The diameter of an axon is proportional to the speed at which action potentials are conducted along its length. Therefore any change in the distributions of axon diameters within a white matter tract will impact the operation of brain networks.

By acquiring multiple diffusion-weighted images with a range of diffusion gradient areas and diffusion times, it is possible to extract information about the diameter and density of axons based on theoretical models of “diffusion diffraction” patterns. Axon diameter and density mapping has been limited to in vitro and pre-clinical models because the necessary encoding gradients have only been available on small bore MRI scanners. We capitalize on recently developed gradient technology with much stronger maximum gradients strengths to measure axon diameter distributions in the in vivo human brain for the first time.

The Impact of Gradient Strength on In Vivo Diffusion MRI Estimates of Axon Diameter

Huang SY, Nummenmaa A, Witzel T, Duval T, Cohen-Adad J, Wald LL, McNab JA

NeuroImage, 2015, 106:464-72.

The Human Connectome Project and Beyond: Initial Applications of 300mT/m Gradients

McNab JA, Edlow BL, Witzel T, Huang SY, Bhat H, Heberlein K, Feiweier T, Liu K, Keil B, Cohen-Adad J, Tisdall MD, Folkerth RD, Kinney HC, Wald LL

NeuroImage, 2013, 80:234-45.

In vivo characterization of axonal damage in multiple sclerosis using high-gradient diffusion magnetic resonance imaging

Huang S.Y., Tobyne S.M., Nummenmaa A., Witzel T., Wald L.L., McNab J.A., Kalwiter E.C.

Radiology, doi: 10.1148/radiol.2016151582.

In Vivo Mapping of Human Spinal Cord Microstructure at 300 mT/m

Duval T, McNab JA, Setsompop K, Witzel T, Schneider T, Huang SY, Keil B, Klawiter EC, Wald LL, Cohen-Adad J

NeuroImage, 2015, 118:494-507.