<div dir="ltr"><div><div>Hi,<br></div>Looking at the CPU code (which is more recent), it's because the width of the detector is computed at the isocenter. You can have a look at function <a href="https://github.com/SimonRit/RTK/blob/master/code/rtkThreeDCircularProjectionGeometry.cxx#L519">ToUntiltedCoordinateAtIsocenter</a> (in the standard case, you have sx=px=cosa=0). This complication comes to deal with tilted detector, see <a href="http://dx.doi.org/10.1118/1.4945418">this pa<span id="goog_634464650"></span><span id="goog_634464651"></span>per</a>.</div><div>There seems to be a bug in the GPU code, I'll submit an issue that it should be fixed by making the two codes similar.<br></div>Simon<br><div><span class="gmail-pl-c1"></span></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Sep 25, 2017 at 2:01 PM, Fredrik Hellman <span dir="ltr"><<a href="mailto:fredrik.hellman@gmail.com" target="_blank">fredrik.hellman@gmail.com</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">Hi,<div><br></div><div>In rtkParkerShortScanFilter.hxx (line 113) and rtkCudaParkerShortScanFilter.<wbr>cxx (line 95), the overscan angle is checked to be large enough for the used beam fan angle. (There is a difference between how this check is performed in the two cases. It seems like the CUDA-version assumes that the piercing point is in the middle of the detector. That's not what this question is about though.)</div><div><br></div><div>The beam fan angle seems to be computed as</div><div><br></div><div>arctan( halfDetectorWidth / sourceToIsocenterDistance )</div><div><br></div><div>Why sourceToIsocenterDistance? Shouldn't it be sourceToDetectorDistance? If the detector is far away from the isocenter, the beam fan angle should also be small as far as I understand. This is not reflected in this computation.</div><div><br></div><div>Best regards,</div><div>Fredrik Hellman</div></div>
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