<div dir="ltr">Hi Helen,<div><br></div><div>We've been looking into this very issue here over the last year or so. We have data acquired using a sequence that is essentially identical to what you describe, and also using a 64 direction, b=2,500 sequence. The tracking is improved using the higher b-value, but I'm not sure what the optimal value actually is. In this population, it might very well be the case that a slightly lower b-value would give enough information (the diffusion signal is much smoother as a function of orientation in this age range than it is in adults). For this reason, you can probably afford to lower the b-value to some extent compared to adults, and you also don't need to sample as densely over the sphere (i.e. you can use fewer directions). We haven't got as far as really testing this out thoroughly, though. On the other hand, Kerstin Pannek had an abstract on this issue (ISMRM 20: 3161; 2012), which suggested b=1,500 gave the best results. So my gut feeling is b=1,500 or so, and as many directions as you feel comfortable with... As long as you have at least ~30, angular sampling will be sufficient - any further increase will essentially improve your overall SNR. </div><div><br></div><div>Hope this helps,</div><div>Donald.</div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On 4 December 2014 at 18:11, Helen Carlson <span dir="ltr"><<a href="mailto:Helen.Carlson@albertahealthservices.ca" target="_blank">Helen.Carlson@albertahealthservices.ca</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal">Hi there<u></u><u></u></p>
<p class="MsoNormal">First, thank-you for all the previous help you have given our team through this list. It has been absolutely crucial!<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I am wondering about the minimum scan requirements for running CSD and getting realistic, useable results. Ideally we would have >60 directions and a high b-value but in reality we scan a paediatric population and so scan duration ends
up being the most important variable in the equation.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">We currently use:<u></u><u></u></p>
<p><u></u><span>-<span style="font:7.0pt "Times New Roman"">
</span></span><u></u>32 directions<u></u><u></u></p>
<p><u></u><span>-<span style="font:7.0pt "Times New Roman"">
</span></span><u></u>3 b0<u></u><u></u></p>
<p><u></u><span>-<span style="font:7.0pt "Times New Roman"">
</span></span><u></u>B-value=750<u></u><u></u></p>
<p><u></u><span>-<span style="font:7.0pt "Times New Roman"">
</span></span><u></u>Voxel size 2.2 isotropic<u></u><u></u></p>
<p><u></u><span>-<span style="font:7.0pt "Times New Roman"">
</span></span><u></u>0 repetitions<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Is this sequence sufficient to run CSD and get meaningful results? We have successfully run the CSD and the tracts look great, I just need your expert opinions as to whether we are too far off with our parameters to really capitalize on
the benefits of CSD?<u></u><u></u></p>
<p class="MsoNormal">Thanks<u></u><u></u></p>
<p class="MsoNormal">Helen<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr"><b><font color="#990000">Dr J-Donald Tournier (PhD)</font></b><br><div><font color="#990000"><br></font></div><i><font color="#990000">Senior Lecturer, </font></i><i><font color="#990000">Biomedical Engineering</font></i><div><i><font color="#990000">Division of Imaging Sciences & Biomedical Engineering<br>King's College London</font></i><div><i><font color="#990000"><br></font></i></div><div><i><font color="#990000"><b style="font-family:Calibri,sans-serif;font-size:15px"><span style="font-size:10pt">A:</span></b><span style="font-family:Calibri,sans-serif;font-size:10pt"> Department of Perinatal Imaging & Health, 1<sup>st</sup> Floor South Wing, St Thomas' Hospital, London. SE1 7EH</span><br></font></i></div><div><i><font color="#990000"><b>T:</b> +44 (0)20 7188 7118 ext 53613</font></i></div></div><div><i><font color="#990000"><b>W:</b> <a href="http://www.kcl.ac.uk/medicine/research/divisions/imaging/departments/biomedengineering" target="_blank">http://www.kcl.ac.uk/medicine/research/divisions/imaging/departments/biomedengineering</a></font></i><br></div></div></div>
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