CT Scanning

A CT (computed tomography) scan uses X-rays to build detailed cross-sectional images of the body. Where a plain X-ray gives a single flat picture, CT produces a stack of thin "slices" that can be reconstructed into three dimensions. It is the best routine test for looking at bone in fine detail, which makes it especially valuable in the spine for assessing fractures, the exact shape of the vertebrae, and the position of any metalwork after surgery.

An X-ray tube rotates around you inside a ring-shaped part of the scanner while detectors on the opposite side measure how much of the beam passes through from every angle. Dense tissue like bone absorbs more X-rays and appears bright; softer tissue absorbs less. A computer combines these many angled measurements into detailed slice-by-slice images, which can then be rebuilt into three-dimensional pictures or viewed in any plane. The whole acquisition is fast, often taking only seconds of actual scanning once you are positioned.

You lie on a table that moves slowly through the ring-shaped opening — which is short and open at both ends, so CT rarely causes the enclosed feeling some people get with MRI. The scan is painless and quick. You will be asked to keep still, and sometimes to hold your breath briefly. Because CT uses X-rays, you will be asked whether you are or might be pregnant. The radiation dose is higher than a plain X-ray but is kept as low as reasonably possible, and scanning is only done when the benefit clearly justifies it.

CT is the go-to test for bony detail. It shows fractures — including subtle ones hard to see on plain X-rays — with great clarity, defines the exact anatomy before or after spinal surgery, and assesses how well a fusion has healed. It complements MRI rather than replacing it: MRI is better for discs, nerves and the cord, while CT is better for bone. The two are often used together to give a complete picture.

• —Royal College of Radiologists — iRefer: Making the Best Use of Clinical Radiology
• —UK Health Security Agency — Ionising Radiation: Patient Dose Information
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.