Entangled polarisation correlations of annihilation gamma and their applications to PET Imaging

Our current understanding and measurements of photon quantum entanglement in the MeV scale are poor compared to the optical regime. However, recent advances in detector technologies and simulation frameworks are finally allowing for detailed studies at high energy scales. In this thesis we assess the capabilities for two state-of-the-art gamma detector systems to characterise double Compton scattering of positron annihilation photons. The first system comprised two high resolution CZT crystals. The second was composed of two arrays of LYSO crystals with properties representative of current clinical PET scanners. A new quantum entangled Geant4 version was developed and verified against data from these systems. The inclusion of quantum entanglement was shown to be crucial to describe correlations between the azimuthal planes of scattered annihilation photons. Standard (non-entangled) Geant4 failed to accurately describe photon transport and these new modifications have since become part of future Geant4 releases. A first ever measurement of entanglement loss in the MeV regime is obtained, through study of the diminished Compton scatter correlations for data in which one photon has undergone Compton scattering prior to detection. Under these conditions the data are broadly consistent with a complete loss of entanglement between annihilation photons. Finally, the entangled Geant4 was used to obtain the first simulated study of entangled PET imaging. A CZT based PET-scanner was simulated with a standard phantom. Using data from these simulated scans we present a technique to quantify and remove scatter and random backgrounds using only entanglement information in the PET events.