Ultrasound and MRI have no radiation to people, while X-ray photography (including general X-ray photography, CR and DR), CT and PET are used in the same area, and the amount of radiation is from the largest to the smallest: CT>PET>general X-ray photography>CR>DR. Different parts of the body have their own advantages, and there is a certain selection rule, but do not make a generalization, and the specific should be different from person to person and from situation to situation. For superficial organs and abdominal organs, ultrasonography such as B-ultrasound is preferred; for cranio-cerebral trauma, tumors of middle ear, nose and throat, bones and lungs, and some subtle bone trauma, CT is preferred and enhanced scan is added if necessary; for brain tumors and lesions, spinal cord lesions, joint and ligament trauma and lesions, and some subtle occult fractures, magnetic resonance imaging (MR) is preferred. MR). The “ten-day rule”: no X-ray examination within 10 days after the onset of menstruation Women should refrain from X-ray examination during special periods such as pregnancy, pregnancy preparation and menstruation: mammography should not be done for women under 35 years of age, mammography should be prohibited for girls under 15 years of age during their developmental period, and should be used with caution for women during pregnancy and in preparation for pregnancy; before the age of 40 Mammograms more than once a year can do more harm than good; after the age of 40, mammograms 1 to 2 times a year can do more good than harm. It is now advocated to use ultrasound instead of X-ray mammography for screening, and only use X-ray or MR for further examination. Women who are planning to get pregnant should wait six months after the X-ray examination before getting pregnant to avoid fetal malformation due to inadvertent medical examination to the maximum extent possible. Women of childbearing age should follow the “10-day rule”, i.e., no X-ray examination within 10 days after the onset of menstruation. Hysterosalpingography should be performed 5-10 days after menstruation (some experts believe 3-7 days) and pregnancy should be avoided for 3 months after the test.