Circuit for the measurement of small phase delays in MIT

A multi-channel magnetic induction tomography measurement system for human brain model imaging

This paper proposes a multi-channel magnetic induction tomography measurement system for biological conductivity imaging in a human brain model. A hemispherical glass bowl filled with a salt solution is used as the human brain model; meanwhile, agar blocks of different conductivity are placed in the solution to simulate the intracerebral hemorrhage. The excitation and detection coils are fixed co-axially, and the axial gradiometer is used as the detection coil in order to cancel the primary field. On the outer surface of the glass bowl, 15 sensor units are arrayed in two circles as measurement parts, and a single sensor unit for cancelling the phase drift is placed beside the glass bowl. The phase sensitivity of our system is 0.204 degrees /S m(-1) with the excitation frequency of 120 kHz and the phase noise is in the range of -0.03 degrees to +0.05 degrees . Only the coaxial detection coil is available for each excitation coil; therefore, 15 phase data are collected in each measurement turn. Finally, the two-dimensional images of conductivity distribution are obtained using an interpolation algorithm. The frequency-varying experiment indicates that the imaging quality becomes better as the excitation frequency is increased.

Preliminary imaging results of magnetic induction tomography based on physical phantom

Magnetic induction tomography (MIT) is a kind of contactless and noninvasive method to reconstruct the conductivity distribution in a cross-section. We developed a data acquisition system with one exciting coil and 15 measuring coils. By rotating the object placing on a circle plate, the 16*15 measurement data were obtained. The Newton-Raphson algorithm was applied to reconstruct the conductivity distribution. To the conductivity perturbation objects in air field, we made the difference images of MIT. The images were able to demonstrate the location of the objects and identify the conductivity difference between 0.84 S/m and 1.26 S/m, which are in the range of biological tissue.