The radiation dose of CT is much higher than that of X-ray, for example, the radiation dose of an ordinary chest X-ray is 0.02 mSv, the radiation dose of a knee X-ray is 0.005 mSv, the radiation dose of a head CT scan is 2 mSv, the radiation dose of a chest CT scan is 8 mSv. Therefore, the radiation dose of CT is much higher than that of X-ray, but for these two examination methods, the resolution of CT is higher than that of X-ray. CT can show subtle lesions, such as tiny nodules of a few millimeters in the lung, which can be detected by CT but not by X-ray, and CT can obtain the original cross-sectional images and can also show the lesions from multiple angles through 3D reconstruction, while X-ray cannot.