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ABSTRACT: We investigated the relationship between noise equivalent count (NEC) and axial field of view (AFOV) for PET scanners with AFOVs ranging from one-half to twice those of current clinical scanners. PET scanners with longer or shorter AFOVs could fulfill different clinical needs depending on exam volumes and site economics. Using previously validated Monte Carlo simulations, we modeled true, scattered and random coincidence counting rates for a PET ring diameter of 88 cm with 2, 4, 6, and 8 rings of detector blocks (AFOV 7.8, 15.5, 23.3, and 31.0 cm). Fully 3D acquisition mode was compared to full collimation (2D) and partial collimation (2.5D) modes. Counting rates were estimated for a 200 cm long version of the 20 cm diameter NEMA count-rate phantom and for an anthropomorphic object based on a patient scan. We estimated the live-time characteristics of the scanner from measured count-rate data and applied that estimate to the simulated results to obtain NEC as a function of object activity. We found NEC increased as a quadratic function of AFOV for 3D mode, and linearly in 2D mode. Partial collimation provided the highest overall NEC on the 2-block system and fully 3D mode provided the highest NEC on the 8-block system for clinically relevant activities. On the 4-, and 6-block systems 3D mode NEC was highest up to ∼300 MBq in the anthropomorphic phantom, above which 3D NEC dropped rapidly, and 2.5D NEC was highest. Projected total scan time to achieve NEC-density that matches current clinical practice in a typical oncology exam averaged 9, 15, 24, and 61 min for the 8-, 6-, 4-, and 2-block ring systems, when using optimal collimation. Increasing the AFOV should provide a greater than proportional increase in NEC, potentially benefiting patient throughput-to-cost ratio. Conversely, by using appropriate collimation, a two-ring (7.8 cm AFOV) system could acquire whole-body scans achieving NEC-density levels comparable to current standards within long, but feasible, scan times.
Physics in Medicine and Biology 06/2011; 56(12):3629-43. · 2.83 Impact Factor
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ABSTRACT: The aim of this work is to develop a high spatial resolution, high sensitivity, compact PET detector for small animal PET/MR imaging. The key design features are the use of trapezoidal slat crystals (TSC), the use of silicon photomultiplier (SiPM) arrays, and the use of a 3D statistics based positioning (SBP) algorithm. Through simulation, the performance of a detector module consisting of 8 trapezoidal 0.92 mm (0.63 mm) by 47.52 mm by 12 mm crystals readout by a 2×12 SiPM array was evaluated. A PET detector ring with a 57 mm inner ring diameter could be built using 32 of these detector modules. The average intrinsic spatial resolution in Y and X were 0.84 mm and 0.72 mm FHWM, respectively. There was a 28% miscoding error in X, mainly from Compton scatter in the crystal array. The Z or depth of interaction (DOI) resolution is 1.74 mm. The intrinsic spatial resolution is reasonably uniform across the whole detector module.
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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ABSTRACT: We are conducting a two-phase study, which aims to select design parameters of a long-axis positron emission tomography (PET) scanner that are a compromise between detection performance and cost. In this first phase, we examine the effects of axial length, detector thickness and collimator geometry on the noise equivalent count rate per axial length (¿NEC) and noise equivalent count rate per slice (dNEC). We use these metrics as approximate, but quickly computed, indicators of a PET-scanner's performance at a detection task. From this first phase, we select a subset of scanner designs for which we can conduct a detailed study of tumor detectability and quantitation accuracy in whole-body PET imaging.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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ABSTRACT: We are developing a prototype monolithic scintillation camera with optical sensors on the entrance surface (SES) for use with statistically-estimated depth-of-interaction in a continuous scintillator. We opt to use Geiger-Muller mode avalanche photodiodes (GM-APDs) for the SES camera since they possess many desirable properties; for the intended application (SES and PET/MR imaging), they offer a thin attenuation profile and an operational insensitivity to large magnetic fields. However, one issue that must be addressed in using GM-APDs in an RF environment (as in MR scanners) is the thermal dissipation that can occur in this semiconductor material. Signals of GM-APDs are strongly dependent on junction temperature. Consequently, we are developing a temperature-controlled GM-APD-based PET camera whose monitored temperature can be used to dynamically account for the temperature dependence of the output signals. Presently, we aim to characterize the output-signal dependence on temperature and bias for a GM-APD-based scintillation camera. We've examined two GM-APDs, a Zecotek prototype MAPD-3N, and a SensL commercial SPMArray2. The dominant effect of temperature on gain that we observe results from a linear dependence of breakdown voltage on temperature (0.071 V/°C and 0.024 V/°C, respectively); at 2.3 V excess bias (voltage above breakdown) the resulting change in gain with temperature (without adjusting bias voltage) is -8.5% per°C for the MAPD-3N and -1.5 % per °C for the SPMArray2. For fixed excess bias, change in dark current with temperature varied widely, decreasing by 25% to 40% as temperature was changed from 20°C to 10°C and again by 20% to 35% going from 10°C to 0°C. Finally, using two MAPD-3N to read out a pair of 3.5-by-3.5-by-20 mm<sup>3</sup> Zecotek LFS-3 scintillators in coincidence, we observe a decrease from 1.7 nsec to 1.5 nsec in coincidence-time resolution as we lowered tempera-
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ture from 23°C to 10°C.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
