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From: Kris T. <kri...@cs...> - 2002-11-22 12:56:27
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Hi George, > From: George Kontaxakis [mailto:gk...@di...] > Sent: 21 November 2002 17:37 > To: Kris Thielemans > I have a couple of more questions for you: > > We have some simulated sinograms from our small animal PET scanner (3D). > In order to feed them to STIR, we obviously need to create an Interfile > with these data. I am a bit puzzled though how to order the 2D sinograms > (direct, oblique, etc.) that make up our 3D data set into that > Interfile. > Is there any convention that uses STIR regarding the order > of the 2D > sinograms into the input Interfile? > This question has more or less been answered (but not completely) in a previous email. I've now made it into a PDF file (attached), using a nice text that Claire Labb'e wrote for the PARAPET project as starting point. Let me know what you think about it. It does not really tackle Interfile, but I sort of hope that this is obvious once you understood axial compression (and read my Interfile page). > We are now successfully reconstructing ECAT7 2D sinograms (ECAT EXACT HR+) > I notice however an artifact at the circle that defines the field of view, > which gets relatively high values (as if there were activity outside the > field of view) instead of the expected near-zero values. Any suggestion? It's probably there because you are not using a proper model: you subtracted delayed (so negatives in the data, which after truncation to positives gives a bowl shaped profile) and probably didn't have scatter correction. Even if you sorted all that out, you might have a ring when not using matching forward and back projector. We used to truncate it away, but I removed that code, as the ring really shows you do not handle the data correctly. (By the way CTI 7.2 transmission reconstruction has that ring as well, but at very high magnitude). > Could you please also confirm if the voxel values in the output image are > SUVs? > No SUVs no way. uncalibrated ECAT counts if you didn't zoom (i.e. the same values as you get when usin gthe CTI reconstruction). If you did use zoom, there might be a scale factor zoom^2 depends on which projectors you used, not sure about that. sorry. Hope this helps, Kris |