Bioimpedance refers to a broad range of studies dealing with the electrical properties of biological materials as a function of the current flowing through them.

It has long been known that biological matter conducts electricity and that its electrical conduction properties depend on its chemical and physical attributes such as its cellular composition and mechanical structure.  Studies have shown that changes in a tissue result in corresponding changes in its electrical conduction properties, which means that information regarding the state of a biological material may be derived from measurements of its electrical conduction properties.

Bioimpedance science has already been utilized in many innovations in modern-day medical technology. The field of bioimpedance covers a multitude of applications that include impedance spectroscopy, impedance cardiography, impedance tomography, etc.

Figure 1.   Photos of an impedance tomography machine (left) and an impediance cardiography device (right)

Impedance spectrosocopy facilitates the detection of tissue abnormalities in terms of changes in its composition and intra-and extra-cellular fluids. Impedance cardiography (ICG) is a non-invasive technique for measuring clinical parameters pertaining to the heart and the circulatory system. Impedance tomography is an advanced imaging technique for displaying tissue sections in different angles based on the varying electrical resistivities exhibited by different types of tissues.   Other medical applications that involve bioimpedance are: aortic cross-sectional area measurement, impedance pneumography, apnea monitoring, and tissue characterizations using electrode systems.

Each of these applications involves a different system for delivering the electrical excitation to and measuring the electrical response of the biological material it aims to study.  A common factor among them, however, is that the design of the electrodes and electrode interfaces contacting the tissue under study must be optimized to ensure proper electrical measurements and recording. 

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