[Mristudio-users] Gradient Table

Thu Jul 17 20:31:21 EDT 2008

Hi all,

Here I attached tables we are using. Please note that Siemens and GE
changed gradient tables in the past. These should work for latest operating
systems but may not for older versions. If gradient table is wrong, you can
tell it immediately because color maps are not symmetric and the corpus
callosum is not pure red. The best way is to contact the manufacturers, but
we may help to locate the correct tables for older versions.

As Gordon mentioned, Siemens users need to be EXTREMELY careful when they
use oblique planes. Unless you are using the latest version of the
operating system, the gradient table doesn't rotate with imaging place (it
always stick with physical X/Y/Z gradient). That means, we need to
recalculate gradient table based on the oblique information. If you are
using Dicom/Mosaic, this can be automatically done by checking "Rotate
table if applicable" check box. 

Susumu

-----Original Message-----
From: mristudio-users-bounces at mristudio.org [mailto:mristudio-users-
bounces at mristudio.org] On Behalf Of Junqian Gordon Xu
Sent: Thursday, July 17, 2008 4:37 AM
To: DTI Studio, ROI Editor, Landmarker Questions/Support
Subject: Re: [Mristudio-users] Gradient Table

1) Siemens specify DTI table in lab coordinates (i.e. XYZ).
2) The where-abouts of the DTI table info is software version dependent
VA25, VA21 and earlier: hard coded in the ep2d_diff.cpp source file.VB13,
VB15 and later: if you use the standard MDDW (limits your max diffusion
direction to 64?), the table is again hard coded. If you have the license
to use diffusion FREE, the table is in a user supplied ASCII file (you
probably know where it is).
3) You may find something like "diffusion direction" in DICOM headers if
your scanner is VB13/VB15. One caveat is that this table is not the
original table if your slices are oblique. In other words, this table has
already been multiplied with "slice normal vector" which could also been
found from the header. Siemens probably uses this for their color coded FA
map.
Hope this helpsGordon
On 07/16/2008 07:54 PM, 조양제 wrote:> As I know, x,y,z information is not
always necessary.> I have succeeded to load Siemens (Trio, 20 dir) Mosaic
files with > gradient numbers> You only have to not forget to write numbers
of 100, 100, 100 and > finally 0,0,0 at the end of table.> Here is an
example,>  > 0: -1.000000, 0.000000, 0.000000> 1: 0.000000, -1.000000,
0.000000> 2: 0.031984, -0.799591, 0.599693> .> .> .> 18: -0.111012, -
0.264029, -0.958105> 19: -0.031984, -0.799591, -0.599693> 20: 100, 100,
100> 21: 0,0,0>  > If you really want to find the x,y,z information, I'm
afraid I can't > answer it.> But I have heard that the information is not
technically necessary from > the computer technologist> working at the
Siemens company. He have read the instructions and talked > to me like that.
>  > Wish it would be helpful.>  > Regards,>  > YJ Cho> >  > 2008/7/17,
Tapan Jani <icee41 at gmail.com <mailto:icee41 at gmail.com>>:> >     Hello all,>
>     I sent out an e-mail earlier about generating a gradient table and>
am still a little bit confused. In order to use DtiStudio properly,>     it
seems that one needs a gradient table to go along with their>     data. Our
lab is currently using a 3T Excite GE scanner to perform>     our DTI
scans, but we also have a Siemens scanner for which the>     following
questions apply. Within the dicom header of the GE>     scanner, under the
tag #DTI Diffusion Dir (0019, 01E0), we are able>     to tell the number of
gradients, but not able to find the x,y,z>     information.> >     Is there
a program that can generate gradient tables to go along>     with our dicom
data, or can it actually be found within the header ->     and if so,
where? Finally I was curious as to whether there are>     standard gradient
tables that go along with specific scanners every>     time a DTI scan is
performed.> >     Thank you very much for all of your help, it is much
appreciated.> >     Sincerely,> >     Tapan Jani> >     tjani2 at uic.edu
<mailto:tjani2 at uic.edu>>      > >
_______________________________________________>     Mristudio-users
mailing list>     Mristudio-users at mristudio.org <mailto:Mristudio-
users at mristudio.org>>
http://lists.mristudio.org/mailman/listinfo/mristudio-users> > > > > -- >
Yang-Je Cho> > Dept of Neurology, Yonsei University> College of Medicine,
Seoul, Korea> Phone: 82-2-2228-1600, Cell: 016-298-7456, Fax: 82-2-393-
0705> > > ------------------------------------------------------------------
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