Berker Yannick, Li Yusheng
Department of Radiology, University of Pennsylvania, 3620 Hamilton Walk, Philadelphia, Pennsylvania 19104.
Med Phys. 2016 Feb;43(2):807-32. doi: 10.1118/1.4938264.
The problem of attenuation correction (AC) for quantitative positron emission tomography (PET) had been considered solved to a large extent after the commercial availability of devices combining PET with computed tomography (CT) in 2001; single photon emission computed tomography (SPECT) has seen a similar development. However, stimulated in particular by technical advances toward clinical systems combining PET and magnetic resonance imaging (MRI), research interest in alternative approaches for PET AC has grown substantially in the last years. In this comprehensive literature review, the authors first present theoretical results with relevance to simultaneous reconstruction of attenuation and activity. The authors then look back at the early history of this research area especially in PET; since this history is closely interwoven with that of similar approaches in SPECT, these will also be covered. We then review algorithmic advances in PET, including analytic and iterative algorithms. The analytic approaches are either based on the Helgason-Ludwig data consistency conditions of the Radon transform, or generalizations of John's partial differential equation; with respect to iterative methods, we discuss maximum likelihood reconstruction of attenuation and activity (MLAA), the maximum likelihood attenuation correction factors (MLACF) algorithm, and their offspring. The description of methods is followed by a structured account of applications for simultaneous reconstruction techniques: this discussion covers organ-specific applications, applications specific to PET/MRI, applications using supplemental transmission information, and motion-aware applications. After briefly summarizing SPECT applications, we consider recent developments using emission data other than unscattered photons. In summary, developments using time-of-flight (TOF) PET emission data for AC have shown promising advances and open a wide range of applications. These techniques may both remedy deficiencies of purely MRI-based AC approaches in PET/MRI and improve standalone PET imaging.
2001年正电子发射断层扫描（PET）与计算机断层扫描（CT）相结合的设备投入商业使用后，定量PET的衰减校正（AC）问题在很大程度上被认为已得到解决；单光子发射计算机断层扫描（SPECT）也有类似的发展。然而，特别是受到PET与磁共振成像（MRI）相结合的临床系统技术进步的刺激，近年来对PET AC替代方法的研究兴趣大幅增长。在这篇全面的文献综述中，作者首先介绍了与衰减和活度同时重建相关的理论结果。作者接着回顾了该研究领域的早期历史，特别是在PET方面；由于这段历史与SPECT中类似方法的历史紧密交织，因此也将涵盖SPECT。然后我们回顾PET中的算法进展，包括解析算法和迭代算法。解析方法要么基于拉东变换的赫尔加松 - 路德维希数据一致性条件，要么基于约翰偏微分方程的推广；关于迭代方法，我们讨论衰减和活度的最大似然重建（MLAA）、最大似然衰减校正因子（MLACF）算法及其衍生算法。方法描述之后是对同时重建技术应用的结构化阐述：该讨论涵盖器官特异性应用、PET/MRI特有的应用、使用补充透射信息的应用以及运动感知应用。在简要总结SPECT应用之后，我们考虑使用除未散射光子之外的发射数据的最新进展。总之，使用飞行时间（TOF）PET发射数据进行AC的进展已显示出良好前景，并开启了广泛的应用。这些技术既可以弥补PET/MRI中基于纯MRI的AC方法的不足，又可以改善独立的PET成像。
