Back in July I posted about a strangely-failed fMRI run, and yesterday I discovered that we had another case not quite two weeks ago. This is the same study, scanner (3T Siemens Prisma), headcoil (32 channel), task, and acquisition protocol (CMRR MB4) as the July case, but a different participant. I've contacted our physicists, but we probably can't investigate properly until after the holidays, and are hampered by no longer having access to some of the intermediate files (evidently some of the more raw k-space/etc. files are overwritten every few days).
I've asked our experimenters to be on the lookout, and while hopefully it won't happen again, if it does, I hope they can catch it during the session so all the files can be saved. If anyone has ideas for spotting this in real time, please let me know.
A possibly-relevant data point: the participant asked to have the earbuds adjusted after the first task run. The technician pulled the person out of the bore to fix the earbuds, but did not change the head position, and did not do a new set of localizers and spin echo fieldmaps before starting the second task run (the one with the problem). I've recommended that the localizers and spin echo fieldmaps be repeated whenever the person is moved out of the bore, whether they get up from the table or not, but the technician for this scan did not think it necessary. What are your protocols? Do you suggest repeating localizers? No one entered the scanning room before the problematic July run, so this (pulling the person out) might be a coincidence.
Here's what the this most recent case looks like. First, the three functional runs' DICOMs (frame 250 of 562) open in mango, first with scaling allowed to vary with run:
In July the thinking was that this is an RF frequency issue, possibly due to the FatSat RF getting set improperly, so that both fat and water were excited. But this seems hard to confirm from the DICOM header; this time, the Imaging Frequency DICOM field (0018,0084) is nearly identical in all three runs: 123.258928, 123.258924, 123.258924 (runs 1, 2, and 3 respectively), which is very similar to what it was in July (123.258803).
