[Mristudio-users] cut operation

[susumu]

Hi John,

 

That is a good question. I need Hangyi's answer for more detail, but my
guess is the following points are related to this issue;

 

1) As you know, in DtiStudio fiber tracking is completed in the beginning
from the center of all pixels with FA values above the threshold.

2) If we draw two ROIs and select fibers that penetrate the both ROIs, there
are two classes of fibers;

a) The seed pixels are within the two ROIs

b) The seed pixels are outside the two ROIs

3) If there are fibers that penetrate one ROI twice, the (a) and (b) class
may pick up different points for the crossing. Also, it may become sensitive
to the order of ROI drawing. Of course, this becomes an issue only when we
use the "CUT" operation.

 

Hangyi, do you think this is really the case?

 

I hope these differences cause only minor problems, but if not please let us
know. 

 

Susumu

 

  _____  

From: mristudio-users-bounces at mristudio.org
[mailto:mristudio-users-bounces at mristudio.org] On Behalf Of Woo, John
Sent: Wednesday, August 13, 2008 2:52 PM
To: mristudio-users at mristudio.org
Subject: [Mristudio-users] cut operation

 

Hi, I've been trying to understand the "cut" operation of defining the
voxels between two ROIs.

 

Each fiber intersects both ROIs.  I can see that "nSelectFiberStartPoint"
and "nSelectFiberEndPoint" determine the indices of the cut points.  If the
fiber intersects each ROI in exactly one point, I can confirm that these are
precisely the points.

 

But if say ROI 1 intersects the fiber in two points, it is not entirely
clear to me which point is chosen.  It seems that sometimes the first is
chosen, sometimes the second.

 

Interestingly, in an attempt to elucidate the process further, I tried
swapping the two ROIs of the cut operation (by altering the ".map" file).
The resulting fiber depends on the order of the ROIs.  That is,
cut(ROI1,ROI2) does not always equal cut(ROI2,ROI1), although they are
almost identical.

 

Thanks to anyone who can help.

 

-John.

 


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