Wieczorek H, Thon A, Dey T, Khanin V, Rodnyi P
Philips Research Eindhoven, High Tech Campus 34, 5656 AE Eindhoven, The Netherlands.
Phys Med Biol. 2016 Jun 21;61(12):4699-710. doi: 10.1088/0031-9155/61/12/4699. Epub 2016 Jun 1.
The coincidence resolving time (CRT) of scintillation detectors is the parameter determining noise reduction in time-of-flight PET. We derive an analytical CRT model based on the statistical distribution of photons for two different prototype scintillators. For the first one, characterized by single exponential decay, CRT is proportional to the decay time and inversely proportional to the number of photons, with a square root dependence on the trigger level. For the second scintillator prototype, characterized by exponential rise and decay, CRT is proportional to the square root of the product of rise time and decay time divided by the doubled number of photons, and it is nearly independent of the trigger level. This theory is verified by measurements of scintillation time constants, light yield and CRT on scintillator sticks. Trapping effects are taken into account by defining an effective decay time. We show that in terms of signal-to-noise ratio, CRT is as important as patient dose, imaging time or PET system sensitivity. The noise reduction effect of better timing resolution is verified and visualized by Monte Carlo simulation of a NEMA image quality phantom.
闪烁探测器的符合分辨时间（CRT）是决定飞行时间PET中噪声降低的参数。我们基于两种不同原型闪烁体的光子统计分布推导了一个解析CRT模型。对于第一种以单指数衰减为特征的闪烁体，CRT与衰减时间成正比，与光子数量成反比，对触发水平有平方根依赖性。对于第二种以指数上升和衰减为特征的闪烁体原型，CRT与上升时间和衰减时间乘积的平方根除以两倍光子数量成正比，并且几乎与触发水平无关。通过对闪烁体棒的闪烁时间常数、光输出和CRT的测量验证了该理论。通过定义有效衰减时间来考虑俘获效应。我们表明，就信噪比而言，CRT与患者剂量、成像时间或PET系统灵敏度同样重要。通过对NEMA图像质量体模的蒙特卡罗模拟验证并可视化了更好的时间分辨率的降噪效果。
