We have analyzed a dataset using tractography in ExploreDTI and we have extracted the tract information. There are a few questions I have about the spreadsheet when we are converting the mat files of the tracts into a text file:
1. Mean tract length seems to be (((number of points)/(number of tracts))-1). So, does this mean that the number of points is simply the number of voxels that the tracts are passing through? Why that -1 is included in the calculation?
2. How the approximate tract volume is computed? I thought that it is the number of voxels multiplied by the voxel volume, but I calculated those (using points = voxels!) and figured out that it's not!
3. Is the mean angle the average of the angles each glyph makes with the next one in each tract averaged for all the tracts?
4. MD is (lambda1+lambda2+lambda3)/3 and RD is (lambda2+lambda3)/2. One can calculate each of these separately by having the values for the mean lambdas. Is there a specific reason why RD is included in the spreadsheet, but not MD (or AD), though they both can be calculated from the lambdas?