Purpose

SimPET/M7 system is a small-animal dedicated simultaneous positron emission tomography and magnetic resonance imaging (PET/MRI) scanner. The SimPET insert has been upgraded from its prototype with a focus on count rate performance and sensitivity. The M7 scanner is a 1-T permanent magnet-based compact MRI system without any cryogens. Here, we present performance evaluation results of SimPET along with the results of mutual interference evaluation and simultaneously acquired PET/MR imaging.

Procedures

Following NEMA NU 4-2008 standard, we evaluated the performance of the SimPET system. The M7 MRI compatibility of SimPET was also assessed by analyzing MRI images of a uniform phantom under different PET conditions and PET count rates with different MRI pulse sequences. Mouse imaging was performed including a whole-body ¹⁸F-NaF PET scan and a simultaneous PET/MRI scan with ⁶⁴Cu-NOTA-ironoxide.

Results

The spatial resolution at center based on 3D OSEM without and with warm background was 0.7 mm and 1.45 mm, respectively. Peak sensitivity was 4.21 % (energy window = 250–750 keV). The peak noise equivalent count rate with the same energy window was 151 kcps at 38.4 MBq. The uniformity was 4.42 %, and the spillover ratios in water- and air-filled chambers were 14.6 % and 12.7 %, respectively. In the hot rod phantom image, 0.75-mm-diameter rods were distinguishable. There were no remarkable differences in the SNR and uniformity of MRI images and PET count rates with different PET conditions and MRI pulse sequences. In the whole-body ¹⁸F-NaF PET images, fine skeletal structures were well resolved. In the simultaneous PET/MRI study with ⁶⁴Cu-NOTA-ironoxide, both PET and MRI signals changed before and after injection of the dual-modal imaging probe, which was evident with the exact spatiotemporal correlation.

Conclusions

We demonstrated that the SimPET scanner has a high count rate performance and excellent spatial resolution. The combined SimPET/M7 enabled simultaneous PET/MR imaging studies with no remarkable mutual interference between the two imaging modalities.

中文翻译：

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SimPET：用于同时进行 PET/MR 成像的临床前 PET 插入物。

目的

SimPET/M7 系统是一种小型动物专用同步正电子发射断层扫描和磁共振成像 (PET/MRI) 扫描仪。SimPET 刀片已从其原型升级，重点是计数率性能和灵敏度。M7 扫描仪是一种基于 1-T 永磁体的紧凑型 MRI 系统，没有任何冷冻剂。在这里，我们展示了 SimPET 的性能评估结果以及相互干扰评估和同时获得的 PET/MR 成像的结果。

程序

按照 NEMA NU 4-2008 标准，我们评估了 SimPET 系统的性能。SimPET 的 M7 MRI 兼容性还通过分析不同 PET 条件下均匀体模的 MRI 图像和不同 MRI 脉冲序列的 PET 计数率来评估。进行了小鼠成像，包括全身¹⁸ F-NaF PET 扫描和使用⁶⁴ Cu-NOTA-氧化铁进行的同步 PET/MRI 扫描。

结果

基于 3D OSEM 的无暖背景和有暖背景的中心空间分辨率分别为 0.7 mm 和 1.45 mm。峰值灵敏度为 4.21%（能量窗口 = 250–750 keV）。具有相同能量窗口的峰值噪声等效计数率在 38.4 MBq 时为 151 kcps。均匀度为 4.42%，在充满水和充满空气的腔室中的溢出率分别为 14.6% 和 12.7%。在热棒幻影图像中，可以区分直径为 0.75 毫米的棒。不同 PET 条件和 MRI 脉冲序列的 MRI 图像和 PET 计数率的 SNR 和均匀性没有显着差异。在全身¹⁸ F-NaF PET 图像中，精细的骨骼结构得到了很好的分辨。在^{64 人}的同步 PET/MRI 研究中Cu-NOTA-氧化铁、PET和MRI信号在注射双模态成像探针前后都发生了变化，这与精确的时空相关性很明显。

结论

我们证明了 SimPET 扫描仪具有高计数率性能和出色的空间分辨率。组合的 SimPET/M7 能够同时进行 PET/MR 成像研究，两种成像方式之间没有明显的相互干扰。