[Mristudio-users] Adjusting Gradients for Oblique Angles

[Rajagopalan, Venkateswaran]

Dear Jeff Sadino,
 
This is what I did for manual oblique angle correction
 
multiply your gradient matrix (I don't know how many directions you have) if you have 12 directional data then you will have 3*13 (one b=0 values too) with the "Image Orientation patient" matrix 
 
[ 1 0 0 0 .8846 -.4664] rewritten as (these are unit vectors with z direction being 0 0 1 not mentioned in the Image Image orientation patient from Dicom header 
 
[ 1    0     0
  0  0.8846  -0.4664
  0   0      1]
 
3*3
 
Multiply the ablove Image orientation patient with your gradient matrix.
 
Thanks
 
Venkat

________________________________

From: mristudio-users-bounces at mristudio.org on behalf of Jeff Sadino
Sent: Thu 12/9/2010 6:09 PM
To: DTI Studio, ROI Editor, DiffeoMap Questions/Support
Subject: [Mristudio-users] Adjusting Gradients for Oblique Angles


Hello, 

Thank you for the DTI training session in Turtle Bay last week.  It was very helpful for us!

I am wondering how to manually adjust the gradients for an oblique angle.  I am using Siemens 3T Trio Tim VB17.

My default gradient (for one direction) is:
0.861, -0.366, 0.354

After clicking "Rotate gradients if applicable" in DTIStudio 3.0.2 (March2010), the gradient is:
0.861, -0.489, 0.142

I couldn't find exactly which tag in the DICOM header contains the rotation information.  The closest I could find is "ImageOrientationPatient".  The value for this is:
[ 1 0 0 0 .8846 -.4664]

How do I go from the default gradient to the rotated gradient?  Also, can I use this same method on the VB13 and VA25 software?

Thank you very much for your help!
Jeff Sadino

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