基于飞行时间技术的PET发展历史与现状

简要介绍了基于飞行时间（Time of Flight, 简称TOF）技术的正电子发射断层扫描成像（Positron Emission Tomography, 简称PET）的基本原理, 回顾了TOF-PET成像设备的发展历史, 讨论了影响TOF PET时间分辨率的主要因素, 并对TOF-PET给图像重建技术带来的挑战进行了分析。 最后, 重点介绍了TOF-PET技术所带来的优势, 使用TOF技术可以有效地改善图像质量, 并且为临床诊断和临床前研究带来便利。 The principle of time of flight (TOF) positron emission tomography (PET) and a brief review of the history of TOF-PET are introduced. The factors influencing the time resolution of a TOF-PET scanner are presented, especially focus on the intrinsic properties of scintillators and front end electronics. Challenges and achievements of the structure of data organization and image reconstruction are reviewed. Finally, the benefits of TOF-PET on image quality improvement and tumor detection are emphasized.     

高效液相色谱法同时测定参茸补酒中芍药苷、阿魏酸的含量

建立一种高效液相色谱双波长法同时测定参茸补酒中芍药苷、阿魏酸的含量。该方法采用Symmetry C18色谱柱(150×3.9mm,5μm),流动相为乙腈 水 冰乙酸(12∶88∶1,V/V),检测波长分别为323nm(通道1)、230nm(通道2)。结果显示:芍药苷、阿魏酸分别在21.4～214.0和1.65～16.50μg·mL-1范围内本法有良好的线性关系;平均回收率分别为98.1%(RSD=1.28%)和97.5%(RSD=1.73%)。本法操作简便,快速,重现性好,结果准确,可作为参茸补酒的质量控制方法。     

影响LYSO∶Ce晶体余辉强度的几个主要因素

探究了LYSO∶Ce晶体的余辉现象,以及在不同曝光时间、光照强度下,余辉计数率随时间的变化规律。同时探究了温度对晶体余辉强度的影响,发现加热晶体可以快速缩短余辉持续时间,这一发现为日常的晶体检测和应用带来一定便利。     

Performance evaluation of a parallel-hole collimated detector module for animal SPECT imaging

We have built and investigated a detector module for animal SPECT imaging, especially for use in large field of view (FOV) conditions. The module consists of a PMT-based detector and a parallel-hole collimator with an effective area of 80 mm × 80 mm. The detector is composed of a NaI scintillation crystal array coupled to four H8500 position sensitive photomultiplier tubes (PS-PMT). The intrinsic energy resolution of the detector is 11.5% at 140 keV on average. The planar spatial resolution of the module changes from 2.2 mm to 5.1 mm at different source-to-collimator distances with an unchanged sensitivity of about 34cps/MBq. Additionally, the SPECT Micro Deluxe Phantom imaging was performed with a radius of rotation (ROR) of 40 mm. Using the FBP reconstruction algorithm, a high performance image was obtained, indicating the feasibility of this detector module.     

A compact positron annihilation lifetime spectrometer

Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size γ-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the coincidence counting rate ～8 cps/μCi were achieved. A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested, which is in agreement with the typical values published in the previous lectures.     

Using a LaBr3:Ce scintillator for positron annihilation lifetime spectroscopy

A LaBr₃:Ce scintillator has a high light output (~60000 p.e/MeV) and a short decay constant (<25 ns), which makes it good for time spectrometry. Compared with a BaF₂ scintillator, it can bear a much higher count rate, and can be coupled to photomultipliers without using a quartz window. In this work, a positron annihilation lifetime spectrometer (PALS) consisting of two bulks of φ25 mm×25 mm LaBr₃:Ce scintillator coupled to two XP20D0 photomultipliers, respectively, was built. A time resolution of FWHM=206 ps was measured for the PALS with a ⁶⁰Co source at the energy window for ²²Na. With this spectrometer, a reasonable lifetime value τ=221±4 ps in a pure Si sample is obtained, which means that the utilization of LaBr₃:Ce as the detector for a PALS is feasible.     

Positronium annihilation in silica aerogel studied by a positron age-momentum correlation technique

A high-performance positron age-momentum correlation (AMOC) spectrometer was newly developed. The counting rate is increased up to 200 cps much larger than the value 20~cps reported by other international groups. And at the same time, the time resolution still keeps at the international level of 220 ps. Furthermore, positronium (Ps) annihilation in silica aerogel was investigated by AMOC, which indicates: (1) Ps annihilation between the grains dominantly undergoes pick-off process and spin conversion from o-Ps to p-Ps; (2) Annealing below 400 ℃ changes the grain surface conditions, i. e. the desorption of hydrogen and the decrease of the defect centers concentration.     

脉冲慢正电子束流的直流化装置

在基于加速器的北京慢正电子强束流装置上, 用Penning-Trap技术实现了脉冲慢正电子束流的存储和直流化. 实验表明, 系统的真空度对正电子的存储效率有严重影响, 脉冲正电子的释放方式决定了直流化后束流的能量分散; 改变释放级信号波形以及释放方式可以得到能量分散小于1eV的准直流化慢正电子束流.     

Preliminary study of depth of interaction measurement for a PET detector

In this work we studied the feasibility of detecting the depth of interaction (DOI) with two layers of crystal arrays of LYSO and BGO scintillators coupled to a position-sensitive photomultiplier tube (PS-PMT) R8900-C12. A front-end electronics was designed, with which we got different pulse shapes for different crystals to obtain depth information. With the double integration method, we got the DOI histogram of a divided integration ratio of two crystals as the standard to determine the layer-of-interaction. The DOI accuracy, measured by scanning a ²²Na slit source along the side of the module, was 98% for the LYSO layer and 95% for the BGO layer. The energy resolution at 511keV was 13.1% for LYSO and 17.1% for BGO. We obtained good crystal separation in 2D position histograms of both layers. These results could be useful in the manufacture of PET scanners with high spatial resolutions.     

正电子湮没多普勒谱中的3γ/2γ分析

在慢正电子束研究表面的实验中,一般仍使用高纯Ge γ谱仪测量正电子湮没多普勒展宽能谱,对能谱的分析采用线形参数S,W,这些参数提供的信息有限. 例如,当电子与正电子在材料中形成电子偶素时,简单的线形参数非但不能表征它们,反而因它们的存在使得分析变得复杂. 本工作在对多普勒展宽能谱进行数据处理的过程中,引入正态电子偶素自衰变强度I_3γ参数,建立了从能谱中获得I_3γ参数值的方法. 以标准样品为基准,选用Ag盖帽的气凝硅胶进行I_3γ参数计算,工作表明新参数对研究介孔材料及纳米薄膜能提供更丰富的信息.