Maybe we should add an additional option like -fslgrad to supply both filenames, which would get around the problem. One generally expects the B-Matrix to be a positive semidefinite having non-negative eigenvalues only. Do keep in mind that we need to repeat this process for each volume.
DTI appears to be a tremendously important tool, as it is sensitive to acute brain injury (you can see strokes that can not be detected by conventional MRI) and it correlates with white matter integrity. FSL format supported: files must have '.bvec' and '.bval' extensions and be labeled 'bvec' and 'bval'. This will be reflected in the diffusion parameters FA, MD, AD and RD. Not doing so often prevents one to realise early on that there might be something wrong with the raw data, which could be either easily resolved issues concerning data formatting or organisation or more serious issues concerning the quality of the data. On the other hand, in some areas such as along the fiber bundles of neurons (e.g.
To complete this tutorial you will want the following:
the corresponding NODDI protocol in FSL's bval/bvec format: NODDI_protocol.bval/bvec the expected outputs in the subdirectory output (see below for the detail) Acknowledgement : The example data set is generously provided by Dr. Gavin Winston from the UK Epilepsy Society MRI Unit at Chalfont.
One can not determine the polarity of the bvec.
Note that FSL expect them in column format. (e.g.
If the b-value equals 0, there is no diffusion weighting (reference scan). The standard b-value for adults is 1000.
Until this is resolved, stable releases of dcm2niix will attempt to resolve the B-vector from the B-matrix.
Your files should be saved in your data folder. This is not related to anisotropy. Must be in the same space as the T1 image. In children, you typically use 600. NIfTI Sub-Formats. The L1, 2, and 3 are your eigenvalues, MD is the ADC value (mean diffusivity), and your eigenvectors are V1, 2, and 3 (along and perpendicular to filter if present). The diffusion parameters are derived from the diffusion tensor, a mathematical model that describes the mobility of water within the tissue Fractional anisotropy (FA): a unitless parameter that describes the directional bias of the water diffusion pattern.
This means there is no way to supply an FSL encoding if the name doesn't match that expected. FA can increase or decrease due to pathological tissue changes. The eigenvalues are used to determine which eigenvector corresponds to which direction.
It assumes that you have a basic understanding of the technique itself as well as diffusion MRI.
This will give you the eigenvectors and eigenvalues. On a 8-core workstation, this may take overnight. It is actually a lot simpler to do it than it is to explain it. Tools and files used in this article: dwmri.dcm dcm2niix nifti_utils dwmri_visualizer FSL dwmri.dcm is a 32 direction, 1000 b-value DWMRI dicom file, dcm2niix is a commonly used DICOM to NIFTI converter, nifti_utils is a library to work with NIFTIs in MATLAB, dwmri_visualizer is a visualization …
The Matlab code below shows the B-matrices provided by @isolovey-robarts sample Bruker DICOM data with attempts to estimate b-vector and b-value from these. A list of programs that can convert images from a scanner to the NIfTI format that FSL requires can be found FSL has written the results as NIfTI format files, and you can open then in FSLView. Further, it woul be nice to see the slice angulation is handled correctly as the FSL bvec format reports the vectors with respect to the image, while the DICOM format is oriented relative to the participant. Minimum input requirements: Image must contain full brain DWI dataset. 32 instead of 16) or increasing the number of times each direction is sampled (e.g.
Must be tagged as 'mask'. For example, in the figure below, water is diffusing faster in A than B. DICOM export is recommended, as getting the diffusion directions from PAR/REC is troublesome. So one would therefore strongly advice to This issue has been resolved to the full extent possible with the provided data. the brain's white matter) the diffusion properties are anisotropic - water will move in the direction of the fibers much more rapidly than orthogonal to the fibers. nDirections by 4, or 4 by nDirections, you will need to organize the table accordingly. First, install BVQXTools (NeuroElf) on your computer. The number of columns is the number of directions.
I tried in the private tags, but with no success.I am going to close this issue. There are multiple volumes, but each at a different diffusion direction.