Ahhh, I’m so sorry, for some reason the viewer I was using was rescaling the values… switched to MRIcroGL, and sure enough, the range is between -500 and 499. I think that should solve the mystery for now, because now they look identical to the images I posted above and have the correct range for an actual fieldmap in Hz…
I agree it’s strange that philips would be spitting out a calculated fieldmap… but it does gel with everything I’ve read, including the non-siemens (ie philips) data section in the FSL FUGUE guide.. FSL - FMRIB Software Library
and the Leiden philips fieldmap guide which they link to in that page.
Thanks so much for the linked sdcflows pages. Regarding calculating the EES on philips, I see that both formulas (FSL listserv, and Dr. Rorden’s) are mentioned. I have looked for the ImagingFrequency tag, but I absolutely cannot find it, neither in all of the philips metadata buried in the PAR which I have scoured, nor from the scanner report, so would it be possible to just use the slightly less precise formula (this data is from a philips Achieva 3T, so that should match):
which seems to be equivalent to the FSL listserv (except for the ETL being interchangable with EPI in this case)
"For Philips Acheiva, the best equation for echo spacing is
echo spacing =(1000*wfs)/(434.215 *(etl+1))
If so, then I have all the values I need.
Also, is the ReconMatrixPE value from philips reliable enough to calculate the TotalReadoutTime? I read that it was not possible to calculate ETL from the reconstructed matrix size in philips, but didn’t see anything about ReconMatrixPE not working for calculating TRT.
Let me know,
Again, many thanks. I feel like I’m very very close.