Multi-frequency-difference Imaging Method Of Intracranial Hemorrhage By Magnetic Induction Tomography

Intracranial hemorrhage is one of the major diseases threatening human health which is of high morbidity and mortality.Through real-time,continuous non-invasive monitoring of hemorrhage,the progress of bleeding can be obtained in time and the treatment can be adjusted quickly.However,the clinical imaging technologies for hemorrhage such as computed tomography and magnetic resonance imaging can not be used long-term for patients,and it is impossible to monitor hemorrhage in real time.Magnetic induction tomography(MIT)is one kind of electrical tomography.The MIT with low-cost,safety and nonradiative properties can be used to continuously monitor the development and postoperative rehabilitation process of hemorrhage.Therefore,the research of MIT on hemorrhage imaging is of great significance for the life and health.The target signal is weak and susceptible to interference and the accuracy of image reconstruction is low when detecting the hemorrhage by MIT.The before-lesion reference data set is unavailable for time-difference imaging method in actual applications.Other head tissues cause serious influence on the signal of hemorrhage when using frequency-difference imaging method.A cambered MIT coil array with multi-frequency-difference(MFD)imaging method was proposed,which improved the imaging accuracy of extra-axial hemorrhage by MIT.The specific research work is as follows:(1)For the influence of inter-tissue inductive coupling on the phase shift signals,the multi-frequency phase signal characteristics of the MIT caused by the head tissues were studied based on the equivalent circuit models.The relationship among the phase shift caused by the inter-tissue inductive coupling,the conductivity,and the frequency was proposed.These provided a theoretical premise for the study of MFD imaging methods in different frequency ranges.(2)Other head tissues interfere with the signal of hemorrhage which causes artefacts when imaging the hemorrhage with the frequency-difference method by MIT.The signal of hemorrhage was separated from the detection signals of the head tissues by creating the multi-frequency relational model.The MFD imaging method for hemorrhage by MIT without inter-tissue coupling was studied with the highest frequency of multiple signals no more than 7.5 MHz.And the MFD imaging methods with inter-tissue coupling was studied when the multiple signals contain any frequency more than 7.5 MHz.The results showed that the proposed methods reduced the interference of other head tissues and improved imaging accuracy.Experiment with different conductivity salt solutions was done by a cylindrical MIT test system based on a lock-in amplifier.The MFD imaging method improved the imaging accuracy of the target object.(3)When the MFD imaging method is used to detect the extra-axial hemorrhage by cylindrical MIT coil array,the signals of the other head tissues are large.This increases the difficulty while separating the signal of hemorrhage from the detection signals of the head.The cambered MIT coil array was proposed to improve the detection sensitivity of extra-axial hemorrhage locations.The sensitivity of these locations and the three-dimensional imaging of the head model were studied.The results showed that the proposed coil array improved the signal to noise ratio of hemorrhage with local detection and the imaging accuracy of extra-axial hemorrhage.(4)The MFD imaging method and the cambered MIT coil array were combined and studied to detect the extra-axial hemorrhage.The experiment of MFD imaging was done with different conductivity salt solutions by the cambered MIT test system.The effects of other tissues were reduced and the signal to noise ratio of hemorrhage with local detection was increased.Based on the initial imaging of hemorrhage by cylindrical MIT coil array,the imaging accuracy of hemorrhage was further improved by the cambered MIT.