Luigi Della Torre

Towards the development of a wearable Electrical Impedance Tomography system: A study about the suitability of a low power bioimpedance front-end

Wearable systems for remote monitoring of physiological parameter are ready to evolve towards wearable imaging systems. The Electrical Impedance Tomography (EIT) allows the non-invasive investigation of the internal body structure. The characteristics of this low-resolution and lowcost technique match perfectly with the concept of a wearable imaging device. On the other hand low power consumption, which is a mandatory requirement for wearable systems, is not usually discussed for standard EIT applications. In this work a previously developed low power architecture for a wearable bioimpedance sensor is applied to EIT acquisition and reconstruction, to evaluate the impact on the image of the limited signal to noise ratio (SNR), caused by low power design. Some anatomical models of the chest, with increasing geometric complexity, were developed, in order to evaluate and calibrate, through simulations, the parameters of the reconstruction algorithms provided by Electrical Impedance Diffuse Optical Reconstruction Software (EIDORS) project. The simulation results were compared with experimental measurements taken with our bioimpedance device on a phantom reproducing chest tissues properties. The comparison was both qualitative and quantitative through the application of suitable figures of merit; in this way the impact of the noise of the low power front-end on the image quality was assessed. The comparison between simulation and measurement results demonstrated that, despite the limited SNR, the device is accurate enough to be used for the development of an EIT based imaging wearable system.

Bioimpedance sensing in wearable systems: From hardware integration to model development

Wearable sensors for e-health applications are quickly moving from the research field to market. Bioimpedance has the potential for playing an important role in this scope, especially because of its relatively reliable, electrode based sensing principle and its broad range of applications. On the other hand, there are also some challenges for the successful exploitation of this technique in a wearable device, like the reduction of power consumption and the control and optimization of the measurement for a specific application using a wearable electrode setup, more compact than the ones commonly employed in literature. This work discusses these two aspects, summarizing the results obtained with a low power bioimpedance architecture embedded into a wearable patch, and presenting a 3D finite element model which is used to analyse and investigate the bioimpedance measurements obtained through the patch. A comparison with the traditional electrodes setup shows similarities and differences in terms of sensitivity to organs conductivity, and confirms the suitability of a bioimpedance sensor integrated into a wearable patch.