Susceptibility distortion correction using DTI

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Hello Experts!

I have a 8 factor MB resting fMRI, DTI data but no fieldmap or singleband ref was acquired.
This particular protocol was set from way before, so unfortunately I have to work with what I got…

I understand fMRI scans use gradient-echo (GE) and DTI scans use spin-echo (SE) sequence. From what I was able to find online was that I could use DTI (AP and PA) scans to correct for susceptibility distortion for fMRI data through Topup and applytopup. However, seems like there was no “correction” done on any of the data. It almost seemed like the corrected images had gotten blurrier (or foggier) if that makes any sense. Is there a way to check whether both fMRI and DTI sequences have the same parameters from json file? Or a way I could use fmriprep to do the correction using SE sequence?

Thank you in advance.
Happy holidays!

Best,
Erin

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I would look suggest these comments and links. The amount of sequence information in your JSON and DICOM files depends on the manufacturer (Philips are impoverished relative to GE and Siemens). Assuming you have data from Siemens or GE, the JSON should provide relevant details about phase encoding polarity (blip up or blip down), readout time, etc.

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Alternatively, you could apply the fieldmap-less SDC approach from fMRI/QSIPrep.