MR elastography and MRI volumetry of the aging brain

Background: Physiological aging of the brain is accompanied by ubiquitous degeneration of neurons and oligodendrocytes [1]. An alteration of the cellular matrix of an organ impacts its macroscopic viscoelastic properties, which are characterized by mechanical parameters such as stiffness and internal friction. To date Magnetic Resonance Elastography (MRE) is the only non-invasive technique for measuring the shear viscoelastic properties of living brain [2-4]. Problem: Recently, it was demonstrated that stiffness of the adult brain is continuously decreasing with years of age [5]. However, MRE is based on the solution of the inverse problem of propagating shear waves which is mathematically ill-posed and thus error prone. Changing geometrical boundary conditions as given by brain atrophy in the course of aging may therefore confound MRE-derived elasticity parameters. Objective: In this study, the sensitivity of brain MRE to physiological aging and variations in brain volume was studied in 55 healthy volunteers ranging from 24 to 72 years of age. Aim of the study was to systematically investigate the influence of atrophy and geometrical boundary conditions in cerebral MRE.