Dear all,
sorry that I am asking this question again but till now nobody answered. If the question is not understandable please write me so I can maybe explain it differently.
I am a bit confused. I do not understand why the mean_ph, mean_th files of the bedpostx output are 3d files?
I thought they are describing the spherical coordinates (angles) of the principle diffusion directions thus I supposed to see something like a scalar value (degree, rad) for each voxel. So for example in voxel one phi has a scalar value of x1 and in the next one x2 ...
I also checked the histogram of the mean_phi files but in this case again I do not understand the files. Some of the values are very high, some are almost equal to zero.
For my work I want to compare the principle diffusion directions per voxel calculated from different measurements via bedpostx command.
Therefore I need to calculate some statistic values (mean, covariance matrix, trace) to check which measurement is the best to find direction information. In my experiment I repeat each measurement 5 times to get some statistic. To average these 5 I thought to do flsmaths mean command. From there on getting from the mean image the main direction information via bedpostx. Is this the correct way to do it? Or do I have to do it that way https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT/UserGuide?action=AttachFile&do=view&target=dyads.jpg ? So doing bedpost with every 5 measurements and then average it afterwards. For me it is not really clear why in this approach they calculate a mean dyad tensor instead of just taking the mean vector and the trace of the covariance matrix of all measurements?
1. So how can I interpret the mean_phi? Why is it 3d and for what exactly are the values stand for?
2. Is my idea for the statistical analysis correct? If not, how can I do it correct.
3. Do somebody know where I can find some more detailed explanation of the dispersion calculation or how I can calculate precision and accuracy of a measurement compared to other measurements (different b-value and DWI)?
thank you for any kind of help
cheers
Max
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