In living organisms, the positron-electron annihilation (occurring during the PET imaging) proceeds in about 30% via creation of a metastable ortho-positronium atom. In the tissue, due to the pick-off and conversion processes, over 98% of ortho-positronia annihilate into two 511 keV photons. In this article, we assess the feasibility for reconstruction of the mean ortho-positronium lifetime image based on annihilations into two photons. The main objectives of this work include the (i) estimation of the sensitivity of the total-body PET scanners for the ortho-positronium mean lifetime imaging using 2γ annihilations and (ii) estimation of the spatial and time resolution of the ortho-positronium image as a function of the coincidence resolving time (CRT) of the scanner. Simulations are conducted assuming that radiopharmaceutical is labeled with 44Sc isotope emitting one positron and one prompt gamma. The image is reconstructed on the basis of triple coincidence events. The ortho-positronium lifetime spectrum is determined for each voxel of the image. Calculations were performed for cases of total-body detectors build of (i) LYSO scintillators as used in the EXPLORER PET and (ii) plastic scintillators as anticipated for the cost-effective total-body J-PET scanner. To assess the spatial and time resolution, the four cases were considered assuming that CRT is equal to 500 ps, 140 ps, 50 ps, and 10 ps. The estimated total-body PET sensitivity for the registration and selection of image forming triple coincidences (2γ+γprompt) is larger by a factor of 13.5 (for LYSO PET) and by factor of 5.2 (for plastic PET) with respect to the sensitivity for the standard 2γ imaging by LYSO PET scanners with AFOV = 20 cm. The spatial resolution of the ortho-positronium image is comparable with the resolution achievable when using TOF-FBP algorithms already for CRT = 50 ps. For the 20-min scan, the resolution better than 20 ps is expected for the mean ortho-positronium lifetime image determination. Ortho-positronium mean lifetime imaging based on the annihilations into two photons and prompt gamma is shown to be feasible with the advent of the high sensitivity total-body PET systems and time resolution of the order of tens of picoseconds.

中文翻译：

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全身PET扫描仪对2γron成像的性能评估。

在活生物体中，通过创建亚稳态的正正电子原子，正电子an灭（在PET成像期间发生）的发生率约为30％。在组织中，由于提取和转换过程，超过98％的正正电子ron灭了两个511 keV光子。在本文中，我们评估了基于an没成两个光子重建平均正电子寿命图像的可行性。这项工作的主要目标包括：（i）使用2γni灭估计全身PET扫描仪对正-正电子平均寿命成像的灵敏度，以及（ii）估计正-正电子图像的空间和时间分辨率取决于扫描仪的重合解决时间（CRT）。假设进行放射性模拟，并用44Sc同位素标记放射出一个正电子和一个瞬变伽马的放射性药物。在三次重合事件的基础上重建图像。确定图像的每个体素的正-正电子寿命谱。对以下情况进行了全身检测器构造的计算：（i）EXPLORER PET中使用的LYSO闪烁体和（ii）低成本J-PET扫描仪所预期的塑料闪烁体。为了评估空间和时间分辨率，考虑了四种情况，假设CRT等于500 ps，140 ps，50 ps和10 ps。对于成像三重符合（2γ+γprompt）的配准和选择，估计的全身PET灵敏度要大13.5倍（对于LYSO PET）和5倍。对于使用AFOV = 20 cm的LYSO PET扫描仪进行标准2γ成像的灵敏度，请参见图2（对于塑料PET）。正阴极图像的空间分辨率与已经使用CRT = 50 ps的TOF-FBP算法时可获得的分辨率相当。对于20分钟的扫描，对于平均正电子寿命的图像确定，期望分辨率优于20 ps。随着高灵敏度全身PET系统的出现和数十皮秒量级的时间分辨率的出现，基于the灭成两个光子和即时伽马的正正电子平均寿命成像是可行的。正阴极图像的空间分辨率与已经使用CRT = 50 ps的TOF-FBP算法时可获得的分辨率相当。对于20分钟的扫描，对于平均正电子寿命的图像确定，期望分辨率优于20 ps。随着高灵敏度全身PET系统的出现和数十皮秒量级的时间分辨率的出现，基于the没成两个光子和快速伽马的正电子平均寿命成像被证明是可行的。正阴极图像的空间分辨率与已经使用CRT = 50 ps的TOF-FBP算法时可获得的分辨率相当。对于20分钟的扫描，对于平均正电子寿命图像确定，预期分辨率将优于20 ps。随着高灵敏度全身PET系统的出现和数十皮秒量级的时间分辨率的出现，基于the灭成两个光子和即时伽马的正正电子平均寿命成像是可行的。