CT with Contrast

A CT with contrast is a CT scan in which an iodine-based dye is given, usually into a vein, to make blood vessels and certain tissues show up more clearly. Plain CT is excellent for bone but less informative about soft tissues; adding contrast improves the visibility of things like blood vessels, areas of infection or inflammation, and some tumours. In spinal work it is used in selected situations rather than routinely.

The iodine in the dye absorbs X-rays strongly, so anywhere it travels appears brighter on the scan. Given into a vein, it fills the blood vessels and then passes into tissues that have an abundant or leaky blood supply, such as inflamed or tumour tissue, making them stand out against their surroundings. Images are timed to catch the dye in the vessels or tissues of interest. The dye is then cleared from the body through the kidneys over the following hours.

A small cannula is placed in a vein, usually in the arm, and the dye is injected — often by a pump — during the scan. Many people feel a warm flush spreading through the body and a metallic taste for a few seconds; this is normal and passes quickly. Because the dye relies on the kidneys, your kidney function may be checked beforehand, and you should mention any previous reaction to contrast, asthma, or if you are pregnant or breastfeeding. Otherwise the scan is the same quick, painless process as a standard CT.

Contrast lets CT answer questions about soft tissue and blood supply that plain CT cannot — for example mapping blood vessels before complex spinal surgery, or helping characterise an infection or tumour. For most soft-tissue spinal questions, however, MRI with its own contrast is usually preferred, so CT with contrast is used in specific circumstances chosen by the specialist rather than as a standard spinal scan.

• —Royal College of Radiologists — Standards for Intravascular Contrast Agent Administration
• —Royal College of Radiologists — iRefer: Making the Best Use of Clinical Radiology
• —UK Health Security Agency — Ionising Radiation: Patient Dose Information

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.