Sherbrooke Molecular Imaging Center of CRCHUS and Department of Nuclear Medicine and Radiobiology, Sherbrooke, Québec, Canada.
Instituto de Instrumentación para Imagen Molecular (I3M), Centro Mixto CSIC-Universitat Politécnica de Valéncia, Valencia, Spain.
Phys Med Biol. 2024 Sep 10;69(18). doi: 10.1088/1361-6560/ad70f1.
Acollinearity of annihilation photons (APA) introduces spatial blur in positron emission tomography (PET) imaging. This phenomenon increases proportionally with the scanner diameter and it has been shown to follow a Gaussian distribution. This last statement can be interpreted in two ways: the magnitude of the acollinearity angle, or the angular deviation of annihilation photons from perfect collinearity. As the former constitutes the partial integral of the latter, a misinterpretation could have significant consequences on the resulting spatial blurring. Previous research investigating the impact of APA in PET imaging has assumed the Gaussian nature of its angular deviation, which is consistent with experimental results. However, a comprehensive analysis of several simulation software packages for PET data acquisition revealed that the magnitude of APA was implemented as a Gaussian distribution.We quantified the impact of this misinterpretation of APA by comparing simulations obtained with GATE, which is one of these simulation programs, to an in-house modification of GATE that models APA deviation as following a Gaussian distribution.We show that the APA misinterpretation not only alters the spatial blurring profile in image space, but also considerably underestimates the impact of APA on spatial resolution. For an ideal PET scanner with a diameter of 81 cm, the APA point source response simulated under the first interpretation has a cusp shape with 0.4 mm FWHM. This is significantly different from the expected Gaussian point source response of 2.1 mm FWHM reproduced under the second interpretation.Although this misinterpretation has been found in several PET simulation tools, it has had a limited impact on the simulated spatial resolution of current PET scanners due to its small magnitude relative to the other factors. However, the inaccuracy it introduces in estimating the overall spatial resolution of PET scanners will increase as the performance of newer devices improves.
湮没光子的共线性（APA）会在正电子发射断层扫描（PET）成像中引入空间模糊。这种现象与扫描仪直径成正比，并已被证明呈高斯分布。最后一句话可以从两个方面来解释：共线性角度的大小，或者湮没光子与完全共线性的角度偏差。由于前者是后者的部分积分，因此对结果的空间模糊的错误解释可能会产生重大影响。以前的研究调查了 APA 在 PET 成像中的影响，它假设了其角度偏差的高斯性质，这与实验结果一致。然而，对几个用于 PET 数据采集的模拟软件包的综合分析表明，APA 的大小被实现为高斯分布。我们通过将 GATE 获得的模拟与对 GATE 的内部修改进行比较来量化这种 APA 错误解释的影响，该内部修改将 APA 偏差建模为遵循高斯分布。我们表明，APA 错误解释不仅改变了图像空间中的空间模糊轮廓，而且还大大低估了 APA 对空间分辨率的影响。对于直径为 81 cm 的理想 PET 扫描仪，根据第一种解释模拟的 APA 点源响应具有 0.4 mm FWHM 的尖峰形状。这与第二种解释下重现的预期高斯点源响应 2.1 mm FWHM 有很大的不同。尽管这种错误解释在几个 PET 模拟工具中都有发现，但由于与其他因素相比其幅度较小，因此对当前 PET 扫描仪的模拟空间分辨率的影响有限。然而，随着新型设备性能的提高，它在估计 PET 扫描仪整体空间分辨率方面引入的不准确性将增加。
