Optimization of injected gallium-68 (68Ga) activity for 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT) studies is relevant for image quality, radiation protection, and from an economic point of view. However, no clear guidelines are available for 68Ga-PSMA studies. Therefore, a phantom study is performed to determine the highest coefficient of variation (COV) acceptable for reliable image interpretation and quantification. To evaluate image interpretation, the relationship of COV and contrast-to-noise ratio (CNR) was studied. The CNR should remain larger than five, according to the Rose criterion. To evaluate image quantification, the effect of COV on the percentage difference (PD) between quantification results of two studies was analyzed. Comparison was done by calculating the PD of the SUVmax. The maximum allowable PDSUVmax was set at 20%. The highest COV at which both criteria are still met is defined as COVmax. Of the NEMA Image Quality phantom, a 20 min/bed (2 bed positions) scan was acquired in list-mode PET (Philips Gemini TF PET/CT). The spheres to background activity ratio was approximately 9:1. To obtain images with different COV, lower activity was mimicked by reconstructions with acquisition times of 10 min/bed to 5 s/bed. Pairs of images were obtained by reconstruction of two non-overlapping parts of list-mode data. For the 10-mm diameter sphere, a COV of 25% still meets the criteria of CNRSUVmean ≥ 5 and PDSUVmax ≤ 20%. This phantom scan was acquired with an acquisition time of 116 s and a background activity concentration of 0.71 MBq/kg. Translation to a clinical protocol results in a clinical activity regimen of 3.5 MBq/kg min at injection. To verify this activity regimen, 15 patients (6 MBq/kg min) with a total of 22 lesions are included. Additional reconstructions were made to mimic the proposed activity regimen. Based on the CNRSUVmax, no lesions were missed with this proposed activity regimen. For our institution, a clinical activity regimen of 3.5 MBq/kg min at injection is acceptable, which indicates that activity can be reduced by almost 50% compared with the current code of practice. Our proposed method could be used to obtain an objective activity regimen for other PET/CT systems and tracers.

中文翻译：

---

基于列表模式幻象数据和临床验证优化注射的68Ga-PSMA活性。

从68Ga-前列腺特异性膜抗原正电子发射断层扫描/计算机断层扫描（68Ga-PSMA PET / CT）研究中优化的注入镓68（68Ga）活性与图像质量，辐射防护以及经济角度有关。但是，没有针对68Ga-PSMA研究的明确指南。因此，进行体模研究以确定可接受的最高变异系数（COV），以进行可靠的图像解释和量化。为了评估图像的解释，研究了COV与对比噪声比（CNR）的关系。根据Rose标准，CNR应该保持大于5。为了评估图像量化，分析了COV对两项研究的量化结果之间的百分比差异（PD）的影响。通过计算SUVmax的PD进行比较。PDSUVmax的最大允许值设定为20％。仍然满足两个标准的最高COV定义为COVmax。在NEMA图像质量模型中，以列表模式PET（Philips Gemini TF PET / CT）获得了20分钟/床（2个床位）的扫描。球与背景活性之比约为9：1。为了获得具有不同COV的图像，可以通过重建模拟较低的活动，采集时间为10分钟/床至5 s /床。通过重建列表模式数据的两个不重叠部分获得图像对。对于直径为10毫米的球体，COV仍为25％仍符合CNRSUVmean≥5和PDSUVmax≤20％的标准。该幻影扫描以116 s的采集时间和0.71 MBq / kg的背景活性浓度采集。转换为临床方案会导致注射时3.5 MBq / kg min的临床活动方案。为了验证该活动方案，包括15名患者（6 MBq / kg min），总共22个病变。进行了其他重建以模仿拟议的活动方案。基于CNRSUVmax，该提议的活动方案不会遗漏任何病变。对于我们的机构，可接受的注射时3.5 MBq / kg min的临床活动方案是可接受的，这表明与当前的操作规范相比，活动量可降低近50％。我们提出的方法可用于获得其他PET / CT系统和示踪剂的客观活性方案。进行了其他重建以模仿拟议的活动方案。基于CNRSUVmax，该提议的活动方案不会遗漏任何病变。对于我们的机构，可接受的注射时3.5 MBq / kg min的临床活动方案是可接受的，这表明与当前的操作规范相比，活动量可降低近50％。我们提出的方法可用于获得其他PET / CT系统和示踪剂的客观活性方案。进行了其他重建以模仿拟议的活动方案。基于CNRSUVmax，该提议的活动方案不会遗漏任何病变。对于我们的机构，可接受的注射时3.5 MBq / kg min的临床活动方案是可接受的，这表明与当前的操作规范相比，活动量可降低近50％。我们提出的方法可用于获得其他PET / CT系统和示踪剂的客观活性方案。