Dynamic cardiac PET imaging: Technological improvements advancing future cardiac health.
Dynamic cardiac PET imaging: Technological improvements advancing future cardiac health.
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动态心脏 PET 成像：技术进步促进未来心脏健康。
DOI：
10.1007/s12350-018-1201-3
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Seo,Youngho
中科院分区：
文献类型：
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作者：
Gullberg,GrantT;Shrestha,UttamM;Seo,Youngho
虽然PET与CT结合1已成为肿瘤患者管理的重要工具，到2016年占PET扫描的86%，2但具有衰减和运动校正的PET在未来心脏应用中具有巨大潜力，特别是PET能够执行动态成像以测量心肌灌注-心肌血流量（MBF）和冠状动脉血流储备（CFR），自主神经系统的神经递质的完整性，并将心脏效率与心肌基质的代谢联系起来。它的潜力在于其出色的分辨率和灵敏度，使用半衰期短的示踪剂的能力，允许更高的剂量，以及未来可能使用18F灌注剂的能力，这将消除对现场回旋加速器的需求。在动态成像期间（应为每个程序执行动态扫描），血液输入阶段期间的高计数可能会使相机电子设备瘫痪。因此，需要实施能够接受这些高计数率的改进的飞行时间（TOF）电子设备和质量控制措施，以确定动态心脏PET研究的最大允许注射剂量（如货车Dijk及其同事在本期杂志中所提出的）。然而，有一个警告：限制注射剂量以满足输入阶段期间的计数率能力，这会损害在动态研究的后期阶段获得高计数的能力，此时相机电子设备不太可能瘫痪。使用恒定输注技术可以减少输入阶段期间的高峰计数，但是这降低了准确测量血液向组织隔室转移的频率响应的能力。未来的其他方法，如使用输入函数库或盲估计，可能会减轻动态心脏PET研究中注射有限剂量的限制。然而，人们需要谨慎行事，并考虑到这样一个事实，即从20世纪80年代初到2006年，美国人口的总体辐射负担翻了一番，核心脏病学手术对电离辐射负担的贡献增加了10倍。3因此，新的和改进的硬件、软件和放射性示踪剂开发在动态心脏应用的PET系统性能中发挥了重要作用，以提供超过手术风险的预期临床受益。在货车Dijk及其同事的论文中，最初由Renaud等人提出的一种简单方法，4用于确定82 Rb的最大活性，允许使用具有飞行时间能力的新型Philips数字PET相机来估计MBF。该方法类似于我们在UCSF的小组使用的早期方法，用于确定18F示踪剂的最大活性，允许使用Siemens Biograph 16 PET/CT通过来自心脏的图像衍生血液输入测量进行动力学分析。5基本上，该方法将高水平的放射性注入体模，例如使系统饱和的拟人躯干体模（Data Spectrum Corp）的心脏插入物。随着时间的推移，活动衰减，减少系统中的死区时间或瘫痪，从而允许计数增加（见图1中的图示）。当计数率增加到真实活动和测量活动之间的偏差小于某个准确度水平（例如1%）的水平时，确定活动（针对患者尺寸和体重修改），可以注射该活动以获得用于估计心肌血流量（MBF）的准确动力学参数。在货车Dijk及其同事的工作中，在三个LYSO TOF PET系统上获得了数据：两个模拟
While PET, in conjunction with CT, 1 has been an important tool in the management of oncology patients, accounting for 86% of PET scans by 2016, 2 PET with attenuation and motion correction has significant potential for future cardiac applications, especially with the ability of PET to perform dynamic imaging to measure myocardial perfusion—myocardial blood flow (MBF) and coronary flow reserve (CFR), integrity of neural transmitters of the autonomic nervous system, and connecting cardiac efficiency with metabolism of myocardial substrates. Its potential is found with its excellent resolution and sensitivity, the ability to use tracers with a short half-life allowing higher doses, and possibly in the future the ability to use 18F perfusion agents that would eliminate the need of an onsite cyclotron. During dynamic imaging (a dynamic scan should be performed for every procedure), the high counts during the blood input phase can paralyze the camera electronics. Therefore, improved time-of-flight (TOF) electronics able to accept these high counts rates and quality control measures to determine the maximum allowable injected dose (as presented in this issue of the Journal by van Dijk and colleagues) for dynamic cardiac PET studies need to be implemented. However, there is a caveat: restricting the injected dose to meet the count rate capabilities during the input phase penalizes the ability to obtain high counts during the later phase of the dynamic study when the camera electronics are less likely to be paralyzed. Using constant infusion techniques can reduce high peak counts during the input phase, but this reduces the ability to accurately measure the frequency response of the transfer of blood to tissue compartments. Other approaches in the future such as using a library of input functions or blind estimation may alleviate the limitations of injecting a restricted dose for dynamic cardiac PET studies. Nevertheless, one needs to follow caution and consider the fact that the overall radiation burden to the US population doubled from the early 1980s to 2006, and the contribution of nuclear cardiology procedures to ionizing radiation burden increased 10-fold. 3 Thus new and improved hardware, software, and radiotracer developments play an important part in the performance of the PET system for dynamic cardiac applications to provide expected clinical benefit that outweighs the risks of the procedure. In the paper by van Dijk and colleagues a simple method, originally proposed by Renaud et al., 4 was used to determine the maximum activity of 82Rb allowed for estimating MBF using the new Philips digital PET camera with time-of-flight capability. The method is similar to that of an earlier method used by our group at UCSF for determining the maximum activity of 18F tracers allowed for performing kinetic analysis via image derived blood input measurements from the heart using the Siemens Biograph 16 PET/CT. 5 Basically, the method injects high levels of radioactivity into a phantom such as a cardiac insert of an anthropomorphic torso phantom (Data Spectrum Corp) that saturates the system. With time, the activity decays decreasing the dead time or paralysis in the system allowing the counts to increase (see illustration in Figure 1). When the count rate increases to a level where the bias between the true activity and the measured activity is less than some level of accuracy, such as 1%, that determines the activity—modified for patient size and weight—that one can inject to obtain accurate kinetic parameters for the estimation of myocardial blood flow (MBF). In the work of van Dijk and colleagues, data were acquired on three LYSO TOF PET systems: Two analog