<div>Hi <br>I have been using DTIStudio for a while for tracking fibers in muscle. Muscle fiber FA values are lower than white matter ( in the range 0.2-0.4).<br>I am currently evaluating with a capillary phantom with an FA of 0.20. This is a straight 5 cm capillary imaged with the capillary axis along the z-axis.<br>
I am trying to check the SNR conditions, as well geometry parameters that provide an accurate estimate of the capillary length. Slice by slice evaluation of the capillary region clearly gives a value of +_2 degrees to the z-axis for the leading eigenvector. So our SNR is sufficient to give the correct lead eigenvector orientation but the tracking results are surprising:<br>
A: Tracking condition: FA threshold: 0.15, angle threshold: 10 degree<br>1) if a seed point of 1 voxel is used, the fibers are either short or there are often no fibers tracked from the seed point (even though seed point</div>
<div>and neighbor voxels have values of FA above threshold) <br>2) if the entire capillary array is selected, then there are some fibers yet average length of fibers is 2 cm (and not 5 cm as expected). I guess the difference between 1 and 2 is that in (2) several multiple connections are found by the 'brute force' methods. </div>
<div><br>B: Tracking condition: FA threshold: 0.15, angle threshold: 70 degree<br>The number of fibers are many more for this condition still fiber length does not reach 5 cm average (more like 3 cm)!<br> <br>My questions::<br>
1) Why are the fibers not tracked for 10 degree angle threshold? These are straight capillaries with angle differences only arising from noise (which our measurements show are within 2-3 degrees)<br>2) Examining fibers from a single seed point, we see that fibers are not entirely parallel to the capillary axis; rather short segments and curvature of fiber is seen.<br>
3) Is there a restriction on how anisotropic the slice voxel can be: we have in-plane of 0.3125x0.3125 and thickness of 5mm--- however capillary axis is along the slice axis. I wonder of this affects the interpolation needed for FACT<br>
<br>This has been of great concern-- please do send me some feedback<br>usha sinha<br><a href="mailto:usinha@sciences.sdsu.edu">usinha@sciences.sdsu.edu</a><br><a href="mailto:usinhaster@gmail.com">usinhaster@gmail.com</a></div>