Modeling and simulation of positron range effects for high resolution PET imaging
Modeling and simulation of positron range effects for high resolution PET imaging
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DOI：
10.1109/tns.2005.858264
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发表时间：
2005-10-01
影响因子：
1.8
通讯作者：
Parker, JA
中科院分区：
文献类型：
--
作者：
Palmer, MR;Zhu, XP;Parker, JA
采用单能正电子的扩散近似和众所周知的理论和经验关系，我们对正电子射程分布进行了建模，并表明它们与使用 EGSnrc 生成的蒙特卡罗模拟结果非常一致。我们计算了 21 个具有生物医学意义的正电子发射器的范围模糊对系统分辨率的影响。固有空间分辨率为 1.5 mm FWHM 的断层扫描仪的线扩散函数对于低端点能量发射器 F-18 或 Cu-64 模糊至 1.7 mm FWHM，对于高端能量发射器 Rb-82 和 1-120 模糊至约 4.3 mm FWHM。湮灭分布表现出双相性质——非常尖锐的峰值，具有长距离、低强度的尾部。尖锐的峰值保留了高空间频率，而尾部负责主要的模糊效果，渐近地接近指数项。通过对模型方程的适当处理，我们得出了指数常数（表观质量吸收系数），并发现它与经典估计非常一致。这个长程特征引入了一个模糊分量，可以在迭代重建过程中将其删除。我们的模型虽然不完全明确，但可以方便地公式化以应用于线性算法，例如迭代重建过程中的傅里叶变换和重投影。因此，该模型有利于范围模糊校正，这对于高分辨率 PET（尤其是高能发射器）至关重要。
Employing a diffusion approximation for monoenergetic positrons and well-known theoretical, and empirical relations we model positron range distributions and show them to be in close agreement with Monte Carlo simulation results produced using EGSnrc. We calculate the range-blurring effect on system resolution for 21 positron emitters of biomedical interest. The line-spread function for a tomograph with intrinsic spatial resolution of 1.5 mm FWHM is blurred to 1.7 mm FWHM for the low end-point energy emitters F-18 or Cu-64 and to about 4.3 mm FWHM for the high end-point energy emitters Rb-82 and 1-120. Annihilation distributions exhibit a biphasic nature-very sharply peaked with long-range, low-intensity tails. The sharp peaks preserve high spatial frequencies while the tails, responsible for the predominant blurring effects, asymptotically approach exponential terms. By suitable manipulation of the model equations we derive the exponential constant-an apparent mass absorption coefficient-and find it to be in close agreement with a classical estimate. This long-range character introduces a blur component that can be removed during iterative reconstruction. Our model, while not entirely explicit, is conveniently formulated for application in linear algorithms such as Fourier transformation and re-projection during iterative reconstruction. The model thus facilitates range-blurring corrections, which are essential for high-resolution PET, particularly with high-energy emitters.