Brain Activity Map Extraction of Neuromyelitis Optica Patients Using Resting-State fMRI Data Based on Amplitude of Low Frequency Fluctuations and Regional Homogeneity Analysis

Introduction: Neuromyelitis Optica (NMO) is a rare inflammatory disease of the central nervous system which generally affecting the spinal cord and optic nerve. Damage to the optic nerve can result in the patient's dim vision or even blindness, while the spinal cord damage may lead to sensory and motor paralysis and the weakness of the lower limbs in the patient. Magnetic Resonance Imaging (MRI) is one of the imaging methods for NMO detection. Recently, the fMRI scans in NMO disease is very common. fMRI is a non-invasive method which uses magnetic technology. fMRI images are related to environmental changes in the blood flow of any brain regions. This imaging method is designed to identify parts of the brain cortex activated for specific tasks, and it is mostly used to carry out neurological studies.
Materials and Method: After the initial diagnosis by the neurologist, rest-fMRI imaging was performed on 25 healthy persons as the control group and 25 persons suffering from NMO as the test group. after the data were obtained, the data pre-processing was carried out which included the slice-timing, motion correction, and spatial normalization steps. In order to eliminate the noise and other artifact effects, a band-pass filter was used. Finally, the data were filtered using a Gaussian kernel for the smoothing purposes. The amplitude of low frequency fluctuations (ALFF) and regional homogeneity (ReHo) methods were used to investigate the activity of brain regions. For this purpose, at first, time series associated with each of the brain 3D volume voxels were extracted. After the selection of the brain regions between the two groups, registering the functional images on structural images and the standard atlas, the statistical analysis of the results was carried out. The present research was performed in MATLAB using the Resting-State fMRI Data Analysis Toolkit.
Results: The statistical comparison of the images of the test and control groups which was obtained from the group analyses of the low frequency fluctuations mappings in the resting state pointed to a decrease in the activity of the left Anterior Cingulate Cortex, right precuneus, left Posterior Cingulate Cortex, medial frontal gyrus, and right middle temporal gyrus regions. On the other hand, there was observed an increase in the activity of right inferior frontal gyrus and left thalamus regions.
Conclusion: The findings in the data associated with fMRI images in NMO patients, showed an abnormal brain activity in the regions associated with cognitive, optic, and motor tasks. This may be because of the consistency of the brain with functional disorder in NMO subjects as well as the compensation of this pathophysiological disorder by the other parts of the brain.