Klinikum rechts der Isar der Technischen Universität München, Munich, Germany.
Phys Med Biol. 2010 Aug 7;55(15):4361-74. doi: 10.1088/0031-9155/55/15/011. Epub 2010 Jul 20.
The combination of magnetic resonance imaging (MR) and positron emission tomography (PET) scanners can provide a powerful tool for clinical diagnosis and investigation. Among the challenges of developing a combined scanner, obtaining attenuation maps for PET reconstruction is of critical importance. This requires accounting for the presence of MR hardware in the field of view. The attenuation introduced by this hardware cannot be obtained from MR data. We propose the creation of attenuation models of MR hardware, to be registered into the MR-based attenuation map prior to PET reconstruction. Two steps were followed to assess the viability of this method. First, transmission and emission measurements were performed on MR components (RF coils and medical probes). The severity of the artifacts in the reconstructed PET images was evaluated. Secondly, a high-exposure computed tomography (CT) scan was used to obtain a model of a head coil. This model was registered into the attenuation map of PET/CT scans of a uniform phantom fitted with the coil. The resulting PET images were compared to the PET/CT reconstruction in the absence of coils. The artifacts introduced by misregistration of the model were studied. The transmission scans revealed 17% count loss due to the presence of head and neck coils in the field of view. Important sources of attenuation were found in the lock, signal cables and connectors. However, the worst source of attenuation was the casing between both coils. None of the measured medical probes introduced a significant amount of attenuation. Concerning the attenuation model of the head coil, reconstructed PET images with model-based correction were comparable to the reference PET/CT reconstruction. However, inaccuracies greater than 1-2 mm in the axial positioning of the model led to important artifacts. In conclusion, the results show that model-based attenuation correction is possible. Using a high-exposure scan to create an attenuation model of the coils has been proved feasible. However, adequate registration of the model is mandatory.
磁共振成像（MRI）和正电子发射断层扫描（PET）扫描仪的结合可为临床诊断和研究提供强大的工具。在开发组合扫描仪的挑战中，获得 PET 重建的衰减图至关重要。这需要考虑到视场中存在的 MRI 硬件。该硬件引入的衰减不能从 MRI 数据中获得。我们提出创建 MRI 硬件的衰减模型，以便在 PET 重建之前将其注册到基于 MRI 的衰减图中。为了评估该方法的可行性，我们进行了两个步骤。首先，对 MRI 组件（射频线圈和医疗探头）进行了透射和发射测量。评估了重建 PET 图像中伪影的严重程度。其次，使用高曝光 CT（CT）扫描获得头部线圈的模型。将该模型注册到带有线圈的均匀体模的 PET/CT 扫描的衰减图中。将得到的 PET 图像与没有线圈的 PET/CT 重建进行比较。研究了模型配准不良引入的伪影。透射扫描显示，由于视场中存在头颈部线圈，计数损失了 17%。在锁定装置、信号电缆和连接器中发现了重要的衰减源。然而，衰减最大的源是两个线圈之间的外壳。测量的医疗探头都没有引入大量衰减。关于头部线圈的衰减模型，基于模型的校正重建的 PET 图像与参考 PET/CT 重建相当。然而，模型轴向定位的误差大于 1-2 毫米，会导致严重的伪影。总之，结果表明基于模型的衰减校正可能实现。使用高曝光扫描创建线圈的衰减模型已被证明是可行的。但是，模型的配准必须足够准确。
