Hi Maya,<div><br></div><div>It is expected that diffusion constant like Eig is inverse proportional to the b-value such that b x diffusion constant is a constant.</div><div>If you type in non-physical number like negative b, I believe (Hangyi please correct me if I'm wrong) DtiStudio use b=1. </div>
<div>In your case, b x D = 1.1812.</div><div><br></div><div>If you use b=1 for all the past data, you can simply divide the number with b=700. This is the case of all the numbers with the diffusion constant unit (mm^2/s) like Eigs, mean diffusivity, trace, etc. I believe the unit-less numbers such as FA is not affected.</div>
<div><br></div><div>Susumu<br><br><div class="gmail_quote">On Wed, Apr 18, 2012 at 3:11 AM, maya weinstein <span dir="ltr"><<a href="mailto:weinmaya@gmail.com">weinmaya@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr"><div><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">Hi MRI studio users,</span></p>
<font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt"> </span></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">In DTIStudio, in the "DTI Mapping" I noticed that
the value I put in the "b-value" affects the results I get in the
statistics.</span></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">For example:</span></p>
<font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt"><span> </span>b-val 700: Eig 0=</span><font size="3"><font face="Calibri">
</font><span style="font-family:"Times New Roman","serif";font-size:12pt">1.69E-03</span></font></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">b-val 70: Eig 0=0.0169</span></p>
<font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">b-val 7: Eig 0=</span><span dir="RTL"></span><span style="font-family:"Arial","sans-serif"" dir="RTL"><span dir="RTL"></span><font size="3"> </font></span><span style="font-family:"Times New Roman","serif";font-size:12pt" dir="RTL" lang="HE">0.1687</span><span style="font-family:"Times New Roman","serif";font-size:12pt"></span></p>
<font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt"> </span></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">This seems to affect only the # of integers. </span></p>
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</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt"> </span></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">But- when I use <b>b-val -7</b> (minus seven), I get an
entirely different value: </span></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><b><span style="font-family:"Times New Roman","serif";font-size:12pt">Eig0= 1.1812</span></b></p>
<font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">What does this mean? And is it a valid option?</span></p>
<font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">I used this option (b val= -7) and I want to know if I need
to re-calculate the maps and reanalyze my data.</span></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt"> </span></p><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">Thank you,</span></p>
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</font><p style="margin:0cm 0cm 0pt;text-align:left;line-height:normal;direction:ltr" dir="LTR" class="MsoNormal"><span style="font-family:"Times New Roman","serif";font-size:12pt">Maya</span></p><span class="HOEnZb"><font color="#888888"><font size="3" face="Times New Roman">
</font><p style="margin:0cm 0cm 10pt;text-align:left;direction:ltr" dir="LTR" class="MsoNormal"><font size="3" face="Calibri"> </font></p><font size="3" face="Times New Roman">
</font>-- <br></font></span></div><span class="HOEnZb"><font color="#888888"><div dir="ltr">Maya Weinstein<br>Department of Psychology, Bar-Ilan University<br>Functional Brain Imaging Unit, Wohl Institute for Advanced Imaging, Tel-Aviv Sourasky Medical Center</div>
<br>
</font></span></div>
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