Microwave Tomographic Imaging of the Heart in Intact Swine

Abstract

Microwave tomography is a new imaging modality based on differentiation of tissue dielectric properties. The main objective of our research project is to develop a microwave tomographic approach for non-invasive assessment of functional viability of myocardial tissue, including detection of infarcted tissue. Imaging of the heart in intact, euthanized animals is the first step towards this objective. When microwave tomography is used to image the thorax of intact animals, it faces two major problems: — the structural complexity of the rib area with high reflection of electromagnetic (EM) radiation from its boundaries, and the potential for high reflection of EM radiation from the lung, filled with air. In addition, when a targeted object (a heart in our case) is located inside of a larger high scattered object (a torso), the level of EM field scattered by the internal object has to be technically detectable from the stronger EM field scattered by torso. The goal of this research study is to evaluate the degree of complexity of these problems, to understand some technical requirements for clinically applicable MWT system and to demonstrate the feasibility of microwave tomography for imaging of the heart in intact mammals using a swine model. Experiments were conducted on pigs (Yorkshire Domestic Cross/Farm Pigs) using a modified three-dimensional (3D) microwave tomographic (MWT) system operating at frequency 0.9 GHz. The presence of the heart in torso changes the amplitude of EM field by about 10–20% and changes the phase of EM field by about 7–10 degrees (mean absolute differences). Microwave tomographic images of swine torso and intact euthanized animals were obtained and discussed. Images reveal intra-torso and organ anatomy, including the heart and left ventricular chamber.