CAMRT Nuclear Medicine key terms

An unstable form of an element that emits radiation as its nucleus decays toward a more stable state. In nuclear medicine it supplies the gamma photons or positrons used for imaging and therapy.

A radioactive drug combining a radionuclide with a chemical carrier that determines where it accumulates in the body. Its distribution allows organ function and disease to be imaged or treated.

The time required for half of the radioactive atoms in a sample to decay. It governs how long a tracer remains detectable and how dose activity changes between preparation and injection.

A calculation that adjusts measured activity to a chosen reference time using the radionuclide half-life. It ensures the prescribed activity is delivered despite time passing between assay and administration.

The most widely used imaging radionuclide, emitting a 140 keV gamma ray with a six-hour half-life. It is obtained from a generator and labelled to many compounds for diverse organ studies.

A shielded device holding a parent radionuclide that decays into a shorter-lived daughter, which is eluted for use. It supplies fresh tracer activity on demand in the department.

The process of flushing saline through a generator column to collect the daughter radionuclide in solution. Yield and purity depend on the time since the previous elution.

Unwanted parent radionuclide appearing in generator eluate, which adds unnecessary radiation dose and degrades image quality. It is checked routinely with a dose calibrator before patient use.

The fraction of radioactivity present in the desired chemical form rather than as free radionuclide or other species. Impurities increase background and dose, so purity is tested before administration.

A well-type ionization chamber used to measure the activity of a radiopharmaceutical before injection. Regular accuracy, linearity, and geometry checks keep prescribed doses correct.

The radioactivity left in the vial or syringe after a dose is withdrawn or administered. It is measured so the actual patient dose can be documented accurately.

The pattern of tracer uptake across organs and tissues over time after administration. Normal biodistribution must be recognized to distinguish physiological uptake from pathology.

The accumulation of a radiopharmaceutical in a tissue, reflecting blood flow, metabolism, or receptor binding. Comparing uptake to background and to normal patterns helps identify disease.

The rate at which a tracer is removed from blood or an organ by excretion or metabolism. It influences optimal imaging time and the contrast between target and background.

An imaging device that detects gamma rays from an administered tracer and converts them into a planar image. It uses a collimator, scintillation crystal, and photomultiplier tubes.

A crystal such as sodium iodide that emits light when struck by ionizing radiation. Coupled electronics convert the light flashes into electrical signals used to form images.

A vacuum device that converts faint light pulses from a scintillation crystal into amplified electrical signals. Its output locates the position and energy of each detected event.

A lead shield with holes placed in front of the camera that restricts incoming gamma rays to a known direction. It preserves spatial accuracy but removes most photons, reducing sensitivity.

The dominant energy peak in a spectrum produced by full absorption of a gamma ray in the detector. It defines the energy window used to accept valid imaging events.

A selected range of pulse energies accepted by the camera as valid gamma events. It is centered on the photopeak and excludes most scattered photons that would blur the image.

Gamma rays that change direction and lose energy through interaction in the patient or detector. Scattered events add background and reduce contrast unless rejected by energy discrimination.

The ability of an imaging system to distinguish two closely spaced radioactive sources as separate. It is affected by collimator design, distance from the source, and detector characteristics.

The proportion of emitted gamma rays that the camera actually detects and records. Higher sensitivity shortens imaging time but usually trades off against spatial resolution.

The number of detected events recorded per unit time. It rises with administered activity but can saturate the system at high values, causing dead-time losses.

The brief interval after each detected event when the system cannot process another pulse. At high count rates this causes lost counts and inaccurate activity estimates.

Random variation in counted events that makes images appear grainy. It decreases as more counts are collected, so acquisition time or administered activity may need adjustment.

A drawn boundary on an image used to measure counts within a structure. Comparing target and background regions supports quantitative and semi-quantitative analysis.

A tomographic technique that rotates a gamma camera around the patient to reconstruct cross-sectional slices from emitted single photons. It improves depth localization and lesion contrast.

An imaging method detecting pairs of annihilation photons produced by positron-emitting tracers. Coincidence detection provides high sensitivity and enables quantitative metabolic imaging.

The interaction in which a positron meets an electron and both convert into two 511 keV photons emitted in nearly opposite directions. Detecting this pair is the basis of PET imaging.

Electronic acceptance of two detector events occurring within a very short time window. It identifies true annihilation pairs while rejecting most unrelated background photons.

Two unrelated photons detected within the coincidence window and wrongly counted as one annihilation event. High activity or poor timing resolution increases this background.

A glucose analogue labelled with fluorine-18 that accumulates in cells with high glucose use. PET imaging with it is widely used in oncology and some cardiac and brain studies.

A correction that compensates for gamma rays absorbed or scattered within the patient before reaching the detector. Without it, deep structures appear falsely low in activity.

The mathematical process that converts projection data into cross-sectional images. Filtered back projection and iterative methods differ in noise handling and quantitative accuracy.

Instructions and checks completed before a scan, such as fasting, hydration, thyroid blocking, or stopping interfering medications. Good preparation protects image quality and patient safety.

A documented discussion in which the patient agrees to a procedure after learning its purpose, risks, benefits, and alternatives. It respects autonomy and is required for many nuclear medicine studies.

A check for possible pregnancy before administering radioactivity, since fetal exposure carries higher risk. It guides whether a study is deferred, modified, or performed after discussion.

Practices that limit unnecessary exposure to patients, staff, and the public through time, distance, and shielding. They include monitoring, contamination control, and safe waste handling.

The principle of keeping radiation doses as low as reasonably achievable while still obtaining the needed diagnostic information. It guides protocol choices, shielding, and scheduling.

The calculation and measurement of radiation dose absorbed by organs and tissues. It supports risk assessment, protocol optimization, and compliance with dose limits.

Scheduled testing that verifies equipment and radiopharmaceuticals meet performance standards. It detects drift early, keeping images reliable and doses accurate.