A Novel Method to Detect Interface of Conductivity Changes in Magneto-Acousto-Electrical Tomography Using Chirp Signal Excitation Method

As a non-invasive and hybrid imaging modality, magneto-acoustic-electrical tomography (MAET) is extremely useful for the electrical conductivity measurement in vivo. Based on the Verasonics system and the MC600 displacement platform, we designed and implemented a novel MAET system with a chirp pulse stimulation (MAET-CPS) method for electrical conductivity measurement. In the system, a 2-3 MHz chirp signal was exploited for stimulating ultrasound power probe. Then, the interface positions of conductivity variation were obtained by digital demodulation of the excitation signal and the received voltage signal. Finally, five different homogeneous phantoms with same size were used to investigate the feasibility, accuracy, and repeatability of MAET-CPS. The results showed that: 1) when a chirp signal with pulse duration of 1000 μs was used to stimulate a homogeneous phantom with 0.5% NaCl, the reconstructed B-scan image of the conductivity distribution was highly consistent with the ultrasound B-scan imaging and physical size; 2) the signal-to-noise ratio of the system and the detection resolution of the interface of conductivity variations could be influenced by the linear frequency modulation period. The resolution obtained by using chirp signal with pulse duration of 1000 μs was better than that of 500 μs and 1500 μs; and 3) the interfaces of conductivity variations of homogeneous phantoms with five different concentrations (0.4%, 0.5%, 0.6%, 0.7%, and 0.8%) were clearly presented and the measured thicknesses of each phantom showed good agreement with the thickness of the target sample. This paper has laid the foundation for the MAET-CPS modality in the phantom sample, and MAET-CPS is expected to become an alternative imaging method for early diagnosis and detection of biological cancerous tissues.