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<DIV>Susumu, </DIV>
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<DIV>Thank you so much for your suggestions.</DIV>
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<DIV>Best,</DIV>
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<DIV>Jinsong<BR></DIV>
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<B><SPAN style="FONT-WEIGHT: bold">发件人：</SPAN></B> susumu <susumu@mri.jhu.edu><BR><B><SPAN style="FONT-WEIGHT: bold">收件人：</SPAN></B> "DTI Studio, ROI Editor, Landmarker Questions/Support" <mristudio-users@mristudio.org><BR><B><SPAN style="FONT-WEIGHT: bold">已发送：</SPAN></B> 2009/4/8(周三), 上午1:36:27<BR><B><SPAN style="FONT-WEIGHT: bold">主题：</SPAN></B> Re: [Mristudio-users] re： How to do a Tailarach transformation?<BR></FONT><BR>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">Hi Jinsong,</SPAN></FONT></P>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">It depends on whom you ask the question, but here is my opinion.</SPAN></FONT></P>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">When you are using diffusion “tensor” imaging, all data will be fitted to obtain only the 6 tensor elements. Therefore, you need only 6 directions mathematically. However, such measurement takes only less than 1 min and do not have enough SNR (signal-to-noise ratio). To enhance the SNR, you need to acquire more data.</SPAN></FONT></P>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">Usually people spend 4-10 min of time for DTI, in which you can acquire about 30 – 100 images. Then you have several options. For example, you can repeat the 6-orientation measurement 5 times (total 30) or one 30-orientation measurement within the same amount of time (should be within 5 min). </SPAN></FONT></P>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">Purely from mathematical point of views, I don’t think 6-direction x 5 vs 30-orientation have that much difference in terms of overall SNR. However, it is true that the 6-orientation measurement has more orientation-dependent inhomogeneity in SNR. This means, certain orientations can be measured with higher SNR while some orientation has poorer SNR. By adopting more orientations, such orientation-dependent SNR profile becomes more homogeneous (less orientation dependent).</SPAN></FONT></P>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">In reality, within practical imaging time, I don’t think you can observe such effect clearly. Our past measurement (Landman et al, NeuroImage) suggests once you have 12-orientation or more, you don’t see much differences.</SPAN></FONT></P>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">Some researchers are seeking for diffusion “more than one tensor” imaging. If you want it, you may need more than 30 orientations and higher b-values. So, you may need to design very different protocols.</SPAN></FONT></P>
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<P class=MsoNormal><FONT color=navy size=2 face=Arial><SPAN style="FONT-FAMILY: Arial; COLOR: navy; FONT-SIZE: 10pt">Susumu</SPAN></FONT></P>
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<P class=MsoNormal><B><FONT size=2 face=Tahoma><SPAN style="FONT-FAMILY: Tahoma; FONT-SIZE: 10pt; FONT-WEIGHT: bold">From:</SPAN></FONT></B><FONT size=2 face=Tahoma><SPAN style="FONT-FAMILY: Tahoma; FONT-SIZE: 10pt"> mristudio-users-bounces@mristudio.org [mailto:mristudio-users-bounces@mristudio.org] <B><SPAN style="FONT-WEIGHT: bold">On Behalf Of </SPAN></B>jinsong tang<BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Tuesday, April 07, 2009 12:52 PM<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> DTI Studio, ROI Editor, Landmarker Questions/Support<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> [Mristudio-users] re</SPAN></FONT><FONT size=2 face="MS Mincho"><SPAN style="FONT-FAMILY: 'MS Mincho'; FONT-SIZE: 10pt" lang=JA>：</SPAN></FONT><FONT size=2 face=Tahoma><SPAN style="FONT-FAMILY: Tahoma; FONT-SIZE: 10pt"> How to do a Tailarach transformation?</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT size=3 face="Times New Roman"><SPAN style="FONT-SIZE: 12pt">Hello everyone,</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT size=3 face="Times New Roman"><SPAN style="FONT-SIZE: 12pt">Now the Siemens 3.0 T MRI scanner can collect </SPAN></FONT>30 non-collinear directions diffusion data. Does this helpful for fiber tracking ?</P></DIV>
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<P class=MsoNormal><FONT size=3 face="Times New Roman"><SPAN style="FONT-SIZE: 12pt">But I found most paper only use 12 directions. Does anybody know why?</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT size=3 face="Times New Roman"><SPAN style="FONT-SIZE: 12pt">Best,</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT size=3 face="Times New Roman"><SPAN style="FONT-SIZE: 12pt"> </SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT size=3 face="Times New Roman"><SPAN style="FONT-SIZE: 12pt">Jinsong</SPAN></FONT></P></DIV></DIV>
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