<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div>Dear Gate-users,</div>
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<div>I am currently trying to speed up my SPECT simulations using the concept of the phase-space approach, hence the separation of phantom and detector tracking. I am using a simple point source with a phantom surrounding it (Interfile/CT data, navigator: regularMatrix). My SPECT system consists of 2 detector heads which are rotating (they acquire data at 4 time steps, leading to 8 projections in total). I use these commands for the phantom tracking:</div>
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<div>/gate/stepping/SetMode Tracker</div>
<div>/gate/stepping/SetPolicy StopOnPhantomBoundary</div>
<div>/gate/stepping/SetPolicy KeepAll</div>
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<div>And these commands for the detector tracking:</div>
<div>/gate/stepping/SetMode Detector</div>
<div>/gate/stepping/SetNumberOfTrackerDataFiles 1</div>
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<div>There is only one phantom tracker root file created in the output.</div>
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<div>I also run the simulation in one run (without phantom/detector tracking) to compare the outcomes. However, the numbers of counts detected in the singles files are considerably different from each other. I get roughly 30% fewer counts with the phase-space approach, while all other parameter are the same (collimator, collimator phantom distance, activity/duration of scan). Also, the projections of the phase space approach look very strange; there are only counts visible on the fist 4 images, but not on the last 4. In the singles files however, there are counts visible at every time step and on both heads (just fewer counts). </div>
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<div>Has someone else encountered these differences? Does the phantom/detector tracking not work for tomographic scans?</div>
<div>Furthermore, the root file from the phantom tracking is already quite big for an activity of 10kBq (2.3GB), making acquisitions with activities of 10-100MBq impossible. Has somebody a solution for this problem?</div>
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<div>Thank you very much in advance for your help.</div>
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<div>Best wishes,</div>
<div>Andrea Steuwe</div></div></body></html>