High-Precision Electrical Impedance Tomography System Using Package Excitation
Taweechai Ouypornkochagorn, Napatsawan Ngamdi
Abstract
In this paper, we present a high-precision multi-frequency Electrical Impedance Tomography system for wide areas of medical applications. The system has 32 channels with full parallel data acquisition. Instead of using superposition excitation for producing excitation current, we propose to use package excitation of five different frequencies between 2 kHz and 125 kHz. The excitation period is divided into five sub-periods, where only one frequency of excitation is performed at a sub-period. This excitation method can increase the readout 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 per second. Eighteen-bit analog-to-digital converters are used to obtain a fine resolution with a wide measurement range. The maximum load of the current source is 2000 Ω. The SNR of the current source and the voltage measurement unit is 78.5 dB and 91.7 dB, respectively. However, the SNRs reduce to 67.9 dB and 81 dB, respectively, at the 2 kHz and 0.2 mArms 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.