Noemi G Gyori^{1,2}, Matt G Hall^{2}, Christopher A Clark^{2}, Daniel C Alexander^{1}, and Enrico Kaden^{1}

^{1}Centre for Medical Image Computing, University College London, London, United Kingdom, ^{2}Great Ormond Street Institute of Child Health, University College London, London, United Kingdom

In in-vivo B-tensor encoding measurements, linear tensor encoding (LTE) and spherical tensor encoding (STE) waveforms estimate the same mean diffusivity in brain white and grey matter. Contrary to this, we show that in Monte-Carlo simulations of quasi-spherical restrictions, LTE and STE signal decay curves are markedly different and lead to different mean diffusivity estimates. We investigate this discrepancy in the presence of variable compartment sizes, geometric distortions in cell shapes, permeable cell membranes, and water exchange between connected cellular geometries. Our results suggest that a strict model of restricted diffusion may not be suitable for brain tissue.

In this work, we study the effect of cellular restriction on B-tensor encoding measurements. We use Monte-Carlo simulations to show that within spherical compartments, the diffusion signal is markedly different in linear tensor encoding (LTE) and spherical tensor encoding (STE), contrary to what in-vivo data suggests. We investigate this discrepancy in different cellular configurations.

After informed written consent, a healthy volunteer was scanned on a 3T Siemens Prisma scanner using a 64-channel head coil, and a diffusion-weighted EPI sequence that allows measurement with arbitrary gradient waveforms, developed in-house. Isotropic 2 mm voxels were acquired with TE = 96 ms and TR = 9.5 s, at b-values of [0, 500, 1000, 1500, 2000] s/mm

We performed Monte-Carlo simulations using Camino

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