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</o:shapelayout></xml><![endif]--></head><body lang=ES link=blue vlink=purple><div class=WordSection1><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>Dear all,<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>I’m developing a tractography application based on ITK-VTK. Our immediate aim is to create a visualization of an RGB map of the water diffusion of the brain. <o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>ITK is used in order to read the metaimage file, get the image and the gradients, and, as result, we get an image of tensors, with <b>DiffusionTensor3D</b> as pixel type. Eigenvalues, eigenvectors and FA are computed for each voxel using the <i>ComputeEigenAnalysis()</i> and <i>GetFractionalAnisotropy()</i> methods of <b>DiffusionTensor3D</b> class. In some cases, we realized that the FA was greater than 1.0, as some voxels contained negative eigenvalues, although they had a very low order of magnitude (around 1e-4).<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>Is there any way to correct a tensor, ensuring that all its eigenvalues are positive, before calling GetFractionalAnisotropy ? Or should I just avoid computing the FA on a voxel with a negative eigenvalue?<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US>Thanks in advance,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><table class=MsoNormalTable border=0 cellspacing=0 cellpadding=0 width="60%" style='width:60.0%;border-collapse:collapse'><tr><td width=260 valign=top style='width:195.0pt;padding:3.75pt 0cm 0cm 3.75pt'><table class=MsoNormalTable border=0 cellspacing=0 cellpadding=0 width="100%" style='width:100.0%'><tr><td style='padding:0cm 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'>Alba Garin Muga</span></b><span lang=EN-US style='font-size:12.0pt'><o:p></o:p></span></p></td></tr><tr><td style='padding:0cm 0cm 0cm 0cm'><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-US style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'>Computer Science PhD Student</span><span lang=EN-US style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p></td></tr><tr><td style='padding:0cm 0cm 0cm 0cm'><p class=MsoNormal><span lang=EN-US style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'>Applied Mechanics Department</span><span lang=EN-US style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p></td></tr><tr><td style='padding:0cm 0cm 0cm 0cm'><p class=MsoNormal style='margin-top:6.0pt;mso-margin-bottom-alt:auto'><span lang=EN-US style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'>Paseo Manuel Lardizabal, 15<br>20018 </span><span style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'>Donostia-San Sebastian. </span><span lang=EN-US style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'>Spain<br>Tel. +34 943 212 800 (Ext. 2113)<br>Fax: +34 943 213 076<br>Web: </span><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><a href="http://www.ceit.es/"><span lang=EN-US style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'>www.ceit.es</span></a></span><span lang=EN-US style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p></td></tr></table></td><td width=659 valign=top style='width:494.25pt;padding:0cm 0cm 0cm 0cm'><p class=MsoNormal><span style='font-size:8.0pt;font-family:"Tahoma","sans-serif"'><img border=0 width=227 height=120 id="Picture_x0020_1" src="cid:image001.gif@01CBEE14.47094EA0" alt="http://intranet.ceit.es/PlantillasCEIT/ImagenCorporativa/Firmas/firma_ceit.gif"></span><span style='font-size:12.0pt'><o:p></o:p></span></p></td></tr><tr><td colspan=2 valign=top style='padding:3.75pt 0cm 0cm 3.75pt'><table class=MsoNormalTable border=0 cellspacing=0 cellpadding=0 width="100%" style='width:100.0%'><tr><td width="4%" valign=top style='width:4.0%;padding:0cm 0cm 0cm 0cm'><p class=MsoNormal><img border=0 width=31 height=30 id="Picture_x0020_2" src="cid:image002.jpg@01CBEE14.47094EA0" alt=Verde><span style='font-size:12.0pt'><o:p></o:p></span></p></td><td width="96%" style='width:96.0%;padding:0cm 0cm 0cm 0cm'><p class=MsoNormal><span style='font-size:8.0pt;font-family:"Tahoma","sans-serif";color:#009900'>Antes de imprimir este e-mail piense bien si es necesario hacerlo. </span><span lang=EN-US style='font-size:8.0pt;font-family:"Tahoma","sans-serif";color:#009900'>El medioambiente es cosa de todos.<br>Before printing this e-mail ask yourself if you really need a hard copy. </span><span style='font-size:8.0pt;font-family:"Tahoma","sans-serif";color:#009900'>We are all responsible for the environment.</span><span style='font-size:12.0pt'><o:p></o:p></span></p></td></tr></table></td></tr></table><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>