Intercrystal scatter studies for a 1 mm³ resolution clinical PET system prototype

Abstract

Positron emission tomography (PET) systems designed with multiplexed readout do not usually have the capability to resolve individual intercrystal scatter (ICS) interactions, leading to interaction mispositioning that degrades spatial resolution and contrast. A 3D position sensitive scintillation detector capable of individual ICS readout has been designed and incorporated into a 1 mm3 resolution clinical PET system used for locoregional imaging. Incorporating ICS events increases photon sensitivity by 51.5% compared to using only photoelectric events. A Compton scatter angle error minimization algorithm is used to estimate the first ICS interaction location for accurate line-of-response pairing of coincident photons. An optimal scatter angle error threshold of 15 degrees is used to discard ICS events with a high mismatch between energy-derived and position-derived intercrystal scatter angles. Finally, positioning rather than rejecting ICS events boosts peak contrast to noise ratio by 8.1%, and allows for an equivalent dose reduction of 12% while maintaining equivalent image quality.

The effects of inter-crystal scattering events on the performance of PET detectors

“…For PET detector designs such as individual crystal readout or multi-layered detector, all interaction positions of ICS events are possible to be measured, and the ICS events can then either be rejected or used by applying an ICS events recovery algorithm to find the first interaction position (Gu et al 2010, Geoffroy et al 2015, Abbaszadeh et al 2018, Peng et al 2018, Hsu et al 2019. Since the sensitivity of a PET scanner will be significantly reduced if the ICS events are rejected, recently lots of efforts had been spent on developing ICS event recovery algorithms to find the first interaction positions of the ICS events for different detector designs (Rafecas et al 2003, Gillam et al 2014, Lee et al 2018, Teimoorisichani and Goertzen 2019 or modelling the ICS process in image reconstruction so as to improve the image quality (Qi et al 1998a, 1998b, Alessio et al 2006, Stute et al 2011, Zeraatkar et al 2011.…”

Technical opportunities and challenges in developing total-body PET scanners for mice and rats

“…This deteriorates the spatial resolution, and hence image quality. [176][177][178]. The ratios of inter-detector scatter and inter-crystal scatter can be reduced using scintillators with higher density where the higher effective atomic number reduces the Compton scatter probability.…”

Recovery of inter-detector and inter-crystal scattering in brain PET based on LSO and GAGG crystals

“…Studies related to IDS recovery usually focus on sensitivity increase by adding the recovered IDS events to the practical double coincidences (Wagadarikar et al 2012, Yoshida et al 2014, Lage et al 2015, Michaud et al 2015. ICS recovery studies prove the enhancement of resolution (Comanor et al 1996, Rafecas et al 2003, Pratx and Levin 2009, Gillam et al 2014, Abbaszadeh et al 2018, Surti and Karp 2018, Lee et al 2018a, Hsu et al 2019. However, optimization of the recovery algorithm is still under investigation because the occurrences of IDS and ICS depend on PET geometry, and the impact of the recoveries on image quality is not fully understood.…”