ARRT Nuclear Medicine key terms

A nuclear medicine study in which a technetium-99m labeled diphosphonate tracer is injected and images are acquired hours later to show areas of increased bone turnover, such as fractures, metastases, or infection.

A study using tracers such as technetium-99m sestamibi or tetrofosmin to show blood flow to the heart muscle at stress and at rest, helping identify ischemia or infarction.

A paired lung study comparing how air moves through the lungs (ventilation, often with an inhaled aerosol or gas) with how blood flows through them (perfusion), used mainly to look for pulmonary embolism.

Imaging with a technetium-99m iminodiacetic acid agent that is taken up by the liver and excreted into the biliary tree, used to assess gallbladder function and bile duct obstruction.

A study in which a standardized radiolabeled meal is eaten and images of the stomach are taken over one to four hours to measure how quickly food leaves the stomach.

A technique in which a radiolabeled colloid is injected near a tumor and the first draining lymph node is located with a gamma probe and images, guiding biopsy for cancer staging.

A dual-phase or subtraction study using technetium-99m sestamibi, which washes out of thyroid tissue faster than abnormal parathyroid tissue, to localize a hyperfunctioning parathyroid adenoma.

Whole-body imaging with fluorine-18 fluorodeoxyglucose combined with computed tomography to show tissues with high glucose metabolism, commonly used to stage and restage cancer.

A shielded device containing a long-lived parent radionuclide that decays into a shorter-lived daughter, which is washed out with saline for patient use; the classic example is molybdenum-99 yielding technetium-99m.

The liquid collected from a radionuclide generator after saline is passed through its column; it contains the daughter radionuclide, such as sodium pertechnetate Tc-99m, ready for kit labeling.

The fraction of total radioactivity in a preparation that comes from the intended radionuclide rather than from contaminating radionuclides; it is verified, for example, by measuring molybdenum-99 breakthrough.

The percentage of the total radioactivity in a radiopharmaceutical that is present in the desired chemical form, determined by methods such as paper or thin-layer chromatography.

The presence of parent molybdenum-99 in technetium-99m eluate; because Mo-99 has a long half-life it adds unwanted dose, so regulatory limits apply and the level is measured before use.

A vial of non-radioactive reagents, usually lyophilized, to which pertechnetate or another radionuclide is added so that the tracer forms in a single simple step.

The amount of radioactivity per unit mass of a radionuclide or radiopharmaceutical, often given in becquerels per microgram, showing how much carrier material accompanies the radioactivity.

Leakage of aluminum from a generator column into the eluate, which can make particles clump and reduce labeling yield; it is detected with a simple colorimetric test.

An imaging device that detects gamma rays from a patient with a large scintillation crystal, converts the light flashes to electrical signals with photomultiplier tubes, and builds a picture of tracer distribution.

A vacuum tube that converts faint light flashes from the detector crystal into measurable electrical pulses and amplifies them, letting the system determine the position and energy of each event.

A lead or tungsten plate with holes or channels placed in front of the detector that absorbs obliquely traveling gamma rays, so only those from a limited direction reach the crystal and form an image.

The peak in a gamma-ray energy spectrum produced by full-energy absorption of gamma rays from a given radionuclide; its position identifies the radionuclide and sets the imaging window.

A selected range of pulse heights accepted by the pulse height analyzer, usually centered on a photopeak, so primary gamma rays are counted while most scattered events are rejected.

The ability of an imaging system to show two nearby sources as separate, often described by the full width at half maximum of a line spread function; smaller values mean sharper images.

How evenly a gamma camera responds across its entire field of view when exposed to a uniform source; poor uniformity appears as blotches or rings and requires tuning or correction.

The brief period after each detected event during which the imaging system cannot record another; at high count rates it causes lost counts and inaccurate quantitation.

The axis about which the detector rotates during SPECT; misalignment between this mechanical axis and the computer's reconstruction center causes ring or blurring artifacts and must be checked regularly.

A correction applied to emission data to compensate for gamma rays absorbed or scattered inside the patient, often using a CT-derived map in PET/CT and SPECT/CT.

A PET capability that measures the tiny difference in arrival times of the two annihilation photons, narrowing the probable location of the event along the line of response and improving image quality.

The principle of keeping radiation doses as low as reasonably achievable, taking economic and social factors into account; it guides shielding choices, technique, and daily work habits.

The rule that radiation intensity from a point source falls off with the square of distance, so doubling the distance from the source reduces exposure to one quarter.

The thickness of a specified material that reduces the intensity of a radiation beam by half; it is used to compare shielding materials and to describe beam quality.

The maximum permitted radiation dose for a radiation worker, commonly 50 millisievert (5 rem) per year to the whole body under United States regulations, apart from limited exceptions.

A person who has voluntarily told her employer in writing that she is pregnant and given the expected delivery date, which lowers the dose limit applied to the fetus.

A check for radioactive material on surfaces, equipment, or people, usually done with a survey meter and wipe tests to confirm that an area is clean.

A periodic check in which a sealed radioactive source is wiped and the wipe is counted to detect any radioactive material that has escaped from the capsule.

Leakage of an injected radiopharmaceutical out of the vein into surrounding tissue, which can cause pain, swelling, and altered biodistribution; it is documented and managed promptly.

A check of the patient's blood glucose before fluorine-18 FDG imaging, because high glucose competes with the tracer and can reduce uptake in the tissues of interest.

A daily check that the dose calibrator gives the same reading for a long-lived reference source over time, confirming that measured activities stay accurate.

The practice of confirming a patient's identity with two independent pieces of information, such as full name and date of birth, before giving a radiopharmaceutical or starting a study.

Temporarily stopping breastfeeding after a radioactive dose for a period based on the radionuclide's half-life and its excretion in milk, in order to limit the infant's exposure.