[Medical Q&A] Are there risks associated with enhanced CT scans? What preparations do you need to make before the scan?

Planner: Chinese Medical Association

Reviewer: Wang Xuan, deputy chief physician, Peking Union Medical College Hospital

Enhanced CT scan is based on ordinary CT scan, through intravenous injection of contrast agent (also known as "contrast agent"), to form a more obvious contrast between the diseased tissue and normal tissue, so as to show the lesion more clearly and improve the accuracy of diagnosis. However, because of the use of contrast agent, there are certain risks compared with ordinary CT scan.

First, enhanced CT involves exposure to ionizing radiation, which may damage cell DNA and increase the risk of cancer. However, modern CT equipment has been designed to reduce the radiation dose as much as possible, and the radiation brought by a single or occasional CT examination is usually not enough to cause serious health problems. Secondly, enhanced CT often requires the injection of iodine-containing contrast agents, and some patients may have allergic reactions to iodine agents. Mild cases may experience symptoms such as rash and itching, while severe cases may cause life-threatening reactions such as difficulty breathing and shock. Therefore, for patients with a history of allergies, doctors will conduct detailed allergy history inquiries before the examination and prepare appropriate first aid measures. In addition, contrast agents may also have a certain impact on renal function, especially for patients with kidney disease, special attention should be paid to the dosage of contrast agents used and subsequent monitoring.

It is critical to be fully prepared before undergoing an enhanced CT examination. First, patients should inform their doctors in detail of their medical history, allergy history, and medications they are taking, especially allergies to iodine agents, seafood, etc. Secondly, fasting is required 4 to 6 hours before the examination. This is to prevent nausea and vomiting after the injection of contrast agents, which may lead to aspiration of vomitus and cause serious consequences such as suffocation. Thirdly, patients also need to remove metal objects on their bodies, such as necklaces and watches, to avoid artifacts during the examination. Finally, relax. Excessive tension may cause vasoconstriction and increase the difficulty of venous puncture. During the examination, patients are also required to cooperate in keeping their body position still and relaxing, which will help to better complete the examination.