Broadband electrical impedance spectroscopy for dynamic electrical bio-impedance characterization

Abstract

The electrical impedance of biological samples is known in the literature as Electrical Bioimpedance (EBI). The Electrical Bioimpedance enables to characterize physiological conditions and events that are interesting for physiological research and medical diagnosis. Although the Electrical Bioimpedance weakness is that it depends on many physiological parameters, on the other hand, it is suitable for many medical applications where minimally invasive and real-time measurements with simple and practical implementations are needed.
 The Electrical Impedance Spectroscopy (EIS) techniques based on broadband excitations are expected to help to understand various unsolved problems in biomedical applications. Broadband EIS opens up the possibility to reduce drastically the measuring time for acquiring EBI time-variations but, at the same time, measuring in a short time compromises the EBI accuracy. The way to overcome this intrinsic loss of accuracy relies on the design of the appropriate time/frequency input excitation properties and the use of the suitable spectral analysis processing techniques.
 The presented thesis covers the topics related to study of broadband excitations for Impedance Spectroscopy in biomedical applications and, more specific, the influence of the multisine excitation time/frequency properties on the impedance spectrum accuracy and its optimization. Furthermore, an advanced fast signal processing method has been implemented to process in real-time EBI data corrupted by transients, a common situation when measuring in a short measuring time. Despite being the goal to apply all this knowledge for myocardial tissue regeneration monitoring, at the moment of drafting the thesis, any of the research projects that have supported this thesis have issued functional beating tissue. For that reason, the theory presented has been validated by a set of experimental measurements over animals and patients where the impedance spectrum time-varying properties were pretended to be characterized.
 The thesis presents novel findings of relevance of a successful application of broadband EIS in two different measurement campaigns where it has been put in practice: (1) within the collaboration of the pneumology and cardiology service from Hospital Santa Creu i Sant Pau for in-vivo human lung tissue characterization, and (2), within the measurement of animal healthy myocardium tissue electrical impedance including its dynamic behavior during the cardiac cycle.