Hardware Acceleration of Beamforming in a UWB Imaging Unit for Breast Cancer Detection

The Ultrawideband (UWB) imaging technique for breast cancer detection is based on the fact that cancerous cells have different dielectric characteristics than healthy tissues. When a UWB pulse in the microwave range strikes a cancerous region, the reflected signal is more intense than the backscatter originating from the surrounding fat tissue. A UWB imaging system consists of transmitters, receivers, and antennas for the RF part, and of a digital back-end for processing the received signals. In this paper we focus on the imaging unit, which elaborates the acquired data and produces 2D or 3D maps of reflected energies. We show that one of the processing tasks, Beamforming, is the most timing critical and cannot be executed in software by a standard microprocessor in a reasonable time. We thus propose a specialized hardware accelerator for it. We design the accelerator in VHDL and test it in an FPGA-based prototype. We also evaluate its performance when implemented on a CMOS 45？nm ASIC technology. The speed-up with respect to a software implementation is on the order of tens to hundreds, depending on the degree of parallelism permitted by the target technology. 1. Introduction Prescreening tests aimed at breast cancer diagnosis dramatically reduce mortality. Mammography, the technique currently used for screening, is very effective but has a few significant shortcomings: its high cost prevents a widespread diffusion, thus limiting de facto the organization of pervasive screening campaigns; its rate of false positives in young patients is very high; its use of ionizing radiations does not allow a frequent use; the obtained images are not tridimensional. Other techniques, like ultrasound or magnetic resonance, partially solve these problems but raise other issues. None of these techniques has the characteristics required to promote a widespread diffusion and to permit frequent screening campaigns on large ensembles of individuals. One promising alternative is based on the radar principle and operates at microwave frequencies with Ultrawideband (UWB) pulses [1–3]. A set of antennas is placed around the patient's breast, and UWB pulses are sent to the breast target. The breast tumor typically exhibits a large dielectric contrast with the surrounding fatty tissue and thus reflects more the incident signal. The detection of the tumor requires, however, a significant amount of processing of the reflected signals. Figure 1 is an overview of a full UWB system for breast cancer detection. Figure 1: The UWB-based breast cancer imaging system. The inset is a