Institute of Radiation Protection, Helmholtz Zentrum München, German Research Center for Environmental Health, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany; Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, 81675 Munich, Germany.
Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, 81675 Munich, Germany.
Phys Med. 2018 Dec;56:74-80. doi: 10.1016/j.ejmp.2018.11.009. Epub 2018 Nov 29.
The objective of this study was to evaluate the image degrading factors in quantitative Lu SPECT imaging when using both main gamma photopeak energies.
Phantom measurements with two different vials containing various calibrated activities in air or water were performed to derive a mean calibration factor (CF) for large and small volumes of interest (VOIs). In addition, Monte Carlo simulations were utilized to investigate the effect of scatter energy window width, scatter correction method, such as effective scatter source estimation (ESSE) and triple energy window (TEW), and attenuation map on the quantification of Lu.
The measured mean CF using large and small VOIs in water was 4.50 ± 0.80 and 4.80 ± 0.72 cps MBq, respectively. Simulations showed a reference CF of 3.3 cps MBq for the water-filled phantom considering all photons excluding scattered events. By using the attenuation map generated for 190 keV photons, the calculated CFs for 113 keV and 208 keV are 10% lower than by using the weighted mean energy of 175 keV for Lu. The calculated CF using the TEW correction was 17% higher than using the ESSE method for a water-filled phantom. However, our findings showed that an appropriate scatter window combination can reduce this difference between TEW and ESSE methods.
The present work implies that choosing a suitable width of scatter energy windows can reduce uncertainties in radioactivity quantification. It is suggested to generate the attenuation map at 113 keV and 208 keV, separately. Furthermore, using small VOIs is suggested in CF calculation.
本研究旨在评估使用两种主要伽马光电峰能量时定量 Lu SPECT 成像中的图像降质因素。
在空气中或水中的两个不同小瓶中进行了体模测量，以获得大、小感兴趣区域（VOI）的平均校准因子（CF）。此外，还利用蒙特卡罗模拟研究了散射能窗宽度、散射校正方法（如有效散射源估计（ESSE）和三重能窗（TEW））以及衰减图对 Lu 定量的影响。
在水中使用大、小 VOI 测量的平均 CF 分别为 4.50±0.80 和 4.80±0.72 cps MBq。模拟结果表明，对于充满水的体模，考虑所有排除散射事件的光子，参考 CF 为 3.3 cps MBq。使用为 190 keV 光子生成的衰减图，计算得出的 113 keV 和 208 keV 的 CF 比使用 175 keV 的加权平均能量低 10%。对于充满水的体模，使用 TEW 校正的 CF 比使用 ESSE 方法高 17%。然而，我们的发现表明，适当的散射能窗组合可以降低 TEW 和 ESSE 方法之间的差异。
本研究表明，选择合适的散射能窗宽度可以降低放射性定量的不确定性。建议分别在 113 keV 和 208 keV 下生成衰减图。此外，建议在 CF 计算中使用小 VOI。
