Sensor Optimization And System Design Of Biological Multi-frequency Magnetic Induction Tomography

The intracranial hemorrhage is caused by disease,trauma and other factors,which seriously threatens the health of patients.At present,the medical imaging technology used in the diagnosis of intracranial hematomas has radiation or strong magnetic field,which is not suitable for long-term use.Magnetic induction tomography(MIT)is a new type of tomography,which can reconstruct the conductivity distribution in the measured field.Compared with common medical imaging technology,MIT has the advantages of non-contact,non-invasive,nonradiative and low cost.Therefore,MIT is suitable for the detection of intracranial hematomas.However,due to the soft field nature of magnetic field,the resolution of MIT technique is low.When it is used in the detection of biological tissues,the phase change of the detection signal is weak because of the low conductivity,so it can be interfered by noise easily.This is also the main bottleneck in the development of biological MIT.In order to improve the resolution of MIT system,the optimization of the sensor array was carried out.A 16-channel MIT system with high phase detection accuracy and low conductivity salt solution detection ability was designed and implemented.Specific research work includes:(1)Based on the software COMSOL Multiphysics,the optimization of the coil parameters was completed.In order to improve the resolution of MIT system,the sensitivity matrix under different coil parameters was calculated by the software.The intensity and uniformity of the sensitivity matrix were used as the optimization criteria to optimize the inner diameter,shape and the number of coils.The spatial resolution of the optimal coil detection is 12.38% and the conductivity resolution is 0.25S/m.According to the optimization results,the coils were made as the sensor of MIT system.(2)The modularly designed system was proposed.MIT system has the problem that the high-frequency analog signal can be affected by the noise easily during signal transmission.A modular MIT system was designed to deal with this problem.The detection signal is demodulated before transmitting,which avoids the influence of external noise on the detection signal transmission.The modular design can also increase the flexibility and extensibility of the system and reduce the system upgrade costs.(3)A 16-channel biological MIT system was designed and implemented.The system comprises a main control module,an excitation module,a sensing module,a multiplexing circuit,a data acquisition and an upper computer.The average phase error of the demodulation part is 0.006 degrees.The static experiment of salt solution was carried out.The results show that the spatial resolution of the system is 20 ml,the conductivity resolution is 0.13S/m,and the biggest detection depth is4 cm.The designed system has the ability to detect low conductivity salt solution.