In vivo estimation of the head tissue conductivities by electrical impedance tomography technique and positivity constraint

Reported head tissue conductivities to date are usually obtained from sample investigation in situ or in vitro. However, there are many issues to concern e.g. sample selection and preparation or the deterioration of physiological property over time. In vivo estimation is recently used to estimate based on certain techniques. Electrical impedance tomography (EIT) is a mentioned technique, however regarding the susceptibility to noise of EIT, the estimation often results unexpected outcome. The estimated conductivity values may be inaccurate and/or be negative. The number of tissues in the estimation is then usually not over two. In this work, positivity constraint was employed to restrain the estimate to be only positive. Simulation result shows that the employment of the constraint can improve estimation accuracy and robustness to noise and also modeling error. Simultaneous estimation for all five main tissues is possible as well, even though the estimation of the cerebrospinal fluid conductivity is still not accurate.