Characterization of inter-detector effects in a 3-D position-sensitive dual-CZT detector modules for PET

This study presents results from two 3-D position-sensitive dual-CZT photon detector modules designed for a high-resolution small animal PET system. Each module comprises a stack of two 40 mm × 40 mm × 5 mm monolithic CZT crystals metalized with a cross-strip electrode pattern that achieves better than 1 mm resolution. In contrast to our prior work focusing on single-crystal CZT performance, this study investigated the impact of detector packaging and module construction on detector performance. This study measured five module-level characteristics; the corresponding findings are as follows. First, the study measured the fraction of event triggers potentially induced by intra-module cross-talk, i.e. occurrence of simultaneous triggers on anode or cathode strips of one detector and the corresponding electrode strips on another detector across the thin flex circuit. This was measured to be 1.51±0.34% for anode channels and 6.40±1.21 % for cathode channels - sufficiently low not to be of specific concern for PET imaging. Second, detector photon sensitivity is maintained at detector-detector boundaries, with the edge anode strip detecting approximately equal number of events as other anode strips. Third, the anode energy resolution in dual-module configuration was measured to be 6.18±0.87% and 4.38±0.67% - slightly degraded from previous studies of an individual detector crystal due to either increased anode stray capacitance or crystal variances, or both. Fourth, stray capacitance on cathode channels was seen to increase the readout noise level by a factor of -2.8 for a free-standing dual-detector module, and by a factor of -4.8 for two stacked dual-detector modules. This revealed the need to increase the cathode-cathode separation across flex circuits and the use of a lower dielectric constant flex substrate. Finally, a survey of noisy, intermittent or disconnected electrode channels highlighted the need for tight control of the module assembly process.