Partial Volume Effect as a Hidden Covariate in Tractography Based Analyses of Fractional Anisotropy: Does Size Matter?

Sjoerd B. Vos¹, Derek K. Jones², Max A. Viergever¹, Alexander Leemans¹

Diffusion tensor imaging has been used extensively to investigate brain aging. Fiber tractography has shown a relation between age and fractional anisotropy (FA) along fiber tracts. Partial volume effects are known to affect tractography, and may also influence FA calculations along tracts. In this study, simulations and experiments have been performed to test whether tract volume is a covariate in FA calculations. A strong correlation between tract volume and FA has been found in both the simulations and experiments, proving that partial volume effects affect FA calculations, and that size is indeed a hidden covariate in tractography based FA analyses.