisting of a radionuclide bonded to a biologically active molecule, used for diagnostic imaging or therapy.
Common Administration Methods:
1- Intravenous (IV): Most common, ensuring rapid delivery to target tissues.
2 -Oral: Example: Iodine-131 capsules for thyroid therapy.
3 - Inhalation: Example: 99mTc aerosols for lung ventilation studies.
What are the differences between diagnostic and therapeutic radiopharmaceuticals?
Diagnostic Radiopharmaceuticals:
- Use radionuclides with short half-lives.
- Emit gamma or positron radiation for imaging (e.g., 99mTc, 18F).
Therapeutic Radiopharmaceuticals:
- Use radionuclides with longer half-lives.
- Emit alpha or beta particles to deliver localized radiation to diseased tissues.
How are radiopharmaceuticals purified?
Purification:
- Removes unwanted by-products and impurities from the chemical reaction.
- Ensures only the desired radiopharmaceutical is present.
How are radiopharmaceuticals sterilized after production?
1- Micromembrane Filtration: Removes microorganisms using a 0.22 µm filter before transferring the product into a sterile vial.
2- Autoclaving: Uses steam under pressure to eliminate bacteria and ensure sterility.
Why is automation important in the synthesis of radiopharmaceuticals?
1- Safety: Reduces radiation exposure to staff.
2- Consistency: Produces high-quality radiopharmaceuticals with fewer errors.
3- Efficiency: Allows for faster production, essential for short-lived radionuclides.
Synthesis Modules:
Automated systems that mix, label, and purify radiopharmaceuticals under sterile conditions.
What is PET-CT, and how does it combine functional and anatomical imaging?
PET-CT:
- Combines Positron Emission Tomography (PET) for functional imaging (e.g., metabolism, blood flow) with Computed Tomography (CT) for anatomical localization.
- PET provides data on cellular processes,
- while CT maps the location within the body.
How does SPECT differ from PET in terms of radiotracers and detectors?
Radiotracers:
- PET uses positron emitters (e.g., 18F) that produce annihilation photons.
- SPECT uses gamma emitters (e.g., 99mTc) for direct photon emission.
Detectors:
-PET uses coincidence detection with a ring of detectors.
- SPECT uses rotating gamma cameras with collimators.
What is attenuation in PET imaging, and how is it corrected?
Attenuation:
- The reduction in gamma photon intensity as they pass through tissues.
- Leads to inaccuracies in image localization and quantification.
Correction Methods:
1 - CT Attenuation Correction: Uses CT data to estimate and adjust for photon loss, enhancing accuracy.
What is time-of-flight (TOF) technology in PET, and how does it enhance spatial resolution?
TOF Technology:
- Measures the time difference between the detection of two annihilation photons to pinpoint the annihilation site.
Advantages:
1- Enhances spatial resolution by reducing uncertainty in photon localization.
2- Reduces noise in images.
3- Speeds up scan times, especially for small lesions.
What are the key components of a gamma camera, and what is their function?
1 -Collimator:
- Filters gamma rays based on their direction.
- Ensures only rays traveling in the correct path reach the detector.
2- Scintillation Crystal:
- Converts gamma rays into visible light.
3- Photomultiplier Tubes (PMTs):
- Amplify light signals from the scintillation crystal.
- Convert light into electrical signals for processing.
4- Computer System:
- Processes electrical signals to create images.
- Enhances image resolution and quantifies data.
How do PET detectors work, and what materials are commonly used for scintillation crystals?
PET Detector Workflow:
1- Gamma photons produced by annihilation events are detected.
2- Scintillation Crystals convert gamma photons into visible light.
3- Photodetectors (e.g., PMTs or SiPMs) convert light into electrical signals.
4- Coincidence detection reconstructs images from the paired photons.
Explain the role of calibration tools like phantoms and dose calibrators in nuclear medicine imaging.
Phantoms:
- Test the performance of imaging systems.
Types:
- Uniformity phantoms: Ensure even detector response.
- Resolution phantoms: Evaluate image sharpness.
Dose Calibrators:
- Measure the activity of radiopharmaceuticals before administration.
- Ensure patients receive the correct dose, balancing diagnostic quality and safety.
What are hybrid SPECT/CT system advantages?
Advantages:
1- Shorter scan times with reduced radiation dose.
2- Enhanced image quality with improved contrast and resolution.
3- Precise anatomical localization of functional abnormalities.
4- Useful for oncology (tumour detection), cardiology (myocardial perfusion), and neurology (brain perfusion).
How are dynamic imaging and static imaging used in nuclear medicine?
Dynamic Imaging:
- Records tracer distribution over time to assess processes like blood flow or organ function.
Static Imaging:
Captures a snapshot after the tracer has localized in the body.
Example: Bone scans for detecting metastases.
What safety measures are taken to minimize radiation exposure in nuclear medicine?
- ALARA Principle: Keep radiation exposure “As Low As Reasonably Achievable.”
Key Measures:
- Shielding: Use lead aprons, barriers, and syringe shields.
- Distance: Maximize distance from radiation sources.
- Time: Minimize time spent near radioactive materials.
- Radiation Monitoring: Use personal dosimeters for staff to track exposure.
- Proper Handling: Follow protocols for radiopharmaceutical preparation and administration.
What are the daily quality control procedures for gamma cameras?
Daily Quality Control Procedures:
1- Uniformity Checks:
Ensure even response of detectors across the field of view.
Use uniformity phantoms to verify consistency.
2- Energy Window Calibration:
Confirm proper energy discrimination of gamma photons.
3- Spatial Resolution Checks:
Evaluate the camera’s ability to distinguish small structures using resolution phantoms.
4-Sensitivity Tests:
Measure the gamma camera’s efficiency in detecting radiation.
Why is individual dosimetry important, and how is it determined?
Importance:
1- Ensures patient safety by tailoring the dose to individual physiology.
2- Balances effective imaging or treatment with minimal radiation exposure.
Determination:
1- Organ Uptake: Assessed using pre-treatment imaging or calculations.
2- Biological Half-Life: Measured to estimate retention and clearance.
3- Dosimetry Models: Use mathematical formulas or software to estimate absorbed doses.
