Development of a multi-frequency system for medical applications of focused electrical impedance method (FIM) appropriate for developing countries

Making diagnostic measurements available to the widely geographically spread populations in developing countries is a challenge which is unlikely to be met by the technology used in the west. Multi-frequency electrical impedance techniques are attractive in this context as the instrumentation is relatively simple and research has demonstrated application in cardiac and respiratory medicine and in the characterisation of epithelial tissues. The development of focused impedance measurement (FIM) techniques has potentially gone some way to overcome the complex spatial sensitivity distribution which has been one of the limiting factors in using electrical impedance techniques in diagnosis. This paper describes a simple low cost system based on FIM that can be maintained and repaired in the field by the researchers allowing the potential for electrical impedance based diagnostic technique in developing countries to be evaluated. The microcontroller based multi-frequency system for FIM uses synchronous demodulation which is implemented using IC components readily available in developing countries. The drive current was generated from a microcontroller at 16 different frequencies. A Howland V to I converter delivers current to the tissue. The peak value of the measured voltage signal is determined by a micro-processor controlled analogue synchronous peak detector. Measurements on resistive and reactive phantoms gave a resolution that would allow impedance changes reported in clinical studies (e.g. respiration, epithelial tissue characterization and abdominal fat thickness) to be measured with the system.