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REQUEST: Two successive SBRef with opposite phase encoding directions #210

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CesarCaballeroGaudes opened this issue May 10, 2018 · 2 comments

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@CesarCaballeroGaudes
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It might be very useful to acquire two SBRef volumes with reverse phase encoding so that the two images have minimal head displacement between the two acquisitions. This might prove very beneficial for correction of susceptibility induced distortions (i.e. geometric distortions) using procedures such as topup in FSL or 3dQwarp in AFNI.

@dowdlelt
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I'll second this, capturing reverse phase encoding images within the sequence would simplify and speed things up - the SBREFs are already fantastic for this purpose, but running a seperate sequence does increase dead time in the scan, and participants like to move the moment the scanner gets quiet.

@BenInglis
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Suggest cross reference with #194, acquisition of multiple SBRef, and #193, to set FA separately for SBRef from the time series, and perhaps make the PE direction and FA explicit for an arbitrary number of SBRef. We could then set things up in any combination we like, such as:

N_SBRef = 2
FA_SBRef = 45
PE_SBRef = AP, PA

with the time series FA set normally (say 45 deg here) and PE dir set normally (say AP here) for the actual time series.

Or:

N_SBRef = 10
FA_SBRef = 30,30,30,30,30,60,60,60,60,60
PE_SBRef = AP

with the time series FA set normally again (say 60 deg here) and PE dir also set normally (AP again here) for the time series.

Not sure how the recon should be handled, but at a minimum it would be nice to have a pointer to an array of >1 SBRefs so that we can choose the particular single band data to use for online recon. Maybe RetroRecon suffices for the remaining options when SBRef > 1.

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