Thoracic CT (computed tomography) is an imaging method that uses x-rays to create cross-sectional pictures of the chest and upper abdomen. The complete scan takes 30 seconds to a few minutes. Certain CT scans require a special dye, called contrast, to be delivered into the body before the test starts. Contrast highlights specific areas inside the body and creates a clearer image. If your doctor requests a CT scan with intravenous contrast, you will be given it through a vein (IV) in your arm or hand. A blood test to measure your kidney function may be done before the test. This test is to make sure your kidneys are healthy enough to filter the contrast.