Medical Imaging Systems Group, Research Center for Molecular and Cellular Imaging, Tehran University of Medical Sciences, Tehran, Iran.
Med Eng Phys. 2013 Jun;35(6):754-64. doi: 10.1016/j.medengphy.2012.08.003. Epub 2012 Sep 8.
Applications in imaging and spectroscopy rely on pulse processing methods for appropriate data generation. Often, the particular method utilized does not highly impact data quality, whereas in some scenarios, such as in the presence of high count rates or high frequency pulses, this issue merits extra consideration. In the present study, a new approach for pulse processing in nuclear medicine imaging and spectroscopy is introduced and evaluated. The new non-linear recursive filter (NLRF) performs nonlinear processing of the input signal and extracts the main pulse characteristics, having the powerful ability to recover pulses that would ordinarily result in pulse pile-up. The filter design defines sampling frequencies lower than the Nyquist frequency. In the literature, for systems involving NaI(Tl) detectors and photomultiplier tubes (PMTs), with a signal bandwidth considered as 15 MHz, the sampling frequency should be at least 30 MHz (the Nyquist rate), whereas in the present work, a sampling rate of 3.3 MHz was shown to yield very promising results. This was obtained by exploiting the known shape feature instead of utilizing a general sampling algorithm. The simulation and experimental results show that the proposed filter enhances count rates in spectroscopy. With this filter, the system behaves almost identically as a general pulse detection system with a dead time considerably reduced to the new sampling time (300 ns). Furthermore, because of its unique feature for determining exact event times, the method could prove very useful in time-of-flight PET imaging.
应用于成像和光谱学的脉冲处理方法依赖于适当的数据生成。通常，所使用的特定方法不会对数据质量产生重大影响，但在某些情况下，例如在存在高计数率或高频脉冲的情况下，这个问题需要额外考虑。在本研究中，引入并评估了一种核医学成像和光谱学中脉冲处理的新方法。新的非线性递归滤波器（NLRF）对输入信号进行非线性处理，并提取主要脉冲特征，具有强大的能力来恢复通常会导致脉冲堆积的脉冲。滤波器设计定义的采样频率低于奈奎斯特频率。在文献中，对于涉及 Nal(Tl)探测器和光电倍增管（PMT）的系统，考虑到信号带宽为 15 MHz，采样频率至少应为 30 MHz（奈奎斯特率），而在本工作中，采样率为 3.3 MHz 被证明可以产生非常有前景的结果。这是通过利用已知的形状特征而不是利用通用的采样算法来实现的。仿真和实验结果表明，所提出的滤波器可以提高光谱学中的计数率。通过使用该滤波器，系统的行为几乎与具有大大减少至新采样时间（300 ns）的死时间的通用脉冲检测系统相同。此外，由于其用于确定确切事件时间的独特功能，该方法在飞行时间 PET 成像中可能非常有用。
