PurposeA range of advanced diffusion MRI (dMRI) techniques are currently in development which characterize the orientation of white matter fibers using diffusion tensor imaging (DTI). There is a need for a physical phantom with microstructural features of the brain's white matter to help validate these methods. MethodsHollow, co-electrospun, aligned fibers with a tuneable size distribution have been produced in bulk and with an MR visible solvent infused into the pores. The morphology and size of the phantoms was assessed using scanning electron microscopy (SEM) and compared with DTI results obtained on both a clinical and preclinical scanner. ResultsBy varying inner diameter of the phantom fibers (from SEM: 9.5 m, 11.9 m, 13.4 m) the radial diffusivity and fractional anisotropy, calculated from DTI, vary between 0.380.05 x 10(3) and 0.61 +/- 0.06 x 10(3) cm s(-1) and between 0.45 +/- 0.05 and 0.33 +/- 0.04, respectively. ConclusionWe envisage that these materials will be used for the validation of novel and established methods within the field of diffusion MRI, as well as for routine quality assurance purposes and for establishing scanner performance in multicenter trials. Magn Reson Med 73:299-305, 2015. (c) 2014 Wiley Periodicals, Inc.