Study of spatial resolution and depth of interaction of APD-based PET detector modules using light sharing schemes

Abstract

Using 4 8 Hamamatsu S8550 APD matrices with 1.6 mM 1.6 mm pixels and a 2.3 mm pitch, we compared the spatial resolution of light sharing schemes using block detectors to detector modules using 1-to-1 coupling between individual 2 mm 2 mm 10 mm LSO crystals and APD pixels. In addition, depth of interaction (DOI) measurement capabilities of the block detector were studied.Using neural network methods to determine the interaction position in a 10 mm thick LSO block, we achieved an intrinsic spatial resolution of 1.5 mm FWHM compared to 2.06 mm for individual readout. The DOI resolution varied between 1.8 and 3.0 mm FWHM.Index Terms-Block detectors, neural network, positron emission tomography (PET).

Using Cramer-Rao theory combined with Monte Carlo simulations for the optimization of monolithic scintillator PET detectors

“…These simulations mimic the measurements that are currently being performed within our group [6] and Brussels [7], [8], with the difference that in the simulations a beam width of zero is assumed and electronic noise is not modeled. Simulations with a finite beam width show that the differences between the results presented here and the measurements, are mainly due to the difference in beam width.…”

“…The results obtained for the Cramér-Rao lower bound were compared to results from simulations that resemble the measurements done in our group [6] and in Brussels [7], [8]. In these simulations a beam of 511 keV gamma photons having a diameter of zero is stepped in steps of 250 m over the center of the crystal in the and -direction.…”

Experimental characterization of monolithic-crystal small animal PET detectors read out by APD arrays

“…Subsequently, experiments were performed to determine the influence of the detector geometry and the crystal surface finish on the spatial resolution. The results are compared to previous experimental work [9] and Monte Carlo simulations [10], [11].…”

“…As these designs are generally difficult to implement in a scanner, or lack sufficient spatial resolution for small animal PET, we are currently investigating a new design based on monolithic scintillation crystals read out by one or more avalanche photo diode (APD) array(s) [9]- [11]. Readout of such detector modules is based on estimating the entry point of the annihilation quantum on the crystal's front surface from the light distribution measured by the APD array, using statistical methods or neural networks.…”

“…In this work, we present an experimental comparison between detectors with various geometries and crystal surface finishes. As an extension to previous exper- imental work [9], a new 64-channel setup has been built to accommodate more and different readout geometries, e.g., double sided readout. A statistical method for the estimation of the entry position of the annihilation quanta is used, instead of the neural networks used previously.…”