Hello Mrtrix Team,
for a study I would like to compare DWI data of two groups, one is doing sport and the other not and only serve as comparison. I would like to analyse the WM integrity. I found on your webpage different topics and terms, such as AFD, FC, and FDC. However I have still some questions:
- What would you suggest to do for such project? Doing the fixel based analysis as described in: http://mrtrix.readthedocs.io/en/latest/fixel_based_analysis/mt_fibre_density_cross-section.html?highlight=afd
or is it enough to calculate and compare AFD maps via fod2fixel and fixel2voxel, or is there another approach implemented in MRtriX?
2.What are exactly the differences between the metrics AFD and FC, FC and FDC?
- The fixel based tutorial includes also tractography (19-22), are these steps necessary in case of a WM integrity comparison?
Thank you for your support!!!
Dear Rob, thank you very much for the information and your help. I read the FBA paper, however, may I ask you another question: in case of an longitudinal study what would you recommend for a fixel-based analysis, especially considering step
4. Computing group average tissue response functions and step
9. Generate a study-specific unbiased FOD template?
Should I first register each session of each subject internally to an template and then take the averaged as an input for the subject-wise analysis or can I directly take all data including each session of each subject for the fixel-based analysis from the very first beginning?
Thank you for your support!
I believe the generally accepted best approach for longitudinal studies is:
- Generate an individual template for each subject across sessions.
- Produce the population template using the set of individual templates as the inputs.
- For each session:
- Get a single transformation to population space, based on the composition of (session -> individual template) and (individual template -> population template) transformations
- Transform and reslice image data in population space using this composed transformation
This is perhaps something that we could provide more details on in the documentation? It seems an approach that a number of people around here are converging on.