Mammography is first step in evaluating breasts, but in some instances, it cannot tell whether a growth is benign or cancerous. MRI and ultrasound may be used as a next step, but a biopsy allows for a definite determination. Instead of a surgical biopsy, many women are opting either stereotactic biopsy, ultrasound-guided biopsy or MRI-guided biopsy. In these less invasive methods, a hollow needle is passed through the skin into the lesion with the help of imaging equipment. The small sample is analyzed to see if the lesion is malignant or benign, so that treatment can begin.