PET/MRI phantom studies are challenged by the need of phantom-specific attenuation templates to account for attenuation properties of the phantom material. We present a PET/MRI phantom built from MRI-visible material for which attenuation correction (AC) can be performed using the standard MRI-based AC. A water-fillable phantom was 3D-printed with a commercially available MRI-visible polymer. The phantom had a cylindrical shape and the fillable compartment consisted of a homogeneous region and a region containing solid rods of different diameters. The phantom was filled with a solution of water and [18F]FDG. A 30 min PET/MRI acquisition including the standard Dixon-based MR-AC method was performed. In addition, a CT scan of the phantom was acquired on a PET/CT system. From the Dixon in-phase, opposed-phase and fat images, a phantom-specific AC map (Phantom MR-AC) was produced by separating the phantom material from the water compartment using a thresholding-based method and assigning fixed attenuation coefficients to the individual compartments. The PET data was reconstructed using the Phantom MR-AC, the original Dixon MR-AC, and an MR-AC just containing the water compartment (NoWall-AC) to estimate the error of ignoring the phantom walls. CT-based AC was employed as the reference standard. Average %-differences in measured activity between the CT corrected PET and the PET corrected with the other AC methods were calculated. The phantom housing and the liquid compartment were both visible and distinguishable from each other in the Dixon images and allowed the segmentation of a phantom-specific MR-based AC. Compared to the CT-AC PET, average differences in measured activity in the whole water compartment in the phantom of −0.3%, 9.4%, and −24.1% were found for Dixon phantom MR-AC, MR-AC, and NoWall-AC based PET, respectively. Average differences near the phantom wall in the homogeneous region were −0.3%, 6.6%, and −34.3%, respectively. Around the rods, activity differed from the CT-AC PET by 0.7%, 8.9%, and −45.5%, respectively. The presented phantom material is visible using standard MR sequences, and thus, supports the use of standard, phantom-independent MR measurements for MR-AC in PET/MRI phantom studies.

中文翻译：

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PET / MRI体模的基于MRI的标准衰减校正：使用MRI可见聚合物的新概念

PET / MRI体模研究因需要体模特定的衰减模板来解决体模材料的衰减特性而面临挑战。我们介绍了一种由MRI可见材料制成的PET / MRI体模，可以使用基于MRI的标准AC进行衰减校正（AC）。用市售的MRI可见聚合物3D打印可充水的体模。体模为圆柱形，可填充隔室由均质区域和包含不同直径实心棒的区域组成。幻影充满了水和[18F] FDG的溶液。进行了30分钟的PET / MRI采集，包括基于Dixon的标准MR-AC方法。另外，在PET / CT系统上获得了体模的CT扫描。从Dixon同相，反相和脂肪图像中，通过使用基于阈值的方法从水室中分离幻影材料并将固定的衰减系数分配给各个隔室，生成了幻象特定的AC图（Phantom MR-AC）。使用Phantom MR-AC，原始的Dixon MR-AC和仅包含水室（NoWall-AC）的MR-AC重建PET数据，以估计忽略幻影壁的误差。使用基于CT的AC作为参考标准。计算出CT校正的PET和其他AC方法校正的PET之间测得活性的平均％差异。幻影外壳和液体隔室在Dixon图像中均可见且彼此可区分，并允许对幻影特定的基于MR的AC进行分段。与CT-AC PET相比，基于Dixon体模MR-AC，MR-AC和NoWall-AC的PET，在整个体模空间中测得的活动的平均差异分别为-0.3％，9.4％和-24.1％。均匀区域中幻影壁附近的平均差异分别为-0.3％，6.6％和-34.3％。棒周围的活性与CT-AC PET的差异分别为0.7％，8.9％和-45.5％。使用标准MR序列可以看到呈现的体模材料，因此支持在PET / MRI体模研究中对MR-AC使用标准的，体模无关的MR测量。分别。棒周围的活性与CT-AC PET的差异分别为0.7％，8.9％和-45.5％。使用标准MR序列可以看到呈现的体模材料，因此支持在PET / MRI体模研究中对MR-AC使用标准的，体模无关的MR测量。分别。棒周围的活性与CT-AC PET的差异分别为0.7％，8.9％和-45.5％。使用标准MR序列可以看到呈现的体模材料，因此支持在PET / MRI体模研究中对MR-AC使用标准的，体模无关的MR测量。