A New Statistics-Based Online Baseline Restorer for a High Count-Rate Fully Digital System.
A New Statistics-Based Online Baseline Restorer for a High Count-Rate Fully Digital System.
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DOI：
10.1109/tns.2009.2036914
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发表时间：
2010-04
影响因子：
1.8
通讯作者：
Wong WH
中科院分区：
文献类型：
--
作者：
Li H;Wang C;Baghaei H;Zhang Y;Ramirez R;Liu S;An S;Wong WH
这项工作的目标是开发一种新的，准确的，实时的数字基线恢复器使用在线统计处理的高计数率的数字系统，如正电子发射断层扫描（PET）。在高计数率核仪器应用中，模拟信号是直流耦合的，以获得更好的性能。然而，检测器、前置放大器和其他前端电子器件会在DC耦合系统中引起信号基线漂移，这将降低能量分辨率和定位精度的性能。在高计数率系统中，事件堆积现象普遍存在，基线漂移会给事件堆积校正带来误差。因此，在高计数率系统中需要基线恢复器（BLR）以在堆积校正之前去除DC漂移。从经典的模拟方法到数字滤波器解决方案，已经报道了许多方法用于BLR。然而，采用模拟方法的单通道BLR只能工作在500 kcps计数率以下，对于PET相机等涉及数百个BLR的应用，通常需要模拟前端专用集成电路（ASIC）。我们已经开发了一个简单的基于几何学的在线基线恢复器（SOBLR）的高计数率全数字系统。在这种方法中，我们从数字系统中现有的自激ADC中获取额外的样本，不包括真实的伽马脉冲，并执行在线统计处理以生成基线值。将从数字化波形中减去该基线值，以恢复具有零基线漂移的原始脉冲。该方法无需微控制器就能实现基线的自跟踪。该电路由两个数字计数器/定时器、一个比较器、一个寄存器和一个减法单元组成。仿真结果表明，在堆积条件下，单通道工作在30 Mcps计数率。336基线恢复器电路已实现到12个现场可编程门阵列（FPGA），我们的新的全数字PET系统。
The goal of this work is to develop a novel, accurate, real-time digital baseline restorer using online statistical processing for a high count-rate digital system such as positron emission tomography (PET). In high count-rate nuclear instrumentation applications, analog signals are DC-coupled for better performance. However, the detectors, pre-amplifiers and other front-end electronics would cause a signal baseline drift in a DC-coupling system, which will degrade the performance of energy resolution and positioning accuracy. Event pileups normally exist in a high-count rate system and the baseline drift will create errors in the event pileup-correction. Hence, a baseline restorer (BLR) is required in a high count-rate system to remove the DC drift ahead of the pileup correction. Many methods have been reported for BLR from classic analog methods to digital filter solutions. However a single channel BLR with analog method can only work under 500 kcps count-rate, and normally an analog front-end application-specific integrated circuits (ASIC) is required for the application involved hundreds BLR such as a PET camera. We have developed a simple statistics-based online baseline restorer (SOBLR) for a high count-rate fully digital system. In this method, we acquire additional samples, excluding the real gamma pulses, from the existing free-running ADC in the digital system, and perform online statistical processing to generate a baseline value. This baseline value will be subtracted from the digitized waveform to retrieve its original pulse with zero-baseline drift. This method can self-track the baseline without a micro-controller involved. The circuit consists of two digital counter/timers, one comparator, one register and one subtraction unit. Simulation shows a single channel works at 30 Mcps count-rate with pileup condition. 336 baseline restorer circuits have been implemented into 12 field-programmable-gate-arrays (FPGA) for our new fully digital PET system.