Torso Volume and Breast Cancer Imaging with Electrical Impedance Tomography

Prof. David Isaacson

This project is a collaboration between Center for Integrative Biomedical Computing and Prof. David Isaacson of the Mathematics Department, and the Electrical Impedance Imaging Laboratory, at Rensselaer Polytechnic Institute (RPI) in Troy N.Y. Electrical Impedance Imaging, and more specifically its tomographic variant Electrical Impedance Tomography (EIT), is a relatively cheap, safe, and non-invasive method to image functional and metabolic properties of the body. The approach taken by the RPI laboratory is to inject current from a set of electrodes on the surface of the region to be imaged, and measure the resulting voltage. The currents and voltages are then fed into an imaging algorithm which reconstructs the conductivity (or more generally admittance or impedance) map of the volume being interrogated. EIT has been applied to a number of diagnostic problems as well as a precursor to inverse bioelectric problems.

The current focus of the RPI lab is the detection and characterization of breast tumors. There is considerable evidence that the impedance of tumors, and in addition the frequency dependence of their impedance, has high contrast with non-malignant breast tissue, and even some commercial devices that attempt to exploit this fact, as described below. Prof. Isaacson and his colleagues are currently engaged in theoretical and engineering research to more fully exploit this high contrast, and have current NIH support to develop a system for EIT and spectroscopy of breasts for use in conjunction with mammography, including clinical testing in the laboratory of Dr. Daniel Kopans at Mass General Hospital in Boston, MA, a well-known leader in the field of breast cancer diagnosis.

Prof. Isaacson and his colleagues Profs. Jon Newell and Gary Saulnier have a long-term effort in the development of hardware and algorithms for EIT. Their team is an international leader in the development of this technology and its application to clinical problems. They have built hardware and software needed to test these systems, explore their ultimate limits, and test them in several clinical applications. Prof. Isaacson is also a recognized leader in the field of theory and algorithms for inverse problems.

Electrical impedance imaging systems apply patterns of electrical currents to electrodes placed on a portion of the surface of a body. They measure and record the patterns of resulting voltages on these electrodes. From this electrical data they reconstruct and display an approximation of the electrical conductivity and permittivity inside a portion of the body surrounded by or near the surface electrodes.

Since lungs filled with air have a considerably smaller conductivity then lungs depleted of air, ventilation may be monitored by EIT systems. Since lungs filled with blood have a larger conductivity then lungs depleted of blood, perfusion may also be monitored by EIT systems. Since hearts filled with blood have a greater conductivity then hearts depleted of blood, cardiac performance may be monitored by EIT systems. Since many breast tumors have a significantly higher conductivity then surrounding normal tissue, the diagnosis of breast cancer may be improved by electrical impedance images of the breast's internal electrical conductivity. In fact, a non-tomographic electrical impedance device, the T-Scan 2000, has been reported to be useful as an adjunct to X-ray mammogram imaging and has received FDA approval for this purpose. However, this system does not take full advantage of either the impedance contrast or the localizability that would be afforded by a tomographic system such as the one that Prof. Isaacson and colleagues are now developing and testing.