The nuclide volume source placed in liver and breast tissue were served as target tumor region, and the Monte Carlo software Geant4 was used to simulate the difference between the positron distribution ( representing the lesion size in PET ) and nuclide distribution ( representing the pathological lesion size) , in the case that the internal and external tissues of the volume source were different. The results showed that the pathological lesion size was much smaller than the detected one for small lesions detected with higher-energy positron nuclides. In addition, compared to the breast tissue,the degree of dispersion of the positron distribution was weakened when the sphere source was filled with high-density tissue ( breast calcification) . Therefore, it was suggested that the influence of the physiological properties of tumor lesions on the positron distribution needed to be properly considered in image reconstruction. The employment of a volume-source model provided a new correction method for restoring the pathological size of lesions.%以肝脏和乳腺组织为例,使用蒙特卡罗软件Geant4 模拟了在均匀核素体源内外部组织不同的情况下,其正电子分布(对应于PET成像中的病变尺寸)与核素分布(代表病理学病变尺寸)的差异.模拟结果表明,对于高能正电子核素探测到的小病灶,病理学上的病灶尺寸可能要比之小得多.此外,相比于乳腺组织,体源为高密度组织(钙化乳腺组织)时,正电子扩散程度得到了明显减弱.因此,在图像校正中应适当考虑肿瘤病变组织生理性质对正电子分布的影响.体源模型的建立为还原病理学病灶尺寸提供了一种新的校正方法.
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