Euromedim 2006 :1st European Conference on Molecular Imaging Technology

Towards a Continuous Crystal APD-based PET Detector Design

12 May 2006, 14:15

15m

Palais du Pharo, Marseille

oral S11 Perpectives Perspectives

Speaker

Dr Peter bruyndonckx (Vrije Universiteit Brussel)

Description

Monolithic scintillators are an attractive alternative to pixelated detector schemes in the design of high- sensitivity, high resolution PET systems. The shape of the scintillation light distribution measured by a position sensitive photo detector contains (x,y,z) information on the interaction point in the crystal. The absence of inter-crystal optical reflectors significantly increases the sensitivity of such a detector. In addition, the size of the continuous scintillator block can be larger than the sensitive area of the photo detector used to read it out. This results in a detector design with very high packing fraction without the need for more complex solutions such as coupling crystal pixels to PSPMTs using optical fibers. To test this approach of photon localization in PET, we have examined the performance of prototype detectors, based on continuous 20x10x10 or 20x10x20 mm3 LSO blocks and read out by 1 or 2 Hamamatsu S8550 APD arrays. Cramer Rao lower bound estimation on the spatial resolution,based on simulation data, were less than 0.9 mm FWHM for interactions occurring in 90% of the crystal volume. The lower bound increases for interaction occurring further away from the APD or closer the to crystal edge. The simulation results also allowed us to evaluate the performance of various positioning algorithms (e.g. neural networks, support vector machines) and their training procedures. The advantage of these positioning algorithms is the inherent DOI correction when they are trained for events impinging under a given angle. Furthermore, measurement on experimental setups showed that an average intrinsic spatial resolution of 1.5 +- 0.4 mm can be achieved. A linear regression of the average measured position versus the true incidence position showed a slope of 1.03 (r=0.999) to within 2 mm of the crystal’s edge. The energy resolution is 11-13 % FWHM and a time resolution of 2.5 ns was achieved. To further maximize the sensitivity, the possibility of using trapezoidal LSO blocks was investigated, both through simulation and experimental measurements. No significant difference in spatial and energy resolution was observed in comparison to the rectangular LSO blocks. Finally a prototype demonstrator using two detector modules in a rotating configuration was build to demonstrate the expected performance in a PET system. Images of point sources obtained with this device showed a resolution in the reconstructed image better than 2 mm FWHM.