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Hi, for non-custom angulated recordings they may differ - if xyz is used for reference (for PRS it won't matter). Cheers- Andreas ________________________________________ Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von Martin Kavec [[log in to unmask]] Gesendet: Freitag, 9. April 2010 23:34 An: [log in to unmask] Betreff: Re: [FSL] AW: [FSL] which bvecs to trust? Excellent job, Martin and thanks for posting your experience. I am not sure if I didn't pick it in your message (it's close to midnight), but how do the bvecs from the two programs compare to the Siemens datasheet? A word of causion, you might want to do the same exercise with a custom diffusion gradient table. Philips for instance, which I work with, is rotating my custom gradient table differently than the built in one. Best, Martin On Friday 09 April 2010 22:42:50 you wrote: > Hello all, > > sorry, it took me a while to get some spare time on our TRIO. Here's what I > did: I scanned a person using the standard Siemens > MDDW-20direction-DTI-sequence with 19 slices (5 mm) and set the angulation > to 0° (transverse). Images had been saved in mosaic format. As the > sequence uses four averages, the dataset results in 84 (4*(B0 + 20 > vectors)) mosaic images. The images are saved in the following order: B0, > vector 1, vector 2, ..., vecotr 20, B0, vector 1, vector 2, ..., vector > 20. Then, I used dcm2nii and MRIconvert on a PC AND a MAC and compared the > bvec files with the vector datasheet provided by Siemens. > > MOST IMPORTANT: Both programs give you almost the exact vectors. dcm2nii > seems to smooth a little more than MRIconvert. > > I did notice one thing: MRIconvert sorts the data differently to the > original one and the dcm2nii results. MRIconvert sorts it in: B0, B0, B0, > B0, vector 1, vector 1, ..., vector 20, vector 20, vector 20, vector 20. > But it uses this sorting ordern in all three files: bvec, bval and the > 4D.nii-file. So in my point of view that does not seem to be a problem > (can someonce with a lot more knowledge comment on that?). > > I don't have the bvec-files with me right now, but if interesten I could > also post the files (might be easier than reading the text). > > Have a good weekend, > Martin