Multi-shell multi-tissue constrained spherical deconvolution
Multi-Shell Multi-Tissue Constrained Spherical Deconvolution (MSMT-CSD) exploits the unique b-value dependencies of the different macroscopic tissue types (WM/GM/CSF) to estimate a multi-tissue orientation distribution function (ODF) as explained in [Jeurissen2014] As it includes separate compartments for each tissue type, it can produce a map of the WM/GM/CSF signal contributions directly from the DW data. In addition, the more complete modelling of the DW signal results in more accurate apparent fiber density (AFD) measures and more precise fibre orientation estimates at the tissue interfaces.
MSMT-CSD relies on multi-shell high angular resolution diffusion imaging (HARDI) data, containing multiple b-values. The number of tissue types that can be resolved is limited by the number of b-values in the data (including b=0). To resolve the three primary tissue types in the brain (WM, GM & CSF), the acquisition should contain at least 2 shells along with the b=0 volumes (i.e. 3 unique b-values).
In addition, this command expects that suitable multi-shell multi-tissue response functions have already been computed. A number of approaches are available for this, please refer to the Response function estimation page for details.
Multi-shell multi-tissue CSD can be performed as:
dwi2fod msmt_csd dwi.mif wm_response.txt wmfod.mif gm_response.txt gm.mif csf_response.txt csf.mif
dwi.mifis the dwi data set (input)
<tissue>_response.txtis the tissue-specific response function (input)
<tissue>.mifis the tissue-specific ODF (output), typically full FODs for WM and a single scalars for GM and CSF
Note that input response functions and their corresponding output ODFs need to be specified in pairs.
Typically, you will also want to use the
-mask option to avoid unnecessary computations in non-brain voxels:
dwi2fod msmt_csd -mask mask.mif dwi.mif wm_response.txt wmfod.mif gm_response.txt gm.mif csf_response.txt csf.mif
RGB tissue signal contribution maps can be obtained as follows:
mrconvert -coord 3 0 wm.mif - | mrcat csf.mif gm.mif - vf.mif
The resulting WM FODs can be displayed together with the tissue signal contribution map as:
mrview vf.mif -odf.load_sh wm.mif