[Mristudio-users] Gradient Table

[Junqian Gordon Xu]

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 helps
Gordon

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>
>      
> 
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> 
> 
> 
> -- 
> 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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