Optimised Gradient Waveform Spin-Echo Sequence for Diffusion Weighted MR in a Microstructure Phantom

Bernard M. Siow^1,2, Ivana Drobnjak¹, Mark F. Lythgoe², Daniel C. Alexander¹

Diffusion MRI has been used for probing tissue microstructure and of particular interest is axon radius distribution estimates. Abnormal distributions are found in pathologies such as amyotrophic lateral sclerosis and schizophrenia. PGSE sequences have been traditionally used for diffusion weighting and optimised protocols that use these sequences have been used to provide reliable axon radius estimates >5m. Recently, an in silico study optimised the shape of the gradient waveforms for particular axon radii and showed that protocols that used these optimised waveforms provided improved axon radii estimates <5m. In this study, we implement these optimised gradient waveform protocols on a pre-clinical scanner. These protocols were used to study microcapillary phantoms that have pore radii of 1-10 m. A good agreement between simulated and measured signal was found, giving a strong indication that these sequences can be practically implemented in vitro and in vivo. Potentially, these protocols can provide extra sensitivity to microstructural features <5m.