Ultrasound is primarily used is to help identify and diagnose breast abnormalities detected by a physician or patient on a physical exam. It is also used to characterize potential abnormalities seen on mammography often times to determine if a potential breast abnormality is a benign cyst (fluid-filled) or is solid (which may be a non-cancerous lesion or a cancerous tumor). If a potential breast abnormality is visualized with ultrasound, a needle aspiration/core biopsy may be performed under ultrasound guidance. Ultrasound is often the initial imaging test for women younger than 30 years of age whether pregnant or not because ultrasound does not utilize ionizing radiation.