Study of light transport inside scintillation crystals for PET detectors

Abstract

Scintillation crystal design is a critical component in positron emission tomography system development, which impacts a number of performance parameters including energy resolution, time resolution and spatial resolution. Our work aims to develop a generalized simulation tool to model the light transport inside scintillation crystals with good accuracy, taking into account surface treatments, reflectors, temporal dependence of scintillation decay, and comprehensive experimental validations. The simulation has been validated against both direct analytical calculation and experimental measurements. In this work, the studies were performed for a lutetium-yttrium oxyorthosilicate crystal of 3×3×20 mm(3) dimension coupled to a Hamamatsu silicon photomultiplier, with respect to light output, rise-time slope, energy resolution and time resolution. Four crystal surface treatment and reflector configurations were investigated: GroundMetal, GroundPaint, PolishMetal and PolishPaint. The experiments were performed to validate the Monte Carlo simulation results. The results indicate that the best time resolution (0.96±0.05 ns) and good energy resolution (10.6±0.4%) could be produced by using a polished surface with specular reflector, while the configuration of a polished surface with diffusive reflector produces the best energy resolution (10.2±0.9%). The results indicate that a polished surface with diffusive reflector achieves the best energy resolution (10.2±0.9%) for 511 keV high energy photons, and a polished surface with specular reflector achieves the best time resolution (0.96±0.05 ns) measured against a Hamamatsu fast photomultiplier tube. The ground surface treatment is not recommended for its inferior performance in terms of energy and time resolution. Possible explanations and future improvements to be made to the developed simulation tool are discussed.

Analytical calculation of the lower bound on timing resolution for PET scintillation detectors comprising high-aspect-ratio crystal elements

“…The formulation of the optical transport PDF is shown according to the method outlined in Yang (2012) and Yang et al (2013). However, in that work, the analytical optical path length was given for crystals with no reflector and without regard to the extraction efficiency at the exit boundary.…”

Physics and technology of time-of-flight PET detectors

“…There are many publications on how these factors affect energy resolution, but these only address h ot and, therefore, cannot be extrapolated straightforwardly to timing performance. Understanding how the crystal geometry, surface treatment, and reflectors affect the CRT requires time-resolved simulations (Yang et al 2013, Ter Weele et al 2015c, Roncali et al 2017 and experiments (Gundacker et al 2014, Berg et al 2015, Ter Weele et al 2015b, Nemallapudi et al 2016b.…”

Modelling the transport of optical photons in scintillation detectors for diagnostic and radiotherapy imaging

“…More recent examples of optical MC research on nuclear imaging using gamma cameras include compact gamma cameras based on avalanche photodiodes (Després et al , 2007), dedicated brain SPECT model (Hirano et al , 2012) and faster MC computation (Hunter et al , 2013). A larger number of papers were published on PET including work on monolithic scintillation crystals (van der Laan et al , 2010b; Vinke and Levin, 2014), crystal surface characterization (Roncali and Cherry, 2013b; Yang et al , 2013), and temporal resolution for time-of-flight (TOF) PET (Berg et al , 2015; Derenzo et al , 2014, 2015; Moses et al , 2014; Roncali et al , 2014). …”