Structural and functional neuroimaging using quantitative susceptibility mapping and ultra-high field magnetic resonance imaging

In the last decade, Quantitative Susceptibility Mapping (QSM) has been proven a promising Magnetic Resonance Imaging (MRI) tool for the non-invasive quantification of clinically relevant biomarkers, such as iron stores and myelination. The relative simplicity of QSM implementation, which does not require dedicated hardware or acquisition sequence, and its validation with histological evidence favored the diffusion of this technique in the clinical practice, particularly in the diagnosis and follow-up of neurodegenerative diseases. In this thesis, we discussed a critical issue affecting quantification, namely the dependence on acquisition parameters, and its implications for clinical and fundamental research. Specifically, we investigated QSM potential in the study of synucleinopathies, that is a group of neurodegenerative disorders including Multiple System Atrophy (MSA) and Parkinson’s disease (PD), and its capability of detecting brain function via functional QSM (fQSM). As a first step, we assessed how TE-dependence affects QSM intra- and inter-scanner reproducibility by performing repeated measurements on the same participants acquired with both a 3T and a 7T scanner. Then, we explored the impact of TE on the diagnostic accuracy of this technique by acquiring multi-echo data at 7T on MSA patients with Parkinsonian and cerebellar phenotypes and a group of Healthy Controls (HC). In this study, we also assessed the potential of histogram analysis in enhancing QSM diagnostic power. In a third work, we aimed to identify a presymptomatic biomarker in patients at risk for synucleinopathies using 7T QSM. Specifically, we measured and compared iron deposition in nigrosome 1 (a small ovoid-shaped structure located within the dorsolateral portion of the Substantia Nigra pars compacta (SNc)) of PD, idiopathic Rapid Eye Movement (REM) sleep Behavior Disorder (iRBD) patients and HC. Finally, we implemented fQSM and explored its potential compared to fMRI using xii 7T MRI, a stimulation paradigm for tonotopic mapping, and univariate and multivariate analysis approaches. Overall, these studies emphasize the importance of QSM in both structural and functional studies and prove that QSM is a versatile and powerful tool for a wide range of neuroimaging applications.