[Mristudio-users] motion ocrrection of DTI gradient table

Thu May 14 16:31:51 EDT 2009

Dear Dr. Susumu,

Thank you very much for your kind clarification.

Regards
venkateswaran

________________________________

From: mristudio-users-bounces at mristudio.org on behalf of susumu
Sent: Thu 5/14/2009 4:25 PM
To: 'DTI Studio, ROI Editor, Landmarker Questions/Support'
Subject: Re: [Mristudio-users] motion ocrrection of DTI gradient table

Hi Venkateswaran,

When you run AIR, you can find an option toward the bottom of the window, called "Adjusting the gradients for the diffuion-weighted images if applicable".

By activating this function, the gradient table is rotated if AIR does any rotation.

In regular DTI, you should expect only less than 1-2 degree of rotation in average. If so, the table rotation is not so important. If subject moves much more than that, the table rotation becomes important but there would be many other more problematic artifacts like mis-registration between the odd and even numbered slices within a 3D data and image corruption, which can not be fixed. So, this is a bit "looking at leaves without looking at the tree'.

I believe what the paper stressed, if I'm not mistaken, is when you want to combine data scanned at two different time points, then the position and orientation of the brain could be very different. If you want to co-register raw DWI images between the two separate scans, you have to rotate the gradient table. This is very true, but you don't have many occasions when you want to combine two separate scans with different head positions.

If you have two separate scans, you can calculate tensor first, and then coregister with a proper tensor-reorientation method. Then you don't have to worry about the gradient table rotation. 

Hope these help.

Susumu

________________________________

From: mristudio-users-bounces at mristudio.org [mailto:mristudio-users-bounces at mristudio.org] On Behalf Of Rajagopalan, Venkateswaran
Sent: Thursday, May 14, 2009 3:50 PM
To: mristudio-users at mristudio.org
Subject: [Mristudio-users] motion ocrrection of DTI gradient table

Dear MRI studio Users,

I recently came across the following article "DTI Fiber Tracking: The Importance of Adjusting DTI Gradient Tables for Motion Correction. CATNAP - A Tool to Simplify and Accelerate DTI Analysis". The results in this paper suggested the need for motion correction of gradient tables. I am wondering do i need to carry out this preprocessing step of motion correction of gradient table in CATNAP before supplying the gradient table values in DTI studio for calculation of DTI metrics and tractography or the recent versions of DTI studio takes care of this problem. This being a short article i am not able to understand much about the importance of motion correction of b-tables could anyone please suggest me some additional references to understand the need for this b-table correction.

Thanks

Regards

venkateswaran

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