Study of the Effects of Changing Physiological Conditions on Dielectric Properties of Breast Tissues

This paper addresses the changes in the physical characteristics (temperature and water/blood content) of breast tissue under different physiological conditions. We examined ex vivo specimens of breast tissue excised at the time of surgery to study the effects of physiological conditions on dielectric properties. We observed that the dielectric properties strongly depend on tissue physiological state. When the biological tissues undergo physiological changes, such as those due to disease or those induced by external changes such as variations in the environmental temperature, the microscopic processes deviate from their normal state and impact the overall dielectric properties. This suggests that microwave imaging might be used to monitor the physiological conditions of the body. 1. Introduction In recent years microwave imaging (MWI) has attracted significant interest for biomedical applications. This is due to the fact that microwave signals are able to transmit through and be absorbed and reflected by biological tissues. The difference arises from molecular (dielectric) rather than atomic (density) based interactions of the microwave radiation with the target when compared with X-ray imaging. These factors make microwaves suitable to be used for diagnosis in medicine, especially for the imaging of the biological structures which depend on the tissue’s dielectric properties, that is, the permittivity and the conductivity. The permittivity of a material is linked to the material’s ability to change polarity. Polar compounds, like water, have a high permittivity. Conductivity is related to the amount of electricity that can be transferred through the material. Physiological conditions can have pronounced effects on a tissue’s dielectric properties. Dielectric properties of biological tissue have been investigated for almost eighty years [1–10]. It has been twenty-eight years since Chaudhary et al. measured the dielectric properties of healthy and malignant breast tissues within 3？MHz–3？GHz [2]. Their studies generated interest in the possibility of using nonionizing electromagnetic waves to image the breast to detect tumours. In 1994, a similar study was repeated by Joines et al. [7]. A literature survey by Gabriel et al. reports the characterization of biological tissues over the range of 0.01–20？GHz [5, 6]. In 1988, Surowiec et al. [11] found that the tissue at the infiltrating edge of the tumour had increased dielectric properties. Recent extensive characterization of the dielectric properties of different tissue types, including normal, malignant,