PHYSICS OF NUCLEAR MEDICINE

Physics of Nuclear Medicine

• This field uses physics for biomedical sciences.
• Molecular imaging assesses functional or metabolic aspects of normal tissues or disease through tracer detection.
• Tracers are disease-targeted compounds used in tissue labeling by radiotracers.
• Radioisotope production uses a cyclotron to accelerate subatomic particles.
• Radiopharmaceuticals undergo quality control before human administration.
• PET (positron emission tomography) scanning involves injection of a radiopharmaceutical, detection of signals by the scanner, and 3D image generation.
• PET radiochemistry involves attaching positron-emitting isotopes to molecular substances.
• Image analysis examines tissue concentrations and organ function.
• Molecular imaging facilitates cancer stratification and treatment decisions by visualizing target structures.
• Assignment of patients depends on imaging results, and treatment is tailored to the expected outcome.
• Nuclear medicine uses unstable (radioactive) atoms to create diagnostic and therapeutic images.

Basic Nuclear Physics

• Atoms are the fundamental units of matter and define elements.
• The term "atom" comes from the Greek word for indivisible.
• Atoms consist of protons, neutrons (nucleons) and electrons.
• Protons have a positive charge, neutrons are neutral, and electrons are negatively charged.
• Electrons orbit the nucleus.
• The nucleus contains protons and neutrons.
• The strong force holds the nucleus together, overcoming electrostatic repulsion between protons.
• Binding energy is the energy associated with the strong force.

Nucleus Numbers Representation

• Atomic number (Z) equals the number of protons in an atom's nucleus.
• Neutron number (N) equals the number of neutrons in an atom's nucleus.
• Mass number (A) is the sum of protons plus neutrons in an atom's nucleus.
• The element is denoted by its A and Z, e.g., 12 C6 .

Stable Nucleus

• A stable nucleus is one where the strong force overcomes electrostatic repulsion.
• The strong force is carried by protons and neutrons.
• Increasing the strong force while not increasing the electrostatic repulsion involves more neutrons than protons in the element.

Stable Nucleus: The Strong Force

• The strong force is stronger than electrostatic repulsion.
• Particles require close proximity for the strong force to hold them together.
• Unstable nuclei have insufficient binding energy.
• The more binding energy per nucleon an atom has, the more stable it is.

Unstable Nucleus Example

• Unstable nuclei can undergo radioactive decay to transform into smaller, more stable nuclei.
• Unstable nuclei can have too many protons or too many neutrons.

Line of Stability

• Stable nuclei usually have equal numbers of protons and neutrons.
• Nuclei beyond a certain number of protons deviate from the stability line and have more neutrons.
• Nuclei outside the stability region undergo nuclear transformation.
• Unstable nuclei have lower binding energies relative to their more stable atom counterparts.

Isotopes Definition

• Isotopes are different forms of the same element that have the same number of protons but different numbers of neutrons.
• Isotopes have the same chemical properties but different relative atomic masses.
• Isotopes can be radioactive.

Radioactive Decay

• Unstable nuclei undergo radioactive decay to achieve a more stable state.
• This transformation is spontaneous and releases radiation or particles.
• The process releases energy from the nucleus of an atom.

Modes of Radioactive Decay

• Alpha decay emits an alpha particle (Helium-4 nucleus).
• Beta decay transforms a neutron into a proton (or a proton into a neutron) emitting an electron (or positron) and an antineutrino or neutrino.
• Gamma emission release high-energy photons without changing the number of protons or neutrons, merely the energy state of the nucleus.

Medical Imaging in Nuclear Medicine

• Nuclear medicine uses positrons and gamma rays to image processes inside the body.
• Some diagnostic procedures involve using radioactive tracers.

Alpha Decay

• Alpha decay involves the emission of an alpha particle (a helium nucleus).
• Alpha decay primarily occurs in isotopes with large numbers of protons relative to neutrons.

Beta Decay

• Beta decay occurs when a neutron in a nucleus converts to a proton or vice versa.
• Beta-minus decay emits an electron.
• Beta-plus decay emits a positron.

Gamma Decay

• Gamma decay involves emitting energy as a gamma ray photon.
• Gamma decay is often associated with the transition of an excited nucleus to a lower energy state.

Radioisotopes vs Radiopharmaceuticals

• Radiopharmaceuticals are molecules with a radioisotope attached.
• Radiopharmaceuticals accumulate in specific organs.
• Radioisotopes decay, producing radiation for diagnostic or therapeutic applications.

Administration of Radiopharmaceuticals

• Radiopharmaceuticals can be injected intravenously, subcutaneously, or administered through inhalation or ingestion.

What radioisotopes are used in Nuclear Medicine?

• Radioisotopes are selected based on whether they are suitable for therapy (beta or alpha emitters) or diagnostics (beta-plus or gamma emitters).

Examples of Radiopharmaceuticals

• Various radiopharmaceuticals exist for diagnosis and treatment of diseases.
• Radiotracers target certain tissues or cells according to their specific metabolic activities.

Activity of the Sample

• Activity is the number of radioactive atoms in a sample at a given time.
• The activity of radioactivity follows exponential decay with time.

Decrease of Activity with Time

• The activity of a radioactive sample decays exponentially with time.
• The half-life is the time it takes for half the radioactive atoms to decay.

Half-Life

• The half-life is a constant for specific radionuclides.
• The half-life is the time it takes for half the radioactive nuclei to decay.

Medical Imaging

• Medical imaging creates images of inside the body for diagnosis and treatment of structural and biological issues.
• Techniques like radiography, MRI, ultrasound, and nuclear imaging exist.

Nuclear Medicine Diagnostic

• Emission tomography is used to study biological functions.
• Radioactive tracers are administered to patients, targeting specific organs.
• SPECT uses gamma rays.
• PET uses positrons.

How Different is Nuclear Medicine from Anatomical Imaging?

• Nuclear medicine uses injected radiopharmaceuticals and detects emitted gamma rays.
• Contrast is based on physiological function.
• Anatomical imaging like radiography uses transmitted x-rays.

SPECT vs PET

• SPECT is a nuclear imaging technology, similar to gamma camera imaging.
• Both are considered hybrid technologies in conjunction with CT or MRI.
• PET detects coincident gamma rays as a result of positron-electron annihilation.

SPECT-CT Guided Bone Scintigraphy

• Bone scintigraphy detects possible metastases.
• Follow-up is often needed when abnormal uptake is present.
• A hybrid SPECT/CT approach improves the diagnostic results.

Applications:

• SPECT and PET/CT are used to detect primary or metastatic lesions.
• They can be used to assess malignant diseases and the efficacy of different treatment therapies.

PET Imaging

• Various radiotracers and probes are used in PET to detect different biochemical processes, metabolic studies, or DNA synthesis.

Methods of PET Quantification

• Qualitative PET image assessment relies on visual analysis.
• Semi-quantitative analysis evaluates the standardized uptake value (SUV).
• Quantitative analysis employs kinetic modelling.

PET Quantification with Estimation of SUV

• Tumor segmentation and SUV interpretation help track tumor changes during therapy.

PET/CT in Cancer Management

• PET/CT offers a superior approach that combines anatomical (CT) and physiological (PET) views.
• PET/CT improves diagnostic accuracy and allows more targeted and specific treatments.

PET Imaging Procedure

• The procedure involves producing radiotracers and administering them to patients.
• Activity distribution is measured and interpreted to assess physiological function.

Gamma Camera, SPECT Physics

• Gamma cameras use detectors to capture gamma rays emitted by radioactive elements within patients.
• Physical properties and properties of the materials influence the image production.

SPECT Scans

• SPECT uses rotating gamma cameras to collect projection data, improving the efficiency of image acquisition.

Applications of Nuclear Medicine: SPECT

• SPECT produces high-contrast images of disease and improved depth information.
• SPECT resolution is not as high as PET imaging, however.

Applications of Nuclear Medicine : PET Physics

• PET images are created using a technique where two gamma rays are detected simultaneously.

Applications of Nuclear Medicine: PET Imaging Procedure

• The PET procedure involves injecting a radiopharmaceutical and measuring resulting radioactivity.

Applications of Nuclear Medicine: Gamma Camera, SPECT Physics

• Gamma cameras image the distribution of gamma rays within patients.

Applications of Nuclear Medicine: SPECT Imaging Procedure

• SPECT scans use rotating gamma cameras for accurate, efficient image acquisition.

Applications of Nuclear Medicine : SPECT vs PET

• SPECT and PET offer unique functional imaging capabilities with advantages and disadvantages.

Hybrid Systems

• Hybrid systems combine complementary imaging modalities like SPECT/CT or PET/CT.
• This approach gives more complete information in a single study.

Additional Notes

• Various radiotracers and probes can pinpoint specific metabolic activities.
• Radioactive decay is crucial to medical applications.
• Different radiation modes are used for diagnostic and therapeutic reasons.
• Medical professionals use radioactive substances precisely and safely, with strict guidelines.