Dear Alistair,
> I would like to try out the new EDDY tool, as our lab has high b-value data on a Phillips 3T scanner.
>
> However, in comparison to the traditional eddy_correct, I noticed that there are a few extra compulsory arguments that need to be defined.
>
> For starters, is there any possible way to check the direction of the phase-encoding and the total readout time, after the scans have already been collected.
>
> I have access to the exam card, but the only information I have been able to obtain is the phase-encoding direction for the y-axis (which is ant-post).
are all scans collected with the same polarity (i.e. ant->post)? If so, it is important that the diffusion directions have been sampled on the whole sphere (N.B. that it is quite common that the directions are only sampled on the half sphere which give the same diffusion information but inferior information when it comes to corrections for eddy current distortions).
You can calculate the total readout time as the dwell time multiplied by (n-1) where n is the number of echoes of your EPI acquisition. If you don't have that information you can put any value in there (e.g. 0.1) which means that the fields you calculate will not be scaled correctly but the distortion correction ail still be the same.
I quite think of eddy as a "prospective tool" in the sense that you may need to rethink your acquisition protocol (and what information you record in your scan log) slightly in order to get it to work optimally.
Jesper
>
> Thanks
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