头部碰撞的损伤研究

F2008-SC-044 Head Impact Analysis related to the Mechanism of Diffuse Axonal Injury 1Watanabe, Dai*, 2Yuge, Kohei, 3Nishimoto, Tetsuya, 4Murakami, Shigeyuki, 5Takao, Hiroyuki 1Seikei University, Japan, 2Seikei University, Japan, 3Nihon University, Japan, 4Murakami Clinic, Japan, 5Jikei University School of Medicine, Japan KEYWORDS - passive automobile safety design, diffuse axonal injury, VOXEL head model, impact analysis, and cerebral limbic system ABSTRACT - The simulation of the head subjected to the impact acceleration was conducted to understand the mechanism of a diffuse axonal injury. It is known that the diffuse axonal injury frequently occurs in motor vehicle accidents. Gennarelli et al. proposed that a diffuse axonal injury occurs while a head is subjected to rather a lateral rotational impact than a sagittal or oblique impact. The obtained result shows that the higher stress occurred in a deep area of brain near the leading edge of a falx cerebri and tentorium cerebelli. It was confirmed that the greater stress areas of the brain matched the fact that DAI often involve the injury in a corpus callosum and a brain stem. Moreover, the brain dysfunctions due to an injury in the higher stress areas correspond to the residual disability in the diffuse axonal injury. We expect that the injury in a brain stem and cerebral limbic system is the essential of the diffuse axonal injury. TECHNICAL PAPER - INTRODUCTION A brain injury can be divided into two types. One of this is a focal brain injury and the other is a diffuse brain injury. An epidural hematoma, subdural hematoma, contusion and intracranial hematoma belong to the focal brain injury, which can be found easily by a diagnostic imaging with a CT or MRI. On the other hand, a diffuse brain injury is diagnosed on the basis of physiological response. According to the classification proposed by Gennarrelli et al.(1), a temporary consciousness disorder within 6 hours is called a concussion and a prolonged coma over 6 hours is called a diffuse axonal injury(DAI). The different point of a focal brain injury is that it’s difficult for a diffuse brain injury to find a brain damage area by diagnostic imaging. So the mechanism of a diffuse brain injury has not been clear and a diffuse brain injury has many social issues. For example, there is no effective treatment because of invisible injury, a consciousness disorder might not be certified as the residual disorder caused by a motor vehicle accident because the evidence of a consciousness disorder can’t be found and so on. The only thing that seems to be sure is that a diffuse brain injury frequently occurs in a motor vehicle accident. Therefore, it is quite important to understand the mechanism of a diffuse brain injury for a passive automobile safety design. Several research groups have dedicated decades to understand the mechanism of brain injury includes diffuse brain injury in several approaches. In representative experimental approaches, great achievements of the experimental data using human surrogates(2)(3) and using physical human head models (4)(5) have been proposed. Recent development of computers has made it possible to study the brain injury mechanisms numerically. 2-D simple head models were made to understand the response while an impact(6)(7). In the early works, Nishimoto, one of our authors, et al.(8) used 2-D coronal plane head model to simulate a brain behaviour subjected to the rotational impact. Zhou et al.(9) made a 3-D head FE model, with which they perfomed impact simulations and suggested that focal injuries are induced by pressure while diffuse axonal injuries are induced by shear stresses. Kleiven et al.(10) reported the influence since the size of head model was changed. Zhang et al.(11) developed one of the most detailed models called WSUBIM version 2001 for better understanding the head injury mechanism. Moreover, we have performed to discuss the mechanism of a focal brain injury using the detailed VOXEL head model which we developed(12). In this research impact simulations were conducted to study the mechanism of a diffuse axonal injury which is a more severe injury in diffuse brain injury using the VOXEL head model. THE VOXEL HEAD MODEL FOR IMPACT ANALYSIS The VOXEL head model we developed using CT images is shown in Figure 1. The model consists of 1.22million hexahedron elements and 10 tissues. The employed material properties of each tissue in the simulation are shown in Table 2. The properties were determined by referring to various existing reports. The brain was assumed to be a liner visco-elastic material proposed by Zhang et al. and the skull was treated as elasto-plastic material by Nishimoto et al.(13). The skin and the membrane were treated as elastic material by Ruan et al.(14). It is confirmed that the model is useful in an impact simulation since the head impact experiment by Nahum et al.(15) was simulated. Figure 1 1.22 million elements human head model (d) Brain (e) Falx cerebri and Tentorium cerebelli (f) Ventricle (a) Skin (b) Skull (c) Dura mater tissues young'smodulus[Pa] poisson's ratio density[kg/㎥] yield stress[Pa] tangent modulus[Pa] Skin 1.67×107 0.420 1300 - - Falx cerebri 3.15×107 0.450 1130 - - Dura mater 3.15×107 0.450 1130 - - Tentorium cerebelli 3.15×107 0.450 1130 - - Skull 8.75×109 0.261 1456 4.18×107 4.62×109 tissues bulkmodulus[Pa] short term shear modulus[Pa] long term shear modulus[Pa] density[kg/㎥] decay factor[s-1] Brain 2.19×109 1.25×104 2.5×103 1040 80 Soft tissue 2.19×109 1.25×104 2.5×103 1040 80 Eyes 2.19×109 1.25×104 2.5×103 1040 80 CSF 2.19×109 5.0×102 - 1040 5.0×105 Ventricle 2.19×109 5.0×102 - 1040 5.0×105 Table 1 Material property of tissues in the head model IMPACT SIMULATION Diffuse Axonal Injury (DAI) A diffuse axonal injury is defined as a prolonged coma over 6 hours, in generally, makes a poor prognosis. It is said that Strich(16)(17) found the anatomical evidence of consciousness disorder for the first time. Strich reported that widespread damage to axons in white matter was confirmed since the autopsy to a fatality after prolonged coma was conducted and the consciousness disorder causes a consciousness disorder. The report was well known as the reason why a consciousness disorder occurs afte impacts. After that, Adams et al.(18) called it diffuse axonal injury. One of the greatest achievements by Gennarelli et al.(3) to understand the mechanism of a diffuse axonal injury is representative. They conducted the impact experiments to make a diffuse axonal injury occur using primates. They put instruments like a helmet on primates and observe their pathological response after the instruments sudden moved to sagittal, oblique and lateral directions respectively (Figure 2). The results of the experiments are shown in table 2. According to the report, we can find that a diffuse axonal injury, a severe consciousness disorder, rather occurs in a lateral rotational impact than a sagittal or oblique impact. (a) sagittal (b) oblique (c) lateral Figure 2 Helmet-like instrument on primate and impact to sagittal, oblique and lateral direction in the experiment by Gennarelli et al. 60°60°60°60° 60°60° Mild(16-119min) Moderate(2-6hr) Severe(>6hr) Persisting Coma Sagittal 11(85%) 2(15%) 0 0 0 13 Oblique 2(33%) 3(50%) 1(17%) 0 0 6 Lateral 2(8%) 1(4%) 3(12%) 13(50%) 7(27%) 26 Total 15 6 4 13 7 45 TotalProlonged Traumatic Coma Duration of Coma Cerebral Concussion (<15min) Acceleration Direction 0 500 1000 1500 2000 2500 0 5 10 Duration[mｓ] Ac ce le ra tio n [ｍ /ｓ ２ ] (a) 0.0[ms] (b) 8.0[ms] (c) 11.0[ms] (d) 14.0[ms] Table 1 Relationship of direction of head motion to duration of coma (Gennarelli et al.) Lateral Rotational Impact Simulation A simulation subjected to a lateral rotational impact based on the previous report was conducted to discuss the brain behaviour. In order to make the rotational behaviour of the head, a translational acceleration was applied to the bottom of the head model as shown in the left of Figure 3. The applied acceleration was the sinus curve which peek value was 2000[m/s2] at 5[ms] and duration was 10[ms] as shown in the right of Figure 3. Figure 3 Applied boundary condition Results The time histories of the head behaviour and falx cerebri and tentorium cerebelli are shown in Figure 4 and Figure 5 respectively. It is confirmed that the rotational behaviour of the head was simulated well in Figure 4. Although the shear modulus of falx cerebri and tentorium cerebelli are much higher than brain’s one, they were deformed while impact in Figure 5. Figure 4 Head behaviour while a lateral rotational impact Rotation Acceleration (a) 0.0[ms] (b) 8.0[ms] (c) 11.0[ms] (d) 14.0[ms] (a) 0.0[ms] (b) 8.0[ms] (c) 11.0[ms] (d) 14.0[ms] Figure 5 Behavior of falx cerebri and tentorium cerebelli while a lateral rotational impact Next, the time history of Mises equivalent stress in a coronal plane was shown in Figure 6. In this simulation case, a wide spread distribution of the stress which indicate a diffuse brain injury couldn’t be confirmed. Instead, the stress concentrated in a corpus callosum, cingulated gyrus, brain stem and an inside of temporal lobe. Figure 6 Von-Mises equivalent stress distribution in a coronal plane while a lateral rotational impact [Pa] DISCUSSION Essential of diffuse axonal injury Recently, the localization of brain functions is getting clear since Penfield’s brain function map was known well. So the brain functions or function disorders due to a lesion in areas of greater stresses are shown in Figure 7. Figure 7 the brain functions or function disorders due to a lesion in areas of greater stresses Due to lesion, loss of the ability to execute coordinated movements Center of consciousness Due to lesion, absence of spontaneity emotional blunting Due to lesion, memory disorder disorientation absence of spontaneity personality change depression Inside of temporal lobe Cingulate gyrus Brain stem Corpus callosum Due to lesion, loss of the ability to execute coordinated movements Center of consciousness Due to lesion, absence of spontaneity emotional blunting Due to lesion, memory disorder disorientation absence of spontaneity personality change depression Inside of temporal lobe Cingulate gyrus Brain stem Corpus callosum Higher brain dysfunction moderate temporary unconsciousness Memory disorder Execution dysfunction Emotional disorder severe prolonged coma Personality change persistent vegetative state Disinhibition Degeneration Depression Consciousness disorder A corpus callosum is connecting a left hemisphere and right hemisphere of the brain. It loses the ability to execute coordinated movements due to a lesion. A brain stem is a centre of consciousness. A coma occurs by raising an intracranial pressure due to an acute epidural hematoma or subdural hematoma because their hematomas push down a brain stem. A cingulate gyrus, which is the part of a cerebral limbic system, causes absence of spontaneity and emotional blunting due to a lesion. The inside of temporal lobe, which is also the part of a cerebral limbic system, causes memory disorder, disorientation, absence of spontaneity, personality change and depression due to a lesion. On the other hand, residual disorders in a diffuse axonal injury are shown in table 2. There are two main types, a consciousness disorder and a higher brain dysfunction. In the consciousness disorder, the injury causes temporal consciousness disorder if it is mild or less. But if the injury is severe, it causes prolonged coma or persistent vegetative state. In the higher brain dysfunction, the injury leaves a memory disorder, execution dysfunction, emotional disorder, personality change, disinhibition, degeneration and depression. It is realized that the residual disorders are corresponding to the previous brain functions or function disorders due to a lesion in areas of greater stresses shown in Figure 7. So the several symptoms because of diffuse axonal injury, which have been thought, can be explained even by the injuries in a brain stem and cerebral limbic system. Moreover, the autopsy example of a fatality after a severe diffuse axonal injury in a motor vehicle accident is shown in Figure 8. The figure shows that injuries occur in a corpus callosum and brain stem which are corresponding to the areas shown in Figure 7. Additionally, even Strich, who suggested that a diffuse axonal injury causes a consciousness disorder, described that lesions on corpus callosum and inside of temporal lobe were confirmed as obvious abnormalities in her report(17). These results show that the essential of a diffuse axonal injury could not be a diffuse brain injury but the injuries in a brain stem and limbic system. Table 2 Residual disorder in diffuse axonal injury Figure 8 The autopsy example of a fatality after a severe diffuse axonal injury in a motor vehicle accident (a) 0.0[ms] (b) 8.0[ms] (c) 11.0[ms] (d) 14.0[ms] Influence of a falx cerebri and tentorium cerebelli In order to study why greater stresses distribute on specific areas in a brain, a similar simulation of previous case was conducted. The applied acceleration was the same as previous simulation but the material properties of a falx cerebri and tentorium cerebelli in the head model were replaced into CSF’s one. The results of the simulation are shown in Figure 9. The stress didn’t occur in such areas of previous simulation but the stress did only in a periphery of the brain. So a diffuse axonal injury could be caused by a falx cerebri and tentorium cerebelli. Figure 9 Von-Mises equivalent Stress distribution in a coronal plane of a model replaced falx cerebri and tentorium cerebelli into CSF [Pa] CONCLUTIONS In this research, the simulation of the head subjected to a lateral rotational impact was conducted to understand the mechanism of the diffuse axonal injury. The obtained result showed that the greater stress occurred in a brain stem and cerebral limbic system. It was confirmed that the localizations of brain functions in the greater stress areas correspond to the residual disorders in a diffuse axonal injury. It is expected that the injury in a brain stem and cerebral limbic system is the essential of a diffuse axonal injury and the behaviour of a falx cerebri and tentorium cerebelli could cause the diffuse axonal injury. ACKNOWLEDGMENT “High-Tech Research Center” Project for Private Universities : matching fund subsidy from MEXT (Ministry of Education, Culture, Sports, Science and Technology), 2008. REFERENCES (1) Gennarelli, T. A., “Emergency Department Management of Head Injuries”, Emergency Medicine Clinics of North America, Vol. 2, No. 4, pp. 749-760, 1984 (2) Ommaya, A.K. and Hirsch, A.E., “Tolerances for Cerebral Concussion from Head Impact and Whiplash in Primates”, J. Biomechanics, Vol. pp. 13-21, 1971 (3) Gennarelli, T. 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H., et al, “Diffuse Axonal injury due to nonmissile head injury in humans- An analysis of 45 cases-”, Ann Neurol, Vol. 12, pp. 557-563, 1982 << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /All /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Warning /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJDFFile false /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /LeaveColorUnchanged /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments false /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEnco