| Research background and Objective:With the continuous development of science and technology,the modern warfare mode has undergone fundamental changes compared with the past.The air-ground three-dimensional strike,which combined fighter bombing with the accurate damage of medium and long-range guided weapons,strive to use long-end explosive weapons to destroy enemy command systems and power systems.Due to the fully application of high-energy explosion during the process of war,the wounded casualties have changed from traditional gunshot wounds and fragmentation injury to impact injury and explosive injury.Statistics show that the proportion of traumatic brain injury on the battlefield has an upward tendency,and closed cerebral hemorrhage(CCH)is a very common injury in traumatic brain injury.CCH is caused by shock waves or blunt instruments acting directly on the human head or head movement due to shock waves or other external forces.Primary injury include skull fractures,tissue deformation,vascular tears,cell damage,etc.Primary injury can lead to further brain pathological and functional deterioration.If CCH casualties don't get timely detection,thus causing delays in optimal treatment time,it is likely to cause paralysis and even death.At present,limitations due to battlefield conditions and the situation of the wounded cause CCH cannot be diagnosed by Computed Tomography(CT)and intracranial pressure(ICP)monitoring.Instead,we use the Glasgow Coma Score(GCS)combined with physical indicator measurements and past diagnostic experience to judge CCH.In view of the non-objectivity of the above detection methods,this paper proposes a new detection method-Magnetic Induction Phase Shift(MIPS).It is non-invasive,non-contact,portable and low-cost,which can carry out long-term continuous monitoring of the intracranial physiological activities of the wounded during the early detection and during the way back after TBI.Based on the basic theory of MIPS and the spectral characteristics of biological tissue conductivity,this study carried out experimental studyon early magnetic induction detection of cerebral hemorrhage in closed craniocerebral impact injury.The main research work of this paper is as follows:(1)Basic theory of MIPS and detection of CCH.According to the basic theory of MIPS,the phase shift change has relationship with the excitation signal frequency,the conductivity of measured object and the system geometry.Under certain condition of the excitation signal frequency and the system geometry,the intracranial conductivity change can be detected,which in turns reflecting the changes of disease and physiology of biological tissue.According to the distribution law of intracranial tissue conductivity,a coaxial single-excitation-single detection coil and a simple 4-layer spherical brain conductivity model were established.Besides,according to the main pathological process of CCH,theoretical relationshipwas derived that the mean intracranial electrical conductivity is proportional to MIPS.Through the analysis of the spectral characteristics of biological tissue conductivity,it is found that the biological tissue can reflect the interface relaxation between brain tissues with different dielectric properties in the ? dispersion domain(0.1MHz~100MHz).Magnetic induction detection in this frequency band are more able to reflect the pathological changes of CCH.(2)Magnetic induction brain monitoring device is a small brain trauma detection instrument which medical staff can use easily.It composed of excitation signal source,signal separation module,amplitude-phase receiver,signal processing module,display module,magnetic induction sensor and high frequency coaxial transmission line.The maximum sweep frequency range of the instrument is 300kHz~3GHz,the maximum number of scanning points is 1601,the maximum frequency resolution is 1Hz,andthe maximum output power is 10 dBm.In the experiments,the channel is set to the reflection parameter and the transmission parameter,and the data format is determined as the amplitude and phase.The coil sensor is made of copper wire wrapped around a plexiglass tube.Through simulation in the frequency range of 300 kHz to 300 MHz,it is found that the impedance matching frequency is 67.14 MHz when unloaded.The instrument has the highest sensitivity at this frequency.In addition,the optimal measurement position in the coil that meets the experimental constraints is determined by the spatial distribution of the magnetic field.(3)Analysis of four type of model which is the liquid impact damage model,the control cortical impact damage model,the fall damage model and the explosion damage model.According to the experimental requirements,the cortical impact animal model based on the horizontal biological impactor BIM-II was finally adopted.The brain injury caused by the impact instrument is closer to the injury caused by blunt attack and blast of battlefield.It has the advantages of good reproducibility,high reproducibility,simple experimental operation,low animal mortality,and fixed damage area.The horizontal biological impact machine BIM-II consists of high-speed gas gun device,high-pressure gas source,secondary hammer,limit frame,base,universal animal plate and console.This machine can adjust the impact strength by setting different air pressure values.In this paper,22 rabbits were divided into 3 groups,including 10 rabbits in injury group 1,10 rabbits in injury group 2 and 2 rabbits in CT control group.The injury group 1 and the injury group 2 respectively were hit on the predetermined position of the top of the skull with the pressure values of 600 kPa and 650 kPa,thereby forming two kinds of CCH injuries of different degrees.Subsequently,the rabbit CCH animal model was verified,which proved that the animal model used in this experiment can not only cause CCH in the specified damage area,but also cause CCH with different severity by setting the air pressure.(4)Experimental study on magnetic induction brain monitoring device detection of rabbit CCH.MIPS data were measured and analyzed in the 300 kHz to 300 MHz frequency band in two injury groups,respectively.The results showed that the MIPS of the two groups less than 0.8° before injury.At 0 min after injury,the average phase shifts of the reflection parameter and transmission parameter of 10 rabbits in the injury group 1 were 6.24±1.93° and-3.77±1.64°,respectively.The reflection parameter and the average phase shift of the transmission parameter of 10 rabbits in the injury group 2 were 8.43±1.39° and-9.27±2.34° respectively.At 30 min after injury,the average phase shifts of the reflection parameter and transmission parameter of 10 rabbits in injury group 1 were 10.93±2.86°,-11.17±2.91°,respectively.The average phase shifts of the reflection parameter and transmission parameter of the 10 rabbits in the injury group 2 were 14.01±2.46° and-16.18±2.22°,respectively.The MIPS data within 30 min before and after injuries in group 1 and group 2 were respectively analyzed throught paired sample t test.As a result,there was a significant difference between before and after the injury in injury group 1(P<0.05(?=0.05)).Similarly,a significant difference before and after the injury in injury group 2(P<0.05(?=0.05)).Moreover,the continuous MIPS data can reflect the changes of intracranial tissue,that is,the change of CCH.The Wicoxon signed rank test was performed on the MIPS of the injury group 1 and the injury group 2.The results showed that the MIPS between the two injury groups was significantly different,indicating that MIPS can be used to distinguish the severity of CCH.Then,we compared the absolute difference of average phase shift of the reflection parameter in two groups with the sum of standard deviations in two groups,and the transmission parameter did the same process.It is found that the transmission parameter has a higher discrimination degree for the CCH severity than the reflection parameter.Conclusion: Magnetic induction brain monitoring device can detect the presence of CCH in rabbits and its changes at an early stage.Compared with the reflection parameter,the transmission parameter have a better discrimination degree of CCH severity.In addition,the experimental study on rabbit CCH detection verified that the military magnetic induction brain monitor can be applied to battlefield first-aid to detect CCH in the future.Medical staff can detect CCH casualties and their severity by the instrument which possesses early sensitivity and non-contact quickly and easily.It will achieve early identification and classification of casualties,and more rational allocation of battlefield evacuation and medical resources,which is conducive to maintaining and restoring battle effectiveness of the troops. |
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