RANZCR AIT key terms

A calibrated scale of X-ray attenuation in CT, where water is 0 and air is about -1000. It lets observers compare tissue density between scanners and describe lesions numerically.

Selecting the display range of CT attenuation values mapped to grey shades, defined by window level and width. Optimal settings reveal soft tissue, lung, or bone detail within the same dataset.

Dark streaking or cupping caused when a polychromatic X-ray beam loses low-energy photons passing through dense material. It degrades CT images near bone, metal, or concentrated contrast.

An error in CT or ultrasound where sampling is insufficient to represent high spatial frequencies, producing streaks, wraparound, or false echoes. It reflects violation of the sampling theorem.

The radiation protection doctrine that exposures should be kept as low as reasonably achievable, accounting for economic and social factors. It underpins justification, optimisation, and dose-limiting practice.

The paired legal principles of radiation protection: every exposure must have sufficient net benefit, and each examination must use the lowest dose achieving the required diagnostic information.

A tissue-weighted sum of equivalent doses across the body, expressed in sieverts, estimating stochastic risk from a non-uniform exposure. It allows comparison between different imaging procedures.

A picture archiving and communication system stores, transmits, and displays medical images digitally across a network. It enables remote reporting, comparison with prior studies, and long-term archive retrieval.

The international standard governing medical image file format and network communication. It embeds patient, study, and acquisition metadata with pixel data, allowing interoperability between scanners and workstations.

The conventional organisation of a report into clinical details, technique, findings, and impression. Clear structure, pertinent negatives, and actionable conclusions improve referrer communication and patient safety.

Sensitivity is the proportion of diseased patients correctly identified; specificity is the proportion of healthy patients correctly excluded. Both depend on the chosen diagnostic threshold.

The probability that a patient with a positive test truly has the disease. It depends on disease prevalence as well as test sensitivity and specificity, unlike the likelihood ratio.

A plot of true-positive rate against false-positive rate across all thresholds of a diagnostic test. The area under the curve quantifies overall discriminative performance.

Independent interpretation of the same imaging study by two radiologists, with discrepancy resolution. It improves cancer detection in screening programmes at the cost of increased workload.

A cancer diagnosed after a negative screening test but before the next scheduled screen, or one arising between screens. It is a key quality indicator of screening programme performance.

A standardised lexicon and final assessment category system for breast imaging, ranging from 0 to 6. It harmonises reporting, predicts malignancy risk, and guides biopsy or follow-up decisions.

Consensus recommendations for managing incidentally detected pulmonary nodules on CT, based on size, morphology, and patient risk. They reduce unnecessary follow-up while detecting early malignancy.

A lesion border with radiating linear strands extending into surrounding tissue. In lung, breast, and other organs it raises suspicion of malignancy because tumour infiltrates along interstitial planes.

Hazy increased lung attenuation on CT that does not obscure underlying bronchial and vascular margins. It may reflect oedema, infection, haemorrhage, or neoplasm, including adenocarcinoma spectrum lesions.

Increased lung attenuation that obscures underlying vessels and airway walls on CT. It indicates alveolar airspace filling by fluid, pus, blood, or cells and is typical of pneumonia.

Air-filled bronchi rendered visible against opacified surrounding lung. It confirms an alveolar process such as pneumonia or pulmonary oedema rather than airway obstruction or pleural disease.

Imaging of the liver in unenhanced, arterial, and portal venous phases after intravenous contrast. The phases exploit differing blood supply to characterise hypervascular tumours and detect lesions.

Loss of contrast enhancement of a liver lesion in the portal venous or delayed phase relative to surrounding parenchyma. Combined with arterial hyperenhancement it is a hallmark of hepatocellular carcinoma.

A peripheral rim of enhancement around a liver lesion seen in delayed phases, representing a fibrous capsule. It is a major imaging feature supporting a diagnosis of hepatocellular carcinoma.

A value derived from diffusion-weighted MRI that quantifies water molecule mobility in tissue. Low values suggest restricted diffusion, typical of high cellularity in tumours or infarction.

High signal on diffusion-weighted imaging caused by a long T2 relaxation time rather than true restriction. Checking the apparent diffusion coefficient map distinguishes it from genuine restricted diffusion.

Paramagnetic chelates injected intravenously to shorten T1 relaxation and enhance vessels or lesions on MRI. Risks include nephrogenic systemic fibrosis and, rarely, anaphylactoid reactions.

A rare fibrosing disorder of skin and internal organs linked to gadolinium exposure in patients with severe renal impairment. It has prompted restrictions on certain linear agents.

An adverse response to iodinated contrast medium, ranging from mild urticaria to life-threatening anaphylaxis, or a non-allergic physiological reaction. Management depends on recognition and prompt treatment.

Acute kidney injury occurring shortly after intravascular iodinated contrast administration, after other causes are excluded. Risk is highest with pre-existing renal impairment, diabetes, and dehydration.

Identification and removal of the first draining lymph node using blue dye or radiotracer, then histological assessment. It stages regional nodal disease with less morbidity than full dissection.

A standardised system describing primary tumour extent, regional nodal involvement, and distant metastasis. Accurate radiological staging determines prognosis and guides treatment selection.

Systemic or radiation treatment given before definitive surgery to shrink a tumour or treat micrometastases. Response is assessed by imaging using RECIST or similar criteria.

A standardised method for measuring tumour burden on imaging and classifying response as complete, partial, stable, or progressive disease. It enables comparison across trials and time points.

A minimally invasive technique delivering alternating current through an electrode to heat and destroy tumour tissue. It is used for small hepatic, renal, and pulmonary lesions unsuitable for surgery.

Catheter-directed delivery of chemotherapy into a tumour's arterial supply followed by embolic occlusion. It treats intermediate-stage hepatocellular carcinoma, exploiting the tumour's predominant arterial perfusion.

A CT obtained in the treatment position with immobilisation devices, used to delineate tumour and organs at risk and calculate dose distribution. It underpins conformal and stereotactic radiotherapy.