Structural MRI Research In Young-middle Epileptics With Different Image Performance

Background, Objective and SignificanceIn view of the complicatied etiology of epilepsy, a new classification for focal cortical dysplasia (FCD) and the inconsistent findings of structural magnetic resonance imaging (MRI) research in epilepsy patients, this study uses diffusion tensor imaging (DTI) and tractbased spatial statistic (TBSS) to investigate white matter (WM) microstructural dynamic changes in young-middle epileptics with different imaging features. FA values, MD values, AD values and RD values in all of the brain regions are measured to compare among distinct groups. Course of disease is also recorded to observe the correlation of disease duration and parameters of DTI. The meaning of this research is to explore the potential pathophysiological mechanism of epileptic brain network connection and development model from the perspective of neuroimaging.Materials and methods106 subjects from Grounddong 999 Brain Hospital were recruited:37 with generalized epilepsy and normal MRI (MRI (-)),36 with temporal lobe epilepsy (TLE) and MRI signs of FCD or hippocampal sclerosis (HS) (lesion side:19 left,13 right,4 bilateral) and 33 healthy persons. All of them are right handed, from 15 years old to 50 years old. There was no significant difference in age and sex among the three groups and between the two (left/right) subgroups of temporal lobe epileptics. Before DTI scans, all subjects had completed conventional MRI scans and video electrocardiogram (VEEG). Diagnosis of all the epilepsy patients met the 1981,1989 or 2010 International League Against Epilepsy diagnostic criteria and classification standards. Other inclusion criteria of epilepsy groups were as follows:age 15 to 50 years old; normal blood pressure and heart rate; no history of mental illness and drug dependence; alcohol free. Epilepsy groups of exclusion criteria were as follows:brain trauma and brain surgery; history of cerebrovascular accident; intracranial tumors; vascular malformations; severe congenital brain malformation; intracranial infection; except for FCD and HS, other induced epileptic disease (such as tuberous sclerosis); pregnancy or lactating women. The final groups were matched according to the image performance and VEEG.About the healthy control group:Age 15 to 50 years old; normal mental development; age and gender were matched to epilepsy groups; no history of epileptic seizures; normal blood pressure and heart rate; no history of dependence on alcohol and drugs; no brain trauma and brain surgery; no positive lesions by routine brain MRI scanning; no positive signs of neurological examination; non pregnant or lactating women. The consent was obtained from all subjects.All the MRI data were acquired by a 1.5 T magnetic resonance imaging scanner (Philips Gyroscan Interal.5T) with a six-channel phase display coil (the neurovascular coil 6, NV6) to receive magnetic resonance signals. DTI scans were performed by a single shot spin echo planar sequence (SE-EPI), parallelled to anterior commissure and posterior commissure (AC-PC line), covering the whole brain to get axial diffusion weighted images. The specific parameters were as follows:32 non-collinear difiusion gradient directions with a b-value of 800 sec/mm2, flip angle (FA)= 90°, repetition time (TR)=11000ms, echo time (TE)=72ms, field of view (FOV)=23cm*23cm, matrix size=144*144, excitation frequency (NEX)=1, no slice gap, slice thickness=2mm, layers=67.The preprocessing was to change the form of all the original data from DICOM to NIFTI format. Then, FSL (FMRIB Software Library, www.firirib.ox.ac.uk/fsl, version 4.19) tools were used to analyze the DTI data. The main steps included these following:First, elimination for head movement and correction for eddy current distortion. Second, according to each subject’s BO image, mask image was created by BET tool of the FSL software. Third, DTI parameters were calculated by the DTIFit function, including fractional anisotropy (FA), mean dififusivity (MD) radial diffusivity (RD) and axial diffusivity (AD). Last, DTI data were matched to the standard MNI152 space by following the TBSS algorithm to get the white matter fiber skeleton graph, then randomise tool in FSL software was used to perform the multisubject analysis of FA, MD, RD and AD respectively, as well as the correlation analysis of parameters and patients’clinical course. P value less than 0.05 was considered to have statistical significance.Other statistical analysis in this research was performed by SPSS version 20.0 software. Age data were subjected to Levene test for normality and homogeneity of variance. If data meet normal distribution and homogeneity of variance, parametric test would be used, if they don’t, nonparametric test would be used. A chi-square test was used to compare gender among distinct groups.ResultCompared with the healthy control group, MRI (-) patients exhibited significantly reduced FA in widespread white matter regions including bilateral anterior thalamic radiation, corticospinal tract, cingulum (cingulate gyrus), cingulum (hippocampus), inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, superior longitudinal fasciculus, uncinate fasciculus, superior longitudinal fasciculus (temporal part), forceps minor and forceps major. RD value in these parts increased significantly.TLE patients also exhibited significantly reduced FA in widespread regions, including bilateral anterior thalamic radiation, corticospinal tract, cingulum (cingulate gyrus), inferior fronto-occipital fasciculus, superior longitudinal fasciculus, uncinate fasciculus, superior longitudinal fasciculus (temporal part), forceps minor and left inferior longitudinal fasciculus; increase of MD and RD were exhibited significantly almost in the whole brain. Lesions in left side subgroup displayed significantly reduced FA in generalized regions compared with the right side subgroup; its RD value were significantly increased in bilateral anterior thalamic radiation, corticospinal tract, cingulum (hippocampus), forceps major, right cingulum (cingulate gyrus), inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, superior longitudinal fasciculus, uncinate fasciculus and superior longitudinal fasciculus (temporal part).There was no significant difference between two epilepsy groups.It exhibited a significant correlation of the disease duration and FA, RD values in widespread brain regions.ConclusionsBoth MRI (-) and temporal FCD/HS epileptics had extensive damage of white matter fibers, including brain regions refer to limbic system, default network and pyramidal tract which respectively control the emotion, cognition and movement. The longer the time, the more serious the damage.Two types of epilepsy might have inherent link. Right handed patients with left TLE had greater, more diffuse changes. It might depend on the characteristics of dominant hemisphere. Our result indicates that method of TBSS is more sensitive and accurate than ROI and VBA in DTI analysis.