Print

Print


Dear all,

Hopefully this manual for B0 unwarping with data from a philips scanner can be of use to you: https://osf.io/hks7x/

It took us quite some time to figure it out, but the results after correcting look good (we also ran it by Mark Jenkinson), so I'm happy that others can now use this and maybe even improve it. Please let me know if you have any questions or suggestions. 

For the specific question of shifting voxels in the wrong direction; this may have to do with the scan you acquired, the last part of the manual briefly touches on that. 

Cheers,

Anna van 't Veer



> Op 4 aug. 2017 om 16:02 heeft Ian Malone <[log in to unmask]> het volgende geschreven:
> 
> Hello,
> 
> I re-discovered this old post about a S/I gradient in field maps from Philips scanners, as I'm currently looking at some Philips data which displays exactly the same issue. Did you ever manage to resolve it?
> 
> Best wishes,
> Ian
> 
>> On 09/07/12 16:32, Michael Harms wrote:
>> My apologies for re-posting this one more time, but I'm really stumped.
>> I would REALLY appreciate it (and would be happy to treat you to a
>> beverage of your choice at the next OHBM) if someone that has
>> successfully acquired and applied field map correction from a Philips
>> Achieva could contact me with what they had to do.
>> 
>> I'd be happy to then summarize whatever I learn to the broader FSL-list.
>> 
>> thanks,
>> -MH
>> 
>>> On Fri, 2012-06-29 at 11:38 -0500, Michael Harms wrote:
>>> Hello FEAT users with Philips scanners,
>>> 
>>> I would be highly appreciative if someone that has successfully applied
>>> fieldmapping correction (B0 unwarping) using Philips scanner data would
>>> contact me off the list so that I could pick your brain.
>>> 
>>> We have data from a multi-site study, of which one site was a Philips
>>> scanner.  I *thought* that I knew what needed to be done to apply
>>> fieldmapping correction for the data from this site, but the comparison
>>> in the Prestats report of "undistorted example_func to undistorted
>>> fieldmap" clearly shows that we don't have something right.
>>> 
>>> The odd thing is that the "Unwarping shift map" from the Philips site
>>> data shows a spatial pattern that is completely different from what we
>>> observe from 4 different Siemens sites.  Namely, it has a rather strong
>>> S/I gradient, with negative voxel shifts inferiorly, and positive voxel
>>> shifts superiorly.  This makes me wonder if what we collected wasn't a
>>> proper fieldmap (the site collected a FFE with "B0 field map = yes" and
>>> "delta TE = 2.5 ms"), but if that's the case, I'd like to know what the
>>> site needs to do differently at the time of acquisition.
>>> 
>>> Thanks in advance!
>>> -MH
>>> 
>>>