CHERENCUBE: Concept definition and implementation challenges of a Cherenkov-based detector block for PET
CHERENCUBE: Concept definition and implementation challenges of a Cherenkov-based detector block for PET
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DOI：
10.1118/1.4914857
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发表时间：
2015-04-01
期刊：
影响因子：
3.8
通讯作者：
Ziegler, S. I.
中科院分区：
文献类型：
--
作者：
Somlai-Schweiger, I.;Ziegler, S. I.
目的：一个新的概念，深度的相互作用（DOI）的能力飞行时间（TOF）PET探测器的定义，仅基于切伦科夫光子的检测。拟议的“CHERENCUBE”由一个立方切伦科夫辐射器与位置敏感的光电探测器覆盖每个晶面。通过探测到的光子的空间分布及其到达时间，可以确定晶体中伽马射线的相互作用点。本研究分析通过理论计算和蒙特卡罗模拟的潜在优势的概念，对达到一个切伦科夫只有探测器的TOF-PET与DOI能力。此外，DOI估计的算法，并提出了一个实际的实施所提出的概念的要求是defined.Methods：的Monte Carlo模拟由一个立方体晶体与一个光电探测器耦合到立方体的每一个面。探测器的敏感区域与晶体尺寸完全匹配，晶体尺寸在1x 1x 1 mm（3）和10 x10 x10 mm（3）之间以1 mm的步长变化。对于每种尺寸，在10 mm的固定距离处触发了5个独立的一万个511 keV伽马射线的模拟。它的闪烁特性进行了模拟，但只有切伦科夫光子进行了分析。光电探测器具有理想的光电探测效率和无限的时间分辨率。对于每一个生成的粒子，分析都考虑了它的创建过程、父粒子和子粒子、能量、原点坐标、轨迹以及检测的时间和位置。DOI确定基于每个事件的所有光子的发射时间的分布。这些值作为每个光子的检测坐标和原点的函数来计算。通过寻找具有最相似发射时间点的分布来估计共同起源。探测效率随晶体尺寸的增加而增加，从8.2%（1x 1x 1 mm 3）至58.6%（10 × 10 × 10 mm（3）），并分别将5/10/20光子的光子检测阈值降低至6.3%/4.3%/0.7%和49.3%/30.4%/2.8%。在六个光电探测器的检测率是均匀的，由于近各向同性锥发射。大多数锥起源于光电效应相互作用后，在422.99和441.47千电子伏的电子动能的两个主导峰。相同事件光子之间的探测距离定义了单个光子识别所需的探测器的空间分辨率，其中20%的探测光子在立方体长度的5%的距离内具有它们的最近邻居。同一事件的光子在一个时间窗口内被探测到，该时间窗口的宽度由晶体尺寸决定，对于1 × 1 × 1 mm（3）和10 × 10 × 10 mm（3）立方体，其值分别为30和150 ps。DOI重建的精度约为立方体长度的23%，对于10 x10 x10 mm（3）CHERENCUBE.Conclusions的平均值为2.2 mm：所提出的概念需要具有高光电探测效率的探测器。检测器的敏感表面的结构应该是微单元的二维阵列，能够提供单独的检测坐标和时间戳。微单元的大小决定了识别单个光子的能力，从而影响检测效率。3D DOI识别依赖于时间戳和检测坐标的准确性，而不需要识别光子的投影图案。材料的折射率定义了以降低灵敏度为代价的对散射PET事件的基于检测器固有能量的抑制。(C)2015年美国医学物理学家协会。
Purpose: A new concept for a depth-of-interaction (DOI) capable time-of-flight (TOF) PET detector is defined, based only on the detection of Cherenkov photons. The proposed "CHERENCUBE" consists of a cubic Cherenkov radiator with position-sensitive photodetectors covering each crystal face. By means of the spatial distribution of the detected photons and their time of arrival, the point of interaction of the gamma-ray in the crystal can be determined. This study analyzes through theoretical calculations and Monte Carlo simulations the potential advantages of the concept toward reaching a Cherenkov-only detector for TOF-PET with DOI capability. Furthermore, an algorithm for the DOI estimation is presented and the requirements for a practical implementation of the proposed concept are defined.Methods: The Monte Carlo simulations consisted of a cubic crystal with one photodetector coupled to each one of the faces of the cube. The sensitive area of the detector matched exactly the crystal size, which was varied in 1 mm steps between 1x1x1 mm(3) and 10x10x10 mm(3). For each size, five independent simulations of ten thousand 511 keV gamma-rays were triggered at a fixed distance of 10 mm. The crystal chosen was PbWO4. Its scintillation properties were simulated, but only Cherenkov photons were analyzed. Photodetectors were simulated having perfect photodetection efficiency and infinite time resolution. For every generated particle, the analysis considered its creation process, parent and daughter particles, energy, origin coordinates, trajectory, and time and position of detection. The DOI determination is based on the distribution of the emission time of all photons per event. These values are calculated as a function of the coordinates of detection and origin for every photon. The common origin is estimated by finding the distribution with the most similar emission time-points.Results: Detection efficiency increases with crystal size from 8.2% (1x1x1 mm3) to 58.6% (10x10x10 mm(3)) and decreases applying a photon detection threshold of 5/10/20 photons to 6.3%/4.3%/0.7% and 49.3%/30.4%/2.8%, respectively. The detection rate in the six photodetectors is uniform due to the nearly isotropic cone emission. Most cones originated after a photoelectric effect interaction, with two dominating peaks for the kinetic energy of the electron at 422.99 and 441.47 keV. The detection distance between same-event photons defines the spatial resolution of the detector required for individual photon recognition, with 20% of the detected photons having their closest neighbor within a distance of 5% of the length of the cube. Same-event photons are detected within a time window whose width is determined by the crystal size, with values of 30 and 150 ps for a 1x1x1 mm(3) and a 10x10x10 mm(3) cube, respectively. The DOI reconstruction has an accuracy of approximately 23% of the length of the cube, with an average value of 2.2 mm for a 10x10x10 mm(3) CHERENCUBE.Conclusions: The proposed concept requires a detector with high photodetection efficiency. The structure of the sensitive surface of the detector should be a two dimensional array of microcells, able to provide individual detection coordinates and time stamps. The microcell size determines the ability to recognize individual photons, influencing detection efficiency. The 3D DOI recognition relies on the accuracy of the time stamps and detection coordinates, without the need for a recognition of the projected patterns of photons. The refractive index of the material defines a detector intrinsic energy-based rejection of scattered PET events at the cost of reduced sensitivity. (C) 2015 American Association of Physicists in Medicine.