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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hi Venkateswaran,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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".<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>By activating this function, the gradient
table is rotated if AIR does any rotation.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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'.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hope these help.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Susumu<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
mristudio-users-bounces@mristudio.org
[mailto:mristudio-users-bounces@mristudio.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Rajagopalan, Venkateswaran<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, May 14, 2009 3:50
PM<br>
<b><span style='font-weight:bold'>To:</span></b> mristudio-users@mristudio.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Mristudio-users] motion
ocrrection of DTI gradient table</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'>Dear MRI studio Users,</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I recently came across the following article "<strong><b><font
face=Arial><span style='font-family:Arial'>DTI Fiber Tracking: The Importance
of Adjusting DTI Gradient Tables for Motion Correction. CATNAP – A Tool
to Simplify and Accelerate DTI Analysis".</span></font></b></strong> 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.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Thanks</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Regards</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>venkateswaran</span></font><o:p></o:p></p>
</div>
<pre wrap><font size=2 face="Courier New"><span style='font-size:10.0pt'>===================================<o:p></o:p></span></font></pre>
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