Hello,<div><br></div><div>Thank you Venkat and Hangyi for you insights. �I tried both methods, but I was not able to replicate the values that DTIStudio gave me. �The values that DTIStudio gave me, after clicking the "rotate gradients if applicable" button and for the first direction, is:</div>
<div>0.861, -0.489, 0.142</div><div><br></div><div>Here is my original gradient table:</div><div><div>�� � � � 0 � � � � 0 � � � � 0</div><div>�� �0.8608 � -0.3657 � �0.3538</div><div>�� �0.8643 � �0.3611 � �0.3502</div>
<div>
�� �0.8608 � �0.3657 � -0.3538</div><div>�� �0.8644 � -0.3608 � -0.3502</div><div>�� �0.3582 � -0.3523 � -0.8646</div><div>�� �0.3571 � -0.8658 � -0.3504</div><div>�� �0.3554 � -0.8606 � �0.3648</div><div>�� �0.3566 � -0.3652 � �0.8599</div>
<div>�� �0.3579 � �0.3521 � �0.8648</div><div>�� �0.3571 � �0.8658 � �0.3504</div><div>�� �0.3557 � �0.8609 � -0.3638</div><div>�� �0.3569 � �0.3655 � -0.8597</div><div><br></div><div>And here is my ImageOrientationPatient info:</div>
<div><div>�� �1.0000 � � � � 0 � � � � 0</div><div>�� � � � 0 � �0.8846 � -0.4664</div></div><div><br></div><div>If I do it according to Venkat, it becomes:</div><div><div>��� �1.0000 � � � � 0 � � � � 0</div><div>�� � � � 0 � �0.8846 � -0.4664</div>
<div>�� � � � 0 � � � � 0 � �1.0000</div></div><div><br></div><div>If I multiply my gradient by this, for the first direction, I get:</div><div>�� �0.8608 � -0.3235 � �0.5244</div><div><br></div><div>If I do it according to Hangyi, the rotation matrix becomes:</div>
<div><div>�� �1.0000 � � � � 0 � � � � 0</div><div>�� � � � 0 � �0.8846 � -0.4664</div><div>�� � � � 0 � �0.8846 � -0.4664</div></div><div><br></div><div>If I multiply my gradient by this, for the first direction, I get:</div>
<div>�� �0.8608 � -0.0106 � �0.0056</div><div><br></div><div>The only thing that I can think of is there is probably a step in there that normalizes the gradient to one. �i.e.: sqrt(grad_x^2 + grad_y^2 + grad_z^2) = 1.</div>
<div><br></div><div>Can anybody help point me to the next step? � �Thank you very much!!</div><div>Jeff Sadino</div><br><div class="gmail_quote">On Fri, Dec 10, 2010 at 4:07 AM, Hangyi Jiang <span dir="ltr"><<a href="mailto:hjiang@jhmi.edu">hjiang@jhmi.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">hello,<br>
<br>
the 3rd row should be the outer product of the given two vectors, � not [0,0,1]<br>
<br>
regards<br>
<br>
hangyi<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
________________________________<br>
From: <a href="mailto:mristudio-users-bounces@mristudio.org">mristudio-users-bounces@mristudio.org</a> [<a href="mailto:mristudio-users-bounces@mristudio.org">mristudio-users-bounces@mristudio.org</a>] On Behalf Of Rajagopalan, Venkateswaran [<a href="mailto:rajagov2@ccf.org">rajagov2@ccf.org</a>]<br>
Sent: Friday, December 10, 2010 9:01 AM<br>
<div class="im">To: DTI Studio, ROI Editor, DiffeoMap Questions/Support<br>
</div>Subject: Re: [Mristudio-users] Adjusting Gradients for Oblique Angles<br>
<div><div></div><div class="h5"><br>
Dear Jeff Sadino,<br>
<br>
This is what I did for manual oblique angle correction<br>
<br>
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<br>
<br>
[ 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<br>
<br>
[ 1 � �0 � � 0<br>
�0 �0.8846 �-0.4664<br>
�0 � 0 � � �1]<br>
<br>
3*3<br>
<br>
Multiply the ablove Image orientation patient with your gradient matrix.<br>
<br>
Thanks<br>
<br>
Venkat<br>
<br>
________________________________<br>
From: <a href="mailto:mristudio-users-bounces@mristudio.org">mristudio-users-bounces@mristudio.org</a> on behalf of Jeff Sadino<br>
Sent: Thu 12/9/2010 6:09 PM<br>
To: DTI Studio, ROI Editor, DiffeoMap Questions/Support<br>
Subject: [Mristudio-users] Adjusting Gradients for Oblique Angles<br>
<br>
Hello,<br>
<br>
Thank you for the DTI training session in Turtle Bay last week. �It was very helpful for us!<br>
<br>
I am wondering how to manually adjust the gradients for an oblique angle. �I am using Siemens 3T Trio Tim VB17.<br>
<br>
My default gradient (for one direction) is:<br>
0.861, -0.366, 0.354<br>
<br>
After clicking "Rotate gradients if applicable" in DTIStudio 3.0.2 (March2010), the gradient is:<br>
0.861, -0.489, 0.142<br>
<br>
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:<br>
[ 1 0 0 0 .8846 -.4664]<br>
<br>
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?<br>
<br>
Thank you very much for your help!<br>
Jeff Sadino<br>
<br>
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