I don’t think this will get you very far. The time between echos (delta TE) will just scale the amount of distortion. After figuring this out, you’ll then hit the even more unclear determination of the effective echo spacing (or total readout time) of the EPI data you want to correct for distortions. And you will never know whether the source of problems is one or another.
One important thing is having very clear in your mind what times are relevant for which image:
- phase1/2 or phasediff - you care about EchoTime1/2 or the “delta TE” but you don’t generally care for the effective echo spacing (except you are using a very fast EPI with obvious distortion on your fieldmap magnitude and phase, where you’ll need that information to unwarp the fieldmap first, invert the deformation and proceed with the other EPIs you want to correct - so typically no one does this).
- EPI (dwi, bold) - here you only care about the total readout time or the effective echo spacing (which are to faces of the same coin).
So, for you to get going, the first step is to figure out the delta TE of your fieldmap. The fact that the second phase image has Echo_Time = 0.0 might indicate that the delta TE is exactly the Echo_Time of the first image. A delta TE of 3.2 ms makes sense (Siemens typically has 2.46ms).