The radiation level of chest X-ray is the lowest for other radiological examination methods, but the exact amount of radiation depends on the examination area, the type of equipment, the time of projection and the method of projection. Take the type of machine as an example, the radiation level of CR is relatively high, around 0.3mSv, while the radiation level of DR, which is a digital radiography system, is the lowest, generally around 0.023mSv, because the radiation level may vary depending on the scanning site and time. But no matter which type of examination, as long as it is within the range of medical reasonable examination are far below the national safety threshold, so patients do not need to worry too much when they undergo such examinations.