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<p class="MsoNormal"><span style="color:#1F497D">Thanks very much Hangyi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Venkat<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> mristudio-users-bounces@mristudio.org [mailto:mristudio-users-bounces@mristudio.org]
<b>On Behalf Of </b>Hangyi Jiang<br>
<b>Sent:</b> Thursday, February 14, 2013 2:12 PM<br>
<b>To:</b> DTI Studio, ROI Editor, DiffeoMap Questions/Support<br>
<b>Subject:</b> Re: [Mristudio-users] difference between ADC and MD<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black">hi,<br>
<br>
apparent diffusion coefficient (ADC) is a measurement for a diffusion weighted image in a specific gradient. its definition is:<br>
<br>
ADC = ln(S/S0) / (-b)<br>
here, S is the gradient weighted image, S0 is the B0 image, b is the b value.<br>
<br>
so, if a data set has 30 gradient orientations, there will be 30 ADCs. for each gradient, there will be a ADC map for this particular DW-image.<br>
<br>
<br>
mean- diffusivity is defined as the mean value of eigen values (Lamda 1-3) of the tensor ellipsoid:<br>
Mean_Diffusivity = (Lamda_1 + Lamda_2 + Lamda_3) / 3;<br>
<br>
mathematically, this is equal to the average of the diagonal elements of the tensor matrix:<br>
Mean_Diffusivity = (Dxx + Dyy + Dzz) / 3;<br>
<br>
in noise-free situation (practically, it is impossible), mean-diffusivity is also equal to the mean value of ADCs of the DWI data set.<br>
e.g. given a data set with 30 orientations, then Mean_Diffusivity = (ADC1 + ADC2 + .. ADC30) / 30;<br>
<br>
BTW: the sum of eigen-values or the sum of the diagonal elements of the tensor matrix is called TRACE:<br>
TRACE = (Lamda_1 + Lamda_2 + Lamda_3) = (Dxx + Dyy + Dzz);<br>
<br>
so, Mean_Diffusivity = TRACE/3;<br>
<br>
<br>
best,<br>
<br>
hangyi<br>
<br>
<br>
<br>
<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:black">
<a href="mailto:mristudio-users-bounces@mristudio.org">mristudio-users-bounces@mristudio.org</a> [mristudio-users-bounces@mristudio.org] on behalf of Venkatesh Rajagopalan [VRajagopalan@kesslerfoundation.org]<br>
<b>Sent:</b> Thursday, February 14, 2013 1:40 PM<br>
<b>To:</b> 'DTI Studio, ROI Editor, DiffeoMap Questions/Support'<br>
<b>Subject:</b> [Mristudio-users] difference between ADC and MD</span><span style="font-size:12.0pt;font-family:"Times New Roman","serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Hi All,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">I very often come across apparent diffusion coefficient and mean diffusivity being measured in studies. I am wondering what is the difference between these two measures in terms of the formula used.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Thanks<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Venkat<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif";color:black"><br>
Kessler Foundation is proud to be recognized as one of the Best Places to Work in New Jersey.
<o:p></o:p></span></p>
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