Reconstruction-free three dimensional positron emission imaging

项目总结/摘要 来自正电子发射放射性示踪剂的湮灭光子的符合检测的主要优点是 飞行时间（TOF）信息的可用性，以及测量TOF差异以更好地定位 正电子发射体通常对于正电子发射断层摄影（PET），TOF信息被用作加权 在图像重建过程中的核，并导致有效的灵敏度增益，可用于减少辐射 剂量，提高信噪比，或减少扫描持续时间。这些好处的大小取决于 TOF分辨率，这取决于探测器的定时性能。PET技术的现状 扫描仪为~220 ps，对应于~3.3 cm的定位。就会发生一个巨大的变化， 然而，如果可以实现<30 ps的TOF分辨率，则可以实现更高的分辨率。这将使事件定位在4.5 mm内， 在没有重建算法的情况下，以与 在临床PET扫描仪中实现。我们称之为直接正电子发射成像（PEI）。与此 高超的TOF分辨率和免重建成像，我们进入了一个新的制度，我们预计将大幅增加 在图像信噪比方面，既有由于TOF信息的附加，又有噪声放大的去除 这是利用来自投影数据的噪声校正来重建噪声数据所固有的。我们建议开发第一个 使用超快探测器直接产生横截面图像的概念验证成像系统 没有重建和量化性能的PEI通过模拟和实验。 由于直接PEI不具有与PET相同的数据收集采样约束，因此它创造了机会 用于便携式和灵活的成像设备，涉及患者定制或特定任务成像 应用（即心脏或乳腺成像），以及通用应用的开放式设计。 为了实现直接PEI所需的前所未有的TOF能力，我们将利用迅速发射的切伦科夫 在某些材料（包括微波炉）中，响应511 keV的辐射而产生的小于10 ps的辐射 光子相互作用我们提出的新型探测器设计将切伦科夫辐射器直接集成到入口 超快微通道板光电倍增管的窗口，这是目前最快的光子探测器 响应时间为25 ps。这种方法消除了光点之间的所有光学反射 产生和光电阴极，保持切伦科夫光子的即时定时性质。然后我们将联合收割机 集成的切伦科夫辐射探测器与辅助光电探测器读出稳健的符合检测， 并与我们率先使用卷积神经网络的先进信号处理算法进行补充， 网络从数字化的检测器波形中提取所有可能的定时信息，并最终执行 仅使用数字化波形作为输入的无重建成像。总之，我们的目的是证明，直接 PEI是可能的，以表征其属性，并提供技术和算法基础， 最终转化为人体成像。

Project Summary/Abstract A major advantage of coincidence detection of annihilation photons from positron-emitting radiotracers is the availability of time-of-flight (TOF) information, and the ability to measure TOF differences to better localize the positron emitter. Normally for positron emission tomography (PET), TOF information is used as a weighting kernel during image reconstruction and results in an effective sensitivity gain that can be used to reduce radiation dose, improve signal-to-noise ratio, or reduce scan duration. The magnitude of these benefits depend on the TOF resolution, which is governed by the timing performance of the detectors. Current state of the art for PET scanners is ~220 ps which corresponds to a localization of ~3.3 cm. A transformational change would occur, however, if a TOF resolution of <30 ps could be achieved. This would localize events within 4.5 mm, allowing images to be directly generated without a reconstruction algorithm at a spatial resolution that matches what is achieved in clinical PET scanners today. We refer to this as direct positron emission imaging (PEI). With this superb TOF resolution and reconstruction-free imaging, we enter a new regime where we expect major increases in image signal-to-noise, both due to the additional TOF information, and the removal of noise amplification inherent in reconstructing noisy data with noisy corrections from projection data. We propose to develop a first proof-of-concept imaging system that uses ultra-fast detectors to directly produces cross-sectional images without reconstruction and to quantify the performance of PEI both through simulations and experimentally. Since direct PEI does not have the same sampling constraints for data collection as PET, it creates opportunities for portable, and flexible imaging devices, with implications for patient-tailored or task-specific imaging applications (i.e. cardiac or breast imaging), as well as open designs for general purpose applications. To achieve the unprecedented TOF capabilities needed for direct PEI, we will exploit promptly emitted Cerenkov radiation that is generated with <10 ps in certain materials, including scintillators, in response to a 511 keV photon interaction. Our proposed novel detector design integrates a Cerenkov radiator directly into the entrance window of an ultra-fast microchannel plate photomultiplier tube, which is the fastest photon detector currently available with a response time of 25 ps. This approach eliminates all optical reflections between the point of light generation and the photocathode, preserving the prompt timing nature of Cerenkov photons. We then combine the integrated Cerenkov radiator detector with auxiliary photodetector read-out for robust coincidence detection, and complement this with advanced signal processing algorithms we have pioneered using convolutional neural networks to extract all possible timing information from the digitized detector waveforms and ultimately to perform reconstruction-free imaging using only the digitized waveforms as input. In summary, we aim to prove that direct PEI is possible, to characterize its properties and to provide the technological and algorithmic foundations for eventual translation for human imaging.