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正电子发射断层磁共振成像(PET/MR)衰减校正:问题、新方法和实用解决方案。

Attenuation correction for PET/MR: problems, novel approaches and practical solutions.

机构信息

Nuklearmedizinische Klinik und Poliklinik der Technischen Universität München, Munich, Germany.

出版信息

Z Med Phys. 2012 Dec;22(4):299-310. doi: 10.1016/j.zemedi.2012.08.003. Epub 2012 Aug 25.

Abstract

Attenuation correction in PET is the primary prerequisite for quantification of the radiotracer's signal. Absolute quantification is the key to improve diagnostic performance, to enable comparisons between follow-up examinations and to perform pharmacokinetic modeling. A large fraction of the 511 keV annihilation photons from the positron emitters are scattered by the patient's body. Thus, they are discarded or do not even reach the PET detectors, while others are identified at the wrong location after being scattered. To account for these effects and thus generate quantitative PET images showing the actual activity distribution, it is necessary to determine an attenuation map with the appropriate attenuation coefficients for 511 keV photons at each voxel. In hybrid PET/CT systems, this is achieved using the information about the tissue electron density provided by the CT and adjusting it for the difference in photon energy. In PET/MR systems, there is no mechanism to directly measure the attenuation coefficients of the tissue. Determining the attenuation map in PET/MR is an important challenge involving two problems: the determination of the patient's attenuation map and the determination of the attenuation introduced by additional hardware components. We describe the approaches investigated to deal with these problems and, based on the experience with a fully integrated PET/MR system, we finally discuss potential solutions and limitations in a close to routine setting.

摘要

在 PET 中,衰减校正(Attenuation correction)是量化示踪剂信号的首要前提。绝对量化(Absolute quantification)是提高诊断性能、实现随访检查比较以及进行药代动力学建模的关键。正电子发射体的 511keV 湮没光子中有很大一部分被患者身体散射。因此,它们被丢弃,甚至没有到达 PET 探测器,而其他光子在散射后被错误地识别到了错误的位置。为了考虑这些影响,并生成显示实际活性分布的定量 PET 图像,有必要确定每个体素的 511keV 光子的适当衰减系数的衰减图。在混合 PET/CT 系统中,这是通过利用 CT 提供的组织电子密度信息并针对光子能量差异进行调整来实现的。在 PET/MR 系统中,没有直接测量组织衰减系数的机制。在 PET/MR 中确定衰减图是一个重要的挑战,涉及两个问题:确定患者的衰减图和确定附加硬件组件引入的衰减。我们描述了为解决这些问题而研究的方法,并基于对完全集成的 PET/MR 系统的经验,最后在接近常规设置的情况下讨论了潜在的解决方案和限制。

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