1 of 3 AbstractOne recent application area of EIT is the detection of breast cancer by imaging the conductivity and the permittivity distribution inside the breast. The present gold standard for breast cancer detection is X-ray mammography, and it is desirable that the EIT and the X-ray mammography use the same geometry. This paper presents a simplified model of the mammography geometry for EIT imaging. The mammography geometry is modeled as a rectangular box with electrode arrays on the top and bottom planes. A forward model for the electrical impedance imaging problem is derived for the homogeneous conductivity distribution and validated by experiment using a phantom tank. The effect of unmodeled surface on the sides of the electrodes is studied. KeywordsEIT, Electrical impedance, Breast cancer, Mammography. I. INTRODUCTION Electrical impedance tomography (EIT) is a technique for determining the electrical conductivity and permittivity distribution within the interior of a body from measurements made on its surface. Typically, currents are applied through electrodes placed on the bodys surface and the resulting voltages are measured. Reconstruction algorithms are used to compute the distribution of the conductivity and permittivity inside the body from the current and voltage data measured at the electrodes [1]  [3]. One recent application area of EIT is the detection of breast cancer by imaging the conductivity and the permittivity distribution inside the breast. It was reported in [4]-[6] that the conductivity and the permittivity of the tumors differ significantly from the normal tissues. These studies suggest that EIT is a promising modality to image the breast for malignancies 1 . Electrical impedance imaging has been used clinically to screen for breast cancer using a commercial imaging device called T-SCAN [7]. The T- SCAN is an FDA approved device which uses a hand-held probe carrying a rectangular electrode array. The probe is pressed on the breast, flattening it against the chest wall. A constant voltage is applied between the probe electrodes and a distant ground electrode held in a hand, and two- dimensional images of the currents through the electrode array are displayed. A breast cancer imaging system using EIT technology was also reported in [8], where a hand-held probe carrying a planar circular array of electrodes is used, and the probe is pressed on the breast in a similar way as in T-SCAN. In the work by Kerner et al. [9], clinical imaging results of women obtained using a multi-frequency electrical impedance spectroscopy system were presented, where the patient lies on a bed face down, and a ring-like electrode array is placed around the breast. An algorithm was presented in [10] for the reconstruction of three dimensional conductivity distributions for a geometry similar to that of [7] and [8], but using a planar rectangular array of electrodes and multiple current sources. These studies have suggested that EIT can be used in the diagnosis of breast tumors. A Simplified Model of Mammography Geometry for Breast Cancer Imaging with Electrical Impedance Tomography Myoung H. Choi 1 , Tzu-Jen Kao 2 , David Isaacson 3 , Gary J. Saulnier 4 , Jonathan C. Newell 2 1 Division of Electrical and Computer Engineering, Kangwon National University, Korea 2 Department of Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, New York 3 Department of Mathematical Sciences, Rensselaer Polytechnic Institute, Troy, New York 4 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York The present gold standard for breast cancer detection is X-ray mammography. The breast is compressed between two radiolucent plates and X-ray images of the breasts are taken and analyzed. For the purpose of comparing the results from the X-ray mammography and the EIT imaging, it would be highly desirable to use the geometry of the X- ray mammography in the EIT. If the two imaging modalities used the same geometry, not only would it be easier to analyze the EIT images, but also the EIT images could augment the two dimensional X-ray mammograms by providing three dimensional images of the tissue being imaged. This could provide additional information on the location of the tumor if subsequent biopsy is needed. For this mammography geometry, the distinguishability has been studied experimentally in [11], where it was reported that multiple current sources method was superior to the single current source method or the single voltage source method. This paper investigates a simplified model of the mammography geometry. The mammography geometry is modeled as a rectangular box with electrode arrays on the top and the bottom planes. A forward model of the electrical impedance imaging problem is derived for the homogeneous conductivity distribution and validated by experiment using a phantom tank. The effect of electrode thickness and the resulting electrode side surfaces is also studied. II. FORWARD MODEL In X-ray mammography, the breast is compressed between two radiolucent plates and X-ray images of the breasts are taken [12]. A schematic diagram is shown in Figure 1. In order to image the electrical impedance distribution of the breast, electrodes need to be placed so 1 This study was supported in part by CenSSIS, the Center for Subsurface Sensing and Imaging Systems, under the Engineering Research Center Program of the National Science Foundation (Award number EEC- 9986821).