Wielaard J, Habraken J B A, Brinks P, Lavalaye J, Boellaard R
Department of Medical Physics, St. Antonius Hospital, Nieuwegein, Netherlands.
Department of Medical Physics, Diakonessenhuis, Utrecht, Netherlands.
EJNMMI Phys. 2020 Apr 15;7(1):20. doi: 10.1186/s40658-020-00289-9.
Optimization of injected gallium-68 (Ga) activity for Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (Ga-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 Ga-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 SUV. The maximum allowable PD was set at 20%. The highest COV at which both criteria are still met is defined as COV. 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 CNR ≥ 5 and PD ≤ 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 CNR, 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.
对于镓-68（Ga）-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（Ga-PSMA PET/CT）研究而言，优化注入的Ga活度在图像质量、辐射防护以及经济层面都具有重要意义。然而，目前尚无针对Ga-PSMA研究的明确指导方针。因此，开展了一项体模研究，以确定可靠的图像解读和定量分析可接受的最高变异系数（COV）。为评估图像解读，研究了COV与对比噪声比（CNR）之间的关系。根据罗斯准则，CNR应保持大于5。为评估图像定量分析，分析了COV对两项研究定量结果之间百分比差异（PD）的影响。通过计算SUV的PD进行比较。最大允许PD设定为20%。仍满足两项标准的最高COV被定义为COV。在NEMA图像质量体模中，在列表模式PET（飞利浦Gemini TF PET/CT）中以20分钟/床位（2个床位位置）进行扫描。球体与背景活度比约为9:1。为获得具有不同COV的图像，通过将采集时间从10分钟/床位重建至5秒/床位来模拟较低的活度。通过重建列表模式数据的两个不重叠部分获得成对图像。对于直径10毫米的球体，25%的COV仍满足CNR≥5和PD≤20%的标准。此次体模扫描的采集时间为116秒，背景活度浓度为0.71 MBq/kg。转换为临床方案后，注射时的临床活度方案为3.5 MBq/kg·分钟。为验证该活度方案，纳入了15例患者（6 MBq/kg·分钟），共22个病灶。进行了额外的重建以模拟提议的活度方案。基于CNR，采用该提议的活度方案未遗漏任何病灶。对于我们机构而言，注射时3.5 MBq/kg·分钟的临床活度方案是可接受的，这表明与当前的操作规范相比，活度可降低近50%。我们提出的方法可用于为其他PET/CT系统和示踪剂获取客观的活度方案。
