An experimental and computational evaluation of a novel Timepix3 detector for Compton imaging in nuclear medicine

Abstract In this paper, we investigate the use of a MiniPIX (Timepix3) hybrid pixel detector as a single layer Compton camera for low-energy (< 200 keV) photons for Nuclear Medicine imaging applications. Literature to date has focused on using Compton camera imaging for high energy photons emitted from non-clinically relevant radionuclides. This paper aims to investigate Compton imaging for nuclear medicine specific radionuclides such as Tc 99m (140 keV). For this, a Timepix3 chip with a 1 mm CdTe sensor has been fully characterised in terms of efficiency, energy and timing resolution using a range of point sources, and a detailed model of the detector developed using the EGSnrc Monte Carlo toolkit. Knowledge of the specific interaction points within the detector in the simulation allowed a prediction to be made of the performance of the detector as a Compton camera. Comparison with experimental measurements showed good agreement with simulations, providing validation of the methods employed for image reconstruction. Simple Back Projection (SBP), Filtered Back Projection (FBP) and List Mode-Maximum Likelihood Expectation Maximisation (LM-MLEM) techniques were used for image reconstruction. For all experimental acquisitions, measured Full Width Half Maximum (FWHM) values were within 6% of the modelled values, with Doppler broadening identified as the main limiting factor of the spatial resolution of the system. LM-MLEM consistently returned the highest spatial resolution images, with a 7.3 ± 0.5 mm FWHM achieved for 99m Tc point sources, consistent with current clinical gamma cameras. Our results demonstrate the potential of the Timepix3 as a single layer CdTe Compton camera for clinical applications using low energy gamma emitters. The developed MC model will provide a means of investigating larger area, single layer CdTe Compton cameras for nuclear medicine imaging.