The aim of this paper is to investigate the feasibility and limitations of activity-concentration estimation for 223Ra using SPECT. Phantom measurements are performed using spheres (volumes 5.5 mL to 26.4 mL, concentrations 1.6 kBq mL-1 to 4.5 kBq mL-1). Furthermore, SPECT projections are simulated using the SIMIND Monte Carlo program for two geometries, one similar to the physical phantom and the other being an anthropomorphic phantom with added lesions (volumes 34 mL to 100 mL, concentrations 0.5 kBq mL-1 to 4 kBq mL-1). Medium-energy and high-energy collimators, 60 projections with 55 s per projection and a 20% energy window at 82 keV are employed. For the Monte Carlo simulated images, Poisson-distributed noise is added in ten noise realizations. Reconstruction is performed (OS-EM, 40 iterations, 6 subsets) employing compensation for attenuation, scatter, and collimator-detector response. The estimated concentrations in the anthropomorphic phantom are also corrected using recovery coefficients. Errors for the largest sphere in the physical phantom range from -25% to -34% for the medium-energy collimator and larger deviations for smaller spheres. Corresponding results for the high-energy collimator are -15% to -31%. The corresponding Monte Carlo simulations show standard deviations of a few percentage points. For the anthropomorphic phantom, before application of recovery coefficients the bias ranges from -16% to -46% (medium-energy collimator) and -10% to -28% (high-energy collimator), with standard deviations of 2% to 14% and 1% to 16%. After the application of recovery coefficients, the biases range from -3% to -35% (medium energy collimator) and from 0% to -18%. The errors decrease with increasing concentrations. Activity-concentration estimation of 223Ra with SPECT is feasible, but problems with repeatability need to be further studied.

中文翻译：

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223 Ra定量SPECT检测的可行性和局限性。

本文的目的是研究使用SPECT估算223 Ra的活动浓度的可行性和局限性。使用球体（体积5.5 mL至26.4 mL，浓度1.6 kBq mL-1至4.5 kBq mL-1）进行幻像测量。此外，使用SIMIND Monte Carlo程序对两种几何图形进行SPECT投影模拟，其中一种类似于物理模型，另一种是拟人模型，具有增加的损伤（体积34 mL至100 mL，浓度0.5 kBq mL-1至4 kBq mL -1）。使用中能和高能准直器，每个投影55 s的60个投影和82 keV的20％能量窗口。对于蒙特卡洛模拟图像，在十种噪声实现中添加了泊松分布噪声。进行重建（OS-EM，40次迭代，6个子集）采用衰减，散射和准直仪-检测器响应补偿。拟人体模中的估计浓度也可以使用恢复系数进行校正。对于中能准直器，在体模中最大的球体的误差范围为-25％至-34％，对于较小的球体，其误差较大。高能准直仪的相应结果为-15％至-31％。相应的蒙特卡洛模拟显示标准偏差为几个百分点。对于拟人模型，在应用恢复系数之前，偏差范围为-16％至-46％（中能准直仪）和-10％至-28％（高能准直仪），标准偏差为2％至14 ％和1％至16％。应用恢复系数后，偏差范围为-3％至-35％（中能准直器）和0％至-18％。误差随着浓度的增加而减小。用SPECT估算223Ra的活性浓度是可行的，但是重复性问题需要进一步研究。