MRI-based Morphometric Study On The Cortical Anatomic Structure Of Occipital Lobe In Children With Ametropic Amblyopia

Backgrounds and objective:Ametropic amblyopia caused by abnormal visual experience in the early life is one of the most common diseases in children. BOLD (blood oxygenation level dependent) technique utilizes paramagnetic deoxyhemoglobin as an endogenous contrast agent, it was found that visual cortical function of the amblyopia stimulation decreased compared to the normal sighted people. Recently, the anatomical structure of the amblyopia was researched by the VBM (voxel-based morphometry), which showed that gray matter volume of children's visual cortex was decreased obviously. However, these experiments remained to study the change of the cortical volume, without inclusion of the change of the thickness and area. During the past few years, advances in computing methods for analyzing MRI have enabled high-resolution structural analysis of the human brain. For example, a well known software package, FreeSurfer (http://www.nmr.mgh.harvard.edu/freesurfer/), allows quantification and characterization of the cortical thickness and the areas of different brain regions precisely. In fact, the capability of this software has given rise to its widespread use in nervous system disease. The purpose of the present study was therefore to apply this method in the investigation of the changes of cortical thickness, GMV (gray matter volume) and area in ametropic amblyopia, aiming at characterizing the cortical morphometry and assessing the development patterns of the cortex in children with this disease.Using MRI (Magnetic resonance imaging) technique and the FreeSurfer software to research the occipital lobe's cortical anatomic structure in children with ametropic amblyopia.Methods:The expriment group divide into two groups, the amblyopic group and the control group with normal sighted. These two groups were age–matched. All subjects were provided informed consent. The ethics committee of the Third Military Medical University approved all study protocols. Anyone with known or suspected neurological conditions and ocular injuries were excluded from the study. The brain MRI was performed on the SIEMENS AVANTO 1.5 Tesla scanner. Standard T1-weighted high-resolution anatomic scans with MPRAGE sequence were obtained for each subject. Scanner noise was attenuated with earplugs. Subject's head motion was restricted with soft padding around the head. Before the data processing, we confirmed by visual inspection that all datasets were uncontaminated with head motion artifacts and the children had no brain lesions. For the cortical thickness analysis, 3-demensional MPRAGE images were analyzed with FreeSurfer software package. The whole analysis procedures included segmentation of white matter, tessellation of the gray/white matter junction, automatic correction of topological defects, inflation of the folded surface tessellation patterns and registration into an average spherical surface template. All the cortical thickness was smoothed with a 10-mm full width at half height Gaussian kernel to improve the SNR. After taken about 20 hours, the patient group and the normal group's occipital lobe's related cortical thickness, GMV (gray matter volume), area (cuneus, later occipital, lingual, pericalcarine)were calculated. The statistic analyses of the data between these two groups were performed with the student t test.Results:1. The cortical thickness of the lingual, pericalcarine on the left hemisphere and the cuneus, lateraloccipital , lingual on the right hemisphere in amblyopic group were thinner than the normal control group (P<0.05).2. The surface area of the lingual, pericalcarine, cuneus of bilateral hemisphere and lateraloccipital on the left hemisphere in amblyopic patients were smaller than that of the normal children (P<0.05).3. There were no significant differences between the amblyopia group and the normal group in the GMV of the occipital lobe (P>0.05). Conclusions:The cortical area difference between these two groups implies that the morphological and the functional changes are closely related to the development of the ametropic amblyopia. MRI techniques can be used to observe the structures of the brain in vivo. Through 3D anatomic datasets analysis, observing the morphological variation of the occipital lobe without invasive is possible. This analysis technique has a potential value in the clinical application.