Department of Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Siemens Healthcare GmbH, Erlangen, Germany.
Eur J Radiol. 2017 Nov;96:12-20. doi: 10.1016/j.ejrad.2017.09.007. Epub 2017 Sep 13.
To explore the value and reproducibility of a novel magnetic resonance based attenuation correction (MRAC) using a CAIPIRINHA-accelerated T1-weighted Dixon 3D-VIBE sequence for whole-body PET/MRI compared to the clinical standard.
The PET raw data of 19 patients from clinical routine were reconstructed with standard MRAC (MRAC) and the novel MRAC (MRAC), a prototype CAIPIRINHA accelerated Dixon 3D-VIBE sequence, both acquired in 19 s/bed position. Volume of interests (VOIs) for liver, lung and all voxels of the total image stack were created to calculate standardized uptake values (SUV) followed by inter-method agreement (Passing-Bablok regression, Bland-Altman analysis). A voxel-wise SUV comparison per patient was performed for intra-individual correlation between MRAC and MRAC. Difference images (MRAC-MRAC) of attenuation maps and SUV images were calculated. The image quality of in/opposed-phase water and fat images obtained from MRAC was assessed by two readers on a 5-point Likert-scale including intra-class coefficients for inter-reader agreement.
SUV correlations of VOIs demonstrated high linearity (0.95<Spearman's rho<1, p<0.0001, respectively), substantiated by voxel-wise SUV scatter-plots (1.79×10 pixels). Outliers could be explained by different physiological conditions between the scans such as different segmentation of air-containing tissue, lungs, kidneys, metal implants, diaphragm edge or small air bubbles in the gastrointestinal tracts that moved between MRAC acquisitions. Nasal sinuses and the trachea were better segmented in MRAC. High-resolution T1w Dixon 3D VIBE images were acquired in all cases and could be used for PET/MRI fusion. MRAC images were of high diagnostic quality (4.2±0.8) with 0.92-0.96 intra-class correlation.
The novel prototype MRAC extends the value for attenuation correction by providing a high spatial resolution DIXON-based dataset suited for diagnostic assessment towards time-efficient whole-body PET/MRI.
探索一种新型基于磁共振的衰减校正（MRAC）方法在体部 PET/MRI 中的应用价值和可重复性，该方法使用了 CAIPIRINHA 加速的 T1 加权 Dixon 3D-VIBE 序列，与临床标准相比。
从临床常规中重建了 19 例患者的 PET 原始数据，采用标准的 MRAC（MRAC）和新型的 MRAC（MRAC），这两种方法都使用 CAIPIRINHA 加速的 Dixon 3D-VIBE 序列在 19 秒/床位位置采集。为计算标准化摄取值（SUV），创建了肝脏、肺和整个图像堆栈的所有体素的感兴趣区（VOIs），然后进行方法间的一致性（Passing-Bablok 回归、Bland-Altman 分析）。对每位患者进行了个体内的 MRAC 和 MRAC 之间的 SUV 比较。对衰减图和 SUV 图像进行了差异图像（MRAC-MRAC）的计算。通过两位读者对水/脂同相位图像的质量进行了 5 分李克特量表评估，包括读者间的内类系数一致性。
VOI 的 SUV 相关性表现出高度的线性（0.95<Spearman's rho<1，p<0.0001，分别），这是通过体素间 SUV 散点图（1.79×10 像素）得到证实的。离群值可以用两次扫描之间的不同生理条件来解释，如空气含组织、肺、肾、金属植入物、膈缘或胃肠道中的小气泡的不同分割，这些组织在 MRAC 采集之间移动。MRAC 中更好地分割了鼻旁窦和气管。在所有病例中都采集了高分辨率的 T1w Dixon 3D VIBE 图像，并可用于 PET/MRI 融合。MRAC 图像具有高诊断质量（4.2±0.8），内类相关系数为 0.92-0.96。
新型原型 MRAC 通过提供适合诊断评估的高空间分辨率 DIXON 数据集，扩展了衰减校正的价值，实现了高效的全身 PET/MRI。
