Abstract
When a positron annihilates, two gamma photons are created with orthogonal polarizations. It is possible to use coincidence measurements where both photons undergo Compton scattering to estimate their initial relative polarization orientation. This information is of great interest in gamma imaging systems, such as Positron Emission Tomography, where it may be used as an additional tool to distinguish true coincidence events from scatter and random background. The successful utilization of this principle critically depends on the detector’s angular and energy resolution, which determine its polarimetric performance. In this study, we use Monte Carlo simulations based on the Geant4 toolkit to model two multi-pixel detector configurations identified as prospective for the measurement of gamma-ray polarization in PET. One is based on 2 mm × 2 mm × 20 mm LYSO scintillators and the other is based on 3 mm × 3 mm × 20 mm GAGG scintillators. Each configuration has a pair of modules, each consisting of 64 crystals set up in a single 8 × 8 matrix, where both the recoil electron and the Compton-scattered photon are absorbed. We simulate positron annihilation by generating two back-to-back gamma photons of 511 keV with orthogonal polarizations. The Compton scattering is successfully identified and the modulation of the azimuthal angle difference is clearly observed. The configuration based on GAGG crystals demonstrates slightly better polarimetric performance than the one based on LYSO crystals, reflected in the more pronounced azimuthal modulation.
Highlights
In the event of positron annihilation, a pair of entangled 511 keV gamma photons that are dominantly created in the process have close to opposite momenta and mutually orthogonal polarizations (Figure 1)
The former characteristic of the process has been used in medical imaging with Positron Emission Tomography (PET), by exploiting the fact that two gammas will travel in a straight line path
In-silico studies have shown that the polarization correlations can be used as an additional tool to discriminate spurious random coincidences and body scatter events in PET, since these background events must be lacking in any such correlation [1,2,3]
Summary
In the event of positron annihilation, a pair of entangled 511 keV gamma photons that are dominantly created in the process have close to opposite momenta and mutually orthogonal polarizations (Figure 1). The former characteristic of the process has been used in medical imaging with Positron Emission Tomography (PET), by exploiting the fact that two gammas will travel in a straight line path. The latter characteristic, polarization correlation of the created photons, has not yet been utilized in medical imaging. The polarization correlations can be used to create the image profile of the background events, which can be statistically subtracted from the final image, contributing to better contrast in PET [4].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
