Research on magneto-acoustic-electrical tomography method based on liquid metal contrast agent and M sequence coded excitation / 生物医学工程学杂志

Magneto-acoustic-electric tomography (MAET) boasts high resolution in ultrasound imaging and high contrast in electrical impedance imaging, making it of significant research value in the fields of early tumor diagnosis and bioelectrical monitoring. In this study, a method was proposed that combined high conductivity liquid metal and maximum length sequence (M sequence) coded excitation to improve the signal-to-noise ratio. It was shown that, under rotational scanning, the liquid metal significantly improved the signal-to-noise ratio of the inter-tissue magneto-acoustic-electric signal and enhanced the quality of the reconstructed image. The signal-to-noise ratio of the signal was increased by 5.6, 11.1, 21.7, and 45.7 times under the excitation of 7-, 15-, 31-, and 63-bit M sequence code, respectively. The total usage time of 31-bit M sequence coded excitation imaging was shortened by 75.6% compared with single-pulse excitation when the same signal-to-noise ratio was improved. In conclusion, the imaging method combining liquid metal and M-sequence coding excitation has positive significance for improving MAET image quality.

Research on Time-frequency Characteristics of Magneto-acoustic Signal of Different Thickness Medium Based on Wave Summing Method / 生物医学工程学杂志

Functional imaging method of biological electrical characteristics based on magneto-acoustic effect gives valuable information of tissue in early tumor diagnosis, therein time and frequency characteristics analysis of magneto-acoustic signal is important in image reconstruction. This paper proposes wave summing method based on Green function solution for acoustic source of magneto-acoustic effect. Simulations and analysis under quasi 1D transmission condition are carried out to time and frequency characteristics of magneto-acoustic signal of models with different thickness. Simulation results of magneto-acoustic signal were verified through experiments. Results of the simulation with different thickness showed that time-frequency characteristics of magneto-acoustic signal reflected thickness of sample. Thin sample, which is less than one wavelength of pulse, and thick sample, which is larger than one wavelength, showed different summed waveform and frequency characteristics, due to difference of summing thickness. Experimental results verified theoretical analysis and simulation results. This research has laid a foundation for acoustic source and conductivity reconstruction to the medium with different thickness in magneto-acoustic imaging.

System study on magneto-acoustic imaging in frequency domain / 医疗卫生装备

Objective To design a new frequency domain magnato-aoustic imaging system to image the conductivity of medium.Methods A continuous sine wave signal was adopted to stimulate the MAT signal. The lock-in technique was applied to measuring the amplitude and phase of the magneto-acoustic signal. The drive control program of the imaging system was designed using virtual instrument tools. The experiments were conducted on the phantom made of coper wire.Results The amplitude precision was improved up to 10-7 Pa, while the system could locate the sonic source with locating precision of millimeter.Conclusion A new magneto-acoustic imaging system is proposed with high locating precision as well as low frequency excitation, which is significative to the study on the sonic source theory and improvement of the imaging precision.

Research on acoustic source generating mechanism of magnetoacoustic tomography based on acoustic dipole theory / 生物医学工程学杂志

Magnetoacoustic tomography (MAT) has some advantages such as high sensitivity and high spatial resolution. The generating mechanism of acoustic source is the research foundation of forward and inverse problems. A coustic signals were respectively simulated by using monopole and dipole radiation theory in the experimental conditions, then the differences between their acoustic pressures were discussed, and furthermore the contrast and validation were conducted by physical experiments in this study. The physical experimental results showed that acoustic waveform of MAT had a certain directivity and therefore they indicated that dipole model showed higher approximation to the real facts than monopole model. It can be well concluded that this research has cardinal significance for the accurate algorithm of MAT.