AN54.1-4 | Radiodiagnosis — Glossary

Degree of X-ray absorption by a tissue; determines its appearance on X-ray from white (radiopaque) to black (radiolucent)

CT density measurement scale: water = 0, bone +400 to +1000, fat -100, air -1000; named after the inventor of CT

Loss of the normal border between two adjacent structures of similar density on X-ray; indicates disease in the adjacent tissue

Free air in the peritoneal cavity; seen as a crescent under the diaphragm on erect X-ray; indicates visceral perforation

Insoluble radiopaque contrast agent used to coat the GI mucosa; contraindicated if perforation is suspected (use water-soluble iodine-based contrast instead)

Barium coating the mucosa plus air distension of the lumen; provides superior mucosal detail for detecting polyps and early cancers

Endoscopic retrograde cholangiopancreatography — endoscopic cannulation of the ampulla of Vater for imaging and treating biliary and pancreatic duct pathology

MR cholangiopancreatography — non-invasive MRI technique using heavily T2-weighted sequences to visualise the biliary and pancreatic ducts

Intravenous pyelogram — IV contrast excreted by the kidneys outlining the renal pelvis, calyces, ureters, and bladder

HSG — contrast injected through the cervix to outline the uterine cavity and fallopian tubes for assessing tubal patency in infertility

MRI sequence where fat appears bright and fluid appears dark; best for anatomical detail

MRI sequence where fluid appears bright (white) and muscle appears dark; best for detecting pathology and fluid collections

Administration of iodine-based IV contrast during CT that highlights vascular structures and increases visibility of tumours

Failure of the lower oesophageal sphincter to relax; barium swallow shows dilated oesophagus with 'bird beak' narrowing at the cardia

Classic barium enema appearance of colonic carcinoma showing circumferential narrowing with overhanging edges

Horizontal interface between air above and fluid below seen on erect abdominal X-ray; multiple air-fluid levels indicate bowel obstruction

Lateral border of the psoas major muscle visible on abdominal X-ray; obliteration suggests retroperitoneal pathology

Digital subtraction angiography — pre-contrast image digitally subtracted from the post-contrast image to show only the contrast-filled vessels

18F-fluorodeoxyglucose — radioactive glucose analogue used in PET scanning; accumulates in metabolically active tissues like tumours

Stone in the common bile duct; seen as a filling defect on ERCP or as duct dilation on MRCP/ultrasound

Property of elastic arteries (aorta) to stretch during systole and recoil during diastole, maintaining continuous blood flow