Prototype of a Low-Cost Impedance Tomography Based on the Open-Hardware Paradigm

Introduction

Electrical Impedance Tomography (EIT) is a noninvasive and nonionizing technology for tomographic imaging. It is based on the application of a low amplitude, high frequency, alternating electric current pattern through electrodes (Tehrani, Jin, Mcewan & Schaik, 2010). These electrodes are arranged around the surface of the body section and the resulting potential in the electrodes is, then, measured. EIT images are the computational reconstruction of the estimated mapping of electrical conductivity or permittivity within the body section, calculated from the relationship between excitation data and response data. This imaging technique is starting to be used in the process of breast cancer diagnosis.

Breast cancer is the type of cancer that most affects women in the world (Walker & Kaczor, 2012;). The best strategy to fight this disease is still the early detection of the tumor. In other words, the best way to decrease the fatality rate associated to breast cancer is detecting it in early stages (Zou & Guo, 2003). As highlighted by Zou & Guo (2003), there is evidence that malignant tumors have lower electrical impedance value than neighboring tissues. Following from this premise, some studies have been pursued to evaluate if the EIT can be applied as a breast cancer detection method. Cherepenin et al. (2001) performed 3-D breast images to detect breast cancer through a planar array of electrodes arranged in a square shape. In 2002, he did the same procedure using a circular matrix (Cherepenin et al., 2002). Comparing his approaches, the circular matrix is ​​more adequate rather than the square matrix because the electrodes on the square corners have low contact with the breast. This fact results in blurs on the reconstructed image corners, therefore, the central region of the image is the only region appropriate for analysis. The three-dimensional image of the breast is made from several images made in different slices at different distances from the electrode matrix (Cherepenin et al., 2001; Cherepenin et al., 2002). When applied to breast images, some authors also call the technique Electrical Impedance Mammography (EIM) (Trokhanova, Okhapkin, & Korjenevsky, 2008; Huber et al., 2010; Zhang, Wang, Sze, Barber, & Chatwin, 2014). Currently, the most widely accepted technique for early detection of breast cancer is mammography, which is a method that uses ionizing radiation and causes discomfort to the patient. So, in this case, EIT is a promising method, mostly because it is noninvasive and free of ionizing radiation.