CT scan

A CT (computed tomography) scan is like slicing a loaf of bread and looking at each slice on its own. Instead of one flat shadow, the scanner spins an X-ray tube around the body while a computer reconstructs hundreds of thin cross-sectional images. Lying still for a few seconds, the patient is imaged in fine detail from collarbone to upper abdomen, and the slices can be stacked to recreate the chest in three dimensions.

Because the overlap that plagues a plain radiograph is removed, CT shows lung tissue, airways, blood vessels, lymph nodes and the pleura with far greater clarity. It can resolve nodules a few millimetres across, characterise the texture of diffuse lung disease, and map exactly where a tumour sits relative to vital structures. Intravenous contrast dye can be added to make blood vessels stand out, which is essential for some studies.

The trade-off is radiation dose and cost. A chest CT delivers many times the radiation of a single plain film, so it is ordered when the added detail will change management, not reflexively. Specialised protocols tailor the scan to the question — high-resolution thin slices for diffuse disease, timed contrast for the pulmonary arteries, or low-dose technique for lung-cancer screening.