Hmmmm, please check the following;<div><br></div><div>List up the number of DWIs that are affected (e.g. 4th, 8th, 9th, etc)</div><div>Look at the gradient table at the listed number.</div><div>Try to find if the identified table lines always contain gradient values of X, Y, or Z.</div>
<div><br></div><div>Also please show us the color map. </div><div><br></div><div>For example, if this artifact shows up every time you apply X, the color map should become red for the area of the artifact.</div><div><br></div>
<div>If you find this type of correlation between the applied gradient and artifacts, this is not a typical motion artifacts. You should contact to the manufacturer.<br><br><div class="gmail_quote">On Mon, Oct 25, 2010 at 7:58 AM, Katja Doerschner <span dir="ltr"><<a href="mailto:katja@bilkent.edu.tr">katja@bilkent.edu.tr</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div style="word-wrap:break-word">Thank you for your response, Susumu.<div><br></div><div>I am attaching an example of the artifact.</div>
<div>If Siemens had issues in the past it sounds as if they must have resolved this? </div><div>Thank you very much.</div><div><br></div><div><div><img height="194" width="200" src="cid:37FECDD6-F706-4945-ABA7-8E73F1184454"></div>
<div><br></div><div><div><div></div><div class="h5"><br><div><div>On Oct 25, 2010, at 2:43 PM, susumu mori wrote:</div><br><blockquote type="cite">Hi Katja,<div><br></div><div>It is difficult to say anything without looking at the images. Usually if you find a localized signal drop, that is due to motion. However, they appear typically around the 4th ventricle and rarely around the central sulcus. Also, 10 out of 30 seem too many. Siemens had some issues in the past with signal drop usually in the occipital lobe.</div>
<div><br></div><div>I thought you can attach a small file with some screenshots?<br><br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">
<div><div><br></div><div>My questions are: 1) what causes these artifacts (I have seen them in other scans/patients at different locations, e.g. posterior tip of the occipital lobe) - could it be the effect of a large blood vessel or other kinds of motion)?</div>
</div></div></blockquote><div>> I have to see the images. If you want, you can upload your data to our ftp site.</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word"><div><div>2) How can I avoid such artifacts?</div></div></div></blockquote><div> > see above.</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word"><div><div>3) Is there any way of 'saving' the data - other than throwing those images out</div></div></div></blockquote><div>> 10 out of 30 seem too many to save. Usually the artifacts are linked to a particular gradient axis; for example, whenever X axis is applied, the artifact appears. If so, you lose all X gradient orientations and the data can't be saved.</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div>4) If I have to remove these images - how will that affect the tensor calculation/FA maps/fibertracking?</div>
</div></div></blockquote><div>> see above </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div><br></div><div>Thank you very much.</div>
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<div><font face="Arial">--</font></div><div><font face="Arial"><br></font></div><div><font face="Arial">Katja Doerschner</font></div><div><font face="Arial">Assistant Professor</font></div><div><font face="Arial">Department of Psychology </font></div>
<div><font face="Arial">& National Center for</font></div><div><span style="font-family:Arial">Magnetic Resonance </span><span style="font-family:Arial">Research </span><span style="font-family:Arial">(UMRAM)</span></div>
<div><span style="font-family:Arial">Bilkent University</span></div><div><span style="font-family:Arial">Bilkent Cyberpark, C-Blok, 2. Kat</span></div><div><span style="font-family:Arial"><a href="http://www.bilkent.edu.tr/~katja/" target="_blank">http://www.bilkent.edu.tr/~katja/</a></span></div>
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