NNC NSREN Specialist key terms

The full-energy peak in a gamma spectrum produced when a photon deposits its entire energy in the detector through the photoelectric effect; used to verify energy calibration and window settings.

The ability of a detector to distinguish photons of similar energy, usually expressed as the full width at half maximum of a photopeak divided by its peak energy, in percent.

A selected range of pulse heights accepted by the pulse height analyzer, centered on a photopeak, so that only photons of the desired energy are counted for imaging.

An electronic circuit that sorts detector pulses by amplitude and passes only those falling within preset energy limits, enabling energy discrimination in gamma cameras and well counters.

A vacuum tube that converts light flashes from a scintillation crystal into electrical pulses and amplifies them, with gain set by the applied high voltage.

A device pairing a crystal such as sodium iodide with a light sensor, which emits light when ionizing radiation deposits energy; the basis of gamma cameras and dose calibrators.

A lead or tungsten shield with holes placed in front of the camera crystal that restricts incoming photons to defined directions, trading sensitivity for spatial resolution.

The smallest separation at which two point sources remain distinguishable in an image, commonly reported as full width at half maximum of a line spread function in millimeters.

The consistency of detector response across the camera field of view; assessed with a flood source as integral and differential uniformity, since nonuniformity produces ring or spot artifacts.

A uniform radioactive source, often cobalt-57 or a filled sheet source, used to irradiate the whole camera face and evaluate uniformity and sensitivity.

The number of counts recorded per unit of activity or per unit of fluence, reflecting how efficiently a system detects radiation; measured in counts per minute per microcurie or similar units.

The interval after each detected event during which the system cannot register another pulse, causing count loss and nonlinear response at high activity; corrected using decay or split-source methods.

A well-type ionization chamber with an electrometer used to measure the activity of radiopharmaceutical doses before administration, requiring daily constancy checks and periodic accuracy testing.

A gas-filled detector operating at high voltage that produces a large output pulse for each ionization event, useful for surveying contamination and exposure rate rather than for spectroscopy.

A portable radiation detector used to measure exposure or dose rate in work areas and to check for contamination; must be calibrated and have its battery and response verified before use.

A wipe or direct probe check of surfaces, equipment, and personnel for removable radioactive material, with results documented and compared against established action levels.

The principle of keeping radiation doses as low as reasonably achievable, considering economic and social factors, achieved through time, distance, shielding, and contamination control.

The maximum permitted radiation dose to a radiation worker, typically an annual effective dose of 50 mSv with a lifetime cumulative guidance value, tracked by a personal dosimeter.

A badge or ring worn by a worker to record cumulative radiation dose, exchanged at defined intervals and used to demonstrate compliance with dose limits.

The time for the amount of a radionuclide in the body to fall by half, combining physical decay and biological clearance; determines dose to organs and timing of imaging.

The time required for the body to eliminate half of a substance by physiological processes, independent of radioactive decay, and a key input to dosimetry models.

A formalism and reference dataset used to estimate absorbed dose to organs from internally administered radionuclides, based on biodistribution, residence time, and S values.

The average time that activity remains in a source organ, calculated from the time-integrated activity curve and used to compute absorbed dose in internal dosimetry.

The fraction of total activity attributable to the intended radionuclide, with contaminating radionuclides limited by compendial specifications; verified by gamma spectroscopy or decay measurement.

The proportion of radioactivity present in the desired chemical form, separated from free radionuclide and impurities by chromatography or other analytical methods before patient administration.

A rapid planar chromatography method using impregnated strips to separate and quantify radiochemical species, routinely used to verify radiochemical purity before releasing a radiopharmaceutical.

The radioactive solution obtained by eluting a parent-daughter generator, such as molybdenum-99 and technetium-99m; tested for activity, purity, and breakthrough before use.

An assay of generator eluate for parent radionuclide contamination, such as molybdenum-99 in technetium-99m, with the limit set by regulation and checked before patient use.

A radioactive drug combining a radionuclide with a carrier molecule to target specific physiology or tissue, used for diagnosis or therapy under strict quality specifications.

Treatment using systemically or locally administered unsealed radioactive sources, such as iodine-131 or lutetium-177 agents, requiring dosimetry, release instructions, and contamination precautions.

Regulatory conditions allowing a treated patient to leave without holding, based on measured dose rate, retained activity, and written instructions to limit exposure to others.

The proportion of detected counts arising from photons that have lost energy through Compton interactions, estimated with energy windows and reduced by appropriate window or correction settings.

A method that compensates for photon absorption and scatter within the patient, using transmission or computed tomography data, to improve quantitative accuracy of emission images.

A semiquantitative index of tracer accumulation in a region, normalized to injected activity and body size, widely used to compare lesion uptake between studies and over time.

A defined area drawn on an image for which counts, activity, or uptake are measured and compared with background or reference tissue to support interpretation.

The scheduled set of measurements and limits applied to instruments, radiopharmaceuticals, and images to confirm they meet performance criteria before clinical use and to detect drift early.

The process of explaining a procedure's purpose, risks, benefits, and alternatives so the patient can voluntarily agree, documented before imaging or therapy involving radiation.

Routine questioning of patients of childbearing potential about pregnancy and breastfeeding before administering radioactivity, guiding deferral or dose modification to protect the fetus.