Very helpful thank you Rachelle!

Il Gio 14 Giu 2018, 19:22 Rachelle Ho <[log in to unmask]> ha scritto:

Hi Carlotta,

Fieldmap unwarping is helpful but not necessary. If you have B0 scans, you'll be able to create a fieldmap with FSL. The fieldmap corrections help fix any distortions you see in your functional scans. If you register your functional images to an anatomical and find that the functional image looks odd / warped / doesn't match the boundaries of the anatomical, fieldmap corrections can help correct and improve the quality of your data before you analyze it. 

Functional / EPI data is susceptible to distortions in the magnetic field, which causes some of the distortions to the shape of your images. That's why we collect information about the fieldmap when the data is acquired.

Hope this helps answer your questions. 

Best wishes,

Rachelle

On Thu, Jun 14, 2018 at 5:48 AM, Carlotta Fabris <[log in to unmask]> wrote:

Hi Matthew, sorry to bother you again, but I was wondering if the B0 unwarping is a necessary step in a preprocessing pipeline.

I am asking you this, because I never did it and I don't have a field map to put as input, but should I perform this step or is it required only in certain conditions?

The information I have on my data are these: Data were acquired on a 3 Tesla Siemens Vereo MRI scanner with a 32-channel birdcage radio frequency headcoil (neckcoil was not used, leaving 28 channels). For the functional scans, a 28 slice axial prescription (5 mm thickness) gave whole brain coverage. For each imaging run, a series of 190 gradient echo echoplanar volumes were acquired over each: TE = 35 ms, TR = 2000 ms, Flip Angle =75O, NEX = 1, BW = 100.0, FOV = 24mm, matrix =128 x 128 (in-plane resolution of 1.875mm2).

Thank you,
Carlotta.

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