Investigation of the relationship of amplitude of low frequency fluctuation (ALFF) with anatomical measurements and functional connectivity findings in resting state functional magnetic resonance imaging

Objective: Magnetic Resonance Imaging (MRI) is a neuroimaging technique that allows us to examine the brain structurally and functionally. This thesis aims the comparative analysis of the anatomic MRI findings and the findings of the Amplitude of Low Frequency Fluctuation (ALFF) and functional connectivity (FC) analyses carried out on resting-state functional MRI (fMRI) measurements. For this purpose, complementary features of the three methods have been investigated on Alzheimer's Disease that results to a progressive neurodegeneration. Patients and Methods: Neuroimaging methods have been evaluated and compared on 33 Subjective Cognitive Impairment (SCI), 34 Mild Cognitive Impairment (MCI) and 21 Alzheimer's Disease Dementia (ADD) patients. Gray matter intensities were obtained by performing voxel-based morphometry (VBM) analyses on anatomical MRI data. Functional MRI data were analyzed by applying ALFF measurements and seed-based FC analyses based on areas of statistically significant ALFF differences. Results: Gray matter intensities decreased in the ADD group compared to the MCI and SCI groups in bilateral temporal, frontal, limbic and cerebellar areas, while ALFF values significantly increased in the left hippocampus, left parahippocampal gyrus, left amygdala and right hippocampus. Overlapping areas of high ALFF and largest gray matter loss indicates that the neurodegeneration leads to increase in local neural activity. On the other hand, left parahippocampal gyrus displayed a high FC with the neighboring areas in contrast to the negative FC between right hippocampus and left frontal regions, whereby both structures displayed high ALFF. Conclusions: Although both display increased neural activity, increase rather than decrease of the neural activity in the areas with highest neuronal loss and changes of the functional connectivity of the medial temporal lobes of both hemispheres in opposite directions show that integrated analyses of three MRI metrics provides opportunity to interprete neural processes underlying neuropsychiatric disorders in a more extensive manner.