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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 Igor,<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'>Axial diffusivity is the same as
Eigenvalue0 in DtiStudio.<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'>Radial diffusivity is (Eigenvalue1 +
Eigenvalue2)/2. DtiStudio doesn't provide this number. I think we should add
this for the next version.<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'>You can create (Eigenvalue1 + Eigenvalue2)
image using the calculation function of RoiEditor, once you saved Eigenvalues.<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'>The advantage of using the axial / radial
diffusivity is this;<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 observe "lower FA",
there are two possible mechanisms;<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'>1) It's low because the longest axis
(Eigenvalue0 or axial diffusivity) decreased<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'>2) It's low because the second and third
(Eigenvalue1 and Eigenvalue2 or radial diffusivity) increased.<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'>These two possible mechanisms can't be
differentiated by FA (information degeneration), which may carry important
biological information. In many cases, #1 and #2 occur simultaneously, though.<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'>You may want to read the SK (Victor)
Song's series of papers on this subject. I'm not aware of review papers about
it.<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>
<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>
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<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>Igor Korolev<br>
<b><span style='font-weight:bold'>Sent:</span></b> Sunday, April 27, 2008 10:57
PM<br>
<b><span style='font-weight:bold'>To:</span></b> mristudio-users@mristudio.org<br>
<b><span style='font-weight:bold'>Cc:</span></b> Andrea Bozoki<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Mristudio-users] Axial /
radial</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Dear All,<br>
<br>
Is there a way to obtain the radial and axial diffusivity values from a 3D
image in DTIStudio in the same way that FA values can be obtained?<br>
<br>
Also, are there any solid review articles you would recommend on the biological
significance of radial and axial diffusivity as measured with DTI?<br>
<br>
Thank you,<br>
Igor<br clear=all>
<br>
-- <br>
------------------------------------------------------------------<br>
Igor O. Korolev<br>
Physician-Scientist Training Program (D.O./Ph.D.)<br>
College of Osteopathic Medicine<br>
Neuroscience Program<br>
<st1:place w:st="on"><st1:PlaceName w:st="on">Michigan</st1:PlaceName> <st1:PlaceType
w:st="on">State</st1:PlaceType> <st1:PlaceType w:st="on">University</st1:PlaceType></st1:place><br>
Email: <a href="mailto:Igor.Korolev@radiology.msu.edu">Igor.Korolev@radiology.msu.edu</a>
<o:p></o:p></span></font></p>
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