[Mristudio-users] Sagital DTI

[Vadim Malis]

We are acquiring a DTI sagital slice of the lower leg on a 1.5 T GE scanner (feet first, supine).  When we look at the bvec values in the DICOM header, they are correctly (re) oriented.  This is by comparison to an axial DTI scan (our regular orientation for DTI).  We also confirmed from the mristudio-users group that indeed GE scanners give the correct bvec orientation that tracks slice orientation.  However, when we extract the eigenvectors for the sagittal slice using the bvecs from the DICOM headers, the lead eigenvector shows the X axis (LR) and the Z axis (SI) switched.  Where we expect fiber eigenvectors to point SI, they are in LR.  When we switched gradient values in the bvec file (X-->Z and Z--> X) we did get the DTI lead eigenvector to be in the correct direction, but when fiber tracking it appears somehow the tracking switches X and Z again.  We would really appreciate if an expert could tell us what we are doing wrong.

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Vadim Malis
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