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MASILab / Synb0-DISCO

Distortion correction of diffusion weighted MRI without reverse phase-encoding scans or field-maps
https://my.vanderbilt.edu/masi
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Questions on acqparams #44

Closed lyhoo23618-csu closed 1 year ago

lyhoo23618-csu commented 1 year ago

Dear experts,

I am wonderring how to set the acqparams file. In my case, my phase encoding direction is "j-", so I set my acqparams.txt as “0 -1 0 0.043 0 -1 0 0”

Can you help me check this is correct or not? I want to know whether the parameters of the synthesized, undistorted, b0 should keep consistent with my orginal real b0 volume.

Thanks a lot.

Kind regards, Hao Li, MD, PhD candidate, Radboud UMC, Nijmegen, the Netherlands

njhunsak commented 1 year ago

Great question. I would love to know the answer as well. Does the synthesized, undistorted b0 image match the PED of the original b0, should it be set with opposing PED, or is it always set to 0, 1, 0, 0?

schillkg commented 1 year ago

Hi all - sorry for the delayed response. The answer is that it doesn't matter, as long as the total readout time (the 4th index) is set to 0! The acqparams in the documentation just happens to be how we tested and validated the algorithm, but TOPUP is smart enough that you can actually do 1 0 0 0, -1 0 0 0, 0 1 0 0, 0 -1 0 0, 0 0 1 0, etc., these in theory will all lead to the same distortion (i.e. no distortion).

njhunsak commented 1 year ago

Thank you for the clarification.