Averaging Reoriented FODs

Hi mrTrix,

I created a HCP population template from T1/T2 anatomical volumes using ANTs and reoriented the FODs into the template space using warpinit/warpcorrect/mrtransform. I would like to average these FODs to create a population FOD. Can I simply average the SH coefficients at each voxel across the subjects or how do you recommend to create the average? Also how does this approach compare to the population_template command I see it just uses MSD.


Yes, assuming the FOD images are normalised, you can simply average them. population_template does the same.

population_template creates a template using the FODs but does not work with cross-modality input. Your approach aligns everything to anatomical space while the typical use-case of population_template is to align the diffusion images to the average diffusion-space and then - if needed - warp the anatomical images to that average diffusion space, for instance, using the warps you get from population_template. It really depends on the type of analysis you are interested in but the advantage of aligning the FODs is that besides amplitude you have orientational information (and possibly multiple tissue contrasts) to guide registration.