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We report on a high resolution, monolithic crystal PET detector design concept that provides depth of interaction (DOI) positioning within the crystal. Our design utilizes a novel sensor on the entrance surface (SES) approach combined with a maximum likelihood positioning algorithm. We compare the intrinsic spatial resolution characteristics (i.e., X, Y and Z) using our SES design versus conventional placement of the photo-sensors on the rear surface of the crystal. The sensors can be any two-dimensional array of solid state readout devices (e.g., silicon photomultipliers (SiPM) or avalanche photodiodes (APD)). SiPMs are a new type of solid-state photodetector with Geiger mode operation that can provide signal gain similar to a photomltipiler tube (PMT). Utilizing a multi-step simulation process, we determined the intrinsic spatial resolution characteristics for a variety of detector configurations. The SES design was evaluated via simulation for three different two-dimensional array sizes: 8 x 8 with 5.8 x 5.8 mm² pads; 12 x 12 with 3.8 x 3.8 mm² pads; and 16 x 16 with 2.8 x 2.8 mm² pads. To reduce the number of signal channels row-column summing readout was used for the 12 x 12 and 16 x 16 channel array devices. The crystal was modeled as a 15 mm monolithic slab of a lutetium-based scintillator with the large area surface varying from 48.8 x 48.8 mm² up to 49.6 x 49.6 mm² depending upon the dimensions of the two-dimensional photo-sensor array. The intrinsic spatial resolution for the 8 x 8 array is 0.88 mm FWHM in X and Y, and 1.83 mm FWHM in Z (i.e., DOI). Comparing the results versus using a conventional design with the photo-sensors on the backside of the crystal, an average improvement of ~24% in X and Y and 20% in Z is achieved. The X, Y intrinsic spatial resolution improved to 0.67 mm and 0.64 mm FWHM for the 12 x 12 and 16 x 16 arrays using row-column readout. Using the 12 x 12 and 16 x 16 arrays also led to a slight improvement in the DOI positioning accuracy. [ABSTRACT FROM AUTHOR]

We report on methods to speed up the calibration process for a continuous miniature crystal element (cMiCE) detector. Our cMiCE detector is composed of a 50-mm by 50-mm by 8-mm-thick monolithic LYSO crystal coupled to a 64-channel, flat-panel photomultiplier tube (PMT). It achieves an average intrinsic spatial resolution of ~1.4 mm full width at half maximum (FWHM) over the useful face of the detector through the use of a statistics-based positioning algorithm. A drawback to the design is the length of time it takes to calibrate the detector. We report on three methods to speed up this process. The first method is to use multiple point fluxes on the surface of the detector to calibrate different points of the detector from a single data acquisition. A special multisource device that can produce up to 16 point fluxes has been custom designed for this purpose. The second scheme is to characterize the detector with coarser sampling and use interpolation to create lookup tables with the desired detector binning (e.g., 0.253 mm). The intrinsic spatial resolution performance was investigated for sampling intervals of 1.013, 2.026, 3.039, and 4.052 mm. The third method is to adjust the point flux diameter by varying the geometry of the setup. A larger point flux diameter will increase the coincidence counting rate. The average intrinsic spatial resolution was 1.38 mm FWHM using four point fluxes, 1.013 mm detector sampling, and ~0.5 mm point flux on the surface of the detector. The average intrinsic spatial resolution increased slightly to 1.45 mm FWHM when using 16 point fluxes with a detector sampling of 3.039 mm. Adjusting the point flux size degraded the intrinsic spatial resolution the most (~9%) and provided the smallest speed up factor. In conclusion using 16 point fluxes and a sampling interval of 3.039 mm, the characterization time for a cMiCE detector can be reduced by a factor of 144 with minimal impact on the intrinsic spatial resolution of the detector. [ABSTRACT FROM AUTHOR]