Ultra-Wideband Imaging for Detection of Early- Stage Breast Cancer X. Zhuge, M. Hajian, A.G. Yarovoy, L.P. Ligthart IRCTR Dept. Electrical Engineering, Delft University of Technology, Mekelweg 4, 2628 CD Delft, the Netherlands X.Zhuge@ewi.tudelft.nl Abstract—Ultra-wideband imaging for medical applications has been of interest for many years due to its high resolution and capability of detection and classification. In this paper, ultra- wideband near-field imaging is applied for detection of small malignant tumors inside breasts. Multiple antenna and focusing algorithm are used to form a spatial image of reflectivity, and to identify the presence and location of malignant lesions from their scattering signatures. The method is demonstrated by successful detection of a 2 mm diameter tumor in a three-dimensional numerical breast model. I. INTRODUCTION Nowadays the standard diagnose for breast cancer is mammography, X-ray imaging of a compressed breast. Mammography has been proved to be quite sensitive to the presence of lesions in the breast. However, associations of this diagnose method with uncomfortable breast compression and unhealthy exposure to ionizing radiation may prevent patients from early-stage examination, which is the best and effective phase for medical treatment. These concerns provoke motivation for engineers to develop new breast imaging techniques. Ultra-wideband imaging is an important alternative for mammography. The procedure is safe, simple and more comfortable for patients. The feasibility of UWB microwave imaging relies on two fundamental properties. Firstly, malignant tumors that have higher water content have higher dielectric properties than normal breast tissues, which have relatively lower water content. Therefore, strong scattering takes place at the boundary between normal tissue and lesions. Secondly, microwave attenuation in normal breast tissue is less than 4 dB/cm up to 10 GHz. This permits microwave devices to have enough sensitivity and dynamic range to detect early-stage tumors in this frequency band. By choosing an appropriate bandwidth, UWB technique can ensure images with high sensitivity and resolution. Microwave imaging for breast cancer detection has been proposed and proven experimentally [1]-[7]. By using monostatic scanning system and MIST beamforming [1]-[3], malignant tumors are detectable by focusing backscattered signals while compensating for dispersive propagation through human body. In this paper, we proposed a multistatic UWB near-field imaging technique to detect tumors inside breasts. The proposed imaging technique uses a 2D synthesized aperture array and a generalized near-field algorithm. This provides breast imaging with full 3D resolution and faster scanning. The imaging technique is subject to a number of assumptions. The dielectric properties of tissues are known (i.e., the complex permittivity as a function of frequency) from medical experiments. The normal breast tissue is supposed to be perfectly homogeneous except the region occupied by the malignant tumors. This paper is organized as follows. Section II introduces the formulation of the proposed UWB imaging technique. Section III describes the three-dimensional numerical model and preliminary processing for further imaging. In section IV the numerical results of the imaging technique, based on the proposed method and MIST beamforming are presented and compared. Conclusions are given in section V. II. FORMULATION The geometry of the setup is illustrated in Fig. 1, in which a transmit antenna illuminates the breast while an antenna array receives simultaneously the scattered field. The transmit/receive array mechanically moves around the breast to create a synthetic cylindrical aperture. Antennas are assumed to be point like and isotropic. The operational bandwidth is selected from 1 to 10 GHz. It is important to note that the observation distance will be within the near-field of the target. From imaging viewpoint, the target is the breast surface illuminated by the radar. Consequently, the image has to be focused using space-variant near-field focusing technique. Merging the breast in a tissue-mimicking material could be an option in order to minimize the distortion caused by complex refraction and also couple more power into the breast tissue. A. Scenario with tissue-mimicking dielectrics Considering a point like tumor in the breast, its associated phase story will be defined by the electrical length of the two- way path travelling from the transmit antenna to the tumor, and scattering back to one of the receive antennas. When the breast is merged in a tissue-mimicking dielectric, we can assume that waves can pass breast boundary without refraction. This approach simplifies the estimation of propagation. Meanwhile, more power will be coupled into breasts, which increases the signal-to-interference-noise ratio (SINR) and eases the requirement of the dynamic range. The 978-2-87487-004-0 © 2007 EuMA October 2007, Munich Germany Proceedings of the 4th European Radar Conference 39