CNMT key terms

A system that produces a short-lived radioactive daughter from a longer-lived parent, allowing on-site elution of a usable isotope such as technetium-99m from a molybdenum-99 column.

A condition in which a daughter radionuclide grows to a maximum activity slightly greater than its parent and thereafter decays at the parent's rate, typical of a molybdenum-99/technetium-99m generator.

The percentage of available daughter activity actually removed from a generator column during elution, calculated by dividing the activity eluted by the activity expected on the column.

Unwanted leakage of the parent radionuclide or column material into the eluate; molybdenum-99 breakthrough must stay below regulatory limits before patient use.

The fraction of total radioactivity in a preparation that comes from the intended radionuclide, excluding contaminating isotopes that could add unnecessary dose to the patient.

The proportion of the total radioactivity present in the desired chemical form, such as free pertechnetate versus bound tracer, measured by methods like chromatography.

Unbound technetium-99m that has not attached to the labeling agent; it accumulates in thyroid, stomach, and salivary tissue and degrades image quality when present in excess.

The percentage of radioactivity successfully bound to the radiopharmaceutical molecule during preparation, a practical measure of how much usable tracer is available for injection.

The time required for half of the atoms in a radioactive sample to decay; physical half-life is fixed for each isotope while biologic and effective half-lives describe clearance from the body.

The combined result of physical decay and biologic clearance, describing how quickly activity in a patient's body actually falls; it is always shorter than either component half-life.

Mathematical adjustment of measured or prescribed activity for radioactive decay between the calibration time and the time of use or imaging.

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

A daily quality test confirming that a dose calibrator, gamma camera, or other instrument responds consistently to a known source, detecting drift before it affects patient studies.

The ability of a gamma camera or detector to distinguish gamma rays of similar energy, usually expressed as the full width at half maximum of a photopeak.

The peak in a gamma spectrum produced when a gamma ray deposits its full energy in the detector, used to set the energy window for imaging.

Electronic circuitry that accepts detector signals falling within a chosen energy window and rejects scattered or background events outside that range.

Gamma photons that change direction and lose energy through Compton interactions in the patient or detector; scatter degrades contrast and is reduced by energy windowing and correction algorithms.

A lead device placed in front of the camera crystal with holes that restrict incoming photons to a preferred direction, trading sensitivity for spatial resolution.

The smallest separation at which two point sources can still be distinguished in an image, commonly reported as full width at half maximum in millimeters.

The number of detected counts per unit of activity for a given imaging system and collimator, reflecting how efficiently emitted photons are captured.

A measure of how evenly a gamma camera images a uniform flood source; poor uniformity produces ring or spot artifacts and is assessed with daily flood images.

The scheduled testing program that verifies equipment and radiopharmaceutical performance against accepted standards, including daily, weekly, and periodic tests.

The principle of keeping radiation exposure as low as reasonably achievable by using time, distance, and shielding while still obtaining the needed diagnostic information.

Radiation dose received by a worker during job duties, monitored with a personal dosimeter and compared against annual regulatory limits.

A badge or ring worn to record cumulative radiation exposure of an individual worker, typically read periodically by a monitoring service.

A scaled CT number expressing tissue attenuation relative to water, where water is zero, air is about minus 1000, and dense bone is strongly positive.

Display settings that map a range of CT numbers to visible gray shades; level sets the center and width sets the range, controlling contrast and brightness.

In helical CT, the table travel per gantry rotation divided by the beam collimation; higher pitch speeds coverage but can affect image noise and dose.

Volume computed tomography dose index, an estimate of the average absorbed dose within the scanned volume for a given protocol, displayed on the scanner console.

The product of CTDIvol and scan length, used to estimate total radiation output for a CT examination and to compare protocols.

Correction of PET or SPECT images for photon loss as signal passes through body tissue, typically using a CT-derived map so deeper structures are not falsely shown as cold.

A semiquantitative PET metric comparing lesion activity to injected dose and body size, used to help distinguish benign from malignant uptake and to track response.

A three-dimensional rendering that displays the brightest voxel along each viewing ray, commonly used to survey whole-body PET images quickly.

The PET principle of recording two annihilation photons detected nearly simultaneously on opposite sides of the detector ring, which defines a line of response.

A PET capability that measures small arrival-time differences between annihilation photons to localize the event along the line of response, improving signal-to-noise.

Leakage of injected activity into tissue around the vein, which can cause false nodal uptake, alter dosimetry, and require documentation and follow-up.

Delivery of a radiopharmaceutical or contrast agent into surrounding tissue rather than the vein, potentially causing local irritation and invalidating uptake measurements.

Puncture of a vein to administer a radiopharmaceutical or withdraw blood, requiring proper site selection, aseptic technique, and safe sharps handling.

The location chosen for administering a radiopharmaceutical; it should be documented and imaged when needed to identify dose infiltration or residual activity.

Nuclear cardiology study using tracers taken up by heart muscle to assess blood flow at stress and rest, revealing ischemia or scar.

A perfusion abnormality present on stress images but normal on rest images, indicating tissue that is ischemic but still viable.

A perfusion abnormality seen on both stress and rest images, usually representing scar from prior infarction rather than reversible ischemia.

Acquisition synchronized to the electrocardiogram so images can be binned by cardiac phase, allowing assessment of wall motion and ejection fraction.

The percentage of ventricular volume ejected per heartbeat, derived from gated studies or blood pool imaging to evaluate systolic function.