<div dir="ltr"><div><div>Hi,<br></div>I haven't implemented the ADMM algorithm but adding a constraint such as positivity in iterative reconstruction is not a straightforward thing. The way it's done in SART and ROOSTER is heuristic and there is no proof of convergence. Still, you can easily add it in this way if you want to but you'll have to modify the code. There is a wealth of literature on the topic if you want to read it. To illustrate this complexity, you can read the paper of Cyril Mory at the <a href="http://www.ct-meeting.org/data/ProceedingsCTMeeting2014.pdf">CT meeting</a> last year.<br></div>Simon<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Aug 6, 2015 at 10:58 AM, Guangming Zang <span dir="ltr"><<a href="mailto:guangming.zang@kaust.edu.sa" target="_blank">guangming.zang@kaust.edu.sa</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_default" style="font-family:'trebuchet ms',sans-serif;color:rgb(0,0,255)">Hi Simon,</div><div class="gmail_default" style="font-family:'trebuchet ms',sans-serif;color:rgb(0,0,255)">thanks for the explanation in detail.</div><div class="gmail_default" style="font-family:'trebuchet ms',sans-serif;color:rgb(0,0,255)">i can understand why there is only post-processing for fdk algorithm now,</div><div class="gmail_default" style="font-family:'trebuchet ms',sans-serif;color:rgb(0,0,255)">but why don't we do the non-negative checking during each ADMM iteration? after all, in my opinion, in most of applications, only volume values that between [0,positive infinite) make sense. </div><div class="gmail_default" style="font-family:'trebuchet ms',sans-serif;color:rgb(0,0,255)">Regards</div><span class="HOEnZb"><font color="#888888"><div class="gmail_default" style="font-family:'trebuchet ms',sans-serif;color:rgb(0,0,255)">Guangming </div></font></span></div><div class="gmail_extra"><span class=""><br clear="all"><div><div><div dir="ltr"><div><div dir="ltr"><font style="line-height:23.32400131225586px" face="arial, helvetica, sans-serif" color="#674ea7"><b><i>Guangming Zang (Alex)</i></b></font><div style="line-height:23.32400131225586px"><font face="arial, helvetica, sans-serif"><b><i><font color="#0b5394">King Abdullah University of Science and Technology</font><font color="#073763">(KAUST)</font></i></b></font></div><div style="line-height:23.32400131225586px"><span style="font-family:arial;font-size:13px;line-height:20.020000457763672px"><font color="#0b5394"><b><i>University of Chinese Academy of Sciences(UCAS)</i></b></font></span><font face="arial, helvetica, sans-serif"><b><i><font color="#073763"><br></font></i></b></font></div><div style="line-height:23.32400131225586px"><span style="font-family:arial;font-size:13px;line-height:20.020000457763672px"><font color="#0b5394"><b><i><br></i></b></font></span></div><div style="line-height:23.32400131225586px"><span style="font-family:arial;font-size:13px;line-height:20.020000457763672px"><font color="#0b5394"><b><i><br></i></b></font></span></div><div style="line-height:23.32400131225586px"><br></div></div></div></div></div></div>
<br></span><div><div class="h5"><div class="gmail_quote">2015-08-06 8:27 GMT+03:00 Simon Rit <span dir="ltr"><<a href="mailto:simon.rit@creatis.insa-lyon.fr" target="_blank">simon.rit@creatis.insa-lyon.fr</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div>Hi,<br></div>No there is no option to force the output volume to 0. This is not the same as sart where you might want to do it during the iterations. In the FDK case, it's only post-processing so there is not really a reason to put it in rtkfdk.<br></div>The nonneg option is the minimum value of the intensity that you allow the Boellaard algorithm to reach after scatter correction. This does not prevent negative values in the volume because the ramp filter might create negative values from positive projections.<br></div>Simon<br></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div>On Thu, Aug 6, 2015 at 2:00 AM, Guangming Zang <span dir="ltr"><<a href="mailto:guangming.zang@kaust.edu.sa" target="_blank">guangming.zang@kaust.edu.sa</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><div dir="ltr"><div class="gmail_default" style="font-family:trebuchet ms,sans-serif;color:#0000ff">Dear Simon and RTK community,</div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif;color:#0000ff">considering in rtksart ,we have --positivity to force the reconstructed volume values to be positive(i guess, not tested yet), i was wondering if we have any options and commands to have the same effect in algorithms fdk and admmtv since --positivity can not be found?</div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif;color:#0000ff">the Boellaard scatter correction: --nonneg is what i am looking for?</div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif;color:#0000ff">Thanks in advance.</div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif;color:#0000ff">Guangming</div><div><div><div dir="ltr"><div><div dir="ltr"><font style="line-height:23.32400131225586px" face="arial, helvetica, sans-serif" color="#674ea7"><b><i>Guangming Zang (Alex)</i></b></font><div style="line-height:23.32400131225586px"><font face="arial, helvetica, sans-serif"><b><i><font color="#0b5394">King Abdullah University of Science and Technology</font><font color="#073763">(KAUST)</font></i></b></font></div><div style="line-height:23.32400131225586px"><span style="font-family:arial;font-size:13px;line-height:20.020000457763672px"><font color="#0b5394"><b><i>University of Chinese Academy of Sciences(UCAS)</i></b></font></span><font face="arial, helvetica, sans-serif"><b><i><font color="#073763"><br></font></i></b></font></div><div style="line-height:23.32400131225586px"><span style="font-family:arial;font-size:13px;line-height:20.020000457763672px"><font color="#0b5394"><b><i><br></i></b></font></span></div><div style="line-height:23.32400131225586px"><span style="font-family:arial;font-size:13px;line-height:20.020000457763672px"><font color="#0b5394"><b><i><br></i></b></font></span></div><div style="line-height:23.32400131225586px"><br></div></div></div></div></div></div>
</div>
<br>
</div></div><div><hr></div><font face="Arial" size="1">This message and its contents, including attachments are intended solely for the original recipient. If you are not the intended recipient or have received this message in error, please notify me immediately and delete this message from your computer system. Any unauthorized use or distribution is prohibited. Please consider the environment before printing this email.</font></blockquote></div><br></div>
</blockquote></div><br></div></div></div><div class="HOEnZb"><div class="h5">
<br>
<div><hr></div><font face="Arial" size="1">This message and its contents, including attachments are intended solely for the original recipient. If you are not the intended recipient or have received this message in error, please notify me immediately and delete this message from your computer system. Any unauthorized use or distribution is prohibited. Please consider the environment before printing this email.</font></div></div></blockquote></div><br></div>