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7 How is the procedure performed?Prior to, or on the day of the procedure, you may be asked to complete a questionnaire to ensure your safety during this procedure. A nurse or technologist will insert an intravenous (IV) catheter into a vein, usually in your arm or hand. Rarely, a small amount of blood is withdrawn through the catheter or finger stick to test kidney function. The technologist begins by positioning you on the CT exam table, usually lying flat on your back. Straps and pillows may be used to help you maintain the correct position and remain still during the exam. An automatic injection pump connected to the IV will inject contrast material at a specified rate. In some cases, especially in children and patients with fragile and small veins, the contrast may be hand-injected using a syringe. During scanning, the table is positioned at the start point of imaging and will then move through the opening of the machine as the actual CT scanning is performed. A single scan takes approximately one to two minutes, but multiple scans may be required. During CT angiography of the heart, electrocardiogram (ECG) leads (sticky patches) will be placed on your chest to synchronize CT scanning with your heartbeats. If your heart beats too fast, it may be temporarily slowed down with medication to obtain clear images of the heart. If you receive heart rate control medication, you will be closely monitored during and after the procedure. You may be asked to hold your breath during the scanning. Any motion, including breathing and body movements, can lead to artifacts on the images. This loss of image quality can resemble the blurring seen on a photograph taken of a moving object. Occasionally, sedation is required for children to keep them still during scanning. Your doctor will help determine if sedation is needed and, if so, will arrange it. Preparation for sedation may include no eating and drinking for several hours before the exam to prevent complications. Also, an extended close observation following the scan may be required until the medication used for sedation wears off. When the exam is complete, you will be asked to wait until the technologist verifies that the images are of high enough quality for accurate interpretation. Following the exam, the technologist will remove the intravenous catheter and place a bandage over the needle puncture site. The entire CT angiography exam may be over within a few seconds. However, the actual time in the scanner room may be longer, as the technologist will have to appropriately position you on the table, verify placement of the IV line, do preliminary imaging, and set up the scanner and contrast injection pump settings based on the part of the body being imaged. CT angiography is rarely performed in children as they are more sensitive to radiation than adults. For children and for adults of reproductive age, radiologists administer low radiation dose CT scans with dose reduction measures.
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