Linking dielectric dispersion and age in brain tissues via water content-based Electric Properties Tomography

Popular dielectric dispersion models of biological tissues, which describe dielectric properties as a function of frequency, do not account for age-related variations. In particular, existing databases have limited validity in pediatric populations. In this work, we applied water content-based Electric Properties Tomography in vivo to healthy subjects across the lifespan to incorporate age-related information into dielectric dispersion models of white and grey matter. Water content, derived from magnetic resonance fingerprinting-based T₁ mapping, was modelled as a function of age. The age-water relationships was then integrated with Cole-Cole dispersion via water-dependent permittivity and conductivity equations. The resulting model allows obtaining age-specific conductivity and permittivity of brain tissues at frequencies higher than 50 MHz. In addition, it provides confidence intervals accounting for both intra-subject and inter-subject variability. In terms of applications for brain studies, this model enables age-specific electromagnetic simulations for pediatric subjects and evaluations on the safety of electromagnetic exposure in developing brains. An open code is freely available online to compute electrical properties and their uncertainties as a function of frequency and age.