<html>
<head>
<style><!--
.hmmessage P
{
margin:0px;
padding:0px
}
body.hmmessage
{
font-size: 10pt;
font-family:Tahoma
}
--></style>
</head>
<body class='hmmessage'>
Hi, Luca<BR>
<BR>
The MI algorithm optimizes the normalized mutual information.<BR>
<BR>
Thanks! <BR><BR>KEGANG(LUKE) HUA<BR>Department of Radiology<BR>Johns Hopkins University School of Medicine<BR>720 Rutland Ave Traylor217<BR>Baltimore, MD, 21205<BR><BR><BR><BR> <BR>
> Date: Mon, 27 Dec 2010 09:38:00 +0100<BR>> From: luca.binotto@unipd.it<BR>> Subject: [Mristudio-users] update of gradient table in DtiStudio<BR>> To: mristudio-users@mristudio.org<BR>> <BR>> Hello Susumu,<BR>> <BR>> I would like to know something about the way DtiStudio performs the update<BR>> of the gradient table after the realignment of the dti dataset with<BR>> respect to the mean_b0 volume.<BR>> <BR>> The registration algorithm implemented in DtiStudio using mutual<BR>> information (MI):<BR>> 1) does it uses normalized mutual information or which other formulation ?<BR>> 2) how is the gradient table updated ? (rough simple theory)<BR>> After realignment of the DWI volumes, b-matrix (the gradient table) must<BR>> be updated.<BR>> <BR>> Patient motion and eddy currents can cause errors in the calculation of<BR>> parameters that describe diffusion in each voxel of a DWI dataset.<BR>> In normal conditions eddy
currents contribution should be<BR>> very small (< 1% ?).<BR>> But the b-matrix (gradient table) is calculated with respect to a fixed<BR>> coordinate system (at the acquisition time) so the b-matrix must be<BR>> rotated accordingly to the transformation applied for image registration<BR>> otherwise we should get poor fiber statistics and some fibers possibly<BR>> deviate.<BR>> <BR>> So the gradient table is affected by rotations. Translations don't<BR>> change it.<BR>> But what does it happen with resampling (applying a scaling factor: es.<BR>> affine transformation) to a dwi dataset?<BR>> According to you is normally its effect small (as for eddy currents<BR>> effect) or can be more important?<BR>> For example a scaling factor such that a volume with a voxel size of<BR>> 2x2x2 mm3 is resliced to a 1x1x1 mm3 voxel size can be important its<BR>> effect or "only" a lower image quality (eg. I read somewhere of a<BR>> "red
background" superimposed to the correct color map)?<BR>> <BR>> <BR>> thanks in advance,<BR>> best regards,<BR>> <BR>> Luca<BR>> <BR>> <BR>> <BR>> <BR>> _______________________________________________<BR>> mristudio-users mailing list<BR>> mristudio-users@mristudio.org<BR>> http://lists.mristudio.org/mailman/listinfo/<BR>> Unsubscribe, send a blank email to: mristudio-users-unsubscribe@mristudio.org<BR> </body>
</html>