Bernard Siow1, 2, Andrada Ianus1, Ivana Drobnjak1, Mark F. Lythgoe2, 3, Daniel C. Alexander1
1Centre for Medical Image Computing, UCL, London, United Kingdom; 2Centre for Advanced Biomedical Imaging, UCL, London, United Kingdom; 3Institute of Child Health, UCL, London, United Kingdom
We map axon radius index in the corpus callosum of an ex-vivo rat brain using orientationally invariant optimised oscillating gradient spin-echo (OGSE) diffusion MRI protocols. Reliable estimates of axon diameter estimates require high gradient amplitudes and short diffusion times. OGSE sequences can have have shorter diffusion times compared to Pulsed Gradient Spin Echo (PGSE) sequences, thus allowing shorter length scales to be probed. We optimised OGSE protocols and estimated tissue microstructure parameters by adapting the ActiveAx technique. We found that the estimated parameters are consistent over all OGSE protocols investigated. Furthermore, our results suggest that the square wave OGSE protocol has greater precision compared to the other OGSE protocols investigated.