ACVR Veterinary Radiology key terms

Any observable feature on an image that suggests a specific tissue change, such as loss of a fascial plane or gas within an organ. Signs are descriptive findings interpreted together with clinical context.

Replacement of normally air-filled or fat-filled tissue by material of greater physical density, making that region appear whiter on radiographs or CT. Common causes include fluid, cells, fibrosis, and mineral.

Loss of a visible border between two structures of similar opacity when they contact each other, indicating they are adjacent rather than separated by air or fat.

Obliteration of a normal cardiac or diaphragmatic margin by adjacent soft-tissue or fluid opacity, used to localize pulmonary or pleural lesions to a specific lung lobe or compartment.

Incomplete expansion or collapse of lung, producing increased opacity and volume loss. Radiographic clues include mediastinal shift, rib crowding, and displacement of fissures toward the collapsed lobe.

Radiographic appearance of thickened airway walls seen end-on as rings or longitudinally as parallel lines. It indicates bronchial or peribronchial disease rather than alveolar filling.

Poorly marginated, coalescing soft-tissue opacity that obscures pulmonary vessels and often contains air bronchograms. It reflects filling of alveoli by fluid, cells, or hemorrhage.

Air-filled bronchi rendered visible as dark branching tubes against surrounding opaque lung. Its presence confirms that the opacity lies within lung parenchyma rather than in the pleural space.

Fine linear, nodular, or reticular opacities that do not obscure pulmonary vessels. It reflects disease of the pulmonary interstitium, such as fibrosis, edema, or infiltrative neoplasia.

Accumulation of fluid in the pleural space, seen as soft-tissue opacity that gravitates ventrally, blunts costophrenic angles, and may create fissure lines or a scalloped lung margin.

Air within the pleural space that separates visceral from parietal pleura. Radiographically it produces a visible pleural line with absent peripheral vessels and, if severe, cardiac and mediastinal shift.

Pneumothorax under positive pressure that progressively collapses the lung and displaces the mediastinum away from the affected side. It is a rapid clinical deterioration and imaging emergency.

Free fluid in the peritoneal cavity, recognized as generalized loss of serosal detail, ground-glass opacity, and separation of organs. Small volumes may be invisible and require ultrasound.

Normal radiographic visibility of abdominal organ margins created by small amounts of intra-abdominal fat. Its loss is a sensitive but nonspecific sign of effusion, inflammation, or cachexia.

Localized blurring of organ margins indicating a regional mass, granuloma, abscess, or adhesion rather than generalized fluid. It helps direct ultrasound to the affected region.

Mechanical ileus is obstruction with dilated bowel loops proximal to a blockage; paralytic ileus is generalized dilation without a physical obstruction. Gas distribution and loop caliber help distinguish them.

Closely stacked, parallel gas-filled small intestinal loops suggesting a linear foreign body or severe enteritis. The pattern reflects bunching of bowel rather than simple dilation.

Loss of bone mineral appearing as focal or geographic radiolucency. Aggressive lesions show ill-defined margins, cortical destruction, and periosteal reaction, whereas benign lesions are often well demarcated.

New bone formed on the outer cortical surface in response to injury, infection, or tumor. Its pattern (smooth, lamellar, spiculated, or sunburst) helps grade the aggressiveness of a lesion.

A radiographic classification based on margin definition, cortical destruction, periosteal reaction, and rate of change. Aggressive lesions are poorly defined and destructive; nonaggressive lesions are well marginated and slow-growing.

A calibrated CT attenuation value scaled so that water is zero and air is approximately negative one thousand. It allows objective comparison of tissue density before and after contrast administration.

Adjustment of window width and window level to display a selected range of CT attenuation values. Narrow windows increase contrast for soft tissue; wide windows display bone and lung detail.

Increase in tissue attenuation after intravascular or intrathecal contrast administration, reflecting blood supply or disruption of barriers. It distinguishes vascular, neoplastic, and inflammatory lesions from cysts and necrosis.

Reduction in ultrasound echoes behind a structure that strongly reflects or absorbs sound, such as bone or mineral. Shadowing helps identify calculi and gas but can hide deeper tissues.

Increased echo intensity deep to a fluid-filled structure because sound is attenuated less than in surrounding tissue. It supports the diagnosis of a cyst or other anechoic fluid collection.

The energy deposited per unit mass of tissue by ionizing radiation, expressed in gray (one joule per kilogram). It describes physical dose delivered, not biologic effect.

Absorbed dose weighted by radiation type to reflect relative biologic harm, expressed in sieverts. It is used for radiation protection and occupational exposure limits rather than tumor prescribing.

The SI unit of absorbed radiation dose, equal to one joule per kilogram of tissue. Veterinary radiotherapy prescriptions are commonly stated in gray per fraction and total gray.

The SI unit of equivalent dose, combining absorbed dose with a radiation weighting factor. It is used for personnel monitoring and population dose limits.

Division of a total radiation dose into multiple smaller treatments to spare normal tissue while allowing tumor repopulation and reoxygenation between fractions. Common schemes are daily, hypofractionated, or palliative.

A radiobiologic parameter describing tissue sensitivity to fraction size. Tissues with low ratios are more sensitive to large fractions, guiding hypofractionation for tumors such as canine osteosarcoma.

A mathematical model predicting cell survival after radiation as a function of dose, using linear and quadratic components. It underpins fractionation calculations and biologically effective dose comparisons.

The radiation protection principle of keeping exposures as low as reasonably achievable through time, distance, and shielding. It governs occupational and owner-adjacent exposure during imaging and therapy.

A badge or ring worn by occupationally exposed staff to record cumulative radiation dose. Regular monitoring verifies that exposures remain below regulatory limits and identifies poor technique.

Injury to non-target tissues occurring during or after radiotherapy, classified as acute (skin, mucosa) or late (fibrosis, bone necrosis, neuropathy). Total dose, fraction size, and volume irradiated determine risk.

The defined region of tissue intended to receive the prescribed dose, encompassing gross tumor plus margins for microscopic spread and setup uncertainty. Accurate delineation balances tumor control against normal tissue injury.

Special equine projections (upright pedal, palmaroproximal-palmarodistal, and skyline) that isolate the navicular bone. They detect flexor cortical irregularities, lucent lines, and enthesophytes associated with navicular syndrome.

A clinical syndrome of forelimb lameness linked to pain in the navicular region, supported by radiographic changes in the distal sesamoid bone and its supporting structures. Radiographs may be normal in early disease.

A set of lateromedial, dorsal-palmar, and oblique projections of the metacarpo- or metatarsophalangeal joint. It is used to evaluate joint effusion, sesamoid fracture, osteochondral lesions, and subchondral bone.

A radiolucent zone beneath articular cartilage indicating bone resorption, often from overload, osteoarthritis, or osteochondrosis. Its location and margin help distinguish developmental from degenerative disease.

A developmental disorder of endochondral ossification producing cartilage retention and subchondral bone changes. In equine joints it appears as flattening, lucency, or fragments at typical sites such as the stifle and fetlock.