PET的多通道Si制光电倍增管_1270954杨英健

1、基于多通道Si制光电倍增管前端模拟电路的PET数据采集Base on A Front-end Analog Circuit for Multi-channel SiPM Readout of PET 杨英健 1270954质量湮没现象电子对湮没电子对湮没缺中子核素缺中子核素衰变产生衰变产生e+介质中介质中e-光子光子, 511KeV光子光子, 511KeV keV:1000电子伏特，是为使电子加速通过1000V电压差所需要的能量。正电子核素标记的放射性药物常用的正电子核素常用的正电子核素11C、13N、15O、18F电子回旋加速器产生电子回旋加速器产生短半衰期短半衰期正电子核素标记的放射性药物

2、正电子核素标记的放射性药物肿瘤代谢示踪剂：葡萄糖及氨基酸类似物肿瘤代谢示踪剂：葡萄糖及氨基酸类似物血流灌注显像剂血流灌注显像剂肿瘤特异性显像剂：单抗及受体显像肿瘤特异性显像剂：单抗及受体显像其他：核酸显像、缺氧显像其他：核酸显像、缺氧显像 放射性核素衰变，质子转变为中子发射正电子，正电子很快与周围 的电子相结合，发生湮没现象。符合检测电路 利用两个射线光子向相反方向传播的这一特性，通过“符合检测”技术来实现投影数据的采集，并由此实现断层成像。重建算法，形成某个断面上放射性同位素的分布图。符合检测电路原理框图检测器滤波滤除高频噪音脉冲高度分析投影数据成像装置数据采集A、B、C、D四个光电倍增管的

3、输出决定光子的入射点，也决定接下来要进行的脉冲高度分析。A、B、C、D四个光电倍增管的输出分别是IA 、 IB、 IC、 ID。BDAC0ABCD0(I +I )-(I +I )x =(I +I )-(I +I )y =ABCDABCDIIIIIIII+脉冲高度分析 脉冲过高可能是由于多个射线光子同时到达。 脉冲过低可能是由于入射光子同时到达检测器前经过了散射。 PET系统中，有效的入射光子的能量是511keV为中心，大致在350650keV的范围内。数据存储 湮没事件发生的位置、响应线的位置都具有不确定性。 PET系统中数据的存储只能一个一个事件进行。检测器发生符合事件的位置湮没时间发生的位

4、置我们知道的只是符合检测器的位置，并由此判断出在这两个检测器连线的位置上发生了湮没时间，不能判断湮没事件发生的准确位置。采样数据的正弦图的表示方法 有关在特定响应曲线 上发生的湮没事件可以在正弦图上记录下来。 只要把每次发生的湮没事件都以累加的方式在正弦图上记录下来，待数据相对完整后，就可以现实断层图像的重建。( , )Rq衰减校正 在图像重建之前要对数据进行衰减校正 衰减校正是为了准确地确定放射性核素在人体内的密度分布。人体组织的传播距离PET衰减校正示意图1和2为传播路径上人体组织的平均衰减系数。 在上图中，射线在人体组织中衰减分别为 。1 12 2xxeemm-、 湮没时间发生后相对的两

5、个光子到达检测器B和C 在等效图中，射线在人体组织中衰减等效为 。1 12 2xxemm- 为了准确进行衰减校正，可用体外辐射源绕人体旋转一周，用透射的方法测出响应路径上的衰减，然后在图像重建之前对数据进行衰减校正。Photomultiplier: transfers light to elektrical signal (photoemissive sensor) Silicon photomultipliers (SiPM) is regarded as a promising device in many photon counting applications including hi

6、gh-energy physics, astroparticle physics, and medical imaging. SiPMs are suitable for signal readout schemes using block detectors in PET. To construct block detectors, a number of single-channel SiPMs were arranged in a rectangular array with relatively large dead space. Special frames or materials

7、 required for fixing them are troublesome in the construction of arrays and extension of the detection area. On the contrary, the recent development of tileable multi-channel SiPMs enables the easy construction of block detectors. Moreover, the multi-channel SiPMs have a relatively small dead space

8、between each channel. We employed these multi-channel SiPMs for the development of MR-compatible PET block detectors with and without the use of short optical fibers between scintillation crystals and SiPMs. We applied the same front-end readout modules for multi-channel SiPMs although the numbers o

9、f SiPM channels were different in each detector configuration. we therefore present the detailed design scheme of this front- end readout module based on the charge division network that was employed for the easy extension of the module to a wider detection area. The detector configuration and physi

10、cal performance of various detectors developed for small animal PET/MR , optical fiber PET/MR , and double layer depth of interaction (DOI) PET using this front-end readout module will be presented. In this situation, a very sophisticated and complicated system is necessary to process this large num

11、ber of signals individually. Furthermore, the large number of signal lines has some potential risk in simultaneous PET/MR applications because it would require very careful shielding for the large number of signal cables to reduce RF interference between PET and MRI.Electronics for signal multiplexi

12、ng and data acquisition We designed theSiPM front-end readout module with which the four tileable 4X4 channel SiPMs can be combined(Fig.1). This means that the detector module needs at least 64 signal lines for a single signal readout scheme or 128 signal lines for a differential signal readout sche

13、me if no signal multiplexing is involved. In this situation, a very sophisticated and complicated system (i.e. ASIC) is necessary to process this large number of signals individually. Furthermore, the large number of signal lines has some potential risk in simultaneous PET/MR applications because it

14、 would require very careful shielding for the large number of signal cables to reduce RF interference between PET and MRI.Photomultiplier: transfers light to elektrical signal (photoemissive sensor)Fig. 1. Schematic of the front-end analog circuit for the SiPM readout module.(a)SiPM biasing circuit.

15、(b )Resistive charge division network (RCN). (c)Differential amplifier circuit. 成像装置Data Acquisition A、B、C、D四个光电倍增管的输出(four position encoding signals)决定光子的入射点，也决定接下来要进行的脉冲高度分析。 A、B、C、D四个光电倍增管的输出分别是IA 、 IB、 IC、 ID。BDAC0ABCD0(I +I )-(I +I )x =(I +I )-(I +I )y =ABCDABCDIIIIIIII+ To verify whether this

16、front-end readout module was suitable for SiPMs, electric circuit simulation was performed. We multiplexed the signals from the 64SiPM channels to four position encoding signals(A, B, C, and D) using a resistive charge divisio nnetwork (RCN) (Fig. 1(b). This front-end readout module based on RCN mak

17、es the PET block detector easily extendable. Fig. 2(a) shows the output pulses measured at positions AD when only the SiPM cell nearest to A was fired.The SiPM cell positions were successfully separated using these four multiplexed position signals as illustrated in Fig. 2(b). Fig. 2. Electrical sti

18、mulation results of the SiPM block detector. (a) Output pulses measured at positions AD when only the SiPM cell nearest to A was fired. (b) Position map of 64 channels obtained using the decoding scheme shown in Eqs. (1)and(2). This simulation was only for SiPM cells and analog front-end circuits without consideration of scintillation,light loss and other effects because the linearity of X a