Iraqi Board Radiology key terms

A radiation protection principle stating that occupational and public exposures should be kept As Low As Reasonably Achievable, taking economic and social factors into account. It underpins dose optimisation in every imaging modality.

A tissue-weighted sum of radiation doses to organs, expressed in sieverts, estimating overall stochastic risk from a given exposure. It allows comparison of risk between different examinations such as chest radiography and CT.

A dose benchmark, usually set at the third quartile of a national survey, used to flag examinations delivering unusually high radiation for a given protocol. Values are advisory for optimisation rather than legal limits.

A scaled measure of CT attenuation in which water is zero and air is approximately minus 1000, derived from the linear attenuation coefficient. It allows characterisation of tissues such as fat, fluid, calcium and acute blood.

The preferential absorption of low-energy photons as an X-ray beam passes through matter, shifting the spectrum toward higher energies. In CT it produces cupping and dark streaks between dense structures such as bone or metal.

A reconstruction artefact occurring when the sampled spatial frequency exceeds what the system can resolve, producing wraparound or ghosting. In CT it appears as streaks outside the scan field or as duplication at the edge of the field of view.

The range of CT attenuation values mapped to the full grey scale of a displayed image. A narrow width increases contrast between tissues of similar density, while a wide width suits lung or bone assessment.

An MR angiography technique that generates vascular contrast by detecting the inflow of fresh, fully magnetised blood into a slice, without requiring intravenous gadolinium. It is commonly used for intracranial arterial imaging.

A quantitative map derived from diffusion-weighted imaging that expresses the magnitude of water molecule diffusion in tissue. Low values indicate restricted diffusion, seen in acute infarction, abscess and highly cellular tumours.

An MRI sequence that exploits the random motion of water protons to generate contrast, with restricted diffusion appearing bright on high b-value images. It is central to detecting acute stroke and distinguishing abscess from oedema.

A paramagnetic chelate administered intravenously to shorten T1 relaxation and enhance signal on MRI. Agents differ in stability and route of elimination, which affects suitability in renal impairment and pregnancy.

A rare fibrosing disorder of skin and internal organs occurring in patients with severe renal impairment after exposure to certain unstable gadolinium chelates. Risk is minimised by avoiding high-risk agents and checking renal function.

An adverse response to intravascular iodine-based contrast, ranging from mild urticaria to anaphylaxis, or from transient nausea to contrast-induced acute kidney injury. Premedication and hydration are used for selected at-risk patients.

An impedance method for sizing and counting particles, including blood cells, as they pass through an aperture and change electrical resistance. In radiology it explains the basis of automated cell counting used before contrast administration.

Respiratory distress in premature neonates caused by surfactant deficiency, producing diffuse ground-glass opacity, air bronchograms and low lung volumes. Complications include pneumothorax and bronchopulmonary dysplasia.

A phospholipid mixture secreted by type II pneumocytes that lowers alveolar surface tension and prevents alveolar collapse at end-expiration. Deficiency underlies neonatal respiratory distress syndrome and is treated with exogenous replacement.

A chest image in a newborn, usually supine and often portable, interpreted with attention to lung volume, position of tubes and lines, and symmetric aeration. Normal thymic shadow and physiological findings must not be mistaken for disease.

Loss of the normal border between two structures of similar radiographic density when they become contiguous, such as the right heart border with right middle lobe consolidation. It localises opacity to a specific lobe.

Branching air-filled bronchi made visible against surrounding opacified lung, indicating alveolar disease rather than bronchial obstruction. It is a classic feature of pneumonia and pulmonary oedema.

On a lateral chest radiograph, the lower thoracic spine should appear progressively darker; loss of this normal lucency suggests lower lobe or posterior mediastinal opacity. It is a useful clue to subtle consolidation.

Small centrilobular nodules connected to branching linear opacities on high-resolution CT, reflecting bronchiolar impaction with mucus or pus. It suggests infectious bronchiolitis, aspiration or endobronchial spread of tuberculosis.

A ground-glass opacity surrounding a nodule or consolidation on CT, classically seen with invasive pulmonary aspergillosis in neutropenic patients. It may also occur with haemorrhagic metastases, vasculitis or organising pneumonia.

Two gas-filled structures on an abdominal radiograph of a neonate, representing a distended stomach and a dilated proximal duodenum. It indicates duodenal atresia or obstruction and is usually associated with distal bowel gas absence.

A tapered, beak-like narrowing at the transition point of a dilated bowel loop, seen in volvulus or achalasia depending on the segment involved. In sigmoid volvulus the twist occurs at the sigmoid colon.

A markedly dilated, ahaustral sigmoid loop shaped like a coffee bean, pointing toward the right upper quadrant on abdominal radiography. It indicates sigmoid volvulus and often prompts endoscopic decompression.

A palpable, non-tender gallbladder in a jaundiced patient suggests a malignant obstruction rather than gallstones, because chronic stone disease usually produces a fibrotic, non-distensible gallbladder. It is a classic clinical-radiological correlation.

A parasitic liver cyst caused by Echinococcus granulosus, showing a well-defined fluid collection that may contain daughter cysts, a detached membrane or peripheral calcification. Rupture into the biliary tree or peritoneum is a serious complication.

A Doppler-derived ratio of peak systolic to end-diastolic velocity differences, used to assess renal parenchymal vascular resistance. Elevated values may indicate obstruction, transplant rejection or intrinsic renal disease.

Twisting of the ovary and its vascular pedicle, causing venous congestion and arterial compromise. Ultrasound shows an enlarged ovary with peripheral follicles, reduced Doppler flow and sometimes a twisted pedicle.

A swirling pattern of vessels on colour Doppler or contrast imaging, representing torsion of a vascular pedicle. It is described in ovarian torsion, testicular torsion and midgut volvulus.

Brain injury in a neonate from impaired cerebral perfusion and oxygenation around birth, shown on MRI as restricted diffusion in the basal ganglia, thalami or white matter. Severity on imaging correlates with neurodevelopmental outcome.

A triangular filling defect within the superior sagittal sinus on contrast-enhanced CT or MRI, with enhancing dural margins. It indicates dural venous sinus thrombosis.

Progressive stenosis of the distal internal carotid arteries with a compensatory network of small collateral vessels at the base of the brain. Angiography shows a puff-of-smoke appearance, and children present with ischaemia while adults may bleed.

Extra sutural bones within the cranial sutures, prominent in osteogenesis imperfecta, cleidocranial dysplasia and some normal variants. Their number and size help distinguish pathological from incidental findings.

A fracture involving the growth plate, classified by the Salter-Harris system from type I through type V. Types III to V cross the physis and carry a higher risk of growth disturbance.

A focal subchondral bone lesion with potential separation of a bone fragment and overlying cartilage, typically affecting the knee, ankle or elbow in young patients. MRI assesses stability of the fragment and guides management.

A standardised lexicon and final assessment category system for breast imaging reports, ranging from category 0 (incomplete) to 6 (known malignancy). It guides management and audit by conveying the likelihood of malignancy.

A three-dimensional mammographic technique acquiring multiple low-dose projections to reconstruct thin breast slices. It reduces tissue overlap and improves cancer detection, particularly in dense breasts.

A breast abnormality in which normal tissue architecture is disrupted by radiating spicules or focal retraction without a dominant mass. It is a suspicious finding often associated with invasive lobular carcinoma.

The spontaneous transformation of an unstable nucleus into a more stable configuration, emitting alpha, beta or gamma radiation. The rate is characterised by a half-life specific to each radionuclide.

The most widely used diagnostic radionuclide, with a six-hour half-life and a 140 keV gamma emission suited to gamma camera imaging. It is eluted from a molybdenum-99 generator and bound to various tracers.

An imaging technique detecting pairs of annihilation photons produced when positrons from a radionuclide interact with electrons. Combined with CT or MRI it provides metabolic and anatomic information, most often with fluorine-18 fluorodeoxyglucose.

A semi-quantitative measure of radiotracer accumulation in a region of interest, normalised to injected activity and body size. It is used in oncology to characterise lesions and assess treatment response.

A method of gaining vascular access by puncturing a vessel with a needle, passing a guidewire, then exchanging the needle for a catheter. It is the foundation of most percutaneous angiographic and interventional procedures.

The deliberate occlusion of a blood vessel by injecting coils, particles, glue or sclerosants through a catheter. It is used for haemorrhage control, tumour devascularisation and treatment of vascular malformations.

A rise in serum creatinine occurring within days of intravascular iodinated contrast administration, after other causes are excluded. Risk is reduced by hydration and limiting contrast volume in patients with pre-existing renal impairment.