For many CT scans it will be recommended that you have an injection of intravenous contrast.
This allows much better differentiation of the soft tissues and can also help define the type of lesion seen on the scan. Contrast is necessary to perform angiogram studies. Overall this injection is relatively safe.
To have contrast, a small plastic cannula is placed in a vein in your arm before the scan. The contrast looks clear and will be injected through the cannula during the scan. At this time you may notice a sensation of warmth and a metallic taste in the mouth which lasts for a minute or two. Occasionally some people may feel nauseated. These feelings are not the same as an allergic reaction. The contrast is excreted by your kidneys very rapidly and will not stay in your body.
You will be provided with an information sheet about contrast and asked to fill out a questionnaire which will alert our staff and doctors about any increased risks you may have in relation to the contrast injection. This is an iodine based substance and if you have a known iodine allergy you are likely to be allergic to the contrast. If you have no known allergy to contrast there is a small risk of allergic reaction. This is still possible even if you have had the contrast before without a problem. A mild allergic reaction occurs in 1/1000 injections and includes a rash, hives or sneezing. More severe reactions such as difficulty breathing are less common. A severe life-threatening reaction is extremely rare (1 in 170,000). Each site has equipment and staff trained to deal with any reaction.
It may not be appropriate to administer contrast if your kidneys are not working properly. As the X-Ray contrast dye contains small amounts of free iodine, patients with Graves disease or multinodular goitre are at a slight risk of developing thyroid toxicosis, though this is also rare. We may need to obtain a blood test result of your kidney function prior to the scan.
You will have plenty of opportunities to discuss the injection with our staff so please raise any concerns you have with them prior to your scan. While there are some associated risks, in many cases having the injection is necessary to answer the clinical question. It is not possible to do an angiogram study without contrast.