The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) (PET-MRI) is a unique hybrid imaging modality mainly used in oncology and neurology. The MRI-based attenuation correction (MRAC) is crucial for correct quantification of PET data. A suitable phantom to validate quantitative results in PET-MRI is currently missing. In particular, the correction of attenuation due to bone is usually not verified by commonly available phantoms. The aim of this work was, thus, the development of such a phantom and to explore whether such a phantom might be used to validate MRACs. Various materials were investigated for their attenuation and MR properties. For the substitution of bone, water-saturated gypsum plaster was used. The attenuation of 511 keV annihilation photons was regulated by addition of iodine. Adipose tissue was imitated by silicone and brain tissue by agarose gel, respectively. The practicability with respect to the comparison of MRACs was checked as follows: A small flask inserted into the phantom and a large spherical phantom (serving as a reference with negligible error in MRAC) were filled with the very same activity concentration. The activity concentration was measured and compared using clinical protocols on PET-MRI and different built-in and offline MRACs. The same measurements were carried out using PET-CT for comparison. The phantom imitates the human head in sufficient detail. All tissue types including bone were detected as such so that the phantom-based comparison of the quantification accuracy of PET-MRI was possible. Quantitatively, the activity concentration in the brain, which was determined using different MRACs, showed a deviation of about 5% on average and a maximum deviation of 11% compared to the spherical phantom. For PET-CT, the deviation was 5%. The comparatively small error in quantification indicates that it is possible to construct a brain PET-MRI phantom that leads to MR-based attenuation-corrected images with reasonable accuracy.

中文翻译：

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用于PET-MRI的逼真的人体头部幻像。

正电子发射断层扫描（PET）和磁共振成像（MRI）（PET-MRI）的结合是一种独特的混合成像方式，主要用于肿瘤学和神经病学。基于MRI的衰减校正（MRAC）对于正确量化PET数据至关重要。当前缺少用于验证PET-MRI定量结果的合适模型。特别是，通常不通过通用的体模来验证由于骨骼引起的衰减的校正。因此，这项工作的目的是开发这种模型，并探讨这种模型是否可用于验证MRAC。研究了各种材料的衰减和MR特性。为了替代骨骼，使用了水饱和石膏灰泥。511 keV ni灭光子的衰减通过添加碘来调节。脂肪组织分别被有机硅和琼脂糖凝胶模仿。关于MRAC比较的实用性检查如下：插入幻影的小烧瓶和大球形幻影（用作MRAC中误差可忽略的参考）充满了相同的活性浓度。使用PET-MRI上的临床方案以及不同的内置和脱机MRAC测量并比较活性浓度。使用PET-CT进行相同的测量以进行比较。幻影充分模仿了人的头部。如此检测包括骨骼在内的所有组织类型，从而可以对人体模型进行PET-MRI定量准确性的比较。从数量上讲，使用不同的MRAC确定的大脑活动浓度 与球形模型相比，其平均偏差约为5％，最大偏差为11％。对于PET-CT，偏差为5％。定量误差相对较小表明，有可能构建大脑PET-MRI体模，以合理的精度生成基于MR的衰减校正图像。