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

Abstract

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 x 40 mm x 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 channelssufficiently 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.

Positioning true coincidences that undergo inter-and intra-crystal scatter for a sub-mm resolution cadmium zinc telluride-based PET system

“…We are developing a small animal positron emission tomography (PET) system based on cross-strip CZT detectors configured to achieve high spatial resolution and high sensitivity (Figure 2) [11, 12, 13, 14, 3, 15, 16, 17]. This system comprises four panels providing an adjustable, box-shaped field of view with maximum field-of-view (FOV) of 100 mm × 100 mm × 80 mm.…”

Characterization of a sub-assembly of 3D position sensitive cadmium zinc telluride detectors and electronics from a sub-millimeter resolution PET system

“…The contacts are made using a conductive silver epoxy to facilitate the electrical connections. This structure increases the packing fraction and reduces the dead space between CZT crystals (Gu and Levin 2012). The cathode and anode bias voltages are −500 V and 0 V, respectively, while the steering bias voltage is −80 V (Gu and Levin 2014).…”

“…Dependence on depth (interaction location between the anode and cathode) arises from hole trapping, which leads to photopeak broadening towards lower energies (Gu et al 2011). For calculating energy resolution after calibration, the anode signal amplitude was plotted and fitted as a function of cathode to anode signal ratio (C/A) Gu and Levin (2012).…”

“…It should be noted that the readout circuit in Gu and Levin (2012) was designed for testing one dual-crystal module. The energy resolution of this scaled up system was expected to degrade due to increased stray capacitances in the full system's circuitry and crystal variations.…”

“…The electrode pattern geometry design has been extensively studied and optimized to provide high detector performance. The detail of the CZT detector design, optimization, and packing can be found in Matteson et al (2008), Gu et al (2011), Gu and Levin (2012) and Gu and Levin (2014).…”