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A b s t r a c t --This work reports on performance characteristics of a second generation micro crystal element (MiCE2) detector for a dedicated PET system to image mice. Our MiCE2 detector consists of a 22x22 array of 0.8x0.8x6 mm mixed lutetium silicate (MLS) crystals. Five sides of the crystals are polished with one 0.8x0.8 mm face left unpolished. The crystals are placed within a grid made of a highly reflective polymer film material. The grid optically isolates the crystals and also functions as a reflective wrap. The detector unit is directly coupled to a 6+6 cross-anode position sensitive PMT. The crystal of interaction is determined using simple Anger style logic. Crystal maps have been created for a 22x22 crystal array. All 484 crystals are visualized in the full detector module's crystal map. The average peak to valley ratio between neighboring crystals was 6.4. There was greater than a factor of two difference between the photopeak energy channel for high versus low light collection efficiency crystals. The energy resolution for individual crystals varied between 14% and 23%. Partial detector arrays (e.g., 22x4) using 0.8x0.8x10 mm crystals with an etched surface finish have also been built and decoded. A miniature line source phantom consisting of five 1 mm diameter lines with 2 mm center-tocenter spacing has been imaged using two partial MiCE2 detectors. All lines are distinguished and the average peak to valley ratio between lines is 2.7.

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This paper investigates optimum slat collimator design parameters for dual-head coincidence imaging (DHCI) systems. Noise equivalent count (NEC) rate was examined with respect to the activity concentration under various system conditions. All results are derived from Monte Carlo simulations with a digital anthropomorphic (Zubal) phantom. The DHCI system was modeled after the Millennium VG gamma camera (GEMS, Waukesha, WI). The dead-time characteristics of the camera were experimentally determined. Our results suggests that substantial NEC gains can be achieved by varying the slat-to-slat separation, such that the peak of the NEC curve is located at clinically relevant levels (i.e., 0.07 0.10 Ci/cc). The NEC was also found to increase with the use of longer slats with appropriately selected slat-to-slat separation. Furthermore, the NEC performance also depends on the count-rate performance (i.e., dead-time losses) of the system. Therefore, as improvements are made to the count-rate capabilities of DHCI systems, the slat geometry should be modified. Further study is required to determine the effect that slat collimator design has on image quality and lesion detection for clinically realistic imaging situations. Index Terms-Dual-head coincidence imaging (DHCI), noise equivalent count (NEC), salt collimator. ).Publisher Item Identifier S 0018-9499(02)01653-2.