Hi FSL-forum,
I try to use eddy_correct on a subset of sagital DTI-data. Only the centre of the brain (main part of corpus callosum; 10 slices to either side) has been included.
It looks "eddy_correct" has difficulties with handling the affine transformation of such a subset since it cannot perform a decent ECC for each gradient encoding.
Some transformation matrices are completely screwed, e.g.
regular (well behaved transform) matrix would look like this:
Final result:
1.006631 -0.000593 0.000401 0.140801
0.002273 1.002451 -0.006194 0.016195
-0.001417 -0.001287 1.008597 -0.137913
0.000000 0.000000 0.000000 1.000000
but for some volumes (gradient orientations) I get matrices like this:
Final result:
0.566810 0.150488 -0.212689 67.358504
-0.107210 0.875570 -0.004303 8.674744
0.138302 0.020314 0.880910 22.970297
0.000000 0.000000 0.000000 1.000000
which leads to completely useless results.
I don't know why ECC is not able to correctly register the individual volumes. The susceptibility induced distortions
between all volumes is minor and other registration software can perfectly handle this. When I also use a complete
sagital set of data (60 slices accross the brain) this behaviour does not occur.
Any help appreciated, as always.
Burkhard.
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