A valid photon attenuation correction (AC) method is instrumental for obtaining quantitatively correct PET images. Integrated PET/MR systems provide no direct information on attenuation, and novel methods for MR-based AC (MRAC) are still under investigation. Evaluations of various AC methods have mainly focused on static brain PET acquisitions. In this study, we determined the validity of three MRAC methods in a dynamic PET/MR study of the brain. Nine participants underwent dynamic brain PET/MR scanning using the dopamine transporter radioligand [11C]PE2I. Three MRAC methods were evaluated: single-atlas (Atlas), multi-atlas (MaxProb) and zero-echo-time (ZTE). The 68Ge-transmission data from a previous stand-alone PET scan was used as reference method. Parametric relative delivery (R1) images and binding potential (BPND) maps were generated using cerebellar grey matter as reference region. Evaluation was based on bias in MRAC maps, accuracy and precision of [11C]PE2I BPND and R1 estimates, and [11C]PE2I time-activity curves. BPND was examined for striatal regions and R1 in clusters of regions across the brain. For BPND, ZTE-MRAC showed the highest accuracy (bias < 2%) in striatal regions. Atlas-MRAC exhibited a significant bias in caudate nucleus (− 12%) while MaxProb-MRAC revealed a substantial, non-significant bias in the putamen (9%). R1 estimates had a marginal bias for all MRAC methods (− 1.0–3.2%). MaxProb-MRAC showed the largest intersubject variability for both R1 and BPND. Standardized uptake values (SUV) of striatal regions displayed the strongest average bias for ZTE-MRAC (~ 10%), although constant over time and with the smallest intersubject variability. Atlas-MRAC had highest variation in bias over time (+10 to − 10%), followed by MaxProb-MRAC (+5 to − 5%), but MaxProb showed the lowest mean bias. For the cerebellum, MaxProb-MRAC showed the highest variability while bias was constant over time for Atlas- and ZTE-MRAC. Both Maxprob- and ZTE-MRAC performed better than Atlas-MRAC when using a 68Ge transmission scan as reference method. Overall, ZTE-MRAC showed the highest precision and accuracy in outcome parameters of dynamic [11C]PE2I PET analysis with use of kinetic modelling.

中文翻译：

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动态 [11C]PE2I PET-MR 脑成像的零回波时间、单图集和多图集衰减校正的准确性和精密度

有效的光子衰减校正 (AC) 方法有助于获得定量正确的 PET 图像。集成 PET/MR 系统不提供有关衰减的直接信息，基于 MR 的 AC (MRAC) 的新方法仍在研究中。对各种 AC 方法的评估主要集中在静态脑 PET 采集上。在这项研究中，我们确定了三种 MRAC 方法在大脑动态 PET/MR 研究中的有效性。九名参与者使用多巴胺转运蛋白放射性配体 [11C]PE2I 接受了动态脑部 PET/MR 扫描。评估了三种 MRAC 方法：单图集 (Atlas)、多图集 (MaxProb) 和零回波时间 (ZTE)。使用先前独立 PET 扫描的 68Ge 透射数据作为参考方法。使用小脑灰质作为参考区域生成参数相对传递（R1）图像和结合电位（BPND）图。评估基于 MRAC 图的偏差、[11C]PE2I BPND 和 R1 估计的准确性和精密度以及 [11C]PE2I 时间-活性曲线。检查 BPND 的纹状体区域和整个大脑区域簇中的 R1。对于 BPND，ZTE-MRAC 在纹状体区域显示出最高的准确度（偏差 < 2%）。Atlas-MRAC 在尾状核中表现出显着偏差 (− 12%)，而 MaxProb-MRAC 在壳核中表现出显着的非显着偏差 (9%)。所有 MRAC 方法的 R1 估计值均存在边际偏差 (− 1.0–3.2%)。MaxProb-MRAC 显示 R1 和 BPND 的最大受试者间变异。纹状体区域的标准化摄取值 (SUV) 显示出 ZTE-MRAC 的最强平均偏差 (~ 10%)，尽管随着时间的推移保持恒定，并且受试者间变异性最小。Atlas-MRAC 随时间的偏差变化最高（+10 至 − 10%），其次是 MaxProb-MRAC（+5 至 − 5%），但 MaxProb 显示出最低的平均偏差。对于小脑，MaxProb-MRAC 显示出最高的变异性，而 Atlas- 和 ZTE-MRAC 的偏差随着时间的推移保持恒定。当使用 68Ge 传输扫描作为参考方法时，Maxprob- 和 ZTE-MRAC 的表现均优于 Atlas-MRAC。总体而言，ZTE-MRAC 在使用动力学模型的动态 [11C]PE2I PET 分析结果参数方面表现出最高的精度和准确度。