Hi Josh,
Thanks for sharing that.
I am not sure what the reason for that might be. Can I please ask you to confirm whether the two acquisitions are indeed identical? Are you sure you don’t change phase encoding direction or b-value between the first and the second acquisition?
Otherwise, do you take out the subject/patient between the two scans? Or, does that scanner perform automated re-shimming after the first acquisition?
Cheers,
Matteo
> On 23 Jul 2019, at 18:14, Josh Robinson <[log in to unmask]> wrote:
>
> Hi experts,
>
> Me again. In trying to solve my question regarding the numbers in eddy_parameters, I tried eddy_quad and saw something concerning in the outlier distribution on the last page.
>
> My output is here: https://drive.google.com/file/d/1JhGi2bzeHLFXHJ-R-9wPeJIqeTmvomWO/view?usp=sharing
>
> The first and second half are extremely different - in the first half slices skew almost exclusively negative, and the second half is predominantly positive. I saw on the eddy documentation that positive outlier slices are uncommon, and it isn't recommended. I get that positive outliers can occur, but I am wondering why they only really occur in the latter half.
>
> I am worried this is an issue with our acquisition/correction scheme. We collect two identical acquisitions (1 b=0, 32 b=700, A>P) and concatenate them for analysis.
>
> Help would be much appreciated, thanks.
>
> Josh
>
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