<div dir="ltr"><div>Yes, there is no such limitation as far as I know, you can use negative numbers and value above 1.</div><div>Your result is really strange, it it supposed to be a square? I don't know what is the problem but that's clearly a geometry issue. We can always have a look if you're able to share some data.</div><div>Simon<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Jun 3, 2020 at 1:56 PM Andreas Andersen <<a href="mailto:andreasga22@gmail.com">andreasga22@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">I don't think there are any restrictions technically.<br>You should be able to use negative values, as the main arithmetic is just a <a href="https://github.com/SimonRit/RTK/blob/master/include/rtkBackProjectionImageFilter.hxx#L106" target="_blank">sum</a> and a <a href="https://github.com/SimonRit/RTK/blob/master/include/rtkBackProjectionImageFilter.hxx#L115" target="_blank">multiplication</a>.<br><br>The only restriction I can see is that this sum and multiplication should not overflow (or underflow for negative values) the underlying type of the output image, as that would be undefined behaviour. Over- and underflow is unlikely for float, unless you have extremely high values (<a href="https://en.wikipedia.org/wiki/Floating-point_arithmetic#Range_of_floating-point_numbers" target="_blank">see wikipedia for floating point range</a>).<br><br>/Andreas<br clear="all"><div><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><p style="margin-bottom:0.0001pt"><span style="color:rgb(31,73,125)" lang="EN-US"><span style="font-size:11pt;line-height:16.8667px;font-family:Calibri,sans-serif" lang="EN-US">__________________________________</span></span></p><p style="margin-bottom:0.0001pt"><span style="color:rgb(31,73,125)" lang="EN-US"><span style="font-size:11pt;line-height:16.8667px;font-family:Calibri,sans-serif" lang="EN-US">Andreas Gravgaard Andersen</span></span></p><p style="margin:0cm 0cm 0.0001pt;font-size:12pt;font-family:"Times New Roman",serif;color:black"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Danish Center for Particle Therapy, </span></p><p style="margin:0cm 0cm 0.0001pt;font-size:12pt;font-family:"Times New Roman",serif;color:black"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Aarhus University Hospital<u></u><u></u></span></p><p style="margin:0cm 0cm 0.0001pt;font-size:12pt;font-family:"Times New Roman",serif;color:black"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)" lang="DA">Palle Juul-Jensens Blvd. 99,</span></p><p style="margin:0cm 0cm 0.0001pt;font-size:12pt;font-family:"Times New Roman",serif;color:black"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)" lang="DA">8200, Aarhus</span></p><div><p style="margin:0cm 0cm 0.0001pt;font-size:12pt;font-family:"Times New Roman",serif;color:black"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)" lang="DA">Mail: <a href="mailto:agravgaard@protonmail.com" target="_blank">agravgaard@protonmail.com</a></span></p><p style="margin:0cm 0cm 0.0001pt;font-size:12pt;font-family:"Times New Roman",serif;color:black"><span style="color:rgb(31,73,125);font-family:Calibri,sans-serif;font-size:11pt">Cell: </span><span style="color:rgb(31,73,125);font-family:Calibri,sans-serif;font-size:11pt"> </span><a value="+4523382411" style="font-family:Calibri,sans-serif;font-size:11pt;color:rgb(17,85,204)">+45 3165 8140</a></p></div></div></div></div></div></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, 3 Jun 2020 at 03:34, Benjamin W. Maloney <<a href="mailto:Benjamin.W.Maloney.TH@dartmouth.edu" target="_blank">Benjamin.W.Maloney.TH@dartmouth.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Hi,</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
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<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
I thought the same in regards to trying to rotating in the other direction. Unfortunately, that has a similar artifact but with the reconstruction flipped. </div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
Interestingly the overlap happens in a similar place but the internal structures are flipped</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<br>
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<div><span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">1. Thanks!</span><br>
</div>
<div><span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">2. I should have worded that better. My projection images will be preprocessed in a float format. I wanted to check if there were restrictions on these
float values. Can input image data have negative values or high values? Or are they expected to have values between 0 and 1? I ask because some of the tools I have used to do this preprocessing (outside of RTK) have given negative values or 'stretched' the
data from 0 to 255 before saving.</span></div>
<div><span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)"><br>
</span></div>
<div><span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">Ben</span></div>
<div><span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)"><br>
</span></div>
</div>
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<div id="gmail-m_1203934353642809590gmail-m_6776844938196564169appendonsend"></div>
<hr style="display:inline-block;width:98%">
<div id="gmail-m_1203934353642809590gmail-m_6776844938196564169divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> Simon Rit <<a href="mailto:simon.rit@creatis.insa-lyon.fr" target="_blank">simon.rit@creatis.insa-lyon.fr</a>><br>
<b>Sent:</b> Tuesday, June 2, 2020 5:28 PM<br>
<b>To:</b> Benjamin W. Maloney <<a href="mailto:Benjamin.W.Maloney.TH@dartmouth.edu" target="_blank">Benjamin.W.Maloney.TH@dartmouth.edu</a>><br>
<b>Cc:</b> <a href="mailto:rtk-users@public.kitware.com" target="_blank">rtk-users@public.kitware.com</a> <<a href="mailto:rtk-users@public.kitware.com" target="_blank">rtk-users@public.kitware.com</a>><br>
<b>Subject:</b> Re: [Rtk-users] Reconstruction Artifact</font>
<div> </div>
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<div>
<div dir="ltr">
<div>Hi,</div>
<div>Sometimes rotating in the wrong direction gives this kind of artefacts. It's quite possible that we don't use the same convention as other toolkits regarding this.</div>
<div>For other questions:</div>
<div>1. Yes, you can use pixel as the unit. Then the image spacing should be 1 obviously and indeed, sdd and sid should be in pixels.</div>
<div>2. I don't fully understand. If your data is the output of a count detector, then you either rely on RTK to guess the counts without object to compute the line integral, or your preprocess your projections to pass line integrals in a float format.</div>
<div>Simon<br>
</div>
</div>
<br>
<div>
<div dir="ltr">On Tue, Jun 2, 2020 at 4:51 PM Benjamin W. Maloney <<a href="mailto:Benjamin.W.Maloney.TH@dartmouth.edu" target="_blank">Benjamin.W.Maloney.TH@dartmouth.edu</a>> wrote:<br>
</div>
<blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
Hi all,<br>
<br>
Not sure if this is the right group to post to but here's my question:<br>
<br>
I have a code that pulls in my own projection images and uses the FDKConeBeamReconstructionFilter for reconstruction<br>
<br>
The reconstruction I am getting has an artifact where it looks like there are two overlapping objects rotated. <br>
I have used other reconstruction toolboxes (mainly TIGRE in MATLAB) with the similar geometry inputs and not had this issue. I suspect the difference is in the parts of the geometry that are set by default. My question is if anyone has seen this before and
what input I should look into?<br>
<br>
I have a few more questions I may or may not be related:<br>
1. I assume that since I set the origin etc of my images in pixel, sid and sdd should be in pixels as well? <br>
2. Are there restrictions related the scalar values of the projection data? My data will be in detector counts rather than linear attenuation coefficients, is that okay?<br>
I have attached an image to show this issue. It is supposed to be a rectangular mammography phantom. It is a slice in XZ plane<br>
<br>
Thanks for the help!<br>
Ben<br>
<br>
<br>
<br>
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