Combination Of RS-fMRI And DTI In Research Of Diffuse Axonal Injury Patients With Disorder Of Consciousness In Early Stage

Background:In recent years,with the increasing traffic accidents,the rate of traumatic brain injury(TBI)is raising.TBI can produce both focal brain damage and diffuse axonal injury(DAI).Focal brain damage often leads to local neurological dysfunction,whereas DAI causes mainly disorder of consciousness(DOC).These patients loss their consciousness immediately after the acquitted brain injury,with high mortality and morbidity.Maintaining the consciousness state depends on the function and the interaction between different systems within the brain,mainly including the cerebral cortex,thalamus and the ascending reticular activating system(ARAS).The ARAS located in the central axis portion of the brainstem attributes to the state of awareness,and the cerebral cortex contributes to contents of consciousness,while the thalamus is a crucial relay station in the central nervous system in which there are many neural circuits,and any fails occuring can lead to DOC.Such as the mesocircuit model,a common mechanism is that reduction of thalamocortical and thalamostriatal outflow following deafferentation and loss of neurons from the thalamus withdraws important afferent drive to the medium spiny neurons of the striatum,which may then fail to reach firing threshold because of their requirements for high level of synaptic background activity.Loss of active inhibition from the striatum allows neurons of the globus pallidus interna to tonically fire and provide active inhibiton to their synaptic targets,including relay neurons of the already strongly disfacilitated central thalamus,and possibly also the projection neurons of the pedunculopontine nucleus.Severe DOC mainly includes coma,minimally conscious state(MCS)and the vegetative state(VS).Level of consciousness of the DAI patients and the waking time after the coma are crucial for a neurosurgeon fo manage clinical treatment and communication with patients' relative.Traditional evaluation measures are subjective,such as the Glasgow Coma Scale(GCS),Glasgow Outcome Scale(GOS)and CT scan.Recently,many researchers are looking for some more available and objective measures,such as biochemical markers,electroencephalography(EEG),blood oxygenation level dependent functional magnetic resonance imaging(BOLD-fMRl),diffusion tension imaging(DTI),magnetic resonance spectrum(MRS),event related potentials(ERPs)and somato-sensitive evoked potentials(SSEPs),all of those measures provide novel treatmen and management.Resting state fMRI(RS-fMRv)indirectly explores the brain function by detecting rapid changes of the blood oxygen level independent inside the brain functional area activities when the subject is in a resting state(no external stimuli task).RS-fMR1 mainly include amplitude of low-frequency fluctuation(ALFF),regional homogeneity(Reho)and functional connectivity(FC).Many studies have indicated that the correlated low-frequency(<0.1Hz)fluctuations in the MRI signa identify the brain functional areas where signal changed that associated with the time.Functional connectivity mainly focuses on the functional correlation of cortical structures.The default mode network(DMN)including the medial frontal cortex(MPFC),the precuneus/posterior cingulate cortex(Pcu/PCC),the inferior parietal lobe(IPL)and bilateral temporal cortex is crucial to maintain the balance of brain activation between positive and negative in resting state,and is the key connective nodes of structure and function in brain.RS-fVMRI is suitable for study the function of patients with DOC,but scarcely studies have been taken in comatose patients in early stage.Diffusion tensor imaging(DTI)technology could carry out quantitative analysis and evaluation of white matter fiber tracts by taking advantage of the water molecule diffusion imaging.Many studies have shown that DTI can detect and quantitatively evaluate structural damage of DAI patients noninvasively.Current study combines the RS-fMRI and DTI to explore the neurological dysfunction and structural damage in DAI patients.On one hand,we study the mesocircuit model to uncover the relationship between the structure and the function,on the other hand,we study the characteristics of DMN in DAI patients with DOC providing evidence for evaluating the degree of comatose patients,predicting the level of consciousness and scientific intervention as soon as possible.Methods:Part1 Combination of RS-fMRI and DTI in research of the mesocircuit model in DAI patients with DOC.1.1 Participants:Ptients diagnosed as DAI with DOC were recruited according to the following specifications between July in 2013 and July in 2014.The inclusion criterion for DAI were:1)closed head injury and received conservative treatment;2)linear and angular acceleration injuries,and shearing and centrifugal force injuries;3)CT or MRI showed small multiple diffuse brain swelling of white matter without occupying bleeding in cerebral hemisphere,corpus callosum and brain stem;4)Inconsistency between the degree of increased intracranial pressure and severity(CT or MRI can't detect significant change and have severe DOC);5)Sedative drugs were not used in any of recruited patients.The exclusion criterion were:1)experienced head trauma and received operation treatment for skull defect;2)history of psychiatric disorders,or addiction such as heroin or alcohol;3)body is not suitable for MRI examination.Eleven DAI patients with DOC(5 females,mean age,43.1±15.6 years)and 11 age,gender matched normal control subjects(4 females,mean age,38.0 ± 7.7 years)were enrolled in the study.The overall research protocol was approved by the Institutional Review Board at Wuhan General Hospital of Guangzhou Military,and the informed consent was obtained from patients' or their legal guardians.1.2 MRI acquisition:The experiment was carried out on a 1.5T GE(GE Singna,HDxt,USA)scanner.Firstly,a high-resolution structural image for each subject was acquitted using three-dimensional MRI sequences with a voxel size of 1 mm3 and with an axial Fast Spoiled Gradient Echo sequence(TR/TE = 11.5/5.1 ms,matrix size = 256 x 256,FOV = 240 x 240 mm2 and 232 slices).Then,a DTI image was collected using a spin-echo plannar imaging sequence with the following parameters:15 gradient orientations,TR/TE = 9000/98.4 ms,FOV = 240 x 240 mm2,matrix size = 128 x 128,FA = 90 degree,slice thickness/gap = 5.0/0 mm,b = 1000 s/mm2.Finally,a T2*-weighted echo-planar imaging(EPI)sequence was acquired that was sensitive to the BOLD contrast with TR = 2000 ms,TE ? 40 ms,slice thickness of 5.0 mm with an interslice gap of 1 mm,field of view of 240 x 240mm2,matrix size of 64 x 64 and flip angle of 90°.The total scan time was 6 min 12.seconds,containing 186 time points.The control subjects were instructed to remain in a resting state with their eyes closed,no movement and no thinking.None of the included control subjects showed structural abnormality in the brain as determined on inspection by an experienced neurologist.Besides,evaluating the total GCS at the time of MRI scan.Image preprocessing:All of the imaging data were preprocessed and analyzed using Statistical Parametric Mapping 8(SPM8,http://www.fil.ion.uclac.uk/spm).The functional images first underwent slice-timing correction for within-scan acquisition time differences between slices and were then realigned to the first volume to correct for interscan head motions.Next,the realigned images were spatially normalized to the standard EPI template and resampled them to a voxel size of 3 x 3 x 3 mm3.Finally,the functional images were spatially smoothed with a Gaussian kernel of 6×6×6 mm3 full-width at half-maximum(FWHM)to decrease spatial noise.After linear trends were removed,a band-pass filter between 0.01 and 0.08 Hz was applied to the data to remove the effects of very low frequency drift and high frequency noise using the DPARSF(http://rfmri.org/DPARSF).ALFF analysis was carried out using DPARSF software.Voxel-wise twosample t-tests were employed to compare differences in ALFF between patients with DOC and controls using SPM5 software.The brain regions showing significant ALFF alterations were used as a mask for defining the ROIs,and they were also selected as the ROIs for the study..The ALFF values for each ROI were then averaged across both groups.TBSS analysis:Fractional anisotropy(FA)and mean diffusivity(MD)was carried out using FMRIB Software Library(http://www.fmrib.ox.ac.uk/fsl).Firstly,we adopted FDT(part of FLS)to process DTI and generate FA maps within brain mask that was obtained by BET(also part of FSL)after eddy current correction.Secondly,we used FA maps as input to investigate the groups WM differences between DOC and NC in a voxel-wise manner by Tract-Based Spatial Statistics(TBSS)methodology.All FA data of subjects were aligned onto standard space and the mean FA image was generated and thinned to create a mean FA skeleton,representing the center of all tracts common to the group.Each subject's FA data was then projected onto the skeleton and underwent statistical analyses with age and gender as covariates.A permutation nonparametric test(5,000 permutations)was employed to assess group-related differences using threshold-free cluster enhancement.Clusters were formed at FWE corrected(P<0.05).Finally,according to ICBM-DTI-81 white-matter labels atlas,each cluster was disassembled into sub-regions(intersection of clusters and atlas).All the sub-regions were labeled according to atlas and were defined as ROIs whereby mean FA was extracted across all subjects including DAI patients and normal control.MD was similarly analyzed.Statistical analysis:In ALFF analysis,one sample test was used within each group,while the two sample test was used between the two groups within the SPM8 software.In TBSS analysis,a permutation nonparametric test was employed to assess group-related difference using threshold-free cluster enhancement,clusters were formed at FEW corrected(P<0.05).We conducted the partial correlation analysis between the clinical variables and ALFF values of brain functional regions and mean FA/MD values of WM,as well as the cross modalities association for ROIs with significant difference of ALFF and FA/MD values,respectively.Part 2 The default mode network investigation in diffuse axonal injury patients with disorder of consciousness in early stage.2.1 Participants:Ptients diagnosed as DAI with DOC were recruited according to the following specifications between July in 2013 and July in 2014.The inclusion and exclusion criterions for DAI were the same as part 1.Fifteen DAI patients with DOC(6 females,mean age,44.3 ± 11.2 years)and 15 age,gender matched normal control subjects(4 females,mean age,39.3 ± 7.0 years)were enrolled in the study.The overall research protocol was approved by the Institutional Review Board at Wuhan General Hospital of Guangzhou Military,and the informed consent was obtained from patients' or their legal guardians.2.2 MRI acquisition and image preprocessing were the same as part 1.The preprocessed RS-fMRI data were further decomposed into 20 components using group independent component analysis(ICA)with MICA Toolbox(http://www.nitrc.org/projects/cogicat/).This involved data reduction,independent component estimation using the Informax algorithm,and back reconstruction to compute single-subject time course and spatial maps.For each component,maps of individual controls were entered into random effect one-sample t-tests in SPM8 and thresholded at P<0.05 with correction for multiple comparisons using the false discovery rate(FDR)procedure to create sample-specific component maps.Resting state networks were identified by visual inspection,with these component maps serving as marks in group analysis of functional connectivity.Group analysis were performed using two-sample t-tests and thresholded at P<0.05 with correction for multiple comparisons using the AlphaSim procedure.Results:Part11.1 There is no significant difference between two groups in gender(P = 0.682)and age(P = 0.852).1.2 Compared with the health controls,the DAI patients with DOC exhibited augment ALFF in the anterior cingulate cortex(ACC),insula(INS),amygdala(AMY)and hippocampus(fHIPP).In contrast,ALFF values were attenuated in thalamus(THA),precuneus,pre-and postcentral gyri.1.3 After controlling for age and gender,results revealed decreased cellular density,integrity,and tract directionality in specific brain areas in DAI patients with DOC.The patients had lower FA values in corpus collosum(body and genu)(BCC and GCC),right external capsule(EC)and superior corona radiate(SCR),posterior thalamic radiation(PTR)and superior cerebral peduncle(SCP)relative to healthy controls.1.4 Correlation analysis between the clinical measurement and ALFF and FA values of the brain structures displaying significant alterations uncovered a positive association between GCS and ALFF value of precuneus,GCS was inversely correlated with the ALFF value of the thalamus.The FA in both left PTR and SCP were associated with GCS.Cross modalities association analysis identified a positive correlation between the ALFF value of AMY and FA value of right EC,and between that of the postcentral gyrus and left PTR.Part 22.1 There is no significant difference between two groups in gender(P = 0.48)and age(P = 0.15).2.2 Within both groups,the DMN could be reproducibly identified as a set of areas encompassing precuneus/posterior cingulate cortex(Pcu/PCC),medial prefrontal cortex(MPFC),inferior parietal lobe(IPL)and bilateral temporal lobes(bTLs)mainly.2.3 Compared with normal controls,brain areas within the default mode network connectivity were decreased significantely in DAI patients(P = 0.001,AlphaSim corrected).2.4 Pcu/PCC connectivity was found to have a power correlation with the GCS(R2 = 0.29,P = 0.04)and CRS-R(R2 = 0.62,P = 0.001)total scores.Conclusion:Part 11.1 We had showed that stucture damage and function disruption within brain areas of the mesocircuit model.1.2 The lower FA value of the thalamus,the cerebral peduncle,corpus collosum(body and genu),right external capsule and superior corona radiate is,the lower level of consciousness is.1.3 A combination of effects of direct deafferentation of central thalamic neurons and active inhibition of some of these cells by the globus pallidus interna,as a result of ALFF value increasing in the globus pallidus interna and striatum,conspire to produce broad reductions in global cerebral synaptic activity,as reflected in the very low cerebral metabolic rates that are typical in patients with DOC.1.4 Structure damage is the basis of function disruption.Part 22.1 The default mode network could be found in both of normal controls and DAI patients with DOC.2.2 Compared with controls,the connectivity within the network in DAI patients with DOC is abnormal significantly.2.3 Pcu/PCC connectivity disruption in acute phase could be a good biomarker to reflect the degree of clinical consciousness impairment and evaluate the prognosis of DOC patients.