The Application Of DTI And FMRI In Anterior Ischemic Optic Neuropathy

Background and purpose Ischemic optic neuropathy is very common optic neuropathy in the middle-aged and old patients, which can cause patients'visual significant decrease, even lose sight. The disease is difficult in clinical diagnosis because clinical symptoms and signs of patients lack specificity. CT imaging has no ability to demenstrate structural changes of ischemic optic neuropathy and conventional MRI examination could only found small part of these cases. Thus ischemic optic neuropathy is also difficult diagnosis according to conventional imaging methods. Diffusion tensor imaging (DTI) could discover earlier injuries of the axon and myelin, so DTI has revealed broad application in the central nervous system disorders. Blood oxygenation level dependent functional magnetic resonance imaging (BOLD-fMRI) could reflect the the brain cortex functional status, and can could quantitatively analysis degree and activative scope of brain cortex's activety. Therefore this research applied DTI and fMRI to study ischemic optic neuropathy in order to discover the application value of DTI and fMRI in anterior ischemic optic neuropathy.Materials and methodsThe subjects were 20 normal persons in control group and 28 patients diagnosed as unilateral anterior ischemic optic neuropathy from July,2008 to October,2009. Two patients were removed because of bad images. Finally, twenty-six patients were in experimental group(14 males,12 females). All subjects were examined with routine brain MRI in order to exclude intracranial diseases using SIEMENS Trio Tim 3.0T superconducting magnetic resonance scanner. Then Then they were underwent with examinations of MRI, DTI and BOLD for optic nerves. DTI examination uses single-shot spin echo planar imaging (SE-EPI) sequence. NEURO 3D post-processing was carried on at Syngo MR B15 workstation and optic nerve's DTI parameters including the value of the FA, ADC,λ∥,λ⊥, RA, VR were obtained. All subjects underwent pattern reversal visual evoked potentioals (P-VEP) tests and the parameter value (latency and amplitude) of visual evoked potential were obtained. Using the SPSS13.0 software package for statistical analysis, the parameter value of the optic nerve DTI and pattern reversal visual evoked potentioals were recorded as mean±standard deviation. Wilcoxon signed ranks test and Wilcoxon test were used for the group analysis Analysis of correlation was by Spearman's rank correlation. By a= 0.05 level, P<0.05 has statistics significance.Data preprocessing, statistics, results of the fMRI data were made in the MATLAB platform using SPM2 software. Analysis includes:①To left eye, right eye and of the normal control group employed group analysis respectively and average activation maps were obtained, respectively.②To left eye and right eye of the patients group employed group analysis and the average activation maps were obtained, respectively.③To left eye and right eye of the patients group and normal group respectively used the group analysis and the differences between activation maps of the two groups were obtained.ResultsDTI Results1. Diseased optic nerve's FA value and RA value decreased, ADC value,λ⊥value,VR value increased. DTI parameter values butλ∥between the optic nerve's diseased side and the healthy side in patient group.2. There were not statistically significant differences (P>0.05) in all of DTI parameter values of optic nerves between the patient group heathy side and the control group.3. The dseased optic nerve ADC correlated with P-VEP amplitude (rs=-0.63, P <0.05). The dseased optic nerveλ⊥correlated with P-VEP amplitude (rs=-0.47, P <0.05).). The dseased optic nerve FA correlated with both P-VEP whole-field latency (rs=-0.71, P<0.05) and P-VEP whole-field amplitude (rs=0.37, P<0.05).fMRI relults1. In the normal group, the most obvious activation areas of the single eye and bilateral eyes are both sides's primary visual cortex of the calcarine sulcus, that is Brodmann17 area (striate cortex), as well as lingual gyrus, fusiform gyrus, cuneate lobe, superior occipital gyrus, middle occipital gyrus, inferior occipital gyrus presented the activation, which is at Brodmann18 area and 19 (besides and around of striate cortex). Moreover the brain stem tegmentum, anterior colliculi, superior temporal gyrus and middle temporal gyrus (Brodmann22) also presented few activation areas. Some patients's lateral geniculate also appeared activated.2. Compared stimulating the left eye's activation maps of ischemic optic neuropathy group and the normal control group showed bilateral visual cortex activated area decreased significantly, the right side visual cortex activation area reduced more obviously. Bilateral precuneus, bilateral cerebral ganglion, cerebellar vermis, left cingulate gyrus, corpus callosum, left Subiculum hippocampi and brain sterm center appeared abnormal activation. The activation area became large in the right angular gyrus, bilateral cuneate lobe, bilateral superior temporal gyrus, middle temporal gyrus.3. Comparing stimulating the right eye's activation maps of ischemic optic neuropathy group and the normal control group showed bilateral visual cortex activated areas decreased significantly, the right side visual cortex activation area reduced more obviously; the right cerebral ganglion, right subiculum hippocampi and cerebellar vermis appeared abnormal activation;the activation area became large in the bilateral cuneate lobe, bilateral superior temporal gyrus and middle temporal gyrus.Conclusion1. DTI can sensitively detect the diffusion disorder of ischemic optic nerves. It may provide imaging evidences for ischemic optic nerves.2. DTI parameters and visual evoked potential parameters have favourable correlation. The two methods can complement when diagnosing ischemic optic neuropathy.3. Normal person's visual cortex exists asymmetry, the right side has obvious superiority.4. Stimulating the ischemic side, the activation area and activation degree of visual cortex significantly decreased. The other cerebral cortexs was abnormally activatedthat may explain the visual cortex's adaptability reconstitution.