A Modified Howland Current Source Design for Simultaneous EIT/ECG Data Acquisition

The current source is one of the most critical circuits in electrical impedance tomography (EIT) hardware systems. The simplicity and excellent performance of the Howland current source makes it a prime candidate for this role in EIT systems. Although the Howland source and its family may be the best option for the high-frequency EIT operation, its low frequency noise may also limit the implementation of a system to simultaneously collect electrocardiogram (ECG) and EIT signals from the electrodes. This paper proposes modifications to the conventional Howland source to make is suitable for simultaneous EIT and ECG. The preliminary experimental results of this modified Howland show significant improvement in the collected ECG signal quality in the presence of the EIT signal.