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Abstract #0576

Dependence of Axon Diameter Index on Maximum Gradient Strength

Tim B. Dyrby1, Penny L. Hubbard2, Maurice Ptito3, Matt G. Hall4, Daniel C. Alexander4

1Danish Research Centre for Magnetic Resonance, Copenhagen Univerviersity Hospital, Hvidovre, Denmark; 2Imaging Science and Biomedical Imaging, University of Manchester, Manchester, United Kingdom; 3School of Optometry, University of Montreal, Montreal, Canada; 4Centre for Medical Image Computing, University College London, London, United Kingdom

We aimed to elucidate the dependence of the axon diameter index on the maximum available gradient strength (Gmax). Optimised protocols were produced that were sensitive to a-priori axon diameters of 1, 2 and 4 μ m for Gmax = 60, 140, 200 and 300mT/m, and data were acquired on fixed monkey brain. The mapped axon diameter index was sensitive to Gmax but relatively constant for >140mT/m. Simulations suggest that at low Gmax (60mT/m), axon diameters <3μ m are indistinguishable, which explains the unexpectedly high values at low Gmax.