An injection of intravenous contrast is recommended for many CT scans. Intravenous contrast allows better differentiation of the soft tissues and can help define the type of lesion seen on the scan. Contrast is necessary to perform angiogram studies. Overall, this injection is relatively safe.
To be given contrast, first you will have a small plastic cannula placed in a vein in your arm. 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 nauseous (a bit sick). These feelings are different from an allergic reaction. The contrast is excreted by your kidneys rapidly and will not stay in your body.
You will be given 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 clinic 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 get a blood test result of your kidney function before the scan.
You will have plenty of opportunities to discuss the injection with our staff, so please raise any concerns you have with them before 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.
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