A magnetic induction tomography system for samples with conductivities below 10 S m−1

A 16-channel magnetic induction tomography (MIT) system has been constructed for imaging samples with low conductivities (andlt;10 S m-1) such as biological tissues or ionized water in pipelines. The system has a fixed operating frequency of 10 MHz and employs heterodyne downconversion of the received signals, to 10 kHz, to reduce phase instabilities during signal distribution and processing. The real and imaginary components of the received signal, relative to a synchronous reference, are measured using a digital lock-in amplifier. Images are reconstructed using a linearized reconstruction method based on inversion of a sensitivity matrix with Tikhonov regularization. System performance measurements and images of a pipeline phantom and a human leg in vivo are presented. The average phase precision of the MIT system is 17 millidegrees.