As SC mentioned, it is not easy to measure SNR for DTI using parallel imaging. First of all, SNR has spatial dependency; higher at the edge (closer to the coils) and lower in the center.<br><br>As for your point #2, SNR is important for cross-institution calibration because FA has SNR dependence for low SNR regions; the lower the SNR, the higher the FA. Therefore, you have to make sure that you have a protocol with SNR high enough so that small difference in SNR across institutes won't affect the DTI results that much. Namely, if SNR is high enough, the FA values are stable against SNR difference.<br>
<br>We published empirical measurement results of the SNR-FA relationship in;<br><br><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 12"><meta name="Originator" content="Microsoft Word 12"><link rel="File-List" href="file:///C:%5CUsers%5CSUSUMU%7E1%5CAppData%5CLocal%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_filelist.xml"><link rel="themeData" href="file:///C:%5CUsers%5CSUSUMU%7E1%5CAppData%5CLocal%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_themedata.thmx"><link rel="colorSchemeMapping" href="file:///C:%5CUsers%5CSUSUMU%7E1%5CAppData%5CLocal%5CTemp%5Cmsohtmlclip1%5C01%5Cclip_colorschememapping.xml"><style>
<!--
/* Font Definitions */
@font-face
{font-family:"MS Mincho";
panose-1:2 2 6 9 4 2 5 8 3 4;
mso-font-alt:"ＭＳ 明朝";
mso-font-charset:128;
mso-generic-font-family:modern;
mso-font-pitch:fixed;
mso-font-signature:-536870145 1791491579 18 0 131231 0;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;
mso-font-charset:0;
mso-generic-font-family:roman;
mso-font-pitch:variable;
mso-font-signature:-1610611985 1107304683 0 0 415 0;}
@font-face
{font-family:Times;
panose-1:2 2 6 3 5 4 5 2 3 4;
mso-font-charset:0;
mso-generic-font-family:roman;
mso-font-pitch:variable;
mso-font-signature:-536859905 -1073711039 9 0 511 0;}
@font-face
{font-family:"\@MS Mincho";
panose-1:2 2 6 9 4 2 5 8 3 4;
mso-font-charset:128;
mso-generic-font-family:modern;
mso-font-pitch:fixed;
mso-font-signature:-536870145 1791491579 18 0 131231 0;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{mso-style-unhide:no;
mso-style-qformat:yes;
mso-style-parent:"";
margin:0in;
margin-bottom:.0001pt;
mso-pagination:widow-orphan;
font-size:12.0pt;
mso-bidi-font-size:10.0pt;
font-family:"Times","serif";
mso-fareast-font-family:"MS Mincho";
mso-bidi-font-family:"Times New Roman";
mso-fareast-language:EN-US;}
.MsoChpDefault
{mso-style-type:export-only;
mso-default-props:yes;
font-size:10.0pt;
mso-ansi-font-size:10.0pt;
mso-bidi-font-size:10.0pt;
mso-ascii-font-family:"New York";
mso-fareast-font-family:"MS Mincho";
mso-hansi-font-family:"New York";}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;
mso-header-margin:.5in;
mso-footer-margin:.5in;
mso-paper-source:0;}
div.WordSection1
{page:WordSection1;}
-->
</style><span style="font-size: 11pt; font-family: "Times New Roman","serif";">Farrell, JAD, Landman, BA, Jones, CK, Smith, SA,
Prince, JL, van Zijl, PCM, <b style="">Mori, S. </b>"Effect
of SNR on the accuracy and reproducibility of DTI-derived fractional
anisotropy, mean diffusivity, and principal eigenvector measurements at
1.5T", J. Magn. Reson. Imag., 26, 756-767 (2007)</span><br><br>Currently we are trying to see if this kind of SNR (scan time) - FA relationship can be used for cross-insitution calibration. This type of measurement may not be enough for calibration, but certainly important.<br>
<br><div class="gmail_quote">On Tue, Jun 29, 2010 at 10:23 AM, [Seongjin] <span dir="ltr"><<a href="mailto:choisj70@gmail.com">choisj70@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
My opinions to (3) and (4)<div><br></div><div>(3) In parallel imaging, SNR decreases as acceleration factors increases (R in Philips system).</div><div>But increased acceleration factors improves geometric distortions (i.e. better shape). </div>
<div>You need to find trade off point with your data. In Philips 3T system, I observed significant noise in the images using acceleration factor larger than 3 (R > 3).</div><div><br>(4) When you do DTI using parallel imaging, normal SNR methods will not work. You need to have signal image and noise only image. Get the mean signal and noise standard deviation from an ROI then calculate the SNR. You can get noise-only image in RF-off mode.</div>
<div><br></div><div>-Seongjin</div><div><br></div><div><br><div class="gmail_quote"><div><div></div><div class="h5">On Mon, Jun 28, 2010 at 7:37 PM, Juranek, Jenifer <span dir="ltr"><<a href="mailto:Jenifer.Juranek@uth.tmc.edu" target="_blank">Jenifer.Juranek@uth.tmc.edu</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div><div></div><div class="h5">
<div link="blue" vlink="purple" lang="EN-US">
<div>
<p>While the issue of SNR effects on DTI metrics is
discussed in the published literature, I have found relatively little
information regarding calculating SNR as a screening procedure for image
quality. A few authors have reported the SNR range (or cut-off) of their
datasets - but not many. I'm curious about the following questions...any
responses/opinions would be very helpful.</p>
<p> </p>
<p>1) Is calculation of SNR an effective screening tool for
image quality in DTI research?</p>
<p>2) Is calculation of SNR helpful for determining the
feasibility of pooling 3T DTI data from different scanner platforms (e.g.
Siemens and Philips)</p>
<p>3) To what extent do parallel imaging and acceleration
factors affect measures of SNR?</p>
<p>4) If calculation of SNR is a "good thing to do and
report", then what is the best approach? </p>
<p> </p>
<p>In particular, datatype for analysis (e.g. b=0, trace,
DW) and location "inside the brain" seem to be important things to
consider. In terms of datatype, I have seen folks use single non-averaged b=0
for each subject, and a mathematical relation between sequential b=0 images,
and some have averaged their b=0 data on the scanner.</p>
<p> </p>
<p>Many thanks for any feedback,</p>
<p>Jenifer</p>
</div>
</div>
<br></div></div>_______________________________________________<br>
Mristudio-users mailing list<br>
<a href="mailto:Mristudio-users@mristudio.org" target="_blank">Mristudio-users@mristudio.org</a><br>
<a href="http://lists.mristudio.org/mailman/listinfo/" target="_blank">http://lists.mristudio.org/mailman/listinfo/</a><br>
Unsubscribe, send a blank email to: <a href="mailto:Mristudio-users-unsubscribe@mristudio.org" target="_blank">Mristudio-users-unsubscribe@mristudio.org</a><br>
<br></blockquote></div><br></div>
<br>_______________________________________________<br>
Mristudio-users mailing list<br>
<a href="mailto:Mristudio-users@mristudio.org">Mristudio-users@mristudio.org</a><br>
<a href="http://lists.mristudio.org/mailman/listinfo/" target="_blank">http://lists.mristudio.org/mailman/listinfo/</a><br>
Unsubscribe, send a blank email to: <a href="mailto:Mristudio-users-unsubscribe@mristudio.org">Mristudio-users-unsubscribe@mristudio.org</a><br>
<br></blockquote></div><br>