Diagnostic and Interventional Radiology, Department of Radiology, University of Tübingen, Tübingen, Germany.
J Nucl Med. 2013 Mar;54(3):464-71. doi: 10.2967/jnumed.112.105296. Epub 2013 Jan 3.
Hybrid PET/MR combines the exceptional molecular sensitivity of PET with the high resolution and versatility of MR imaging. Simultaneous data acquisition additionally promises the use of MR to enhance the quality of PET images, for example, by respiratory motion correction. This advantage is especially relevant in thoracic and abdominal areas to improve the visibility of small lesions with low radiotracer uptake and to enhance uptake quantification. In this work, the applicability and performance of an MR-based method of respiratory motion correction for PET tumor imaging was evaluated in phantom and patient studies.
PET list-mode data from a motion phantom with (22)Na point sources and 5 patients with tumor manifestations in the thorax and upper abdomen were acquired on a simultaneous hybrid PET/MR system. During the first 3 min of a 5-min PET scan, the respiration-induced tissue deformation in the PET field of view was recorded using a sagittal 2-dimensional multislice gradient echo MR sequence. MR navigator data to measure the location of the diaphragm were acquired throughout the PET scan. Respiration-gated PET data were coregistered using the MR-derived motion fields to obtain a single motion-corrected PET dataset. The effect of motion correction on tumor visibility, delineation, and radiotracer uptake quantification was analyzed with respect to uncorrected and gated images.
Image quality in terms of lesion delineation and uptake quantification was significantly improved compared with uncorrected images for both phantom and patient data. In patients, in head-feet line profiles of 14 manifestations, the slope became steeper by 66.7% (P = 0.001) and full width at half maximum was reduced by 20.6% (P = 0.001). The mean increase in maximum standardized uptake value, lesion-to-background ratio (contrast), and signal-to-noise ratio was 28.1% (P = 0.001), 24.7% (P = 0.001), and 27.3% (P = 0.003), respectively. Lesion volume was reduced by an average of 26.5% (P = 0.002). As opposed to the gated images, no increase in background noise was observed. However, motion correction performed worse than gating in terms of contrast (-11.3%, P = 0.002), maximum standardized uptake value (-10.7%, P = 0.003), and slope steepness (-19.3%, P = 0.001).
The proposed method for MR-based respiratory motion correction of PET data proved feasible and effective. The short examination time and convenience (no additional equipment required) of the method allow for easy integration into clinical routine imaging. Performance compared with gating procedures can be further improved using list-mode-based motion correction.
在体模和患者研究中评估基于 MR 的呼吸运动校正方法在 PET 肿瘤成像中的适用性和性能。
在同时进行的混合 PET/MR 系统上采集具有（22）Na 点源的运动体模和 5 例胸部和上腹部有肿瘤表现的患者的 PET 列表模式数据。在 PET 扫描的前 3 分钟内，使用矢状 2 维多切片梯度回波 MR 序列记录 PET 视场中的组织变形。在整个 PET 扫描过程中采集 MR 导航数据以测量膈肌的位置。使用从 MR 获得的运动场对呼吸门控 PET 数据进行配准，以获得单个运动校正的 PET 数据集。分析了运动校正对肿瘤可见度、描绘和放射性示踪剂摄取定量的影响，与未校正和门控图像进行了比较。
与未校正图像相比，体模和患者数据的图像质量在肿瘤描绘和摄取定量方面均有显著改善。在患者中，在 14 个表现的头足线廓中，斜率陡峭度增加了 66.7%（P = 0.001），半最大值全宽减小了 20.6%（P = 0.001）。最大标准化摄取值、病变与背景比（对比度）和信噪比的平均增加分别为 28.1%（P = 0.001）、24.7%（P = 0.001）和 27.3%（P = 0.003）。病变体积平均减少了 26.5%（P = 0.002）。与门控图像相反，未观察到背景噪声增加。然而，与门控相比，运动校正在对比度（-11.3%，P = 0.002）、最大标准化摄取值（-10.7%，P = 0.003）和斜率陡峭度（-19.3%，P = 0.001）方面的性能较差。
所提出的基于 MR 的 PET 数据呼吸运动校正方法是可行且有效的。该方法的检查时间短，方便（无需额外设备），易于整合到临床常规成像中。与门控程序相比，使用基于列表模式的运动校正可以进一步提高性能。
