The radiation dose of a chest CT is usually about 8 mSv, while the radiation dose of an ordinary chest X-ray is only about 0.02 mSv, and it varies for different parts of the examination and different examination methods. With the improvement of people’s health awareness, the current scanning methods try to choose low-dose scanning methods, early lung cancer screening are selected to scan with low-dose spiral CT, and the radiation dose of some chest CT is only about 3-4 mSv. Although the radiation dose of chest X-ray is low, the information that can be obtained is relatively small and easy to be missed. In contrast, chest CT can clearly show the lung parenchyma and the lesions in the mediastinum, so it is not easy to miss the diagnosis, and CT is still the first choice for chest examination.