Here are a few preliminary plots performed on this scan.
First, I investigated the zig-zag effect and found that a correction of 3 to 4 samples could improve things. This needs to be further understood and corrected at a lower level of TOI processing. Here are a few plots of the beam centroids of valid pixels near the center of the 2mm matrix computed with only the forward scans and only the backward scans for various shifts of the timeline. The last plots shows a fit of the total distance between beams as a function of the shift and shows an optimum at -3.5. We choose to apply a correction of -3 in the following.