Brain perfusion SPECT analysis: New insights in mild cognitive impairment and neuromyelitis optica

The aim of this thesis was to demonstrate that brain perfusion SPECT can help to clarify important questions regarding the prodromal mild cognitive impairment (MCI) stage of Alzheimer's disease (AD) and relapsing Neuromyelitis Optica (NMO). This is not only pertinent considering our limited understanding of these neurological diseases but also because brain perfusion SPECT is a low cost and worldwide accessible technology. A general introduction of this neuroimaging technology is provided, including a novel image analysis approach, based on graph theory, to study brain connectivity. MCI and relapsing NMO are also briefly described as well as relevant questions related to brain perfusion in these diseases. Our findings indicate that the study of brain connectivity, based on perfusion SPECT combined with graph theoretical analysis, is feasible and useful both for investigating complex problems such as cerebrovascular reactivity alterations in MCI, as well as for clinical use. On the other hand, brain perfusion SPECT combined with voxel-based analysis provided evidence that brain microvasculature is an early disease target in relapsing NMO which suggests that perfusion alterations could be important in the development of brain structural abnormalities in this disease. In addition, our findings indicate that the number of optic neuritis attacks per patient is a potential confounder when comparing relapsing NMO patients with controls, for both tissue volumes and perfusion, and calls for attention in future studies. Thus, the findings presented in this thesis could have significant clinical implications and, therefore, the potential for practical applicability.