TOPUP not compatible with rodent images

[eilidhmacnicol]

Rodent image headers are often scaled ~x10 to get 'human-sized' images
Estimating the field with topup will not work well without this step, so using unscaled images will cause poor estimation of the distortion.

@eugenegkim adjusted FSL's default b02b0.cnf configuration file by dividing the --warpres and --fwhm numbers by 10 to account for this, and ran topup with unscaled images and compared it to the results we get when we scale the headers by 10 and use the original settings (obtained with FSL 5.0.10 running on a Linux server).

scaled images:


unscaled images:

These do not demonstrate the worst case, but it was what we had to hand. There is probably some other setting hard-coded (possibly b-spline distance?) that is defined in mm and consequently not optimal for rodent images.

[oesteban]

https://github.com/nipreps/sdcflows/tree/master/sdcflows/data/flirtsch