Anders Dyhr Sandgaard from the Neurophysics group at CFIN recently defended his Masters thesis on: "Probing White Matter Microstructure with Magnetic Susceptibility Imaging using MRI"

28.06.2019 | Henriette Blæsild Vuust

Anders Dyhr Sandgaard
Probing White Matter Microstructure with Magnetic Susceptibility Imaging using MRI

Abstract:

For decades, Diffusion MRI has been the main field of research in order to achieve information about the tissue microstructure from an MRI signal. However, diffusion alone can not determine the biophysical parameters.
Magnetic susceptibility has shown great promise as a way to obtain "orthogonal" information about the microstructure but models relating microstructure and magnetic susceptibility are less developed.

My thesis will describe and test how magnetic susceptibility in nervous tissue affects an MRI signal.
By simulating the MRI signal from numerical white matter phantoms we will show how demyelination affects the signal, and how we can increase the demyelination sensitivity by higher applied magnetic fields.
Many well-established theories relating the MRI signal and tissue microstructure exists, and as a part of this thesis we will show how the validity of the General Lorentzian Tensor Approach depends on the echo time and the applied magnetic field strength.
In order to quantify the magnetic susceptibility in white matter, Susceptibility Tensor Imaging (STI) is regarded as the gold standard.

This thesis will describe an alternative approach: Demagnetization and Susceptibility Tensor Imaging (DSTI), and show that it outperforms STI in calculating the secondary field generated by the magnetic tissue. Using DSTI we show how fiber dispersion affects the MRI signal and greatly dampens susceptibility effects.
Lastly, real MRI data from rat spinal cord will be fitted to a susceptibility signal model in order to show the precision of current signal models and to emphasize the need for secondary signal protocols to obtain information about water exchange, diffusion and fiber dispersion.

The thesis is available and if you are interested in getting a copy of Anders' work, please contact him at:
Anders Dyhr Sandgaard 201407835@post.au.dk