MR has been widely used abroad for screening and diagnosis of breast diseases because of its high sensitivity in the diagnosis of breast diseases, which can detect lesions of about 3 mm in the breast, and the advantage of no ionizing radiation. However, it is important to choose the appropriate time window for mammography. The blood circulation in the female breast follows hormonal changes, with the result that the contrast agent used in mammography varies with the different phases of the menstrual cycle, and this effect is lowest in the second week of menstruation and highest in the first and fourth weeks of menstruation. Therefore, the best time window for breast MR exams is the second week after menstruation, followed by the third week, while avoiding the first and fourth weeks of breast MR exams as much as possible.