Department of Electrical and Computer Engineering, Oakland University, Rochester, MI, 48309, USA.
Department of Radiology, Johns Hopkins University, Baltimore, MD, 21287, USA.
Med Phys. 2017 Sep;44(9):4536-4547. doi: 10.1002/mp.12429. Epub 2017 Aug 9.
Myocardial perfusion (MP) PET imaging is a powerful tool in risk assessment and stratification of patients with coronary artery disease. Involuntary organ motion degrades cardiac PET image resolution, while respiratory and/or cardiac gating to freeze the motion leads to noisier reconstructed images due to reduced counts in the gated frames. In this work, we propose an MRI-assisted dual motion correction method to compensate for respiratory and cardiac motion in MP PET data and study the impact of dual motion correction on MP defect detection using systematically designed experiments.
The proposed dual motion correction method addresses the respiratory motion before correcting the cardiac motion among the respiratory motion corrected cardiac gates. The respiratory motion is estimated from the respiratory-gated only PET images and compensated within a 4D motion-incorporated image reconstruction algorithm. The cardiac motion is then corrected using the motion vector fields estimated from the corresponding cardiac-gated MR images. To evaluate the proposed method, we performed experiments using the standard XCAT phantom and two individual-specific volunteer XCAT phantoms. For each of the three phantoms, we simulated four dual-gated Rb-82 MP PET imaging datasets, one with normal perfusion and the other three with 50% nontransmural, 75% nontransmural, and transmural regionally reduced perfusion. The corresponding cardiac-gated MR images were simulated by the SIMRI simulator, with the sequence specified to be 3D T1-weighted as used in a protocol of a clinical PET/MRI scanner. We quantitatively evaluated the reconstructed images with no motion correction, only respiratory motion correction and dual motion correction, in terms of the myocardium to blood pool contrast and the trade-off between the noise and the normal to defect contrast. Using the channelized Hotelling observer, we performed receiver operating characteristic analysis for the task of detecting perfusion abnormalities with various myocardial coverages.
Compared with no motion correction, the respiratory motion correction was demonstrated to improve the myocardium to blood pool contrast as well as the trade-off between the noise and the normal to defect contrast, on top of which the cardiac motion correction furthered the improvement. In the task of detecting regional perfusion defects, transmural or different levels of nontransmural, the respiratory motion correction significantly increased the defect detectability compared with no motion correction. Additionally, the respiratory and cardiac motion correction significantly improved the defect detection compared with the respiratory motion correction alone. Furthermore, the separability of the transmural and nontransmural defects was also improved by the proposed MRI assisted dual motion correction method.
The proposed dual respiratory and cardiac motion correction technique improves the accuracy of PET quantification and MP defect detection and classification, which shows its promise for clinical applications especially in cardiac PET/MR imaging.
心肌灌注（MP）PET 成像在评估和分层冠状动脉疾病患者风险方面是一种强大的工具。非自愿器官运动降低了心脏 PET 图像的分辨率，而呼吸和/或心脏门控冻结运动导致门控帧中的计数减少，从而导致重建图像噪声更大。在这项工作中，我们提出了一种 MRI 辅助的双运动校正方法，以补偿 MP PET 数据中的呼吸和心脏运动，并使用系统设计的实验研究双运动校正对 MP 缺陷检测的影响。
所提出的双运动校正方法在纠正呼吸门控心脏门中的心脏运动之前解决呼吸运动。从仅呼吸门控的 PET 图像中估计呼吸运动，并在 4D 运动合并图像重建算法中进行补偿。然后使用从相应的心脏门控 MR 图像中估计的运动矢量场来校正心脏运动。为了评估所提出的方法，我们使用标准的 XCAT 体模和两个个体特定的志愿者 XCAT 体模进行了实验。对于三个体模中的每一个，我们模拟了四个双门控 Rb-82 MP PET 成像数据集，一个具有正常灌注，另外三个具有 50%非透壁、75%非透壁和透壁区域性灌注减少。使用 SIMRI 模拟器模拟了相应的心脏门控 MR 图像，指定序列为 3D T1 加权，如临床 PET/MR 扫描仪的协议中使用的那样。我们使用通道化 Hotelling 观察者，根据各种心肌覆盖率，对无运动校正、仅呼吸运动校正和双运动校正的重建图像进行了心肌与血池对比度和噪声与正常至缺陷对比度之间的权衡的定量评估。在检测区域性灌注缺陷的任务中，透壁或不同程度的非透壁，呼吸运动校正与无运动校正相比，显著提高了缺陷可检测性。此外，呼吸和心脏运动校正与单独的呼吸运动校正相比，显著提高了缺陷检测。此外，所提出的 MRI 辅助双运动校正方法还提高了透壁和非透壁缺陷的可分离性。
所提出的双呼吸和心脏运动校正技术提高了 PET 定量和 MP 缺陷检测和分类的准确性，这表明其在临床应用中具有潜力，特别是在心脏 PET/MR 成像中。
