Breast cancer is the most prevalent malignant tumor among women worldwide. It is characterized by high prevalence, high death rate, high health care expenditure and low awareness rate. Research shows that the median age of female breast cancer patients in China is 48 years old, which is about 10 years earlier than that of western countries. Therefore, improving the standardized diagnosis and treatment of breast cancer is an important issue for people’s health. So first of all, let’s understand the anatomical structure and characteristics of the mammary gland. Breast tissue is mainly composed of fibrous glands (parenchyma) and connective tissue (stroma). As a gonadal organ, the breast is regulated by the level of estrogen and progesterone in the body and undergoes changes. Changes in breast fibroglandular tissue occur not only during pregnancy and breastfeeding, but also slightly during the menstrual cycle. Breast tissue is fully developed only after experiencing the 1st full-term pregnancy, and in most women fatty infiltration of breast tissue appears after the 1st breastfeeding. The breast parenchyma consists of 15-20 lobes or segments, each of which is connected to 1 duct. The terminal ductal lobular unit is the most basic tissue unit, and it consists of the extrafollicular terminal ducts, the intrafollicular terminal ducts, and the terminal alveolar ducts. The innermost cuboidal epithelial cells are arranged along the ducts. Myoepithelial cells form a discontinuous layer between the line-like arrangement of cuboidal cells and the basement membrane. The basement membrane separates the epithelial cells from the connective tissue. If the basement membrane is invaded by tumor cells, the tumor is an invasive carcinoma. Near the nipple, the cuboidal cells of the duct are replaced by squamous cells. The connective tissue within the mammary gland determines the type and density of the mammary gland and consists of interlobular and intralobular components. The interlobular connective tissue surrounds the terminal ductal lobular units, which show edematous changes under the influence of the hormones of the menstrual cycle. Since the edema phase occurs during the secretory phase of the menstrual cycle (about 7 d before menstruation), in order to avoid the interference of this sex hormone-related physiological hyperplasia in lesion detection and diagnosis, it is recommended that breast imaging examinations be scheduled 7-14 d after menstruation as far as possible when the condition of the disease permits. Currently, the methods of detecting breast cancer mainly consist of clinical examination (palpation), and imaging examinations. Clinical examination is usually possible to be detected when the lesion reaches a certain volume or when the patient develops obvious clinical symptoms, and by then the tumor has already reached a progressive stage. Currently recognized breast imaging methods include mammography, ultrasonography and MRI.