Characterisation of dynamic biologic systems using multisine based impedance spectroscopy

The characterization of biological materials and systems using electrical impedance spectroscopy has traditionally been performed using the frequency sweep technique. When applied to in-vivo measurements, the movement induced modulation has often a period shorter than the sweep time. This drawback can be overcome using broadband signal bursts. Given that the energy amount to be injected to the biological material is limited for safety reasons, the best choice is the use of multisine signals, which concentrate all that energy in the measurement frequencies, then achieving an optimal signal-to-noise ratio. The uniform distribution of frequencies is not adequate due to the system nonlinearities and to the need of covering a three-decade frequency range. This work is concerned with the design of a quasilogarithmic multisine with a similar number of frequencies at each decade and with a safety band around each measurement frequency. This band will be free of harmonics and quadratic intermodulation products. The system has been implemented using a virtual instrument based on an arbitrary waveform generator, a digital oscilloscope and an analog frontend. The system has been validated using passive RC networks and has been applied to the in-vivo characterization of infarcted myocardium in pigs.