Switching Algorithm and Data Acquisition for Pigeon Hole Imaging System

Bioelectrical impedance based imaging has emerged as a non-ionizing technique for physiological monitoring in the human body. Pigeon Hole Imaging (PHI) is an impedance based novel imaging modality that maps the spatial distribution of electrical impedance within a volume conductor. In PHI, impedance is measured at multiple locations placing an array of electrodes on the surface of a volume conductor and an image of the localized impedance distribution is reconstructed. Recent simulation studies demonstrated the use of PHI in the detection of subcutaneous vein and similar applications. However, the instrumentation of a PHI system is in need for experimental measurements to investigate its utility in practice. The aim of the present work is to design and develop the necessary hardware and software including switching algorithm and data acquisition peripherals for a PHI measurement system. A constant current source capable of driving alternating current of amplitude 0.5 mA at 10kHz in biological tissues was designed. An amplifier circuit minimizing common mode noise was also designed for measurement of the pickup voltage. An algorithm for switching current drive and voltage sensing electrodes for impedance measurement on a 5×5 PHI matrix is designed using multiplexers. Experimental measurements were performed on a cubic phantom containing 5×5 PHI electrode array. Software was developed in Matlab platform for acquiring data and visual presentation of the image reconstructed from PHI measurements. The implemented PHI system may be useful in the imaging of impedance distribution of human body for disease diagnosis and monitoring.