05/29/2014

# Mark S. Brown$${}^1$$, Stefan Gundacker$${}^2$$, Alaric Taylor$${}^1$$, Clemens Tummeltshammer$${}^1$$ Etiennette Auffray$${}^2$$, Paul Lecoq$${}^2$$, Ioannis Papakonstantinou$${}^{1,\ast}$$ 1 Electrical and Electronic Engineering, UCL, London, UK 2 PH-CMX Group, CERN, Geneva, Switzerland $$\ast$$ E-mail: Corresponding i.papakonstantinou@ucl.ac.uk

Abstract

The uncertainty in time of particle detection within a scintillator detector, characterised by the coincidence time resolution (CTR), is explored with respect to the interaction position within the scintillator crystal itself. Electronic collimation between two scintillator detectors is utilised to determine the CTR with depth of interaction (DOI) for different materials, geometries and wrappings. Significantly, no relationship between the CTR and DOI is observed within experimental error. Confinement of the interaction position is seen to degrade the CTR in long scintillator crystals by 10%.

# Introduction

Detection of ionising radiation is typically accomplished by transducing the incoming particle into light. This light can then be converted to an electrical signal and subsequently analysed. Scintillator detectors are comprised of three primary components, as shown in figure \ref{fig:doi-ctr}. Namely a scintillator crystal for creation of thousands of optical photons, a photodetector for conversion of the light to an electrical signal and a layer of optical grease between the two components to improve coupling. Reductions in the scintillator detector detection time uncertainty, known as the time resolution, are important for reducing statistical noise in positron emission tomography (PET) images(Moses 2006).

In this work we investigate the relationship between the interaction position of 0.511 MeV gamma ray photons and the timing and energy performance of the scintillator detector. The depth of interaction (DOI), shown in figure \ref{fig:doi-ctr}, is the shortest distance to the photodetector from the gamma ray photon ($$\gamma$$) interaction position. The DOI is a potential source of degradation to the timing and energy performance of the scintillator detector due to photon time of flight and light loss from increased path lengths within the scintillator crystal. Furthermore determination of the DOI, of a given interaction, is of importance for PET to negate or reduce the contribution of parallax error upon the spatial resolution (Moses