[Mristudio-users] Gradient Table

[susumu mori]

Hi all,

There are several inquiries about gradient table issues. This is very
complicated. In the past, we have tried several times to make it more
transparent and we are still trying. In the latest DtiStudio V3.0.2, you
might have found a couple of new buttons to get a table relatively easily.
However, because there are so many different possibility to get different
tables, it is not easy to make it completely automated. Therefore, users
need to have some degree of knowledge. There are several ways to notice
wrong gradient tables;

1) Totally wrong table: If the table is totally wrong, the color map doesn't
make sense. So check color map first.
2) X/Y/Z permutation: If X/Y/Z is miss signed, the color of the color maps
doesn't look right. For example, the corpus callosum should look red, not
green
3) +/- sign error: Perform tractography. If sign is wrong, it doesn't make
any sense.
4) More subtle errors: Look at fitting residual (error) map. There is a file
called "DtiStudioUpdate.doc" at
https://www.mristudio.org/wiki/changelog/dtistudio-3.0.2. This explains how
to get the fitting error maps.
5) Oblique angle: The attached file explains in detail. To make sure
everything is right, you can scan a person twice. One in a regular position
and one in severe oblique. If everything is working, you should get
anatomically comparable tractography results.

The attached documents explains the gradient issues. Hope this helps.

Susumu
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