Reconstruction-free three dimensional positron emission imaging

项目摘要/摘要 符合探测发射正电子的放射性示踪剂中的湮没光子的一个主要优点是 飞行时间(TOF)信息的可用性，以及测量TOF差异以更好地定位 正电子发射器。对于正电子发射断层扫描(PET)，通常使用TOF信息作为权重 并产生可用于减少辐射的有效灵敏度增益 剂量、提高信噪比或缩短扫描持续时间。这些好处的大小取决于 TOF分辨率，由探测器的定时性能决定。聚酯的最新进展 扫描仪为~220ps，相当于定位~3.3 cm。一场变革性的变化将会发生， 然而，如果飞行时间分辨率达到&lt；30ps。这将把事件定位在4.5毫米以内，从而 以匹配的空间分辨率直接生成图像，而无需重建算法 今天在临床PET扫描仪中实现了这一点。我们称之为直接正电子发射成像(PEI)。有了这个 卓越的飞行时间分辨率和无重建成像，我们进入了一个新的领域，我们预计会有重大的增长 在图像信噪比中，既有TOF信息的附加，又有噪声放大的消除 用来自投影数据的噪声校正重建噪声数据所固有的。我们建议开发第一个 概念验证成像系统，使用超高速探测器直接生成横断面图像 无需重建，并通过模拟和实验来量化PEI的性能。 由于直接PEI对数据收集没有与PET相同的采样限制，因此它创造了机会 适用于便携、灵活的成像设备，适用于患者定制或特定于任务的成像 应用(如心脏或乳房成像)，以及用于一般用途的开放式设计。 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Cerenkov 在511keV的能量下，某些材料(包括闪烁体)中用~lt；10ps产生的辐射 光子相互作用。我们建议的新型探测器设计将切伦科夫辐射器直接集成到入口处 超快微通道板式光电倍增管的窗口，这是目前最快的光子探测器 可提供25 ps的响应时间。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计时特性。然后我们结合在一起 集成切伦科夫辐射体探测器，具有用于稳健符合检测的辅助光电探测器读出， 并用我们首创的使用卷积神经的高级信号处理算法来补充这一点 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，我们的目标是证明这一点 PEI是可能的，以表征其属性并为以下各项提供技术和算法基础 最终翻译成人类图像。

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.