ABOMR key terms

Interaction in which an incident photon transfers all its energy to an inner-shell electron, ejecting it; probability rises steeply with atomic number and falls with increasing photon energy, producing high subject contrast in bone and metal.

Interaction in which a photon transfers part of its energy to an outer-shell electron and is deflected in a new direction; it degrades image contrast, increases patient dose through scatter, and predominates at diagnostic energies in soft tissue.

Fraction of photons removed from a beam per unit thickness of material, expressed per centimeter; depends on photon energy and tissue density and atomic number, and underlies the differing gray levels of a radiograph.

Thickness of a specified material, usually aluminum, that reduces beam intensity to half its original value; a standard index of beam quality and filtration adequacy in dental x-ray machines.

Attenuation provided by components permanently in the beam path, such as the tube housing, insulating oil, and glass envelope; aluminum-equivalent values are specified in machine performance standards.

Restriction of the useful x-ray beam by diaphragms or lead plates so that only the region of interest is irradiated; rectangular collimation reduces patient dose and improves image contrast by limiting scatter.

Tissue injury whose severity increases with radiation dose above a threshold, such as erythema, mucositis, or cataract; in dentistry these are avoided because doses remain far below thresholds.

Effect, typically carcinogenesis or heritable mutation, whose probability increases with dose while severity does not; assumed to have no threshold, which justifies minimizing even small diagnostic exposures.

Principle that radiation dose to patients and staff should be kept as low as reasonably achievable, consistent with obtaining the needed diagnostic information, achieved through technique selection, collimation, and shielding.

Protective devices worn by patients during intraoral and some extraoral examinations; aprons of at least 0.25 mm lead equivalent attenuate the primary beam and scatter reaching radiosensitive tissues, particularly in children and pregnant patients.

Intraoral projection in which the receptor is placed parallel to the long axis of the tooth and the central ray is directed perpendicular to both, minimizing distortion and producing anatomically accurate images of the dentition.

Intraoral projection in which the receptor is placed against the palate or floor of the mouth and the central ray is angled perpendicular to the plane bisecting the angle between tooth axis and receptor; simple but geometrically distorting.

Small area of the anode where electrons strike and x-rays are generated; a small focal spot improves sharpness by reducing geometric unsharpness, but limits tube current because heat must be dissipated.

Loss of edge sharpness caused by finite focal-spot size, object-to-receptor distance, and source-to-object distance; reduced by a small focal spot, long source-object distance, and short object-receptor distance.

Enlargement of the recorded image relative to the object, determined by the ratio of source-to-receptor distance to source-to-object distance; minimized in intraoral paralleling and cephalometrics by long source distances.

Three-dimensional curved zone in which anatomic structures are imaged sharply by a panoramic unit; objects outside this zone appear blurred or magnified, and patient positioning determines whether the trough matches the dental arch.

Artifactual blurred and magnified duplicate of a radiopaque structure, such as a lead apron edge or earring, appearing on the opposite side of a panoramic image because the structure lies outside the focal trough.

Positioning aid, such as a bite block and guide rod, that aligns the patient's head so the dental arch coincides with the panoramic focal trough and the occlusal plane is level.

Mathematical description of how well an imaging system preserves contrast at each spatial frequency; a widely used objective measure of resolution performance in quality assurance testing.

Highest spatial frequency, expressed in line pairs per millimeter, at which alternating radiopaque and radiolucent lines can still be distinguished; a standard acceptance and quality-control measure for intraoral receptors.

Plot of true-positive rate against false-positive rate across decision thresholds; used to compare observers or imaging systems independent of a single cutoff, with area under the curve summarizing diagnostic accuracy.

Product of absorbed dose and irradiated area, used to express the total radiation burden of a radiographic examination and to compare dose from different machines and techniques.

Bright and dark streaks radiating from dense material such as amalgam, implants, or crowns on CT and CBCT; caused by beam hardening and photon starvation and reduced by artifact-reduction algorithms or higher exposure settings.

Artifactual increase in mean beam energy as low-energy photons are preferentially absorbed in thick or dense tissue, producing cupping or dark bands between dense structures on CT and CBCT images.

Calibrated CT attenuation value scaled so water is 0 and air is -1000; used to characterize tissue densities, though CBCT gray values are not true Hounsfield units and should not be used for absolute density measurement.

Volumetric imaging in which a divergent cone-shaped beam and a flat-panel detector rotate around the patient to reconstruct three-dimensional anatomy; provides high spatial resolution with lower dose than multidetector CT but poorer soft-tissue contrast.

Reconstructed volume of tissue captured in a CBCT or CT examination; smaller fields limit dose and improve resolution, and selection should match the clinical question.

Imaging that uses a strong magnetic field and radiofrequency pulses to exploit proton relaxation properties, giving superior soft-tissue contrast without ionizing radiation; useful for salivary gland, soft-tissue, and TMJ evaluation.

MR sequence emphasizing short relaxation times, in which fat is bright and fluid is dark; provides detailed anatomic depiction of marrow and soft-tissue planes.

MR sequence emphasizing long relaxation times, in which fluid and edema are bright; useful for detecting inflammation, cysts, and salivary duct obstruction.

Well-defined radiolucency in the posterior mandible below the inferior alveolar canal, typically near the angle, representing a developmental lingual bone concavity occupied by submandibular or sublingual gland tissue; usually asymptomatic and requires no treatment.

Focal, well-defined radiopacity of dense bone in an otherwise normal mandible or maxilla, usually near premolars or molars, without symptoms or associated tooth pathology; a developmental variant distinguished from condensing osteitis.

Odontogenic cyst attached at the cementoenamel junction and enclosing the crown of an unerupted tooth, most often a mandibular third molar or maxillary canine; the most common developmental odontogenic cyst.

Odontogenic cyst with a thin corrugated parakeratinized lining and tendency to grow along the bone without marked expansion; appears as a well-defined radiolucency and recurs frequently, sometimes in the setting of a syndrome.

Benign but locally aggressive odontogenic epithelial tumor, most often in the posterior mandible, classically a multilocular soap-bubble radiolucency; requires resection because of high recurrence after conservative removal.

Focal periapical radiopacity of sclerotic bone adjacent to a chronically inflamed, usually necrotic pulp; reactive and reversible after endodontic treatment, distinguishing it from idiopathic osteosclerosis.

Inflammatory lesion of granulation tissue at a tooth apex resulting from pulp necrosis, appearing as a well-defined periapical radiolucency; the most common periapical inflammatory lesion.

Classification of midface fractures: I is horizontal through the maxilla above the apices, II is pyramidal through the nasal bones and orbital rim, and III is complete craniofacial separation through the nasofrontal and zygomatic sutures.

Helical CT of the facial skeleton with axial, coronal, and sagittal reformations; the standard for evaluating maxillofacial trauma because it depicts fracture displacement, orbital involvement, and associated soft-tissue injury.

Abnormal positional relationship of the articular disc to the condyle, commonly anterior disc displacement with or without reduction; MRI is the reference standard for demonstrating disc position and joint effusion.

Injection of radiopaque contrast into a salivary duct followed by radiography to outline ductal anatomy; shows strictures, sialoliths, and ductal dilation, though it has largely been supplanted by ultrasound and MRI.

Formation of calcified stones within salivary ducts or glands, most often submandibular, causing intermittent swelling and pain at meals; calculi appear radiopaque on plain films or CT and echogenic on ultrasound.

Imaging using high-frequency sound waves reflected at tissue interfaces; noninvasive and radiation-free, useful for superficial soft-tissue masses, salivary glands, lymph nodes, and guiding aspiration or biopsy.

Process of disclosing the purpose, risks, benefits, and alternatives of an imaging procedure and confirming the patient's voluntary agreement before it is performed.

Professional judgment that a specific imaging examination is justified by the patient's clinical findings, in accordance with selection criteria, rather than routine or defensive ordering.