<html dir="ltr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style>
<!--
@font-face
{font-family:Calibri}
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif"}
a:link, span.MsoHyperlink
{color:blue;
text-decoration:underline}
a:visited, span.MsoHyperlinkFollowed
{color:purple;
text-decoration:underline}
span.EmailStyle17
{font-family:"Calibri","sans-serif";
color:windowtext}
@page WordSection1
{margin:1.0in 1.0in 1.0in 1.0in}
-->
</style><style id="owaParaStyle" type="text/css">P {margin-top:0;margin-bottom:0;}</style>
</head>
<body ocsi="0" fpstyle="1" lang="EN-US" link="blue" vlink="purple">
<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">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>
<br>
<div style="font-family: Times New Roman; color: #000000; font-size: 16px">
<hr tabindex="-1">
<div style="direction: ltr;" id="divRpF141660"><font color="#000000" face="Tahoma" size="2"><b>From:</b> mristudio-users-bounces@mristudio.org [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<br>
</font><br>
</div>
<div></div>
<div>
<div class="WordSection1">
<p class="MsoNormal">Hi All,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">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.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thanks</p>
<p class="MsoNormal">Venkat</p>
</div>
<br>
Kessler Foundation is proud to be recognized as one of the Best Places to Work in New Jersey.
<center></center>
<br>
<center><a href="http://www.facebook.com/?ref=home#!/pages/Kessler-Foundation/123330414345741?sk=info" target="_blank"><img src="http://www.kesslerfoundation.org/images/emailimages/FaceBook-iconverysmall.png" alt="Kessler Foundation Facebook Page" border="0" height="24" width="24"></a>
<a href="http://www.youtube.com/user/KesslerFoundation" target="_blank"><img src="http://www.kesslerfoundation.org/images/emailimages/Youtube-iconverysmall.png" alt="Kessler Foundation You Tube" border="0" height="24" width="24"></a>
<a href="http://www.twitter.com/KesslerFound" target="_blank"><img src="http://www.kesslerfoundation.org/images/emailimages/Twitter-iconverysmall.png" alt="Kessler Foundation Research Twitter Page" border="0" height="24" width="24"></a><br>
</center>
<br>
The information in this transmission is intended for official use of the Kessler Foundation. It is intended for the exclusive use of the persons or entities to which it is addressed. If you are not an intended recipient or the employee or agent responsible
for delivering this transmission to an intended recipient, be aware that any disclosure, dissemination, distribution or copying of this communication, or the use of its contents, is strictly prohibited. If you received this transmission in error, please notify
the sender by return e-mail and delete the material from any computer. ญญ </div>
</div>
</div>
</body>
</html>