Iran Specialty Board Radiology key terms

The thickness of a specified material that reduces the intensity of a narrow beam of radiation to half its original value; used to characterize beam quality and to plan filtration and shielding.

The principle of keeping radiation doses as low as reasonably achievable, taking economic and social factors into account; drives protocol optimization, shielding design, and dose monitoring in radiology practice.

A dose or activity benchmark, typically set at a high percentile of a surveyed distribution, used to flag unusually high patient exposures and to promote protocol optimization rather than to define a legal limit.

A standardized measure of the radiation dose delivered per unit volume by a CT scanner for a given protocol, expressed in milligray and used to compare protocols and estimate stochastic risk.

The product of volume CT dose index and scan length in centimeters, expressed in milligray-centimeters; it estimates total energy imparted and is converted to effective dose using a body-region coefficient.

A whole-body-equivalent dose calculated by weighting tissue doses by their radiation sensitivity, allowing comparison of stochastic risk across different examinations and modalities, expressed in sieverts.

Added material, usually aluminum, in the X-ray beam path that preferentially absorbs low-energy photons, reducing patient skin dose and hardening the beam at the cost of some contrast.

The increase in mean photon energy as a polychromatic X-ray beam passes through matter because low-energy photons are absorbed preferentially; it causes cupping and streak artifacts in CT.

A normalized CT attenuation scale in which water is zero and air is approximately minus 1000, defined from the linear attenuation coefficient of the material relative to water.

The selection of window width and window level that maps a chosen range of Hounsfield units to displayed gray shades, allowing optimal display of specific tissues such as lung or bone.

Loss of the normal interface between two structures of similar radiographic density, indicating that they are now in contact; for example, a right middle lobe opacity obscures the right heart border.

Lucent branching air-filled bronchi visible within an opacified lung region, confirming that the opacity is alveolar in origin rather than pleural or mediastinal.

Replacement of alveolar air by fluid, pus, blood, or cells, producing increased attenuation that obscures underlying vessels while preserving lung volume, often with air bronchograms.

Small centrilobular nodules connected to branching linear opacities on high-resolution CT, reflecting impaction of bronchioles by mucus or inflammatory material, typical of infectious bronchiolitis.

Patchy regions of differing lung attenuation on inspiratory CT caused by small-airway disease, vascular occlusion, or ground-glass opacity; expiratory imaging helps distinguish air trapping from infiltrative disease.

A CT-derived Agatston score quantifying calcified coronary plaque, used to refine cardiovascular risk estimation and guide decisions about preventive lipid-lowering therapy in asymptomatic adults.

Contrast-enhanced CT of the coronary arteries used to exclude significant stenosis in low-to-intermediate risk symptomatic patients, with high negative predictive value when image quality is adequate.

A tear in the aortic intima allowing blood to enter the media and create a false lumen, classified by Stanford type A or B; CT shows an intimal flap separating true and false lumens.

Hemorrhage within the aortic media without a demonstrable intimal tear, appearing as crescentic high-attenuation wall thickening on unenhanced CT; it is part of the acute aortic syndrome spectrum.

An ulceration of an atherosclerotic plaque that extends through the internal elastic lamina into the media, seen as a focal contrast-filled outpouching beyond the aortic lumen contour.

Simultaneous dilatation of the common bile duct and pancreatic duct, most often caused by a pancreatic head or ampullary mass, though benign strictures can also produce it.

A palpable, non-tender gallbladder in a jaundiced patient, suggesting malignant distal biliary obstruction rather than stone disease, since chronic stone disease usually produces a fibrotic, non-distensible gallbladder.

A post-contrast CT timing of roughly 60 to 80 seconds that maximizes hepatic parenchymal and portal vein enhancement, making it the standard phase for detecting liver metastases and characterizing lesions.

A post-contrast imaging timing of roughly 25 to 35 seconds after injection that opacifies arteries and hypervascular tumors, useful for characterizing hepatocellular carcinoma and hypervascular metastases.

Dilatation of the renal collecting system and ureter due to obstruction or reflux, seen on ultrasound or CT as fluid-filled branching structures within the renal sinus; grading guides urgency of decompression.

Functional or structural impairment of urine flow anywhere from the renal pelvis to the urethra, which if bilateral or in a solitary kidney can rapidly cause acute kidney injury requiring decompression.

A CT-based system categorizing cystic renal masses by wall thickness, septation, calcification, and enhancement, stratifying lesions from benign category I to malignant category IV and guiding management.

The most common primary renal malignancy, arising from tubular epithelium, with clear cell, papillary, and chromophobe subtypes; imaging features and enhancement patterns influence subtype prediction and surgical planning.

Radiating spicules of new bone perpendicular to the cortex, indicating a rapidly growing process that outpaces periosteal attachment; classically associated with osteosarcoma but also seen in other aggressive lesions.

A triangular elevation of periosteum at the margin of an aggressive bone lesion, formed when the periosteum is lifted and new bone fills the angle; it indicates a fast-growing process.

A primary malignant bone tumor producing osteoid, most common in adolescents and young adults at the metaphyses of long bones around the knee, showing aggressive destruction, matrix mineralization, and periosteal reaction.

Displacement of midline intracranial structures across the falx due to a mass effect from hemorrhage, edema, or tumor; it is a sign of raised intracranial pressure and impending herniation.

Downward displacement of medial temporal lobe structures through the tentorial incisura, compressing the brainstem and causing pupillary dilation and deterioration of consciousness; a neurosurgical emergency.

Focal high attenuation along the proximal middle cerebral artery on unenhanced CT, representing acute thrombus; it is an early sign of ischemic stroke and supports reperfusion decision-making.

A standardized lexicon and final assessment category system for breast imaging reports, ranging from category 0 (incomplete) to 6 (known biopsy-proven malignancy), linking findings to management recommendations.

The descriptor of a breast lesion's border, such as circumscribed, obscured, microlobulated, indistinct, or spiculated; spiculated and indistinct margins raise suspicion for malignancy.

A mnemonic for assessing pediatric fractures: whether the fracture is subtle, involves the physis, involves the articular surface, is a toddler's fracture pattern, or is a buckle fracture; it prompts careful search.

A metaphyseal corner fracture in an infant caused by torsional force on a limb, producing a bucket-handle appearance on radiographs; it is a classic marker of non-accidental trauma.

Leakage of contrast medium or infusate outside the vessel into surrounding soft tissue during injection, causing pain and swelling and requiring cessation of injection and limb elevation.

Acute kidney injury occurring within days of iodinated contrast administration after alternative causes are excluded; risk is highest with pre-existing renal impairment, diabetes, and dehydration.

A semiquantitative measure of radiotracer accumulation in a lesion normalized to injected activity and body size, used in oncology PET to assess metabolic activity and treatment response.

A region of reduced or absent radiotracer uptake on a nuclear medicine image, which may indicate a cold defect such as an infarct, cyst, or non-functioning tissue.

Reduced or absent echoes deep to a structure that strongly reflects or absorbs sound, such as bone or a calculus, producing a dark band that helps identify calcifications.

Increased echo amplitude deep to a fluid-filled structure because sound is attenuated less than in adjacent tissue, confirming the cystic nature of a lesion.

A bedside ultrasound examination of pericardial, perihepatic, perisplenic, and pelvic spaces to detect free fluid in hemodynamically unstable trauma patients, guiding immediate operative or angiographic management.

Free gas within the peritoneal cavity, seen on erect chest or abdominal radiographs as subdiaphragmatic lucency and on CT as gas outside bowel; it usually indicates hollow viscus perforation requiring urgent surgery.