Computed tomography, or CT, is a method of imaging the inside of the body. It involves taking a series of images using X-rays, which are then combined by a computer to create a detailed 3D image. During a CT scan, the patient passes through a donut-shaped device relatively quickly.

An older term for a CT scan is a CAT scan, which stands for computed axial tomography. Both terms refer to the same imaging technique, though "CT scan" is now the more commonly used term.

Sometimes, contrast dye is used to make certain structures more visible on a CT scan. In some cases, the dye is administered through an IV. In most people, the kidneys naturally clear the contrast dye from the body within 24 hours. There is also an oral contrast option, where the patient drinks the dye to outline the digestive tract on the scan.

In some situations, it is useful to have CT scans taken both with and without contrast. This process involves first taking images without the contrast dye. After the dye is administered, another set of images of the same tissues is taken. Comparing these two sets of images allows radiologists to better distinguish between different types of tissue.

A multiphase CT scan involves taking several images at different intervals. First, an image is taken without contrast. After contrast is administered through an IV, additional images are captured at two or three different time points. This technique tracks the movement of the dye through the vascular system, helping radiologists identify specific tissue types and assess blood flow.