Lorentz Force Electrical-Impedance Tomography Using Linearly Frequency-Modulated Ultrasound Pulse

Lorentz force electrical-impedance tomography (LFEIT) combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high-contrast and high-resolution hybrid imaging modality. To reduce the peak stimulation power to the ultrasound transducer in LFEIT, linearly frequency-modulated (LFM) ultrasound pulse was investigated in this paper. First, the coherency between LFM ultrasound excitation and the resulting local current density was established theoretically. Then, experiments were done using different agar phantoms of conductivity ranging from 0.2 to 0.5 S/m. The results showed: 1) using electrical signal of peak instantaneous power of 39.54 dBm to the ultrasound transducer, which was 25.5 dB lower than the peak instantaneous power of the high-voltage narrow pulse adopted in traditional LFEIT (65.05 dBm), the LFM ultrasound pulse-based LFEIT can detect the electrical conductivity discontinuity positions precisely; 2) the reconstructed B-scan image of the electrical conductivity discontinuity distribution is comparable to that obtained through LFEIT with high-voltage narrow pulse; and 3) axial resolution of 1 mm was achieved with the experimental setup. The method of LFM ultrasound pulse stimulation and coherent detection initiates an alternative scheme toward the clinical application of LFEIT.