High-Precision Electrical Impedance Tomography System Using Package Excitation

In this article, we present a high-precision multifrequency electrical impedance tomography (EIT) system for wide areas of medical applications. The system has 32 channels with full parallel data acquisition. Instead of using superposition excitation for producing an excitation current, we propose to use package excitation of five different frequencies between 2 and 125 kHz. The excitation period is divided into five subperiods, where only one frequency of excitation is performed at a subperiod. This excitation method can increase the readout signal-to-noise ratio (SNR) by 30 dB. The data of each frequency can be collected simultaneously. The amplitudes are programable with a maximum of 2.83 mArms. The recording speed is 20 frames/s (fps). A 18-bit analog-to-digital converters (ADCs) are used to obtain a fine resolution with a wide measurement range. The maximum load of the current source is
$2000~\Omega $
. The SNR of the current source and the voltage measurement unit are 78.5 and 91.7 dB, respectively. However, the SNRs are reduced to 67.9 and 81 dB, respectively, at the 2 kHz and 0.2 mA
$_{\mathrm{rms}}$
of excitation. With high SNR and a wide measurement range, this system is then applicable for wide medical applications, where high precision is required. The system validation was performed on a phantom tank, a human forearm, and a human chest with satisfactory results.