Validation and characterization of magnetic susceptibility based magnetic resonance techniques for the evaluation of pathological alterations of the brain during aging

• Grant number: 24/02413-5
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: May 01, 2025
• End date: April 30, 2028
• Field of knowledge: Health Sciences - Medicine - Medical Radiology
• Principal Investigator: Maria Concepción García Otaduy
• Grantee: Fábio Seiji Otsuka
• Host Institution: Instituto de Radiologia (INRAD). Hospital das Clínicas da Faculdade de Medicina da USP (HCFMUSP). Secretaria da Saúde (São Paulo - Estado). São Paulo , SP, Brazil
• Associated research grant: 20/09468-9 - The determinants of healthy brain aging in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil), AP.TEM

Abstract

Quantitative magnetic resonance imaging techniques offers biophysical information regarding biological tissue in a quantitative way, giving higher accuracy in determining and characterizing biological tissues compared to qualitative images. Processing of these maps envolves the use of sophisticated models in which a theoretical or empirical model is imposed over the signal. Therefore, understanding the validity of these models, and their accuracy over the contrast, is of extreme importance for its correct interpretation. An example of quantitative maps are techniques based on magntic susceptibility, which explore magnetic properties of the tissue, such as the R2 relaxometry and the Quantitative Susceptibility Mapping (QSM). Despite iron being suggested as the main contrast mechanism of paramagnetism, this relationship was only observed on regions with increased iron concentration, such as the basal ganglia, whereas regions with low iron concentration have shown little iron influence. On the other hand, myelin was pointed as the main contrast mechanism of diamagnetism, however protein accumulation such as the beta-amyloid and tau-protein also presents diamagnetic behavior, also influencing the signal. Additionally, these contributions (paramagnetic and diamagnetic) are mixed on the same voxel, resulting in a combined contribution for the magnetic resonance signal. Recently, a processing tool has been proposed aiming to disentangle the diamagnetic and paramagnetic components of the signal, the DECOMPOSE. Although this technique have shown promising results, its biophysical validation is currently unknown. This study aims to explore different magnetic susceptibility techniques in postmortem subjects at 7T, linking the contrast with spectroscopic and histochemical findings, and apply this results in the analysis of magnetic susceptibility in vivo from patients of the biggest cohort of aging studied in Brazil, the ELSA cohort (Longitudinal Study of the Adults Health)