Investigating the Extracellular Contribution to the Double-Wave-Vector Diffusion-Weighted Signal

Using two independent pairs of gradient pulses it is possible to obtain non-invasive tissue structure information by comparing the signal between different diffusion gradient orientations. The parallel-perpendicular signal difference is analyzed in vivo and in vitro as an indicator of irregularly shaped pores contributing to the diffusion-weighted signal. The results suggest that the acquired signal in the corticospinal tract contains significant contributions from extra-axonal space, consistent with unexpectedly large pore size estimates from earlier experiments.