ABR DMP key terms

Kinetic energy released per unit mass in air by uncharged particles such as photons, expressed in gray. It is the standard quantity for specifying output of radiographic and fluoroscopic x-ray tubes.

Energy deposited by ionizing radiation per unit mass of material, measured in gray (joule per kilogram). It describes energy actually imparted to tissue rather than energy merely present in the beam.

A quantity that weights absorbed dose by radiation type to reflect biological harm, expressed in sievert. In modern usage the operational and protection quantities (equivalent dose, effective dose) supersede it.

Tissue-weighted sum of equivalent doses across organs, expressed in sievert, estimating whole-body stochastic risk from a nonuniform exposure. It allows comparison of risk across different imaging procedures.

The principle of keeping radiation exposures as low as reasonably achievable, accounting for economic and social factors. It underpins shielding design, protocol optimization, and occupational dose monitoring programs.

A dose or activity benchmark, usually set near the third quartile of a survey of facilities, used to flag unusually high exposures for adult imaging. Values are advisory for optimization, not legal dose limits.

Thickness of a specified material that reduces the intensity of a radiation beam to half its original value. It characterizes beam quality and is used in shielding calculations and filtration specifications.

The regulatory ceiling on effective dose to a radiation worker in a year, generally 50 mSv (5 rem) in United States regulation. It applies to declared workers, not to members of the public.

A device worn by a radiation worker that records cumulative occupational dose, commonly a thermoluminescent or optically stimulated luminescence badge. Results are reviewed against regulatory and institutional action levels.

The practice of asking patients of childbearing potential about possible pregnancy before pelvic or abdominal ionizing imaging, so that risk counseling and protocol adjustment can occur. It is not a universal requirement for every examination.

The estimated absorbed dose to a conceptus from a maternal imaging procedure, typically well under 50 mGy for most diagnostic studies. Counseling thresholds for stochastic and deterministic risk are commonly cited around that level.

Interaction in which a photon transfers all its energy to a bound inner-shell electron, which is ejected. Probability rises steeply at low energy and with high atomic number, producing strong contrast between bone and soft tissue.

Interaction in which a photon transfers part of its energy to a loosely bound electron and is deflected with reduced energy. It is the dominant attenuation process in soft tissue at diagnostic energies and a major source of scatter.

A sharp increase in photoelectric absorption that occurs when photon energy just exceeds the binding energy of the K-shell electron of an atom. Iodine and barium K-edges are exploited in contrast imaging.

Probability per unit path length that a photon interacts in a material, dependent on photon energy and material density. It describes exponential attenuation of a narrow beam through matter.

Radiation deflected from its original path by interactions in the patient or surroundings, degrading image contrast and contributing occupational dose. It is controlled with grids, collimation, and shielding.

An array of alternating radiopaque strips and radiolucent spacers placed between patient and detector to absorb obliquely traveling scatter while transmitting primary photons. Grid ratio and frequency govern its effectiveness and dose cost.

The ratio of patient dose with a grid to dose without it for equal detector signal, reflecting the increased exposure needed to compensate for primary attenuation by the grid. It rises with grid ratio.

Variation in x-ray beam intensity across the field, lower on the anode side because photons produced deeper in the target must traverse more anode material. It influences tube orientation for anatomy of differing thickness.

The area on the anode where electrons strike and x-rays are produced. Its size limits spatial resolution; small focal spots improve sharpness but restrict tube current because of heat loading.

A measure of how well an imaging system preserves contrast at each spatial frequency, normalized to one at zero frequency. It describes resolution performance independent of noise.

The squared ratio of output to input signal-to-noise ratio of a detector, indicating how efficiently it converts incident x-ray quanta into image signal. Higher values mean lower dose for equivalent image quality.

A vendor-specific number reported by digital radiography systems that indicates detector exposure level, used to judge whether technique is appropriate. It is not interchangeable across manufacturers.

Radiation exposure produced per unit charge at a given tube potential, typically expressed as air kerma per milliampere-second at a reference distance. It depends on target material, filtration, and voltage waveform.

A metastable radionuclide with a 6-hour half-life and 140 keV gamma emission, produced from a molybdenum-99 generator. It is the workhorse of nuclear medicine because of its favorable energy and versatile chemistry.

The process of extracting sodium pertechnetate from a molybdenum-99/technetium-99m generator using saline. Elution efficiency and molybdenum breakthrough are quality control concerns.

The fraction of total radioactivity in a preparation attributable to the intended radionuclide, excluding contaminating species such as molybdenum-99. It is verified by measuring transmission through lead shielding.

The proportion of radioactivity present in the desired chemical form rather than as free or altered species. It is assessed by chromatography and affects biodistribution and image quality.

The peak in a gamma spectrum corresponding to full absorption of a photon in the detector, used to set the energy window. Photomultiplier gain is adjusted so the peak falls at the expected channel.

A selected range of pulse heights accepted by the gamma camera, usually centered on the photopeak, that determines which events are counted. Narrower windows reject scatter but reduce sensitivity.

An imaging device using a collimator, scintillation crystal, and photomultiplier tubes to detect and localize gamma emissions from a radiotracer. Spatial resolution and sensitivity trade off through collimator design.

A lead structure with holes that restricts the gamma camera to accepting only nearly parallel photons, projecting the source distribution onto the crystal. Hole size, length, and septa set resolution and sensitivity.

Imaging modality detecting pairs of 511 keV annihilation photons emitted in opposite directions from positron decay. Coincidence detection localizes the event along a line of response.

A PET technique that measures small differences in arrival times of annihilation photons to localize the event along the line of response, improving signal-to-noise ratio in large patients.

Correction of emission data for photon loss within the patient, typically using a transmission or computed tomography map. Without it, deep structures appear artificially low in activity.

A bone-forming cell that synthesizes and mineralizes osteoid matrix. Its activity underlies radiotracer uptake on bone scans and explains focal uptake at sites of fracture healing or metastasis.

A large multinucleated cell that resorbs bone matrix. Coupled with osteoblast activity, it drives the remodeling that produces increased tracer uptake in metabolically active bone lesions.

Nuclear medicine imaging of bone using technetium-99m labeled diphosphonates that adsorb to hydroxyapatite, with uptake reflecting regional blood flow and osteoblastic remodeling.

The functional unit of the kidney, comprising a glomerulus and tubule that filter plasma and reabsorb or secrete solutes. Glomerular filtration rate and tubular secretion determine renal tracer clearance.

The volume of plasma filtered by the kidneys per unit time, a key measure of renal function. It can be estimated from the clearance of a filtration-only radiotracer.

Functional renal imaging with radiotracers such as technetium-99m mercaptoacetyltriglycine, assessing perfusion, extraction, and excretion. It is useful when anatomy and function diverge.

The structural unit of the thyroid gland, lined by cells that trap iodide and synthesize thyroid hormones stored as colloid. Its iodide handling allows radionuclide imaging and therapy.

Measurement of the fraction of administered radioiodine concentrated by the thyroid at a set time, reflecting gland activity. It helps distinguish hyperthyroid states and guides therapy dosing.

Imaging of the thyroid after administration of a gamma-emitting iodine or pertechnetate tracer to map functional tissue. It identifies autonomous nodules and ectopic or remnant tissue.