A Novel Time-Based Readout Scheme for a Combined PET-CT Detector Using APDs
A Novel Time-Based Readout Scheme for a Combined PET-CT Detector Using APDs
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DOI：
10.1109/tns.2008.2004036
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发表时间：
2008-10-01
影响因子：
1.8
通讯作者：
Moraes, D.
中科院分区：
文献类型：
--
作者：
Powolny, F.;Auffray, E.;Moraes, D.
本文总结了欧洲核子研究中心在欧盟委员会的FP6生物护理项目框架内所做的研发工作。其目的是开发一种新的基于时间的信号处理技术来读出用于医学成像的LSO-APD光探测器。一个重要的方面是在计算机断层扫描(CT)和正电子发射断层扫描(PET)的组合场景中使用该技术，与传统的单模机器相比，在效率和分辨率方面实际上没有任何妥协。这使得使用低噪声但非常高速的单片前端电子设备是必不可少的，以便确保所需的定时特性以及高信噪比。使用APD进行光子探测，可以识别出两个传统上用于粒子物理的芯片，以满足上述标准。虽然这两种传感器都没有针对其预期的新医疗应用进行优化，但与LSO-APD传感器一起使用时可以获得优异的性能。虽然在511keV光电峰值处测量到的16%的能量分辨率(FWHM)与经典的PMTS相比具有很好的竞争优势，但使用双雪崩光电二极管读出的1.6 ns半高宽的符合时间分辨率通常较低。这归因于LSO中的随机光子产生机制和光电二极管的光子转换特性，以及光子转换过程中的涨落，尽管雪崩光电二极管具有优越的量子效率。此外，在CT计数速度方面，所选择的读出原理受到每条入射X射线在LSO(40 Ns)内的本征光衰减的限制。
This paper summarizes CERN R&D work done in the framework of the European Commission's FP6 BioCare Project. The objective was to develop a novel "time-based" signal processing technique to read out LSO-APD photodetectors for medical imaging. An important aspect was to employ the technique in a combined scenario for both Computer Tomography (CT) and Positron Emission Tomography (PET) with effectively no tradeoffs in efficiency and-resolution compared to traditional single mode machines. This made the use of low noise and yet very high-speed monolithic front-end electronics essential so as to assure the required timing characteristics together with a high signal-to-noise ratio. Using APDs for photon detection, two chips, traditionally employed for particle physics, could be identified to meet the above criteria. Although both were not optimized for their intended new medical application, excellent performance in conjunction with LSO-APD sensors could be derived. Whereas a measured energy resolution of 16% (FWHM) at the 511 keV photo peak competes favorably with that of 'classical' PMTS, the coincidence time resolution of 1.6 ns FWHM with dual APD readout is typically lower. This is attributed to the stochastic photon production mechanism in LSO and the photon conversion characteristic of the photo diode, its well as to the fluctuations in photon conversion, albeit the APD's superior quantum efficiency. Also in terms of CT counting speed, the chosen readout principle is limited by the intrinsic light decay in LSO (40 ns) for each impinging X-ray.