商用3D OSEM重建算法对分子放疗试验中SPECT/CT成像177Lu活性量化的影响

E. Grassi, F. Fioroni, E. Mezzenga, D. Finocchiaro, M. Sarti, A. Filice, A. Versari, M. Iori
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引用次数: 8

摘要

本研究的目的是探讨有序子集期望最大化(OSEM)重建更新对分子放疗中177Lu SPECT/CT成像处理的影响。使用NEMA IEC Body PhantomTM来量化五种不同大小的可填充球体的活性。使用混合双头SPECT-CT成像系统(Symbia T2, Siemens Medical system, Germany)获得具有临床采集协议的图像,并使用商用3D OSEM算法(Flash 3D)重建图像。在重建过程中,考虑了不同的迭代和子集值,并进行了三维高斯重建后滤波和散射和衰减校正。活度恢复系数由每次OSEM更新时每个球体的总重建计数与真实活度之比导出。评估恢复系数和平均分数误差(即加权均方根误差)。同时研究了177Lu的空间分辨率和死区时间,作为活度恢复系数的讨论内容。体积≤5.5 ml的微球受部分体积效应影响显著,对最小微球的活性估计偏差较大。他们的加权分数误差与OSEM更新有关,对于两个最小的球体,分别参考8个子集(8次迭代)和16个子集(10次迭代)的值,范围在85%到79%之间,60%到50%之间。未检测到死区时间。迭代和子集的选择取决于要研究的对象大小和所需的图像质量。无论如何,对于体积≥5.5 ml的物体,使用固定次数的迭代和子集是正确的,在重建的体积中达到总数收敛,但需要使用校正因子来补偿部分体积效应。对于体积≤5.5 ml的物体,定量变得具有挑战性。通讯:Elisa Grassi博士,医学物理组,IRCCS-ASMN, Viale Risorgimento 57, 42123 Reggio Emilia,意大利;电子邮件:elisa.grassi@asmn.re.it
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Impact of a commercial 3D OSEM reconstruction algorithm on the 177Lu activity quantification of SPECT/CT imaging in a Molecular Radiotherapy trial
The purpose of this study was to investigate the influence of the Ordered Subsets Expectation Maximization (OSEM) reconstruction updates implemented in the 177Lu SPECT/CT imaging processing in molecular radiotherapy. A NEMA IEC Body PhantomTM was used to quantify activity in refillable spheres of five different sizes. Images were obtained with a hybrid dual-head SPECT-CT imaging system (Symbia T2, Siemens Medical System, Germany) with a clinical acquisition protocol, and reconstructed using a commercial 3D OSEM algorithm (Flash 3D). In the reconstruction process, different values of iterations and subsets were considered, along with a 3D Gaussian post-reconstruction filter and scatter and attenuation correction. Activity recovery coefficients were derived from the ratio between total reconstructed counts and the true activity for each sphere at each OSEM update. Recovery coefficients, and average fractional error (i.e. the weighted Root Mean Squared Error) were evaluated. At the same time, also 177Lu spatial resolution and dead time were investigated, as matter of discussion about activity recovery coefficients. Results for spheres ≤ 5.5 ml in volume were significantly affected by the partial volume effect, causing a great bias in activity estimation for the smallest spheres. Their weighted fractional error was OSEM update dependent, ranging between 85% to 79% and 60% to 50% for the two smallest spheres, referring to values of 8 subsets-8 iterations and 16 subsets-10 iterations for the two extremes, respectively. No dead time was detected. The choice of iterations and subsets is dependent on the object size to investigate and on the desired image quality. Anyway, using a fixed number of iterations and subsets is correct for objects with volumes ≥ 5.5 ml, reaching the total count convergence in the reconstructed volumes, but the use of correction factors for compensating the partial volume effect is needed. For objects with volumes ≤ 5.5 ml the quantification becomes challenging. Correspondence to: Dr. Elisa Grassi, Medical Physics Unit, IRCCS-ASMN, Viale Risorgimento 57, 42123 Reggio Emilia, Italy; E-mail: elisa.grassi@asmn.re.it
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