Frequency Difference EIT With Localization: A Potential Medical Imaging Tool During Cancer Treatment

Electrical impedance tomography (EIT) has attracted great interest in a number of medical applications. It offers several unique advantages, such as being safe, low cost, and having high temporal resolution over other tomographic imaging protocols. The frequency dependence of electrical conductivity in biological samples gives EIT imaging a renewed chance to be a monitoring technique for new and very important medical applications, such as tumor tracking during radiation therapy. Therefore, frequency difference EIT (fdEIT), which reconstructs images using difference data at two injecting frequencies, is a good candidate for high-speed tissue characterization in dynamical settings. However, a low spatial resolution of EIT is a major drawback that limits its uses. In some cases, such as the treatment of tumors, prior knowledge about the location of a tumor is provided by early diagnostic images. This prior knowledge coupled with the spectroscopic knowledge of the frequency response of a tumor against normal tissue gives a possibility for localized fdEIT imaging, which can significantly enhance the spatial resolution. The experimental results in this paper demonstrate this for the purpose of such monitoring of an inclusion exhibiting frequency-dependent impedance and are quantitatively compared with traditional methods. The new method's performances and robustness are demonstrated numerically using several image quality measures. This could give the EIT new roles to play, for motion compensation in conjunction with the traditional low-speed but high-resolution medical imaging systems and dynamic tumor tracking.