A hybrid device for electrical impedance tomography and bioelectrical impedance spectroscopy measurement

We proposed a hybrid device, which is capable of measuring either bioelectrical impedance spectroscopy (BIS) or electrical impedance tomography (EIT) based on the Magnitude Ratio and Phase Difference Detection method. Frequency range available for measuring is from 1 kHz to 1 MHz. The device is based on The Freescale Tower system module with S08MM Freescale microcontroller. The proposed device is divided into two modules. One of them includes measurement chain, the second one contains four multiplexers, which connect always four electrodes to the circuit from total amount of sixteen electrodes. Both modules are connected via Tower elevator modules. While measuring impedance the systematic error occured, so we used the Quadratic Interpolation Self-calibration algorithm for calculation of the measured impedance. Calibration was applied on the absolute value of impedance. Calibration on the phase shift has not been done yet, since both input signals to GPD are highly disturbed with the noise, although they pass through a low-pass filter with cut-off frequency of 1 MHz. The superposed noise confuses GPD, so it cannot give the correct results. The relative error of impedance measurement after calibration ranges from -4.52 % to 5.98 % with mean value of -0.02 %.