<p class="MsoNormal"> Thanks a lot Sir,</p><p class="MsoNormal"><br></p>
<p class="MsoNormal">I have another question regarding DTI data; I have
longitudinal DTI data of 3 time points. First time point have 4 averages second
time point have 2 averages and third time point have 4 averages, can I combine
these data sets?</p>
<p class="MsoNormal">So finally the question is what the effect of averaging of
DTI data, is it going to the change the DTI matrix such as FA and Trace?</p><p class="MsoNormal"><br></p>
With best Regards,<br><br><br><div class="gmail_quote">On Mon, Nov 26, 2012 at 2:31 AM, susumu mori <span dir="ltr"><<a href="mailto:susumu@mri.jhu.edu" target="_blank">susumu@mri.jhu.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi Santosh,<div><br></div><div>Practically, the slice thickness, which is the thinner the better, is determined by SNR.</div><div>If you use 2.5 mm, you need about 50-55 slices to cover the entire brain.</div><div>2.2 mm needs 55-60 and 2mm needs more than 60. These are all without gaps.</div>
<div><br></div><div>With 5-6 min scans, you can acquire about 40-50 DWIs for 2.5mm/50-slice 3D data. These numbers decrease as the thickness become thinner and thus more slices are required and takes longer time.</div><div>
<br></div><div>40-50DWI means about 4 repetitions of 12-orientations.</div><div><br></div><div>If you use a 1.5T, you may need more than 60 DWIs with 2.5mm, which takes about 7-8min. With thinner slices (e.g. 2.2mm), you need longer scans to achieve good SNR.</div>
<div><br></div><div>With a 3T, 30-40 DWIs would give decent SNR with 2.5mm. With 2-2.2mm slice, you want more than 50-60 DWIs (5-8min).</div><div><br></div><div>These numbers are to achieve a good SNR, which depends on my subjective judgement. So different people could recommend different numbers, but they may not be that much different.</div>
<div><br></div><div>As for image distortion, the most important factor is the size of the image matrix; the smaller the better (I assume that you already use parallel imaging, which reduces the matrix size into half).</div>
<div><br></div><div>For example, 128x128points / 256x256mm and 96x96/192x192mm both give the same 2mm resolution, but 96x96 would give better (less) distortion and better SNR.<br><br><div class="gmail_quote"><div><div class="h5">
On Mon, Nov 26, 2012 at 1:28 AM, Santosh Yadav <span dir="ltr"><<a href="mailto:santoshyadav20076@gmail.com" target="_blank">santoshyadav20076@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5">Hi DTI experts,<div><br></div><div>Thanks for great supports!<br><div><br></div><div>
I would like know the recommended slice thickness and gap between the slice for DTI data acquisition for 12 directions. Is higher Slice thickness( more that 3 mm) have partial volume effect?</div>
<div><br></div><div>Second question: Is eye open during the DTI acquisition have any impact on DTI distortion or image quality?</div><div><br></div><div>With Best Regards,<br>
</div><div><br></div><div>Santosh</div></div>
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