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Fundamentals of Nuclear Medicine
Fundamentals of Nuclear Medicine
• Definition and Nature:
• Definition and Nature:
◦ A diagnostic modality using radionuclides to produce physiological (functional) images rather than purely anatomical ones.
◦ A diagnostic modality using radionuclides to produce physiological (functional) images rather than purely anatomical ones.
◦ Provides information on pathological and physiological processes unattainable through other means.
◦ Provides information on pathological and physiological processes unattainable through other means.
◦ Functional imaging allows for earlier disease detection compared to traditional anatomical systems like CT or MRI.
◦ Functional imaging allows for earlier disease detection compared to traditional anatomical systems like CT or MRI.
• Mechanism of Action:
• Mechanism of Action:
◦ Dosing: Patients receive a small amount of a gamma ray–emitting radioisotope via injection, ingestion, or inhalation.
◦ Dosing: Patients receive a small amount of a gamma ray–emitting radioisotope via injection, ingestion, or inhalation.
◦ Detection: A specialized gamma camera collimates and detects the distribution of the isotope within the body.
◦ Detection: A specialized gamma camera collimates and detects the distribution of the isotope within the body.
◦ Molecular Affinity: Isotopes are usually bound to molecules with specific organ affinities (e.g., phosphonates for bone, sulfur colloids for the liver/spleen).
◦ Molecular Affinity: Isotopes are usually bound to molecules with specific organ affinities (e.g., phosphonates for bone, sulfur colloids for the liver/spleen).
◦ Direct Affinity: Iodine is a notable exception, as it localizes strongly in the thyroid without needing a carrier molecule.
◦ Direct Affinity: Iodine is a notable exception, as it localizes strongly in the thyroid without needing a carrier molecule.
• Commonly Used Isotopes:
• Commonly Used Isotopes:
◦ Metastable technetium Tc 99m is the most frequent choice.
◦ Metastable technetium Tc 99m is the most frequent choice.
◦ Radioactive iodine, indium, thallium, and positron-emitting isotopes (oxygen, nitrogen, carbon, and fluorine) are used in specific instances.
◦ Radioactive iodine, indium, thallium, and positron-emitting isotopes (oxygen, nitrogen, carbon, and fluorine) are used in specific instances.
Data Analysis and Functional Studies:
Data Analysis and Functional Studies:
• Digital Records: Data from gamma cameras are stored digitally and processed by computers to enhance count differences and determine organ margins.
• Digital Records: Data from gamma cameras are stored digitally and processed by computers to enhance count differences and determine organ margins.
• Regions of Interest: Operators can analyze specific areas for isotope content and the rate of accumulation over time.
• Regions of Interest: Operators can analyze specific areas for isotope content and the rate of accumulation over time.
• Dynamic Studies: Used to evaluate the function of metabolized or resident substances in organs like the lungs, kidneys, and heart.
• Dynamic Studies: Used to evaluate the function of metabolized or resident substances in organs like the lungs, kidneys, and heart.
• Metabolic Sensitivity: PET imaging evaluates the localization and metabolism of specific elements with precision down to millimeters, even in large patients.
• Metabolic Sensitivity: PET imaging evaluates the localization and metabolism of specific elements with precision down to millimeters, even in large patients.
Advanced Imaging Modalities
Advanced Imaging Modalities
• SPECT (Single Photon Emission Computed Tomography): Generates cross-sectional images based on radionuclide deposition, offering higher sensitivity than planar images.
• SPECT (Single Photon Emission Computed Tomography): Generates cross-sectional images based on radionuclide deposition, offering higher sensitivity than planar images.
• PET (Positron Emission Tomography):
• PET (Positron Emission Tomography):
◦ Used for staging cancer and evaluating neurodegenerative disorders in small animals.
◦ Used for staging cancer and evaluating neurodegenerative disorders in small animals.
◦ Characterizes disease processes often long before they are visible on CT or MRI.
◦ Characterizes disease processes often long before they are visible on CT or MRI.
• Hybrid Systems (PET/CT and PET/MRI):
• Hybrid Systems (PET/CT and PET/MRI):
◦ Combine anatomical sensitivity (CT/MRI) with physiological sensitivity (PET).
◦ Combine anatomical sensitivity (CT/MRI) with physiological sensitivity (PET).
◦ Considered the standard of care for many human cancerous and metabolic diseases; currently available only for small animals in veterinary medicine.
◦ Considered the standard of care for many human cancerous and metabolic diseases; currently available only for small animals in veterinary medicine.
Equine PET Imaging:
Equine PET Imaging:
• Growth and Usage: Use has increased markedly since 2016, primarily at academic centers and racetracks to screen for catastrophic or prodromal lesions in racehorses.
• Growth and Usage: Use has increased markedly since 2016, primarily at academic centers and racetracks to screen for catastrophic or prodromal lesions in racehorses.
• Examination Types:
• Examination Types:
◦ Recumbent: Requires general anesthesia.
◦ Recumbent: Requires general anesthesia.
◦ Standing: The most common modern method; uses sedation and a breakaway function for safety, allowing a scan of the distal limb in approximately 5 minutes.
◦ Standing: The most common modern method; uses sedation and a breakaway function for safety, allowing a scan of the distal limb in approximately 5 minutes.
• Equine Nucleotides:
• Equine Nucleotides:
◦ 18F-sodium fluoride (18F-NaF): Used for osseous (bone) lesions due to its affinity for hydroxyapatite.
◦ 18F-sodium fluoride (18F-NaF): Used for osseous (bone) lesions due to its affinity for hydroxyapatite.
◦ 18F-fluorodeoxyglucose (18F-FDG): A glucose analog used for identifying soft tissue injuries.
◦ 18F-fluorodeoxyglucose (18F-FDG): A glucose analog used for identifying soft tissue injuries.
• Analysis: Findings (regions of avidity) can be objectively quantified to determine biological activity and clinical relevance.
• Analysis: Findings (regions of avidity) can be objectively quantified to determine biological activity and clinical relevance.
Challenges and Limitations
Challenges and Limitations
• Heavy Regulation: The acquisition and use of radiopharmaceuticals must be strictly documented.
• Heavy Regulation: The acquisition and use of radiopharmaceuticals must be strictly documented.
• Hospitalization Requirements: Unlike human medicine, veterinary patients must generally remain hospitalized until radionuclides are eliminated to limit owner exposure.
• Hospitalization Requirements: Unlike human medicine, veterinary patients must generally remain hospitalized until radionuclides are eliminated to limit owner exposure.
• Image Quality: Physiological images often have poor spatial resolution.
• Image Quality: Physiological images often have poor spatial resolution.
• Specialized Expertise: Interpreting these images requires training provided only through specific veterinary radiology residency programs.
• Specialized Expertise: Interpreting these images requires training provided only through specific veterinary radiology residency programs.
• Cost: While cameras are available on the used market, the radionuclides themselves are expensive.
• Cost: While cameras are available on the used market, the radionuclides themselves are expensive.
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