The main goal of ultrasound tomography (UT) is to provide both a highcontrast imaging and a multi-parametric imaging. Within the frame of soft-tissueimaging, we focus our application to breast inspection for early stage cancerdetection. Conforming with breast anatomy, ANAIS (ANAtomical Imaging andInterventional System) prototype is designed including a semicircular antennawhich enables imaging of ductolobular structures sensitive to cancer initiation.The 200-mm diameter half-ring transducer contains 1024 elements with 3-MHzcenter frequency and 2.25-MHz (6 dB) bandwidth. Chirp excitation is used toimprove contrast with pulse compression method. Performed with a needlehydrophone, calibration studies yield system characteristics such as fielddistribution or transducer element localization. Taking advantage of a nearfield reconstruction algorithm, tomographic images of thin wire and of breastanthropomorphic phantom (CIRS) are presented. The low frequency approach and thehigh density of the ring antenna provide interesting results that, as weexpect, may still be enhanced. © 2010 IEEE.