Feasibility of axon diameter estimation in complex fiber architectures by powder averaging of the diffusion MRI signal

Orientation dispersion bias in axon diameter measurements can be removed by powder averaging of the diffusion MRI signal in isotropically distributed directions, but has not been validated in complex fiber architectures. Here, we demonstrate the success of the spherical mean technique (SMT) and a recent power law (PL) implementation in removing orientation-related bias in diameter estimates of real axons from the splenium corpus callosum and a complex crossing fiber region of the vervet monkey brain. In the crossing fiber region, we find a significant population of very large axons, indicating a need for sensitivity to a wide range of diameters.