超高活度PET/MRI探头读出电子学研究

Multi-modality PET/MRI scanner can provide the high sensitivity required for deriving molecular and metabolic/functional information, complemented by high-resolution/high-definition structural and functional information from MRI. To follow the kinetics of various biological processes, PET acquisition will be simultaneous and perfectly time-correlated with the MRI acquisition on typical time scales of a few seconds duration. In order to compensate the statistics loss induced by the ultra-short acquisition duration, a very high activity will be injected into the animal (up to 500 MBq, one order of magnitude higher than the activity normally employed in standard PET acquisitions), resulting in demanding high rate requirements, both from the detector and from the readout point of view. This research focuses on the subset of the necessary developments toward the complete final PET system namely on the development of electronics and readout components, in order to handle the data from SiPM as foreseen for the proposed ultra-fast and high-rate PET insert. The scope is to develop a demonstrator setup, with a complete electronics readout chain able to handle data from a 500 MBq source. The major effort of this research is to develop a dedicated (DC coupled) amplifier with a special signal shaper and a-priori removal of dark-count induced signals by a novel handling of the time-and energy-related pulses, which may lead to defining the specifications for a possible future ASIC. Another is to develop the high-performance time-stamp measurement technology, time-stamp based digital process framework for PET insert, highlights include a novel distributed coincidence logic design applying the full-mesh topology feature provided by now-days xTCA standard and multiple coincidence engines with dynamic scheduling to handle the ultra-high LOR rates.. The high rate capability, in true simultaneity with MRI, makes the foreseen PET insert a real novelty and a unique development in the vast domain of PET/MR instrumentation. The outcome of a high-speed readout system is also of relevance for the much broader community of the general detector and readout development in the fields of nuclear imaging and particle physics.

PET/MRI双模式系统具有同时获得分子层面功能信息和高分辨率解剖结构信息的优点。生物药物代谢过程研究要求PET/MRI具备数秒量级的超快速动态成像能力，研发超高计数率PET探头是PET/MRI双模式动态成像的急迫需求。.本项目基于采用LYSO晶体和SiPM探测器件的PET探头方案，研究从脉冲处理电路到数字逻辑的完整电子学处理流程，解决限制计数率性能的关键技术问题，使其满足高达500MBq活度条件下的采集成像需求，提升PET/MRI动态成像能力。.项目将发展快速信号成形和处理技术，降低信号堆积几率；利用过阈时间TOT技术简化信号读出结构，提高系统通道密度；提高信号时间测量精度，缩小符合时间窗口宽度，剔除随机符合事件；开发基于数字时间标签的数据处理方法，并利用最新的背板总线技术实现创新的分布式在线符合处理架构，提升高计数率条件下数字处理逻辑的性能。项目将搭建完整的系统样机并完成实际应用测试

PET/MRI双模式系统具有同时获得分子层面功能信息和高分辨率解剖结构信息的优点，本项目研究目标是实现基于新型SiPM硅光电倍增管具有高计数率和高时间分辨率的的PET/MR内嵌探头。.项目对双输出SiPM性能和读出方法、定制的前端ASIC芯片、双层DOI闪烁晶体的SiPM探测阵列模组、全数字化的分布式PET信息处理架构等关键技术展开研究。采用全数字的模块化设计方法，解决从前端探测器模拟处理电路到系统采集的完整数字处理流程，形成可以灵活扩展的PET探测器模块，建设完整的PET内嵌探头的样机，并开展系统级成像研究，达到了较好的成像指标。.项目研究了双输出SiPM器件的信号特征并优化设计了其读出电路，能实现高能量分辨和高时间分辨的信号读出；设计了多通道SiPM读出芯片，采用多阶可调参数的快速信号成形电路，降低了信号堆积率，并通过快慢通道的符合机制滤除了暗噪声；利用FPGA延迟链TDC和采样ADC实现单光子时间的前端数字化，开发了基于全数字化信息的PET信息处理框架，解决了数据到达时间晃动、分布插入式排序和基于时间戳的符合逻辑处理方法等关键逻辑，通过增加流水线深度，提高运行频率能够支持极高的计数率；利用分布式时间网络同步WR技术，无需使用特殊的硬件链接，在单光纤上实现了探测器模块的时间同步、数据采集和系统控制，极大的简化了整机结构，提高了系统灵活性。.项目的研究成果为高性能的PET设备提供了基础，可直接应用到产品开发中，其发展的分布式时间测量和同步技术能够在其他应用领域得到应用。