RANZCR Anatomy key terms

The study of body structure as demonstrated by medical imaging, requiring the candidate to translate two-dimensional cross-sectional images into a three-dimensional mental model of organs, vessels and spaces.

The axial, coronal, sagittal and oblique planes used to display the body; recognising anatomy in each plane and mentally converting between them is a core skill tested in the Phase 1 examination.

A workstation technique that reformats volumetric image data, such as CT or MRI, into planes other than the acquisition plane, allowing anatomy to be followed along its true course.

An image-processing method that projects the brightest voxels along a line of sight onto a single plane, commonly used to display contrast-filled vessels and biliary or urinary ducts.

A three-dimensional display technique that assigns opacity and colour to voxel values so that surfaces and internal structures can be viewed from any angle, useful for surgical planning.

A calibrated scale of CT attenuation in which water is zero and air is approximately minus one thousand; it allows tissues such as fat, soft tissue, bone and metal to be distinguished objectively.

Display settings that map a chosen range of CT attenuation values to the available grey shades; level sets the centre and width sets the spread, controlling contrast for the tissue of interest.

The increase in mean photon energy as a polychromatic X-ray beam passes through matter, because lower-energy photons are absorbed preferentially; it produces streak and cupping artefacts near dense structures.

Bright and dark streaks radiating from high-attenuation implanted material such as prostheses or dental fillings, caused by photon starvation, scatter and beam hardening, and degrading nearby image quality.

An artefact arising when a sampled signal is under-sampled relative to the object, producing wraparound or ghosting; in MRI it appears across the phase-encoding direction and in ultrasound as depth misregistration.

The ratio of the strength of the wanted tissue signal to the strength of background random noise; higher values give smoother images, and it trades against resolution and acquisition time.

The smallest distance at which two separate structures can still be distinguished on an image; it depends on voxel size, detector geometry and reconstruction, and differs from contrast resolution.

Averaging of attenuation or signal from different tissues that share a single voxel, so that small structures appear falsely low in density or blurred at boundaries between materials.

The distribution of a radiopharmaceutical within the body as seen on scintigraphy; uptake reflects perfusion, metabolism or receptor expression rather than structure alone, so normal appearances must be memorised.

The predictable pattern in which a radiopharmaceutical accumulates in normal tissues and is cleared by specific organs, providing the baseline against which abnormal focal uptake is judged.

Lymphoscintigraphy in which tracer injected near a tumour identifies the first draining node; the node is localised on planar or SPECT images and then removed for histological staging.

Sheets of connective tissue and the potential spaces between them that direct the spread of infection, fluid and tumour; knowledge of these planes explains patterns of disease on cross-sectional imaging.

The compartment behind the peritoneal cavity containing the kidneys, adrenals, pancreas, great vessels, ureters and lymph nodes, divided by renal fascia into anterior and posterior pararenal and perirenal spaces.

The subdivisions of the peritoneal cavity formed by reflections of peritoneum, such as the lesser sac and paracolic gutters, whose anatomy predicts where free fluid and tumour deposits collect.

The defined regions of tissue supplied by individual arteries, such as the cerebral, mesenteric or coronary territories; mapping these allows infarction and haemorrhage to be attributed to a vessel.

Alternative arterial or venous routes that supply a region when its main vessel is occluded, often through named anastomoses; their presence modifies the extent of ischaemic injury.

Division of an organ into functionally independent units supplied by defined vessels and drained by defined ducts, as in the Couinaud liver segments or bronchopulmonary segments, guiding resection planning.

The stage of bone development assessed from the appearance, growth and fusion of ossification centres; it is used to estimate age and to decide whether deformity will progress with remaining growth.

Foci where cartilage is progressively replaced by bone during development; their order and timing of appearance and fusion provide a timetable for skeletal age and for distinguishing fracture from normal growth.

The cartilaginous growth plate between epiphysis and metaphysis where longitudinal bone growth occurs; it is a plane of weakness susceptible to Salter-Harris injury and to focal growth disturbance.

A reproducible visual feature on an image that indicates a particular diagnosis or pathological process, such as a gas-fluid level or a displaced fat stripe.

The diagnostic process of matching observed imaging features to memorised disease prototypes, allowing rapid generation of a shortlist of likely diagnoses before analytical reasoning refines it.

An ordered list of conditions that could explain the imaging findings, ranked by likelihood, frequency and clinical context, and refined by further tests or follow-up imaging.

Informal teaching term for an image whose appearance is so characteristic that it permits a confident single diagnosis, such as a classic appearances of a dermoid cyst or osteochondroma.

A fixed, repeated sequence of reviewing each region and structure on a study, designed to prevent satisfaction of search and to ensure that incidental or subtle findings are not overlooked.

A perceptual error in which detection of one obvious abnormality stops further scrutiny, so additional findings, sometimes more clinically important, are missed on the same study.

Judging whether a proposed imaging test will alter management, weighing diagnostic yield against radiation dose, cost, availability and the availability of safer alternatives.

The paired radiation-protection principles requiring that each exposure produce net benefit and that the dose be kept as low as reasonably achievable while still answering the clinical question.

A benchmark dose value for a standard examination, derived from survey data, used to flag unusually high exposures and to drive quality improvement rather than to define a legal limit.

An adverse response to iodinated or gadolinium contrast, ranging from mild urticaria to anaphylaxis, or from physiological flushing to contrast-induced nephropathy, requiring recognition and prompt management.

Determining the anatomical extent of a malignancy, including local invasion, nodal spread and distant metastases, so that treatment can be selected and prognosis estimated using a standard classification.

Assessment of whether a lesion can be completely removed with a clear surrounding plane, based on involvement of adjacent vessels, organs, fascial planes and bone on cross-sectional imaging.

Use of ultrasound, fluoroscopy, CT or MRI to direct a needle or instrument for biopsy, drainage or therapy, requiring accurate three-dimensional anatomical localisation and avoidance of vulnerable structures.