The benefit of developing a way to use ultrasound for target localization is clear. Identification of the target would no longer be dependent on unreliable external landmarks but now on direct internal information. As a consequence, targeting errors, most commonly associated with patient positioning, could be significantly reduced or practically eliminated. Thus, we propose to study the ability of USEI to detect and characterize the lumpectomy bed in-vivo using CT data as ground truth. We will pursue our work in two specific aims: