[Castor-users] question about System Matrix & PSF in CASToR iteration

[赵鑫]

Dear CASToR Users and Developers,
We have using CASToR to recon our PET data for half a year, and it shows impressive ability to provide the image that we urgently needed. But there are two problems that confused me：
1）How does CASToR generate its System Matrix when running OSEM? I used to know that before running MLEM iterative reconstruction, one should precompute the system matrix for the current specific PET scanner system, which will cost a lot, and must re-generate it when changing different PET scanner geometry. But CASToR needs no precomputation and can recon any kind of PET geometry immediately, how does it happen?
2）When does Point Spread Function calculation be used in MLEM iteration? I compared MLEM reconstruction with and without PSF calculation, and find out that the MLEM with PSF provides far better image results than another. In the attachment, I showed the reconstructed image of Derenzo by CASToR with PSF, its image quality is good!  I just what to in which step does PSF work in CASToR MLEM iteration? Does anyone know which article I should read？

Thank you a lot for your help, any answer will be helpful.
Christopher Zhao


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