Objective 1: Validate the sensitivity, specificity, positive predictive value and negative predictive value of optical tomography/US for distinguishing benign and early stage malignant breast tumors. Approximately 300 patients who will undergo ultrasound-guided biopsy are being recruited to this study from the University of Connecticut Health Center and Hartford Hospital. The total hemoglobin concentration and blood oxygen saturation will be the measured indices and the biopsy results will be used as the 'gold' standard.