<div>Dear MRtrixers,</div><div><br></div><div>There are several questions regrading statistical analysis after fiber tracking, which may not necessarily relate to each other. </div><div><br></div><div>1) Given the tracking output file *.tck, is there any way to read out the mean direction of selected fibers in every voxel where crossing fibers have been removed? This voxelwise directional information is anatomically specific and therefore can be very useful in statistical analysis. </div>
<div><br></div><div><div>2) For the purpose of statistics (not fiber tracking), what kinds of metric would you recommend to derive from either the original ODF or fiber ODF? I haven't seen much this kind of work yet in literature. It would be nice to have some brainstorming here. </div>
</div><div><br></div><div>3) I was wondering how to interpret properly the physical meaning of the track number or density that streamtrack generates.<span class="Apple-style-span" style="font-family:Arial;font-size:13px"> </span>The program streamtrack can generate arbitrary large number of tracks by manipulating the option "-number". T<span class="Apple-style-span" style="font-family:Arial;font-size:13px">he track density </span><span class="Apple-style-span" style="font-family:Arial;font-size:13px">(i.e. </span><span class="Apple-style-span" style="font-family:Arial;font-size:13px">"-fraction" outputs of tracks2prob</span><span class="Apple-style-span" style="font-family:Arial;font-size:13px">)</span><span class="Apple-style-span" style="font-family:Arial;font-size:13px"> seems to remain quite stable</span><span class="Apple-style-span" style="font-family:Arial;font-size:13px"> even if I increase </span>the total tracking number <span class="Apple-style-span" style="font-family:Arial;font-size:13px">1000 times in streamtrack with option</span> "<span class="Apple-style-span" style="font-family:Arial;font-size:13px">-number"</span><span class="Apple-style-span" style="font-family:Arial;font-size:13px">. Different than the TDI method based on whole brain tracking, I am only interested in the tracks within a ROI.</span> It seems to me it makes more sense to use the track density instead of track numbers in statistical analysis. Is it reasonable to do so even if the tracking is restricted in a ROI?</div>
<div><br></div><div>Thanks, </div><div>Zhuang</div><div><br></div><div><br></div><div><br></div><div><br></div>