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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi All<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A quick query about the use of phase-space files (PSF). A summary of the following is that I can collect projection data for my SPECT simulation if I use, for example a spherical source of Tc-99m, but as soon as I collect a PSF from the
spherical gps source and then use that PSF as the source, I no longer get counts on my SPECT camera. This is not what I was expecting and assume I have made an error so I have included what I believe to be the essential pieces of code below…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So, I can use the following source definition and successfully collect photon counts (an image of a circle) in my simulated SPECT system<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">/gate/source/addSource source gps<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/particle gamma<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/type Volume<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/shape Sphere<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/radius 25 mm<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/angtype iso<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/energytype UserSpectrum<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/setSpectrumFile data/energy_spectrum_Tc99m.txt<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/setForcedHalfLife 242343.36 s<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/setActivity {ACTIVITY} MBq<o:p></o:p></p>
<p class="MsoNormal">/gate/source/source/gps/centre 0 0 0 mm<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I can also encapsulate this source within a sphere and produce a PSF of photons exiting the sphere<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">/gate/actor/addActor PhaseSpaceActor PhS_g<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/attachTo phsSphere<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/save output/PhS-Gamma-{ACTIVITY}MBq.root<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/useVolumeFrame true #Not using world coordinates<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/storeOutgoingParticles true<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/enableParticleName false<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/enableProductionVolume false<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/enableProductionProcess false <o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/addFilter particleFilter<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/particleFilter/addParticle gamma<o:p></o:p></p>
<p class="MsoNormal">/gate/actor/PhS_g/enableZPosition true<o:p></o:p></p>
<p class="MsoNormal">#/gate/actor/PhS_g/saveEveryNSeconds 20<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Inspection of the PSF produced with root suggests that this works correctly (many 0.14 MV photons exit the sphere and these are visualisable when used as a source in the next bit of code) – but the problem arises when I place the PHS for
the sphere into the identical SPECT simulation and use it to replace the original point source. The issue is I get essentially no counts on the SPECT camera (a few random dots appear only). My code for including the PSF is the following (note, when I include
this I remove the gps definition for the source above)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">/gate/source/addSource src_Heart phaseSpace<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/addPhaseSpaceFile data/PhSData/PhS-Gamma-{ACTIVITY}MBq.root<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/setParticleType gamma<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/attachTo boundingVolume<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/useRandomSymmetry true<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/setForcedHalfLife 21624.12 s #6.0 hrs<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/setForcedUnstableFlag true<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/setForcedHalfLife 21624.12 s<o:p></o:p></p>
<p class="MsoNormal">/gate/source/src_Heart/setActivity {ACTIVITY} MBq<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Am I doing things correctly? I have tried to disentangle it all and it appears to me as though the SPECT detector (as defined in the gate-examples and modified and tested successfully for tc-99m) recognizes and counts photons from the
gps as per above but not for the PSF source as I have included it.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As always any assistance to show me the error of my ways is greatly appreciated
<span style="font-family:Wingdings">J</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best wishes<o:p></o:p></p>
<p class="MsoNormal">Steve<o:p></o:p></p>
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