44Sc has been increasingly investigated as a potential alternative to 68Ga in the development of tracers for positron emission tomography (PET). The lower mean positron energy of 44Sc (0.63 MeV) compared to 68Ga (0.83 MeV) can result in better spatial image resolutions. However, high-energy γ-rays (1157 keV) are emitted at high rates (99.9%) during 44Sc decay, which can reduce image quality. Therefore, we investigated the impact of these physical properties and performed an unbiased performance evaluation of 44Sc and 68Ga with different imaging phantoms (image quality phantom, Derenzo phantom, and three-rod phantom) on two preclinical PET scanners (Mediso nanoScan PET/MRI, Siemens microPET Focus 120). Despite the presence of high-energy γ-rays in 44Sc decay, a higher image resolution of small structures was observed with 44Sc when compared to 68Ga. Structures as small as 1.3 mm using the Mediso system, and as small as 1.0 mm using the Siemens system, could be visualized and analyzed by calculating full width at half maximum. Full widths at half maxima were similar for both isotopes. For image quality comparison, we calculated recovery coefficients in 1–5 mm rods and spillover ratios in either air, water, or bone-equivalent material (Teflon). Recovery coefficients for 44Sc were significantly higher than those for 68Ga. Despite the lower positron energy, 44Sc-derived spillover ratio (SOR) values were similar or slightly higher to 68Ga-derived SOR values. This may be attributed to the higher background caused by the additional γ-rays. On the Siemens system, an overestimation of scatter correction in the central part of the phantom was observed causing a virtual disappearance of spillover inside the three-rod phantom. Based on these findings, 44Sc appears to be a suitable alternative to 68Ga. The superior image resolution makes it an especially strong competitor in preclinical settings. The additional γ-emissions have a small impact on the imaging resolution but cause higher background noises and can effect an overestimation of scatter correction, depending on the PET system and phantom.

中文翻译：

---

在两个临床前PET扫描仪上对⁴⁴ Sc的图像质量分析：与⁶⁸ Ga的比较

在开发正电子发射断层扫描（PET）示踪剂时，越来越多地研究了44Sc作为68Ga的潜在替代品。与68Ga（0.83 MeV）相比，44Sc（0.63 MeV）较低的平均正电子能量可以产生更好的空间图像分辨率。但是，在44Sc衰减期间，高能γ射线（1157 keV）会以高速率（99.9％）发射，这会降低图像质量。因此，我们研究了这些物理特性的影响，并在两个临床前PET扫描仪（Mediso nanoScan PET / MRI）上对带有不同成像体模（图像质量体模，Derenzo体模和三杆体模）的44Sc和68Ga进行了无偏性能评估。西门子microPET Focus 120）。尽管在44Sc衰减中存在高能γ射线，但与68Ga相比，使用44Sc观察到的小结构的图像分辨率更高。通过计算一半的全宽，可以看到和分析使用Mediso系统小至1.3 mm以及使用Siemens系统小至1.0 mm的结构。两种同位素的最大半峰全宽相似。为了进行图像质量比较，我们计算了1-5 mm棒中的恢复系数和空气，水或等效于骨的材料（Teflon）中的溢出比率。44Sc的回收系数显着高于68Ga。尽管正电子能量较低，但44Sc衍生的溢出比（SOR）值与68Ga衍生的SOR值相似或略高。这可能归因于额外的γ射线引起的较高背景。在西门子系统上 观察到了幻影中央部分的散射校正过高估计，导致三杆幻影内部的溢出几乎消失了。基于这些发现，44Sc似乎是68Ga的合适替代品。出色的图像分辨率使其成为临床前环境中特别强大的竞争对手。额外的γ发射对成像分辨率影响不大，但会引起较高的背景噪声，并且可能会根据PET系统和体模而高估散射校正。