Alzheimer's disease (AD) and frontotemporal dementia (FTD) are the most common forms of neurodegenerative dementia. However, their differential and timely diagnosis can be challenging for clinicians, therefore often closing the door for an early and possibly successful treatment before irreversible cerebral damage occurs. Hence, treatment options often become available only at a late point in time. In Alzheimer's disease, early neuroimaging markers are glucose hypometabolism and Amyloid-/Tau-depositions (PET). Recent findings from sodium magnetic resonance imaging (23Na-MRI) point to brain tissue sodium concentration as a metabolic marker of AD progression. Sodium is crucial for neurotransmission and cellular homeostasis maintained by the cellular Na+/K+-ATPase, depending on Adenosine-Triphosphate as energy source from the mitochondrial respiratory chain, also interacting with tau and amyloid. In this project, we aim to characterize disease-specific metabolic patterns in AD vs. FTD by performing 23Na-MRI in association to FDG-PET to support early positive and differential diagnosis and therapeutic follow-up in both diseases in association to clinical parameters such as CSF/blood markers and neuropsychological assessment. Assessment of 7T MRI including 23Na-MRI, 31P-MRS and 1H-MRI is planned with analysis of results in association with FDG-PET, Amyloid- and Tau-PET, blood and CSF biomarkers as well as neuropsychological and clinical assessment.