Radiotherapy of mobile tumors requires specific imaging tools and models to reduce the impact of motion on the treatment. Online continuous nonionizing imaging has become possible with the recent development of magnetic resonance imaging devices combined with linear accelerators. This opens the way to new guided treatment methods based on the real‐time tracking of anatomical motion. In such devices, 2D fast MR‐images are well‐suited to capture and predict the real‐time motion of the tumor. To be used effectively in an adaptive radiotherapy, these MR images have to be combined with X‐ray images such as CT, which are necessary to compute the irradiation dose deposition. We therefore developed a method combining both image modalities to track the motion on MR images and reproduce the tracked motion on a sequence of 3DCT images in real‐time. It uses manually placed navigators to track organ interfaces in the image, making it possible to select anatomical object borders that are visible on both MRI and CT modalities and giving the operator precise control of the motion tracking quality. Precomputed deformation fields extracted from the 4DCT acquired in the planning phase are then used to deform existing 3DCT images to match the tracked object position, creating a new set of 3DCT images encompassing irregularities in the breathing pattern for the complete duration of the MRI acquisition. The final continuous reconstructed 4DCT image sequence reproduces the motion captured by the MRI sequence with high precision (difference below 2 mm).

中文翻译：

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使用动态 MRI 和预先计算的 4DCT 变形场进行连续实时 3D 运动再现。

移动肿瘤的放射治疗需要特定的成像工具和模型，以减少运动对治疗的影响。随着最近与直线加速器相结合的磁共振成像设备的发展，在线连续非电离成像已成为可能。这为基于实时跟踪解剖运动的新引导治疗方法开辟了道路。在此类设备中，二维快速 MR 图像非常适合捕获和预测肿瘤的实时运动。为了在适应性放射治疗中有效使用，这些 MR 图像必须与 X 射线图像（例如 CT）相结合，这对于计算辐射剂量沉积是必要的。因此，我们开发了一种结合两种图像模态的方法来跟踪 MR 图像上的运动，并在一系列 3DCT 图像上实时再现跟踪的运动。它使用手动放置的导航器来跟踪图像中的器官界面，从而可以选择在 MRI 和 CT 模式上可见的解剖对象边界，并使操作员能够精确控制运动跟踪质量。然后，从规划阶段获取的 4DCT 中提取的预先计算的变形场用于使现有 3DCT 图像变形以匹配跟踪的对象位置，从而创建一组新的 3DCT 图像，其中包含 MRI 采集的整个持续时间内呼吸模式的不规则性。最终连续重建的 4DCT 图像序列以高精度（差异低于 2 mm）再现 MRI 序列捕获的运动。