Thomas Leroy Laurence

Investigation of surface treatment of interface for depth of interaction positioning of a 2×2 discrete crystal array

We have previously reported on depth of interaction (DOI) positioning performance of 2×2 discrete LYSO crystal arrays coupled to digital silicon photomultiplier arrays (PDPC arrays). By optimizing the design of the interface between each neighboring crystal, DOI can be estimated from the overall light distribution collected by the 2×2 array of sensors. A significant challenge to the design is controlling how light is shared between neighboring crystals. We have previously used crystals with lapped surfaces to improve light sharing. In this work we investigated four different surface treatments/patterns. The surface treatments were fine etch, coarse etch and sanded. The patterns were treatment for the full length of the interface between crystals and treatment only for the section of the crystals where light was being shared. The LYSO crystals were each 4×4×19 mm3. High index of refraction (i.e., 1.704n) melt mount resin and custom shaped mirror film patterns were used to control light sharing between neighboring crystals. Each detector unit was calibrated using an electronically collimated 511 keV photon flux stepped along the long axis of the crystal. DOI event positioning was done using maximum likelihood. The crystal array fabricated from the crystals with the finely etched surfaces had the best DOI decoding performance. Customizing the surface properties to optimize light sharing can improve DOI positioning for detector designs that utilize light sharing to estimate DOI positioning. The advantage of the etching process used in this work is that it is highly reproducible and can allow for custom patterns to be etched onto crystal surfaces.

Validation of GATE Monte Carlo simulations of the Philips GEMINI TF and TruFlight Select PET/CT scanners based on NEMA NU2 standards

The objective of this study is to validate the in-house GATE simulations of the Philips GEMINI TF and TruFlight Select PET scanners and evaluate their accuracy for further research and optimization of current and future PET products. GATE results are compared to experimental data obtained according to the National Electrical Manufacturers Association (NEMA) NU2-2007 standards. A detailed implementation of the geometrical and functional models of the scanners and the NEMA phantoms was conducted, allowing the evaluation of the simulated absolute sensitivity, spatial resolution, count rates and the image quality of both systems. All Monte Carlo data production was performed according to the NEMA protocols. Simulated data were converted into the Philips list-mode format and analyzed using the same software tools as in the quality control step of the production line. Good agreement was found between the simulated results and the measured data from both scanners. This validation study represents an important step towards the use of these tools as an aid for the optimization of the current acquisition protocols and the validation of reconstruction and data correction techniques.