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Monolithic scintillator detectors, consisting of several cm3 of scintillating material coupled to one or more Hamamatsu S8550 avalanche photodiode (APD) arrays, are proposed as detectors for high resolution positron emission tomography (PET). In this work, the factors contributing to the variance on the signals are investigated, and their effects on the energy, time and spatial resolutions are analyzed. Good agreement was found between a model of the energy resolution and experiments with a 20 x 10 x 10 mm3 LYSO:Ce crystal coupled to a single channel large-area APD (LAAPD). With the same crystal coupled to an APD array, differences between model and experiment were observed at high APD gain. The measured energy resolution of ~11% FWHM was dominated by scintillation photon statistics, with less important roles for the APD excess noise factor and electronic noise. On the other hand, electronic noise was an important factor both for the time and the spatial resolutions. The time resolution was found to depend strongly on the APD bias voltage, and was best at the highest bias. A time resolution of 1.6 ns full width at half maximum (FWHM) was measured against a BaF2 -PMT detector. The best spatial resolution measured was 1.64 mm FWHM, without correction for the ~0.9 mm FWHM measurement beam. It is estimated that an intrinsic spatial resolution of 1.26 mm FWHM can be achieved at the center of the detector with an infinitely narrow test beam. [ABSTRACT FROM PUBLISHER]

Previous experimental results have demonstrated that a PET detector module based on a 20 × 10 × 10 mm LSO block read out by a Hamamatsu S8550 APD array is able to determine the impinging position of perpendicularly incident 511-keV photons with a resolution better than 2-mm FWHM. A prototype PET demonstrator using two of these detector heads was build and evaluated. The axial and transaxial resolution measured in two-dimensional (2-D) OSEM and 2-D FBP reconstructed images is better than 1.5- and 2-mm FWHM, respectively, for radial distances less than 15 mm. A Monte Carlo simulation showed that a four-ring PET scanner based on these monolithic scintillator blocks has a sensitivity which is about 2.5 times higher than the sensitivity of a similar system equipped with detector heads using a 4 × 8 matrix of 2 × 2 × 10 mm LSO pixels. [ABSTRACT FROM AUTHOR]

Minimizing dead space is one way to increase the detection efficiency of small-animal PET scanners. By using mono- lithic scintillator crystals (e.g., 20 mm × 10 mm × 10 mm LSO), loss of efficiency due to inter-crystal reflective material is minimized. Readout of such crystals can be performed by means of one or more avalanche photo-diode (APD) arrays optically coupled to the crystal. The entry point of a gamma photon on the crystal surface can be estimated from the measured distribution of the scintillation light over the APD array(s). By estimating the entry point, correction for the depth-of-interaction (DOI) is automatically provided. We are studying the feasibility of such detector modules. To this end, a 64-channel test setup has been developed. Experiments to determine the effect on the spatial resolution of crystal surface finish and detector geometry have been carried out. The first results of these experiments are presented and compared to simulation results. The crystal surface finish has only a small influence on the spatial resolution. The spatial resolution of 20 mm × 10 mm × 10 mm detectors is significantly better when read out on the front side than when read out on the back side. With a 20 mm × 10 mm × 20 mm crystal coupled to two APD arrays, a very small resolution degradation of only ∼0.2 mm is observed for an incidence angle of 30° compared to normal incidence. [ABSTRACT FROM AUTHOR]

We are investigating the possibility of using monolithic scintillator blocks as detectors for small animal positron emission tomography (PET). These detectors consist of several cm³ of scintillating material, read out by one or more avalanche photo-diode (APD) arrays. The entry point of an incoming gamma photon is estimated from the distribution of the scintillation light over the APD pixels. To optimize the detector design, the influence of different design parameters is investigated using Geant4 simulations. To make it possible to study the influence of individual design parameters on the intrinsic spatial resolution of the detector, the use of a performance measure is proposed that is independent of the algorithm used to estimate the entry point, namely the Cramér-Rao lower bound on the estimation of the coordinates of a point source of light inside the crystal. To illustrate the use of this method, the influence of optical transport inside the detector is investigated for different detector designs, surface finishes and APD pixel sizes. A comparison with resolutions obtained from simulations involving beams of 511 keV annihilation photons indicates that this approach gives valid results. [ABSTRACT FROM AUTHOR]