Evaluation of the attenuation properties of MR equipment for its use in a whole-body PET/MR scanner
Evaluation of the attenuation properties of MR equipment for its use in a whole-body PET/MR scanner
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DOI：
10.1088/0031-9155/55/15/011
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发表时间：
2010-08-07
影响因子：
3.5
通讯作者：
Ziegler, S. I.
中科院分区：
文献类型：
--
作者：
Delso, G.;Martinez-Moeller, A.;Ziegler, S. I.
磁共振成像（MR）和正电子发射断层扫描（PET）扫描仪的组合可以为临床诊断和调查提供强有力的工具。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。这需要考虑视野中MR硬件的存在。该硬件引入的衰减无法从MR数据中获得。我们建议创建MR硬件的衰减模型，在PET重建之前将其注册到基于MR的衰减图中。遵循两个步骤来评估该方法的可行性。首先，对MR组件（RF线圈和医用探头）进行传输和发射测量。评价重建PET图像中伪影的严重程度。其次，高曝光计算机断层扫描（CT）扫描用于获得头部线圈的模型。将该模型配准到装有线圈的均匀体模的PET/CT扫描的衰减图中。将得到的PET图像与不存在线圈的PET/CT重建进行比较。研究了模型配准误差引起的伪影。透射扫描显示，由于视野中存在头部和颈部线圈，计数损失17%。在锁、信号电缆和连接器中发现了重要的衰减源。然而，最差的衰减源是两个线圈之间的套管。所测量的医疗探头均未引入显著的衰减量。关于头部线圈的衰减模型，基于模型校正的重建PET图像与参考PET/CT重建相当。然而，模型轴向定位中大于1-2 mm的不准确性会导致重要的伪影。总之，结果表明，基于模型的衰减校正是可能的。使用高曝光扫描来创建线圈的衰减模型已被证明是可行的。但是，必须对模型进行充分注册。
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.