The full name of CT is Computed Tomography. The difference is that CT is a tomographic scan of a certain part of the body, and the unabsorbed X-rays are received by a detector and processed by a computer to form a clear image. Ordinary X-rays can only do transmission, for example, anterior-posterior, left-right X-rays of the chest. Since the lungs are mainly alveoli containing rich air and tumors in the lungs are substantial tissues, the density of both is very different and ordinary X-rays can show them clearly, but liver tissues and liver cancer tissues are substantial and ordinary X-rays cannot show the tumors. CT is to show the section of liver with thickness of every 0.5~1cm, avoiding the overlap of liver to prevent front and back, left and right, thus can clearly show the size, shape and relationship between liver cancer and surrounding tissues. Usually, it can show liver cancer with a diameter of 2cm or more, and if a 0.5cm thin scan is done, it can show tumors with a diameter of 1.0cm. Moreover, the enhancement scan can also help in the differential diagnosis of liver cancer.