| Background and objectives: Intracranial hemorrhage (ICH) is defined as thehemorrhage induced by vascular rupture in brain parenchyma. As one type of strokes, ICHis featured with acute onset, extreme danger, and very high incidence of disability andmortality. The morbidity of ICH is still rising along with the aging of global population andthe intensification of social pressure. In recent years, the cerebral stroke becomes the firstdeath cause among all diseases in China, and its standardized mortality is the highestworldwide and is rising at a yearly rate of9%. Among2million new sufferers of strokesannually, nearly a half of them die and about3/4of the survivors are subjected to varyingdegrees of disability. The cerebral stroke has brought severe economic burdens to Chinaand numerous families, which highlights the urgency for its prevention and control.The optimal method for reducing the incidence of mortality and disability of ICH isearly diagnosis and treatment. Currently, ICH is mainly detected by large and expensiveimaging equipment such as computed tomography (CT) and magnetic resonance imaging(MRI), but these instruments are unable to satisfy the requirements of continuousmonitoring, first aid and early diagnosis. Though continuous monitoring of intracranialpressure can be realized at bedside, this method is invasive and infective. Thus,development of noncontact, noninvasive, small-size, low-cost, continuous and rapidequipment for ICH detection is urgently needed. Fortunately, magnetic inductiontomography (MIT) and magnetic induction phase shift (MIPS) both meet theserequirements and thus are two of the optimal methods for detection of cerebrovasculardiseases. However, the very low conductivity of biological tissues severely reduces thesensitivity in magnetic induction detection, which largely inhibits their medical applications.To solve this problem, many high-sensitivity methods have been proposed, but most ofthem are unsuitable for ICH detection in vivo. Under this background, in this study, wecomprehensively consider the brain structure and the pathophysiological characteristics of ICH, and design four coil structures especially applicable for ICH detection, aiming toimprove the sensitivity and stability in ICH detection in vivo.In section one, based on the experimental demands of this study, two MIPSmeasurement systems were built. The first system was based on a self-mademulti-frequency high-power signal generator and phase detector. The self-made excitationsource could work at7frequencies (0.2,1,10.7,21.4,30.85,40.05and49.95MHz). Thestability of signal frequency was up to10-8, and the power of excitation signals could beadjusted between10mW and2W. The worst secondary and triple harmonic distortions ofthe output signals were tested to be-48and-56dB, and the4-hour phase drift did notexceed50m°. The self-made phase detector could measure the signal phase difference at1,10.7or21.4MHz. The phase noise of the phase detector was tested to be less than6m°,and the4-hour phase drift did not exceed30m°, which met or exceeded the performancesof MIT systems in China and in the world. Then the self-designed MIPS system was used tomeasure the MIPS changes during injection and reverse of normal saline in an ICH physicalmodel. The results were consistent with a previous report outside China, indicating that thissystem can meet the requirements for practical detection. The second system was based ona commercial signal generator and a PXI data collection system. The signal generator couldoutput bandwith at any preset frequency, and together with the PXI high-speed datacollection card (DAQ) and the compiled LabVIEW phase difference measurement software,it could measure the phase difference at any frequency below50MHz. The tests showedthat at10.7and21.4MHz, the performance of the self-designed system was higher than thePXI system, but the latter could work at any frequency, and thus, these two systems areapplicable to different experimental requirements.In section two, based on the characteristics of brain structure and thepathophysiological characteristics of ICH, and fully considering all factors in the detectionmethods, we designed four coil structures especially suitable for ICH detection in vivo: acontralateral hemisphere cancellation coil (CHC coil), a coaxial coil, a double-end excitioncoil, and a Helmholtz coil. The CHC coil was simulated in details on CST electromagneticsimulation software, and the effects of geometric parameters and positional parameters onsensitivity were investigated. This coil was compared with the traditional structure of singleexcitation coil&receiving coil. The results show that the sensitivity of CHC coil was 50-fold higher. Then the CHC coil was used in normal saline detection experiments and theresults were consistent with the simulation results, indicating that the simulation methodwas reliable. Finally, a four-layer sphere model for simulation of intracranialthree-component coadjustment was built. This model was simulated at10time pointsduring hematoma enlargement, and the simulations were measured using the above fourcoils, and the four MIPS curves with hematoma volume were plotted. The simulationresults were generally consistent with the theoretical analysis about the cerebralICH-induced overall craniocerebral conductivity.In section three, a rabbit internal capsule hemorrhage model via autoblood injectionwas built. The autoblood (3ml) was injected in at a rapid and a slow rate separately. Thenthe MIPS changes during blood injection were detected using the four coils.Conclusions: The results show that the detection results from the four coils weresimilar to the simulation results and were very consistent with the theoretical analysis. Thenthe results from the four coils were statistically analyzed and compared. We found that theCHC coil was a surface measurement coil, and despite the high sensitivity, it could onlydetect the changes of surface cerebrospinal fluid (CSF) at the compensatory phase, butfailed to detect the deep ICH. The coaxial coil was very sensitive to the deep hemorrhage,but was insensitive to CSF changes. The reason was mainly because the axial uniformmagnetic field from the solenoid was very short; the magnetic strength at the middle of thesolenoid is higher than that at the two ends. The axial uniform field can be lengthened byprolonging the solenoid and reducing its diameter. In this way, the uniform field couldcover the whole brain and thus the coaxial coil became sensitive to both CSF andhemorrhage. The double-end excitation coil was efficient at ICH detection, and wassensitive to both CSF and hemorrhage, but was higher sensitive to the changes of surfaceCSF. The use of "upper and lower exciting coils" was sensitive to the upper surface andlower surface CSFs, unlike the CHC coil which could only detect the upper surface CSF.Like the coaxial coil, the Helmholtz coil also applied uniform field to measurement, but thehomogeneity degree was higher. The Helmholtz coil was also sensitive to both upper layerand lower layer CSFs like the double-end excitation coil, and thus could detect thecompensatory CSF changes. However, the results at the compensatory phase wereinconsistent, mainly because the large diameter of Helmholtz coil could not guarantee that the injection points in all animals were at the same site of the central axis. In practice, whatreally matters is the ability of detecting compensatory CSF changes, and thus, thedouble-end excitation coil and the Helmholtz coil are better choices. Nevertheless, if thestructure and the axial uniform field could be improved, the coaxial coil will also beefficient at ICH detection. The sensitivity will be further improved if the CHC idea couldbe applied to the other three coils. The detection direction also affected the results.Detection at horizontal direction will allow the cerebellomedullary cistern and spinal canalat the posterior brain to be both detected by the exciting field, which will affect the MIPS.At the compensatory phase, however, the CSF is discharged and the majority will reflux tothe cerebellomedullary cistern and spinal canal. Thus, if these regions are closer to thedetection region, the overall change of CSF will be reduced, thus lowering the sensitivity.Moreover, with detection at horizontal direction, the results will be affected by the heartbeat and chest breathing to larger degrees. Detection at vertical direction will reduce theseimpacts. Therefore, ICH detection at the vertical direction is the first choice in practice.Moreover, disseminated hemorrhage should be well corresponded only via measurement byuniform field, and thus, coaxial coil and Helmholtz coil are better choices. |
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