[ITK] Registration framework v3 / v4 and Slicer

[Timothee Evain]

Hello everybody,

Question about the difference between the v3 and v4 registration frameworks:
I conducted some experiments on registration in Slicer with the GeneralRegistration module (from the BRAINS suite), and now I try to get the same result in my own program.
I've learned from Github that the module use the v4 framework, but I'm working with ITK 4.5, and unfortunately this version doesn't bring all that's needed for copying the Slicer code.
So, I've tried to mimick the pipeline with the v3 framework, staying as close as possible (same metrics, same optimizers, same transformation chain, same parameters, etc). But results are quite differents, not bad but definetely not as accurate as the Slicer one (even after toying with the parameters). 

I haven't found a clear comparison document, so does the difference between the two frameworks can explain such results ?

Thanks,

Tim