Dear Susumu,<br><br>Do you have relevant literature on your opinion:<br><br>"...<font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">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><br><br>If you had, could you share the literature?<br><br>Thanks.<br><br>- SC<br><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"></span></font><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"><br>
</span></font><br><div class="gmail_quote">2009/4/7 susumu <span dir="ltr"><<a href="mailto:susumu@mri.jhu.edu">susumu@mri.jhu.edu</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Hi Jinsong,</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">It depends on whom you ask the question,
but here is my opinion.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">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>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">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>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">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>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">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>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">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>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Susumu</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
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<p><b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold;">From:</span></font></b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma;">
<a href="mailto:mristudio-users-bounces@mristudio.org" target="_blank">mristudio-users-bounces@mristudio.org</a>
[mailto:<a href="mailto:mristudio-users-bounces@mristudio.org" target="_blank">mristudio-users-bounces@mristudio.org</a>] <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 face="MS Mincho" size="2"><span style="font-size: 10pt; font-family: "MS Mincho";" lang="JA">：</span></font><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma;"> How to do
a Tailarach transformation?</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">Hello everyone,</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><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>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">But I found most paper only use 12 directions. Does anybody know why?</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">Best,</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">Jinsong</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"><a href="http://cn.rd.yahoo.com/mail_cn/tagline/card/*http:/card.mail.cn.yahoo.com/" target="_blank"><font face="MS Mincho"><span style="font-family: "MS Mincho";" lang="JA">好玩</span></font><font face="SimSun"><span style="font-family: SimSun;" lang="JA">贺</span></font><font face="MS Mincho"><span style="font-family: "MS Mincho";" lang="JA">卡等你</span></font><font face="SimSun"><span style="font-family: SimSun;" lang="JA">发</span></font><font face="MS Mincho"><span style="font-family: "MS Mincho";" lang="JA">，</span></font><font face="SimSun"><span style="font-family: SimSun;" lang="JA">邮</span></font><font face="MS Mincho"><span style="font-family: "MS Mincho";" lang="JA">箱</span></font><font face="SimSun"><span style="font-family: SimSun;" lang="JA">贺</span></font><font face="MS Mincho"><span style="font-family: "MS Mincho";" lang="JA">卡全新上</span></font><font face="SimSun"><span style="font-family: SimSun;" lang="JA">线</span></font><font face="MS Mincho"><span style="font-family: "MS Mincho";" lang="JA">！</span></font></a></span></font></p>
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