It has been proposed, and preclinically demonstrated, that 161Tb is a better alternative to 177Lu for the treatment of small prostate cancer lesions due to its high emission of low-energy electrons. 161Tb also emits photons suitable for single-photon emission computed tomography (SPECT) imaging. This study aims to establish a SPECT protocol for 161Tb imaging in the clinic. Optimal settings using various γ-camera collimators and energy windows were explored by imaging a Jaszczak phantom, including hollow-sphere inserts, filled with 161Tb. The collimators examined were extended low-energy general purpose (ELEGP), medium-energy general purpose (MEGP), and low-energy high resolution (LEHR), respectively. In addition, three ordered subset expectation maximization (OSEM) algorithms were investigated: attenuation-corrected OSEM (A-OSEM); attenuation and dual- or triple-energy window scatter-corrected OSEM (AS-OSEM); and attenuation, scatter, and collimator-detector response-corrected OSEM (ASC-OSEM), where the latter utilized Monte Carlo-based reconstruction. Uniformity corrections, using intrinsic and extrinsic correction maps, were also investigated. Image quality was assessed by estimated recovery coefficients (RC), noise, and signal-to-noise ratio (SNR). Sensitivity was determined using a circular flat phantom. The best RC and SNR were obtained at an energy window between 67.1 and 82.1 keV. Ring artifacts, caused by non-uniformity, were removed with extrinsic uniformity correction for the energy window between 67.1 and 82.1 keV, but not with intrinsic correction. Analyzing the lower energy window between 48.9 and 62.9 keV, the ring artifacts remained after uniformity corrections. The recovery was similar for the different collimators when using a specific OSEM reconstruction. Recovery and SNR were highest for ASC-OSEM, followed by AS-OSEM and A-OSEM. When using the optimized parameter setting, the resolution of 161Tb was higher than for 177Lu (8.4 ± 0.7 vs. 10.4 ± 0.6 mm, respectively). The sensitivities for 161Tb and 177Lu were 7.41 and 8.46 cps/MBq, respectively. SPECT with high resolution is feasible with 161Tb; however, extrinsic uniformity correction is recommended to avoid ring artifacts. The LEHR collimator was the best choice of the three tested to obtain a high-resolution image. Due to the complex emission spectrum of low-energy photons, window-based scatter correction had a minor impact on the image quality compared to using attenuation correction only. On the other hand, performing attenuation, scatter, and collimator-detector correction clearly improved image quality. Based on these data, SPECT-based dosimetry for 161Tb-labeled radiopharmaceuticals is feasible.

中文翻译：

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建立用于161Tb成像的临床SPECT / CT协议。

已经提出并在临床上证明，由于其低能量电子的高发射，161Tb是代替177Lu的更好的替代物，用于治疗小前列腺癌病变。161Tb还发射适合于单光子发射计算机断层扫描（SPECT）成像的光子。这项研究旨在为临床中的161Tb成像建立SPECT协议。通过对Jaszczak体模（包括充满161Tb的空心球插入物）进行成像，探索了使用各种γ相机准直器和能量窗口的最佳设置。检验的准直仪分别是扩展的低能量通用（ELEGP），中能量通用（MEGP）和低能量高分辨率（LEHR）。此外，研究了三种有序子集期望最大化（OSEM）算法：衰减校正的OSEM（A-OSEM）；衰减和双能或三能窗口散射校正的OSEM（AS-OSEM）；以及衰减，散射和准直仪-检测器响应校正的OSEM（ASC-OSEM），后者使用了基于蒙特卡洛的重建方法。还使用内在和外在校正图对均匀性校正进行了研究。通过估计的恢复系数（RC），噪声和信噪比（SNR）评估图像质量。灵敏度使用圆形扁平体模确定。在67.1至82.1 keV之间的能量窗口中获得了最佳的RC和SNR。对于67.1和82.1 keV之间的能量窗口，通过非均匀性校正可以消除由于非均匀性引起的环状伪影，而不能进行固有校正。分析48.9和62.9 keV之间的较低能量窗口，均匀度校正后，环伪影仍保留。使用特定的OSEM重建时，不同准直器的恢复情况相似。ASC-OSEM的回收率和SNR最高，其次是AS-OSEM和A-OSEM。使用优化的参数设置时，161Tb的分辨率高于177Lu（分别为8.4±0.7和10.4±0.6 mm）。161Tb和177Lu的灵敏度分别为7.41和8.46 cps / MBq。161Tb的高分辨率SPECT是可行的；但是，建议进行外部均匀性校正，以免产生环伪影。LEHR准直仪是三款获得高分辨率图像的最佳选择。由于低能光子的发射光谱复杂，与仅使用衰减校正相比，基于窗口的散射校正对图像质量的影响较小。另一方面，执行衰减，散射和准直仪检测器校正可以明显改善图像质量。基于这些数据，对161Tb标记的放射性药物进行基于SPECT的剂量测定是可行的。