PET的多通道Si制光電倍增管_1270954楊英健

1、基于多通道Si制光電倍增管前端模擬電路的PET數(shù)據(jù)采集Base on A Front-end Analog Circuit for Multi-channel SiPM Readout of PET 楊英健 1270954質量湮沒現(xiàn)象電子對湮沒電子對湮沒缺中子核素缺中子核素衰變產(chǎn)生衰變產(chǎn)生e+介質中介質中e-光子光子, 511KeV光子光子, 511KeV keV:1000電子伏特，是為使電子加速通過1000V電壓差所需要的能量。正電子核素標記的放射性藥物常用的正電子核素常用的正電子核素11C、13N、15O、18F電子回旋加速器產(chǎn)生電子回旋加速器產(chǎn)生短半衰期短半衰期正電子核素標記的放射性藥物

2、正電子核素標記的放射性藥物腫瘤代謝示蹤劑：葡萄糖及氨基酸類似物腫瘤代謝示蹤劑：葡萄糖及氨基酸類似物血流灌注顯像劑血流灌注顯像劑腫瘤特異性顯像劑：單抗及受體顯像腫瘤特異性顯像劑：單抗及受體顯像其他：核酸顯像、缺氧顯像其他：核酸顯像、缺氧顯像 放射性核素衰變，質子轉變?yōu)橹凶影l(fā)射正電子，正電子很快與周圍 的電子相結合，發(fā)生湮沒現(xiàn)象。符合檢測電路 利用兩個射線光子向相反方向傳播的這一特性，通過“符合檢測”技術來實現(xiàn)投影數(shù)據(jù)的采集，并由此實現(xiàn)斷層成像。重建算法，形成某個斷面上放射性同位素的分布圖。符合檢測電路原理框圖檢測器濾波濾除高頻噪音脈沖高度分析投影數(shù)據(jù)成像裝置數(shù)據(jù)采集A、B、C、D四個光電倍增管的

3、輸出決定光子的入射點，也決定接下來要進行的脈沖高度分析。A、B、C、D四個光電倍增管的輸出分別是IA 、 IB、 IC、 ID。BDAC0ABCD0(I +I )-(I +I )x =(I +I )-(I +I )y =ABCDABCDIIIIIIII+脈沖高度分析 脈沖過高可能是由于多個射線光子同時到達。 脈沖過低可能是由于入射光子同時到達檢測器前經(jīng)過了散射。 PET系統(tǒng)中，有效的入射光子的能量是511keV為中心，大致在350650keV的范圍內。數(shù)據(jù)存儲 湮沒事件發(fā)生的位置、響應線的位置都具有不確定性。 PET系統(tǒng)中數(shù)據(jù)的存儲只能一個一個事件進行。檢測器發(fā)生符合事件的位置湮沒時間發(fā)生的位

4、置我們知道的只是符合檢測器的位置，并由此判斷出在這兩個檢測器連線的位置上發(fā)生了湮沒時間，不能判斷湮沒事件發(fā)生的準確位置。采樣數(shù)據(jù)的正弦圖的表示方法 有關在特定響應曲線 上發(fā)生的湮沒事件可以在正弦圖上記錄下來。 只要把每次發(fā)生的湮沒事件都以累加的方式在正弦圖上記錄下來，待數(shù)據(jù)相對完整后，就可以現(xiàn)實斷層圖像的重建。( , )Rq衰減校正 在圖像重建之前要對數(shù)據(jù)進行衰減校正 衰減校正是為了準確地確定放射性核素在人體內的密度分布。人體組織的傳播距離PET衰減校正示意圖1和2為傳播路徑上人體組織的平均衰減系數(shù)。 在上圖中，射線在人體組織中衰減分別為 。1 12 2xxeemm-、 湮沒時間發(fā)生后相對的兩

5、個光子到達檢測器B和C 在等效圖中，射線在人體組織中衰減等效為 。1 12 2xxemm- 為了準確進行衰減校正，可用體外輻射源繞人體旋轉一周，用透射的方法測出響應路徑上的衰減，然后在圖像重建之前對數(shù)據(jù)進行衰減校正。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. 成像裝置Data Acquisition A、B、C、D四個光電倍增管的輸出(four position encoding signals)決定光子的入射點，也決定接下來要進行的脈沖高度分析。 A、B、C、D四個光電倍增管的輸出分別是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