Quantitative T1 mapping provides a biophysical parametric measurement that is useful in the investigation and diagnosis of the human brain. T1 measurements display sensitivity to microstructural properties such as myelin, lipid, and protein composition, iron forms and content, and tissue organization. I will present T1 application for myelin mapping and disentangling the molecular composition of lipid and iron samples and identify region-specific molecular signatures across the brain. I will argue that the ability to disentangle molecular alterations from water-related changes opens the door to a more specific characterization of brain age-related and neurodegenerative disorders in-vivo.