Ultra-Wideband Pulse-Based Microwave Imaging for Breast Cancer Detection: Experimental Issues and Compensations

Recent research based on numerical modeling (Bond, 2003; Xu, 2001) that ignored hardware characteristics and simple experiments using homogenous breast phantoms (Sill, 2005; Xu, 2004) have shown the potential of ultra-wideband to detect early stage breast cancer. However, clutter interference from heterogeneous breast tissues and hardware characteristics like pulse jitter, finite dynamic range and precision for signal acquisition can severely degrade the detectability of breast tumors. This chapter discusses the experimental issues encountered and compensation methods used to improve the detectability of tumor. In order to bridge the gap between numerical simulations and experiments, it is important to identify the experimental issues before conducting experiments with more realistic breast phantoms so that the source of imaging artifacts can be identified and compensated. An ideal imaging scenario is first created where the simple sum-and-delay algorithm (Xu, 2001) is working perfectly. In this ideal scenario, the breast phantom is round and symmetrical such that the averaging method can perfectly remove the skin reflection. The breast medium is homogeneous such that propagation of signal in the medium is constant with accurate delay time estimation. Skin is approximated by a single interface (air to breast phantom) because its thickness is small compared to UWB pulse width in space. In this chapter, several important experimental issues are discussed.  Impulse Generator – Pulse Jitter Artifact  Real Time Oscilloscope – Limited Dynamic Range  Breast Phantom Positioning Error – Ring Artifact  Signal Loss Compensation – Noise Amplification  Filtering and Correlation – Noise Reduction  Averaging and Antenna Number – Signal SNR vs Image SNR To facilitate the discussion, the experimental setup will first be described in the following subsection 1.1. Experiments discussed in this chapter are conducted in time domain using an impulse generator and a real-time oscilloscope.