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">On Mon, Jun 28, 2010 at 7:37 PM, Juranek, Jenifer <span dir="ltr"><<a href="mailto:Jenifer.Juranek@uth.tmc.edu">Jenifer.Juranek@uth.tmc.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div lang="EN-US" link="blue" vlink="purple">
<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>
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