Magneto-acousto-electrical tomography using frequency-response-compensated nonlinearly frequency-modulated stimulation.

Magneto-acousto-electrical tomography (MAET) based on nonlinearly frequency-modulated (NLFM) signal stimulation achieves large dynamic range of detection while sacrifices a little longitudinal resolution. However, NLFM signal stimulation is also negatively affected by the uneven frequency response in MAET, which results in widening of the main lobe width (MLW) after pulse compression and ultimately leads to the degradation of longitudinal resolution (LR) in the MAET images. To further improve the LR of the MAET using NLFM signal stimulation, an MAET method using frequency-response-compensated NLFM (FRC-NLFM) signal stimulation is proposed. 
Approach: Two types of nonlinear frequency-time curves are generated using the window function method and the piecewise linear frequency modulation method. The cubic spline interpolation method is employed to fit the nonlinear frequency response curves, which are used to generate the FRC-NLFM stimulation signals. Four groups of MAET experiments using respectively pure agar phantom samples and an in vitro multi-layer pork tissue agar phantom sample are conducted. Comparisons in terms of sensitivity, LR and dynamic range of detection are made among MAET using respectively spike, FRC-LFM, FRC-NLFM, and purely NLFM stimulation methods. 
Main results: MAET using FRC-NLFM stimulation improves LR over MAET using purely NLFM excitation, and has higher sensitivity and larger dynamic range over MAET based on FRC-LFM. 
Significance: This method forwards coded-excitation-based MAET to become an imaging method with high sensitivity, high LR and large dynamic range, and paves another way for the clinical application of the MAET.