Breast ultrasound is the most common imaging test for the breast in outpatient clinics. The advantages are that it is suitable for women of all ages, easy to locate tumors, no radiation hazards, can be reviewed within a short period of time, and is less expensive (compared to mammography and MRI). Mammography is a recognized imaging modality for early screening of breast cancer, with the advantage of early diagnosis of breast cancer, especially when the tumor is small. For women between 35 and 40 years old, if they have high risk factors for breast cancer (e.g. history of breast cancer in the immediate family, early menarche, etc.), mammography can also be performed, but the cost is slightly higher (compared to ultrasound).