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Artifacts in digital coincidence timing

机译：数字重合时序中的伪像

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Digital methods are becoming increasingly popular for measuring time differences, and are the de facto standard in PET cameras. These methods usually include a master system clock and a (digital) arrival time estimate for each detector that is obtained by comparing the detector output signal to some reference portion of this clock (such as the rising edge). Time differences between detector signals are then obtained by subtracting the digitized estimates from a detector pair. A number of different methods can be used to generate the digitized arrival time of the detector output, such as sending a discriminator output into a time to digital converter (TDC) or digitizing the waveform and applying a more sophisticated algorithm to extract a timing estimator. All measurement methods are subject to error, and one generally wants to minimize these errors and so optimize the timing resolution. A common method for optimizing timing methods is to measure the coincidence timing resolution between two timing signals whose time difference should be constant (such as detecting gammas from positron annihilation) and selecting the method that minimizes the width of the distribution (i.e. the timing resolution). Unfortunately, a common form of error (a nonlinear transfer function) leads to artifacts that artificially narrow this resolution, which can lead to erroneous selection of the 'optimal' method. The purpose of this note is to demonstrate the origin of this artifact and suggest that caution should be used when optimizing time digitization systems solely on timing resolution minimization.
机译：数字方法在测量时间差方面正变得越来越流行，并且已成为PET相机中的事实上的标准。这些方法通常包括一个主系统时钟和每个检测器的（数字）到达时间估算，该估算是通过将检测器输出信号与该时钟的某个参考部分（例如上升沿）进行比较而获得的。然后，通过从检测器对中减去数字化的估计值，获得检测器信号之间的时间差。可以使用多种不同的方法来生成检测器输出的数字化到达时间，例如将鉴频器输出发送到时间到数字转换器（TDC）或将波形数字化并应用更复杂的算法来提取时序估计器。所有的测量方法都有误差，通常要尽量减少这些误差，从而优化时序分辨率。优化时序方法的常用方法是测量时间差应恒定的两个时序信号之间的重合时序分辨率（例如从正电子an灭中检测伽马），然后选择最小化分布宽度的方法（即时序分辨率） 。不幸的是，常见的错误形式（非线性传递函数）导致伪像人为地使此分辨率变窄，从而可能导致错误地选择“最佳”方法。本注释的目的是演示此工件的来源，并建议仅在时序分辨率最小化上优化时间数字化系统时应谨慎行事。

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