Hi Greg,
Your value for echo spacing sounds very short - on the other hand, 0.55 milliseconds would sound very reasonable. Could it be that you accidentally divided by 1000 twice?
Cheers,
Eelke
> On 2 Oct 2015, at 15:34, Gregory Book <[log in to unmask]> wrote:
>
> Hi Eelke,
> We acquired gradient echo fieldmaps on a Siemens Skyra. I created the fieldmaps using the following command:
>
> fsl_prepare_fieldmap SIEMENS FieldMap_Phase.nii.gz FieldMap_Magnitude_brain.nii.gz FieldMap.nii.gz 2.46 --nocheck # prepare fieldmap for FEAT
>
> In FEAT, I used echo spacing of 0.00055ms and TE of 30ms.
>
> I'm not sure if there are any changes before/after correction. They're not identical, but change very little. I'll try to attach an image.
>
> -G
>
>
> Hi Greg,
>
> Depending on your acquisition the corrections can be quite subtle, but if nothing seems to change something is probably wrong. If all the registrations on the unwarping report page look fine, the first thing I would check are the timing parameters: Echo spacing in the FEAT gui and the delta TE value you used when preparing the fieldmap.
>
> If there are no obvious errors, it would help to know what parameter values you used and how you prepared the fieldmaps (fsl_prepare_fieldmap or some other means?).
>
> Hope that helps,
> Eelke
>
>> On 1 Oct 2015, at 17:55, Gregory Book <[log in to unmask]> wrote:
>>
>> I'm running an fMRI analysis in FEAT and am adding B0 unwarping using gradient echo fieldmaps. I don't get any errors, but I'm not sure anything is really being changed with regards to the fieldmap correction. On the report_unwarp.html page, the example_func to highres images with and without fieldmap correction don't look any different. The movie at the bottom of the page doesn't look like any spatial transformation occurred either, its just changing intensity slightly between corrected and uncorrected.
>>
>> Our EPI data is collected in A>>P phase encoding direction, so I've tried the unwarp direction as y and y-, but both produce the same lack of spatial changes before and after correction.
>>
>> Thanks!
>> -Greg
> <EF_UD_movie.gif>
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