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<DIV><FONT face=Arial size=2>Hi Jeff,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Let me try to answer your question in a generic
way. As you know, we need at least 1 b0 and 6 DWIs for DTI. If you have these 7
images, obtaining the tensor elements requires to "solve" the tensor
equation.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>If you have more than 6 DWIs, then you have to
do "fitting" to obtain the elements. This is very similar to the simple
linear fitting. If you have two points, you solve the equation to get the slope.
If you have 3 points, you do fitting for the best fit.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>When you have more than 6 DWIs, you have two
choices; more orientations or more repetitions. In the analogy of the linear
fitting, if you have 4 points, you can spread the 4 points along the x axis, or
you can sample twice at two locations along the x axis. Statistically, there is
not much difference between these two approaches. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I guess my point is, the two datapoints at a fixed
x value (or two DWIs with the same b-orientation) doesn't have to be averaged or
need any special calculation. These are just dataponts to be fitted. For the
tensor fitting, we can use the same math regardless of multiple points spread
over different gradient orientations or repeated with the same orientation
set.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Hope this answers your question.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Susumu</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=rileyj@uci.edu href="mailto:rileyj@uci.edu">Riley, Jeffrey</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=mristudio-users@mristudio.org
href="mailto:mristudio-users@mristudio.org">mristudio-users@mristudio.org</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, April 21, 2008 6:27
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Mristudio-users] DtiStudio and
multiple acquisitions</DIV>
<DIV><BR></DIV><!-- Converted from text/plain format --><BR>
<P><FONT size=2>Hi -<BR><BR>I have a question regarding multiple dti
acquisitions in DtiStudio; namely, how does the program incorporate both
acquisitions into the tensor calculations (i.e. are the two runs averaged, and
then the tensor calculation is done?) and at what part of the processing
pipeline does this occur?<BR><BR>Thanks for your help,<BR><BR>Jeff</FONT> </P>
<P>
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