Hi Erin,
For completeness sake (I have been asked to confirm this by others), I will add that @smeisler’s answer is correct. The relevant method software is also available in NeuroDesk, see e.g. Problem with Mrtrix3 installation - #2 by orencivier . I will furthermore add this:
We have written a large FBA review work recently: “Fixel-based Analysis of Diffusion MRI: Methods, Applications, Challenges and Opportunities”. Google or copy paste the DOI link: https://doi.org/10.1016/j.neuroimage.2021.118417 as I am not allowed to post any links e.g. to proper references on this forum. This work includes a lot of details on the acquisition requirements, limitations and their implications for FBA. There is also a comprehensive overview of all FBA studies up until the appearance of this review work, including stats/facts on what acquisitions they all have used. You’ll find that many people have been able to publish FBA studies with low b-value single-shell data such as b=1000, etc… Feel free to contact me with any questions you might have on this work. I encourage to also take a look at the supplementary documents: we have had a lot of positive feedback on their practical use recently.
All the best,
Thijs