Integration of fiber tractography and functional connectomics for the investigation of brain neurological diseases

Functional magnetic resonance imaging (fMRI) and diffusion MRI (dMRI) are two complementary neuroimaging techniques widely used in neuroscience and clinical research. Functional MRI measures brain activity by detecting changes in blood flow. Diffusion MRI provides structural information on the brain connectivity by measuring the diffusion of water molecules. Integrating fMRI and dMRI offers a more comprehensive understanding of brain function and structure, as it allows researchers to link dynamic neural activity with underlying structural pathways. This thesis is divided into five chapters. Chapters 1 and 2 introduce the dMRI and fMRI techniques, respectively, and provide the basic knowledge needed for understanding the content of the following chapters. Chapter 3 describes an application of dMRI to reliably reconstruct the course of cranial nerves I, II, III, V and VII-VIII, using a fully automated tractography pipeline; additionally, an application of this pipeline in patients with sellar/parasellar tumors for the reconstruction of the anterior optic pathway is presented. In Chapter 4, the application of resting-state fMRI to a sample of long-COVID-19 patients with persistent olfactory dysfunction is presented; it is shown that, in the absence of structural modifications, functional alterations centered in the right thalamus were found in the olfactory subnetwork. In Chapter 5, a methodological work to integrate fMRI and dMRI is described: based on the original Functionnectome framework, which is used to project the grey matter functional activity onto the underlying white matter pathways, I developed a method to fully translate it at the individual level and tested it on a sample of patients with brain tumors. This thesis seeks to showcase the efficacy and clinical significance of functional and diffusion MRI techniques in characterizing neurological disorders. It also aims to introduce an innovative strategy for integrating both methods to extract personalized data, advancing the application of precision medicine.