Low-dose spiral CT uses the smallest scan area, the lowest dose, and the least amount of X-rays to make a diagnosis of a lesion. Since the radiation dose of a conventional CT scan is about 3-5 mSv, low-dose CT is about 1 mSv, and the radiation dose can be reduced by 2/3, and accurate diagnosis of lesions can be made. Compared with conventional CT scan, one of the advantages is that the dose is small, so that the patient is exposed to less radiation and the tiny nodules can be clearly displayed. It is routinely used for physical examinations or for the follow-up of small nodules in the lungs, so that patients can get an accurate diagnosis without receiving more doses of X-rays.