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.