Single-plane multifrequency electrical impedance instrumentation.

When tissue interacts with electromagnetic radiation it exhibits resistivity and permittivity changes, which decrease with frequency. Above 100 kHz it is expected that dielectric changes in tissue (permittivity) will allow one to distinguish damaged and necrotic tissue. Furthermore, tissue impedance at medium frequencies (100 kHz-1 MHz) have not been well characterized. The aim of this work was to design instrumentation for an impedance tomographic spectrometer to cover the minimum band 10 kHz-1 MHz. In order to produce images sensitive to small changes in resistivity, voltage measurement must be accurate to at least 0.1%. Using commercially available operational amplifiers, PSPICE simulations demonstrated 0.1% accuracy up to 800 kHz, falling off to 0.5% at 1 MHz. Implementation achieved a reasonably flat amplitude (+/- 0.5 dB) and a phase shift of 50 degrees from 10 kHz to 3 MHz and a receive response of 0.13 dB to 5 MHz and phase shift of -40 degrees at 3 MHz. With channel correction this design will provide useful readings up to 3 MHz.