High Field and Hybrid MR Imaging, University Hospital Essen, University Duisburg-Essen, Essen, Germany.
Magnetic Resonance, Siemens Healthcare GmbH, Erlangen, Germany.
Med Phys. 2017 Sep;44(9):4559-4572. doi: 10.1002/mp.12449. Epub 2017 Aug 12.
The objective of this study was to introduce and evaluate a method for MR-based attenuation and truncation correction in phantom and patient measurements to improve PET quantification in PET/MR hybrid imaging.
The fully MR-based method HUGE (B Homogenization using gradient enhancement) provides field-of-view extension in MR imaging, which can be used for truncation correction and improved PET quantification in PET/MR hybrid imaging. The HUGE method in this recent implementation is combined with continuously moving table data acquisition to provide a seamless nontruncated whole-body data set of the outer patient contours to complete the established standard MR-based Dixon-VIBE data for attenuation correction. The method was systematically evaluated in NEMA standard phantom experiments to investigate the impact of HUGE truncation correction on PET quantification. The method was then applied to 24 oncologic patients in whole-body PET/MR hybrid imaging. The impact of MR-based truncation correction with HUGE on PET data was compared to the impact of the established PET-based MLAA algorithm for contour detection.
In phantom and in all patient measurements, the standard Dixon-VIBE attenuation correction data show geometric distortions and signal truncations at the edges of the MR imaging field-of-view. In contrast, the Dixon-VIBE-based attenuation correction data additionally extended by applying HUGE shows significantly less distortion and truncations and due to the continuously moving table acquisition robustly provides smooth outer contours of the patient arms. In the investigated patient cases, MLAA frequently showed an overestimation of arm volume and associated artifacts limiting contour detection. When applying HUGE, an average relative increase in SUV in patients' lesion of 4.2% and for MLAA of 4.6% were measured, when compared to standard Dixon-VIBE only. In specific lesions maximal differences in SUV up to 13% for HUGE and 14% for MLAA were measured. Quantification in truncated regions showed maximal differences up to 40% for both, MLAA and HUGE. Average differences in those regions in SUV for HUGE are 13.3% and 14.6% for MLAA. In a patient with I-124 radiotracer PET-based MLAA contour detection completely failed in this specific case, whereas HUGE as MR-based approach provided accurate truncation correction.
The HUGE method for truncation correction combined with continuous table movement extends the lateral MR field-of-view and effectively reduces truncations along the outer contours of the patient's arms in whole-body PET/MR imaging. HUGE as a fully MR-based approach is independent of the choice of radiotracer, thus also offering robust truncation correction in patients that are not injected with Fluordesoxyglucose (FDG) as radiotracer. Therefore, this method improves the standard Dixon MR-based attenuation correction and PET image quantification in whole-body PET/MR imaging applications.
本研究旨在介绍并评估一种基于磁共振（MR）的衰减和截断校正方法，用于改善 PET/MR 融合成像中的 PET 定量。
完全基于 MR 的 HUGE（使用梯度增强的 B 均匀化）方法可在 MR 成像中提供视野扩展，可用于截断校正和改善 PET/MR 融合成像中的 PET 定量。在最近的实施中，HUGE 方法与连续移动台数据采集相结合，为外患者轮廓的整个身体无截断数据集提供无缝采集，以完成用于衰减校正的既定标准基于 MR 的 Dixon-VIBE 数据。该方法在 NEMA 标准体模实验中进行了系统评估，以研究 HUGE 截断校正对 PET 定量的影响。然后将该方法应用于 24 例全身 PET/MR 融合成像的肿瘤患者。比较了 HUGE 的基于 MR 的截断校正对 PET 数据的影响与基于 PET 的 MLAA 算法用于轮廓检测的影响。
在体模和所有患者测量中，标准 Dixon-VIBE 衰减校正数据在 MR 成像视野边缘显示出几何变形和信号截断。相比之下，通过应用 HUGE 另外扩展的 Dixon-VIBE 基于衰减校正数据显示出明显较小的变形和截断，并且由于连续移动台采集而可靠地提供患者手臂的平滑外轮廓。在研究的患者病例中，MLAA 经常显示出手臂体积的高估和相关伪影，限制了轮廓检测。当应用 HUGE 时，与仅使用标准 Dixon-VIBE 相比，患者病变的 SUV 平均增加了 4.2%，而 MLAA 则增加了 4.6%。在特定病变中，SUV 的最大差异高达 HUGE 为 13%，MLAA 为 14%。在截断区域中的定量显示，MLAA 和 HUGE 的最大差异高达 40%。对于 HUGE，那些区域中的 SUV 的平均差异为 13.3%，而对于 MLAA 则为 14.6%。在一个使用 I-124 放射性示踪剂的患者中，基于 PET 的 MLAA 轮廓检测在这种特定情况下完全失败，而 HUGE 作为基于 MR 的方法提供了准确的截断校正。
HUGE 用于截断校正的方法与连续台运动相结合，扩展了横向 MR 视野，并有效地减少了全身 PET/MR 成像中外患者手臂轮廓的截断。HUGE 作为一种完全基于 MR 的方法独立于放射性示踪剂的选择，因此也为未注射氟脱氧葡萄糖（FDG）作为放射性示踪剂的患者提供了可靠的截断校正。因此，该方法改善了全身 PET/MR 成像应用中的标准 Dixon 基于 MR 的衰减校正和 PET 图像定量。
