1 You may be asked to remove hairpins, jewelry, eyeglasses, hearing aids and any removable dental work that could obscure the images.  You MAY be asked not to eat anything 4 hours before your exam if you will receive contrast material for a CT scan. Contrast is a substance that highlights the tissues and blood vessels. You may continue to drink clear liquids (water, clear juices, or tea) until your scan. It is important for you to drink often before and after your scan. Drinking water helps remove contrast from your kidneys.