Nuclear Medicine Terminology

Use this glossary to explain common terms patients, families, and healthcare professionals may hear when discussing nuclear medicine, radiopharmaceuticals, PET and SPECT imaging, radiopharmacy, diagnostic procedures, molecular radiotherapy, and radiation safety.

Nuclear medicine is a medical specialty that uses small amounts of radioactive material, usually in the form of radiopharmaceuticals or radiotracers, to evaluate how organs, tissues, and biological processes function. Nuclear medicine can support diagnosis, treatment planning, response monitoring, and targeted therapy. It combines clinical medicine, imaging, radiopharmacy, medical physics, and radiation protection.

Core concepts and care professionals

Nuclear medicine: A medical specialty that uses radionuclides and radiopharmaceuticals for diagnosis, evaluation, monitoring, or treatment.
Diagnostic nuclear medicine: The use of radiopharmaceuticals to evaluate organ function, tissue activity, or biological processes for diagnostic purposes.
Therapeutic nuclear medicine: The use of radiopharmaceuticals to deliver radiation to targeted cells or tissues for treatment.
Molecular imaging: Imaging that shows, characterizes, or measures biological processes at the molecular or cellular level.
Nuclear medicine physician: A physician trained to perform, interpret, and manage diagnostic or therapeutic nuclear medicine procedures.
Nuclear medicine technologist: A healthcare professional trained to prepare and administer radiopharmaceuticals, operate nuclear medicine equipment, acquire images, and support patient care.
Radiopharmacist: A pharmacist or other qualified professional who prepares, evaluates, dispenses, and manages radiopharmaceuticals.
Radiochemist: A scientist who works with radioactive compounds and their chemical preparation, analysis, and labeling.
Medical physicist: A specialist who applies physics to medical imaging, radiation measurement, treatment planning, quality assurance, and radiation protection.
Dosimetrist: A professional who calculates and evaluates radiation dose for diagnostic or therapeutic procedures.
Radiology nurse: A nurse who supports patients before, during, and after imaging or therapeutic procedures, including patient education and monitoring.
Nuclear medicine department: A clinical service that provides nuclear medicine imaging, therapy, radiopharmacy, patient care, and quality and safety processes.
Nuclear medicine study: A diagnostic or therapeutic procedure involving a radiopharmaceutical, imaging equipment, laboratory measurement, or targeted treatment.
Indication: The medical reason for ordering or performing a nuclear medicine study or therapy.
Protocol: The planned sequence of preparation, radiopharmaceutical administration, imaging, measurements, and follow-up for a procedure.

Radiopharmaceuticals and radiopharmacy

Radiopharmaceutical: A radioactive drug used for diagnostic imaging or therapeutic treatment. It generally contains a radionuclide and a carrier, tracer, or targeting molecule.
Radiotracer: A tracer molecule labeled with a radionuclide so that its movement, uptake, or distribution can be detected.
Tracer: A chemical or biological compound used to follow a process in the body. A radiotracer uses a radionuclide to make that process detectable.
Radioligand: A radioactive ligand designed to bind to a specific receptor, protein, or other biological target.
Carrier molecule: The nonradioactive part of a radiopharmaceutical that directs or supports delivery to a particular organ, tissue, receptor, or biological process.
Radiolabel: A radionuclide attached to a chemical or biological compound so the compound can be detected or used therapeutically.
Radionuclide: An isotope of an element that has an unstable nucleus and releases radiation as it changes toward a more stable state.
Radioisotope: Another term for a radioactive isotope.
Isotope: One of two or more forms of an element that have the same number of protons but different numbers of neutrons.
Parent radionuclide: A radionuclide that decays to produce another radionuclide, known as the daughter radionuclide.
Daughter radionuclide: A radionuclide produced by the radioactive decay of a parent radionuclide.
Administered activity: The amount of radioactivity given to a patient for a diagnostic or therapeutic procedure, commonly expressed in becquerels or megabecquerels.
Radioactivity: The spontaneous release of radiation from an unstable atomic nucleus.
Physical half-life: The time required for half of the radioactive atoms in a radionuclide sample to decay.
Biological half-life: The time required for the body to eliminate half of a substance through biological processes.
Effective half-life: The combined effect of physical radioactive decay and biological elimination.
Uptake: The accumulation of a radiopharmaceutical in a particular organ, tissue, cell type, or biological target.
Biodistribution: The pattern of how a radiopharmaceutical is distributed throughout the body over time.
Targeting molecule: A molecule selected because it binds to or is taken up by a specific cell, receptor, tissue, or biological process.
Radiochemical purity: The percentage of a radionuclide present in the intended chemical form compared with the total activity in a sample.
Radionuclidic purity: The proportion of the desired radionuclide compared with unwanted radioactive contaminants.
Specific activity: The amount of radioactivity per unit mass or amount of a substance.
Radiopharmaceutical kit: A sterile, nonradioactive set of ingredients used to prepare a specific radiopharmaceutical when combined with a radionuclide.
Compounding: The preparation, modification, fractionation, or formulation of a radiopharmaceutical from ingredients or a commercial kit.
Radionuclide generator: A device that produces a short-lived daughter radionuclide from a longer-lived parent radionuclide.
Quality control: Procedures used to confirm that a radiopharmaceutical, image, instrument, or process meets defined quality and safety requirements.
Radiopharmaceutical preparation: The process of producing, labeling, testing, measuring, and dispensing a radiopharmaceutical for clinical use.

Nuclear medicine imaging and equipment

Nuclear medicine imaging: Imaging performed after a radiopharmaceutical is administered to show the distribution or activity of organs, tissues, or biological targets.
Scintigraphy: Diagnostic imaging that detects radiation emitted from a radiopharmaceutical and creates an image of its distribution.
Planar imaging: Two-dimensional nuclear medicine imaging obtained from one or more fixed camera positions.
Dynamic imaging: Sequential imaging that records changes in radiopharmaceutical distribution or organ function over time.
Static imaging: Imaging acquired during a defined period to show radiopharmaceutical distribution at a particular point in time.
Whole-body scan: Imaging that surveys all or most of the body to evaluate the distribution of a radiopharmaceutical.
Gamma camera: An imaging device that detects gamma radiation from a radiopharmaceutical and produces nuclear medicine images.
Scintillation camera: Another term for a gamma camera.
Single-photon emission computed tomography (SPECT): A nuclear medicine imaging technique that uses a rotating gamma camera to create three-dimensional images of radiopharmaceutical distribution.
SPECT/CT: Hybrid imaging that combines SPECT with computed tomography to show functional and anatomical information in a single study.
Positron emission tomography (PET): A nuclear medicine imaging technique that detects signals from positron-emitting radiopharmaceuticals to evaluate biological and metabolic activity.
PET/CT: Hybrid imaging that combines PET with computed tomography to show metabolic or molecular activity alongside anatomical information.
PET/MRI: Hybrid imaging that combines PET with magnetic resonance imaging to provide molecular, functional, and detailed soft-tissue information.
Hybrid imaging: Imaging that combines nuclear medicine information with anatomical imaging, such as CT or MRI.
Image fusion: Combining images from different imaging methods so that functional and anatomical information can be viewed together.
Co-registration: Aligning images from different imaging methods or time points so that corresponding structures can be compared accurately.
Detector: A component of an imaging device that detects radiation released by a radiopharmaceutical.
Collimator: A device used with a gamma camera to control the direction of incoming radiation and support image formation.
Attenuation: The reduction in radiation intensity as it passes through body tissues or other materials.
Attenuation correction: A technique that adjusts images for the effects of tissue or material that reduces the detected radiation signal.
Image reconstruction: The computational process used to create images from radiation detection data.
Fusion image: An image created by combining information from two or more imaging techniques, such as PET and CT.
Region of interest (ROI): A selected area on an image used to measure activity, uptake, or other image features.
Quantitative imaging: The extraction and use of numerical or statistical information from medical images.

Diagnostic studies and common applications

Bone scan: A nuclear medicine study that evaluates bone activity and may help identify fractures, infection, inflammation, or areas of tumor involvement.
Myocardial perfusion imaging: A nuclear medicine study that evaluates blood flow to the heart muscle, often at rest and during stress.
Stress test: A procedure that evaluates heart function or blood flow while the heart is made to work harder through exercise or medication.
Ventilation-perfusion scan (V/Q scan): A nuclear medicine study that evaluates air flow and blood flow in the lungs.
Thyroid scan: Imaging that evaluates the structure and function of the thyroid gland after administration of a thyroid-seeking radiopharmaceutical.
Thyroid uptake: A measurement of how much radiopharmaceutical the thyroid gland absorbs during a defined period.
Renal scan: A nuclear medicine study that evaluates kidney blood flow, function, drainage, or urinary tract obstruction.
Hepatobiliary scan: A nuclear medicine study that evaluates the liver, gallbladder, bile ducts, and movement of bile. It may also be called a HIDA scan.
HIDA scan: A hepatobiliary scan using a radiopharmaceutical that is taken up by the liver and excreted into the biliary system.
Gastric emptying study: A nuclear medicine study that measures how quickly food or a meal leaves the stomach.
MUGA scan: A multigated acquisition scan that evaluates the movement and pumping function of the heart, especially the ejection fraction.
Sentinel lymph node mapping: Imaging or localization of the first lymph node or group of nodes likely to receive drainage from a tumor or other area of concern.
Infection imaging: Nuclear medicine imaging used to identify areas of infection or inflammation.
Inflammation imaging: Imaging used to identify increased biological activity associated with inflammation.
FDG PET: PET imaging using fluorodeoxyglucose labeled with fluorine-18. FDG behaves similarly to glucose and can show areas of increased glucose metabolism.
PSMA PET: PET imaging using a radiopharmaceutical that targets prostate-specific membrane antigen. It may be used in selected prostate cancer evaluations.
Amyloid PET: PET imaging using a radiopharmaceutical that binds to amyloid plaques in the brain for selected clinical or research purposes.
Perfusion: The flow of blood through tissue or an organ.
Metabolism: The chemical processes that occur within cells and tissues to maintain life and support function.
Physiologic uptake: Radiopharmaceutical accumulation that reflects normal biological activity rather than disease.
Abnormal uptake: Radiopharmaceutical accumulation that differs from the expected pattern and may require clinical interpretation.
Hot spot: An area of increased radiopharmaceutical activity on an image. The significance depends on the organ, tracer, procedure, and clinical context.
Cold spot: An area of reduced radiopharmaceutical activity on an image. The significance depends on the organ, tracer, procedure, and clinical context.
Incidental finding: An unexpected finding discovered during a study performed for another reason.
Follow-up imaging: A later imaging study used to compare findings over time, monitor a condition, or evaluate treatment response.

Image interpretation and measurement

Standard uptake value (SUV): A semiquantitative measurement used primarily in PET imaging to describe radiopharmaceutical concentration in a region of the body relative to an applied reference.
SUVmax: The highest SUV measured within a selected region of interest.
SUVmean: The average SUV measured within a selected region of interest.
Diagnostic reference level (DRL): A benchmark used to identify unusually high or unusually low administered activity for a standardized diagnostic procedure under routine conditions.
Count rate: The number of radiation detection events recorded over a defined period.
Sensitivity: The ability of a test to identify a condition when the condition is present.
Specificity: The ability of a test to identify people who do not have a condition.
False-positive result: A result that suggests a condition or finding is present when it is not.
False-negative result: A result that does not identify a condition or finding that is present.
Diagnostic accuracy: The degree to which a study correctly identifies or excludes a condition.
Treatment response: The change in a condition or measurable finding after treatment.
Response assessment: The evaluation of imaging, laboratory, clinical, or other findings to determine how a condition has changed after treatment.
Image quality: The degree to which an image is clear, accurate, and suitable for interpretation.
Motion artifact: An image distortion caused by movement during image acquisition.
Report: The written interpretation of a nuclear medicine study, including the procedure, findings, impressions, and relevant recommendations.
Impression: The summary section of an imaging report that describes the most important interpreted findings.
Correlation: Comparison of nuclear medicine findings with symptoms, laboratory results, prior imaging, or other clinical information.

Therapeutic nuclear medicine and theranostics

Radionuclide therapy: Treatment that uses a radioactive substance to deliver radiation to selected cells, tissues, or organs.
Molecular radiotherapy: Treatment that uses a radiopharmaceutical to deliver ionizing radiation to targeted pathological cells or tissues.
Targeted radionuclide therapy: A radionuclide treatment that combines a radioactive component with a molecule designed to target a specific biological feature.
Radioligand therapy: A targeted radionuclide treatment that uses a radioactive ligand to bind to a specific receptor or protein on or near a target cell.
Theranostics: A treatment strategy that combines diagnostic imaging and targeted therapy, often using related molecules or targets to select and treat appropriate patients.
Radioiodine therapy: Treatment using radioactive iodine, commonly iodine-131, for selected thyroid conditions.
Peptide receptor radionuclide therapy (PRRT): Targeted radionuclide therapy that uses a radiolabeled peptide to deliver radiation to cells with specific peptide receptors, including selected neuroendocrine tumors.
Radioimmunotherapy (RIT): Targeted radionuclide therapy that combines a radioactive substance with a monoclonal antibody designed to bind to a specific cell type or antigen.
Selective internal radiotherapy (SIRT): Treatment that delivers radioactive microspheres through the blood supply to selected areas, commonly in the treatment of certain liver tumors.
Radioembolization: A form of selective internal radiotherapy in which radioactive microspheres are delivered through blood vessels to reduce blood flow and deliver radiation to a targeted area.
Radiopharmaceutical therapy: Another term for treatment using a radiopharmaceutical to deliver radiation to a target.
Molecular target: A receptor, protein, antigen, or other biological feature selected for diagnostic or therapeutic targeting.
Target expression: The presence or level of a molecular target on or in cells that may determine whether a targeted radiopharmaceutical can bind or accumulate.
Therapeutic index: A comparison between the desired therapeutic effect and the potential effects on healthy tissues.
Dosimetry: The measurement or calculation of radiation dose received by a person, organ, tissue, or target during a procedure or therapy.
Organ-at-risk: A healthy organ or tissue that may receive radiation during a therapeutic procedure and therefore requires monitoring or dose limits.
Treatment cycle: One planned administration of a therapeutic radiopharmaceutical, sometimes repeated at scheduled intervals.
Response monitoring: The use of imaging, laboratory tests, symptoms, or other measures to evaluate the effect of a radionuclide therapy.

Radiation safety and patient care

Radiation: Energy released from atoms or other sources that travels through space or matter. Nuclear medicine uses ionizing radiation for diagnosis or treatment.
Ionizing radiation: Radiation with enough energy to remove electrons from atoms and create ions.
Radiation dose: The amount of radiation energy absorbed by a person, organ, tissue, or material.
Radiation exposure: The condition of being exposed to radiation. Exposure does not necessarily mean that radioactive material has entered the body.
Radioactive contamination: The unwanted presence of radioactive material on a person, surface, object, or area.
Radiation protection: Measures used to reduce unnecessary radiation exposure to patients, workers, caregivers, and the public.
ALARA: An acronym for “as low as reasonably achievable,” a radiation-protection principle that supports minimizing unnecessary exposure while achieving the clinical purpose of a procedure.
Time, distance, and shielding: Basic radiation-protection principles that reduce exposure by limiting time near a source, increasing distance from a source, and using appropriate shielding.
Shielding: Material used to reduce radiation exposure, such as lead, concrete, or other approved protective barriers.
Decay: The process by which an unstable radionuclide changes and releases radiation over time.
Clearance: The removal of a radiopharmaceutical from the body through biological processes such as urination, bowel movements, perspiration, or exhalation.
Excretion: The process by which the body eliminates a radiopharmaceutical or its breakdown products.
Release instructions: Guidance given after a radiopharmaceutical procedure or therapy about activity, contact, hygiene, travel, work, and other safety considerations.
Pregnancy precautions: Instructions used to protect a developing fetus when pregnancy is possible or confirmed. Patients should inform the healthcare team before a nuclear medicine procedure.
Breastfeeding precautions: Instructions about whether breastfeeding should be paused or modified after a procedure or therapy. The required interval depends on the radiopharmaceutical and clinical guidance.
Pediatric nuclear medicine: Nuclear medicine care adapted for infants, children, and adolescents, including weight-based activity, age-appropriate communication, and support with movement or anxiety.
Sedation: Medication used in selected cases to help a patient remain still or tolerate a procedure. Sedation requires additional evaluation and monitoring.
Intravenous (IV) administration: Delivery of a radiopharmaceutical or other medication into a vein.
Oral administration: Delivery of a radiopharmaceutical by swallowing it.
Inhalation administration: Delivery of a radiopharmaceutical as a gas or aerosol that is breathed into the lungs.
Patient preparation: Instructions given before a nuclear medicine study or therapy, such as fasting, hydration, medication changes, blood glucose management, or arrival timing.
Post-procedure instructions: Information provided after a study or therapy about hydration, activity, contact with others, symptoms, and follow-up.

Nuclear medicine terminology, procedure names, radiopharmaceutical availability, and radiation-safety instructions may vary by country, healthcare system, facility, clinical indication, and treatment plan. A qualified healthcare professional can explain how a particular nuclear medicine study or therapy applies to an individual patient.

Nuclear Medicine Terminology

A glossary of common terms related to radiopharmaceuticals, diagnostic imaging, molecular imaging, theranostics, radionuclide therapy, and radiation safety.