We present the performance of a digital phoswich positron emission tomography (PET) detector, composed by layers of pixilated scintillator arrays, read out by solid state light detectors and an application specific integrated circuit (ASIC). We investigated the use of integrated charge from the scintillation pulses along with time-over-threshold (ToT) to determine the layer of interaction (DOI) in the scintillator. Simulations were performed to assess the effectiveness of the ToT measurements for separating the scintillator events and identifying cross-layer-crystal-scatter (CLCS) events. These simulations indicate that ToT and charge integration from such a detector provide sufficient information to determine the layer of interaction. To demonstrate this in practice, we used a pair of prototype LYSO/BGO detectors. One detector consisted of a 19 19 array of 7 mm long LYSO crystals (1.36 mm pitch) coupled to a 16 16 array of 8 mm long BGO crystals (1.63 mm pitch). The other detector was similar except the LYSO crystal pitch was 1.63 mm. These detectors were coupled to an 8 8 multi-pixel photon counter mounted on a PETsys TOFPET2 ASIC. This high performance ASIC provided digital readout of the integrated charge and ToT from these detectors. We present a method to separate the events from the two scintillator layers using the ToT, and also investigate the performance of this detector. All the crystals within the proposed detector were clearly resolved, and the peak to valley ratio was 11.8 4.0 and 10.1 2.9 for the LYSO and BGO flood images. The measured energy resolution was 9.9% 1.3% and 28.5% 5.0% respectively for the LYSO and BGO crystals in the phoswich layers. The timing resolution between the LYSO–LYSO, LYSO–BGO and BGO–BGO coincidences was 468 ps, 1.33 ns and 2.14 ns respectively. Results show ToT can be used to identify the crystal layer where events occurred and also identify and reject the majority of CLCS events between layers.

我们展示了数字磷光正电子发射断层扫描 (PET) 探测器的性能，该探测器由多层像素化闪烁体阵列组成，由固态光探测器和专用集成电路 (ASIC) 读取。我们研究了使用来自闪烁脉冲的积分电荷以及阈值时间 (ToT) 来确定闪烁体中的相互作用层 (DOI)。进行模拟以评估 ToT 测量在分离闪烁体事件和识别跨层晶体散射 (CLCS) 事件方面的有效性。这些模拟表明，此类探测器的 ToT 和电荷积分提供了足够的信息来确定相互作用层。为了在实践中证明这一点，我们使用了一对原型 LYSO/BGO 探测器。一个探测器由 7 毫米长 LYSO 晶体（1.36 毫米间距）的 19 19 阵列与 8 毫米长 BGO 晶体（1.63 毫米间距）的 16 16 阵列耦合组成。另一个探测器类似，只是 LYSO 晶体间距为 1.63 毫米。这些探测器与安装在 PETsys TOFPET2 ASIC 上的 8×8 多像素光子计数器耦合。这种高性能 ASIC 提供了这些探测器的集成电荷和 ToT 的数字读数。我们提出了一种使用 ToT 将事件与两个闪烁体层分离的方法，并研究了该探测器的性能。所提出的探测器内的所有晶体都被清晰地解析，LYSO 和 BGO 洪水图像的峰谷比为 11.8 ± 4.0 和 10.1 ± 2.9。对于磷灰层中的 LYSO 和 BGO 晶体，测得的能量分辨率分别为 9.9%、1.3% 和 28.5%、5.0%。 LYSO-LYSO、LYSO-BGO 和 BGO-BGO 重合之间的时间分辨率分别为 468 ps、1.33 ns 和 2。分别为14纳秒。结果表明，ToT 可用于识别事件发生的晶体层，还可识别和拒绝层间的大多数 CLCS 事件。