PET成像前端读出芯片研究进展
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摘要
在过去的半个多世纪里,虽然正电子发射断层(PET)成像设备在外型上没有多大变化,但在技术和方法上发生了多次革命性的飞跃。微电子技术在PET成像领域的应用将进一步推动PET向更小体积、更高性能、更低成本等方向发展。从PET系统成像原理出发,详细综述了PET前端读出芯片技术的研究进展。将PET探测器信号的前端读出和信号处理分为光电转换、信号采集、脉冲高度分析、峰值探测和保持、信号数字化和数字信号处理等环节,给出了各个环节的微电子电路实现。然后,描述了PET前端读出大规模专用集成电路的研发进展,指出采用数字电路的方法来处理探测器前端读出和模拟信号处理已经成为PET前端电子的发展趋势,而且集成PET专用DSP的多通道智能前端读出电路已经成为一个重要的方向。
In the last half century,the revolution of techniques and methods for positron emission tomography(PET) imaging has been greatly promoted though the PET instruments still remains as the similar profiles as before.Microelectronics techniques will lead several new features such as smaller volume,higher performances and lower cost for PET imaging instruments.Based on the analysis of the imaging principles of the PET systems,the progresses on front-end microelectronics for PET imaging applications are surveyed in detail in the paper.The processes of front-end readout and signal processing for PET detectors are divided into several steps such as optic-electric conversion,signal acquisition,pulse height analysis,peak-detect-and-hold,signal digitizing and digital signal processing.The techniques of front-end microelectronics for each step are presented.In addition,the research progresses on large-scale application-specific integrated circuits(ASIC) for PET imaging are concluded.It is concluded that the method of front-end readout and signal processing implemented by large-scale digital circuits is the trend of the future PET front-end electronics.Moreover,the development of multi-channel monolithic front-end ASIC is an important direction for PET imaging applications.
In the last half century,the revolution of techniques and methods for positron emission tomography(PET) imaging has been greatly promoted though the PET instruments still remains as the similar profiles as before.Microelectronics techniques will lead several new features such as smaller volume,higher performances and lower cost for PET imaging instruments.Based on the analysis of the imaging principles of the PET systems,the progresses on front-end microelectronics for PET imaging applications are surveyed in detail in the paper.The processes of front-end readout and signal processing for PET detectors are divided into several steps such as optic-electric conversion,signal acquisition,pulse height analysis,peak-detect-and-hold,signal digitizing and digital signal processing.The techniques of front-end microelectronics for each step are presented.In addition,the research progresses on large-scale application-specific integrated circuits(ASIC) for PET imaging are concluded.It is concluded that the method of front-end readout and signal processing implemented by large-scale digital circuits is the trend of the future PET front-end electronics.Moreover,the development of multi-channel monolithic front-end ASIC is an important direction for PET imaging applications.
引文
[1]高武.正电子发射断层成像前端读出芯片设计技术研究[D].西北工业大学,2011.
[2]Melcher C L.Scintillation crystals for PET[J].Jour-nal of Nuclear Medicine,2000,41(6):1051-1055.
[3]Spieler H.Semiconductor Detector Systems[M].Ox-ford Univ Press,2005:43-102.
[4]Koli K.CMOS current amplifier:Speed versus non-linearity[D].Helsinki University of Technology,2000.
[5]Chang Z Y,Sansen W M C.Low-noise Wide-bandAmplifier in Bipolar and CMOS Technologies[M].Dordrecht:Kluwer Press,1991:20-100.
[6]Sansen W,Chang Z Y.Limits of low noise perfor-mance of detector readout front ends in CMOS tech-nology[J].IEEE Transactions on Circuits and Sys-tems,1990,37(11):1375-1381.
[7]Gramegna G,Connor P O,Rehak P,et al.CMOSpreamplifier for low capacitance detectors[J].NuclearInstruments and Methods in Physics Research SectionA:Accelerators,Spectrometers,Detectors and Asso-ciated Equipment,1997,390:241-245.
[8]Oo K T Z,Mandelli E,Moses W W,et al.A high-speed low-noise 16-channel CSA with automatic leak-age compensation in 0.35-μm CMOS process for APD-based PET detectors[J].IEEE Transactions on Nu-clear Science,2007,54(3):444-453.
[9]Razavi B,Wooley B A.Design techniques for high-speed,high-resolution comparators[J].IEEE Journalof Solid-state Circuits,1992,27(12):1916-1926.
[10]Degerli Y,Fourches N,Rouger M,et al.Low-powerautozeroed high-speed comparator for the readoutchain of a CMOS monolithic active pixel sensor basedvertex detector[J].IEEE Transactions on NuclearScience,2003,50(5):1709-1717.
[11]Delagnes E,Breton D,Lugiez F,et al.A low powermulti-channel single ramp ADC with up to 3.2 GHzvirtual clock[J].IEEE Transactions on Nuclear Sci-ence,2007,54(5):1735-1742.
[12]Banks D,Toumazou C.Low-power high-speed cur-rent comparator design[J].Electronics Letters,2008,44(3):171-172.
[13]Ollivier-Henry N,Berst J D,Colledani C,et al.Afront-end readout mixed chip for high-efficiency smallanimal PET imaging[J].Nuclear Instruments andMethods in Physics Research Section A:Accelera-tors,Spectrometers,Detectors and Associated Equip-ment,2007,571(1-2):312-316.
[14]Geronimo G D,Connor P O,Kandasamy A.AnalogCMOS peak detect and hold circuits:Parts I.analysisof the classical configuation[J].IEEE Transactionson Nuclear Science,2002,484:533-543.
[15]Vert P E,Lecoq J,Montarou G,et al.InnovativeElectronics Architecture for PET Imaging[C].Nucle-ar Science Symposium Conference Record,2006:3057-3059.
[16]Le B,Rondeau T W,Reed J H,et al.Analog-to-digi-tal converters[J].IEEE Signal Processing Magazine,2005,11:69-77.
[17]Tanaka M,Ikeda H,Ikeda M,et al.Development ofmonolithic time-to-amplitude converter for high preci-sion TOF measurement[J].IEEE Transactions onNuclear Science,1991,38(2):301-305.
[18]Bogdan M,Frisch H,Heintz M,et al.A 96-channelFPGA-based time-to-digital converter(TDC)and fasttrigger processor module with multi-hit capability andpipeline[J].Nuclear Instruments and Methods inPhysics Research Section A:Accelerators,Spectrom-eters,Detectors and Associated Equipment,2005,554:444-457.
[19]Mota M,Christiansen J.A four-channel self-calibrat-ing high-resolution time to digital converter,in elec-tronics[C].Proceedings of IEEE International Con-ference on Circuits and Systems,1998,1:409-412.
[20]Poki C,Liu S I,Wu J.Highly accurate cyclic CMOStime-to-digital converter with extremely low powerconsumption[J].Electronics Letters,1997,33(10):858-860.
[21]Straayer M Z,Perrott M H.A multi-path gated ringoscillator TDC with first-order noise shaping[J].IEEE Journal of Solid-state Circuits,2009,44(4):1089-1098.
[22]Minjae L,Abidi A A.A 9 b,1.25 ps resolutioncoarse-fine time-to-digital converter in 90 nm CMOSthat amplifies a time residue[J].IEEE Journal of Sol-id-state Circuits,2008,43(4):769-777.
[23]Jones W F,Byars L G,Casey M E,et al.Positron e-mission tomographic images and expectation maxi-mization:a VLSI architecture for multiple iterationsper second[J].IEEE Transactions on Nuclear Sci-ence,1988,35(1):620-624.
[24]Newport D F,Young J W.An ASIC implementationof digital front-end electronics for a high resolutionPET scanner[J].IEEE Transactions on Nuclear Sci-ence,1993,40:1017-1019.
[25]Wai-Hoi W,Hu G,Zhang N,et al.Front end elec-tronics for a variable field PET camera using thePMT-quadrant-sharing detector array design[J].IEEE Transactions on Nuclear Science,1997,44(4):1291-1296.
[26]Swann B K,Rochelle J M,Binkley D M,et al.Acustom mixed signal CMOS integrated circuit for highperformance PET tomograph front-end applications[C].IEEE Nuclear Science Symposium ConferenceRecord,2002,1:24-28.
[27]Musrock M S,Young J W,Moyers J C,et al.Per-formance characteristics of a new generation of pro-cessing circuits for PET applications[J].IEEE Trans-actions on Nuclear Science,2003,50(4):974-978.
[28]Saoudi A,Lecomte R.A novel APD-based detectormodule for multi-modality PET/SPECT/CT scanners[J].IEEE Transactions on Nuclear Science,1999,46(3):479-484.
[29]Woodring M L,Christian J F,Shah K S,et al.De-velopment of an ASIC for APD-based small animalPET[C].IEEE Nuclear Science Symposium Confer-ence Record,2001,2:737-741.
[30]Deng Z,Yeom J Y,Ishitsu T,et al.Design of newfront-end electronics for animal PET[C].IEEE Nu-clear Science Symposium Conference Record,2002,3:1543-1546.
[31]Lewellen T K,Laymon C M,Miyaoka R S,et al.Development of a data acquisition system for theMiCES small animal PET scanner[C].IEEE NuclearScience Symposium Conference Record,2002,2:1066-1070.
[32]Habte F,Levin C S.Study of low noise multichannelreadout electronics for high sensitivity PET systemsbased on avalanche photodiode arrays[J].IEEETransactions on Nuclear Science,2004,51(3):764-769.
[33]Pratte J F,De Geronimo G,Junnarkar S,et al.Front-end electronics for the RatCAP mobile animalPET scanner[J].IEEE Transactions on Nuclear Sci-ence,2004,51(4):1318-1323.
[34]Shah K S,Grazioso R,Farrell R,et al.Position sen-sitive APDs for small Animal PET imaging[J].IEEETransactions on Nuclear Science,2004,51(1):91-95.
[35]Pratte J F,Robert S,De Geronimo G,et al.Designand performance of 0.18μm CMOS charge preampli-fiers for APD-based PET scanners[J].IEEE Transac-tions on Nuclear Science,2004,51(5):1979-1985.
[36]Moses W W.Recent advances and future advances intime-of-flight PET[J].Nuclear Instruments andMethods in Physics Research Section A:Accelera-tors,Spectrometers,Detectors and Associated Equip-ment,2007,580(2):919-924.
[37]Conti M.State of the art and challenges of time-of-ight PET[J].Physica Medica,2009,25(1):1-11.
[38]Fischer P,Peric I,Ritzert M,et al.Multi-channelreadout ASIC for ToF-PET[C].IEEE Nuclear Sci-ence Symposium Conference Record,2006:2523-2527.
[39]Pedrali-Noy M,Gruber G,Krieger B,et al.PET-RIC-a positron emission tomography readout integrat-ed circuit[J].IEEE Transactions on Nuclear Science,2001,48(3):479-484.
[40]Pratte J F,Pepin C M,Rouleau D,et al.Design of afast shaping amplifier for PET/CT APD detectorswith depth-of-interaction[C].IEEE Nuclear ScienceSymposium Conference Record,2001,2:807-811.
[41]刘力.正电子断层扫描仪与PET图像重建概述[J].CT理论与应用研究,2003,12(1):47-50.
[42]东软集团.东软PET研制成功并获得美国FDA.http:∥www.neusoft.com/news/html∥20090526/2174061627.html,2009.
[43]中国教育网.华中科技大学成功研制首台全数字化平板PET.http:∥www.edu.cn/cheng-guo-zhan-shi-1085/20101221/t20101221-556657.shtml,2010.
[44]王永纲.基于A PD阵列的PET探测器模块电子学[J].核电子学与探测技术,2002,22(5):399-400.
[45]Jian S,An Q,Liu S.A high-resolution time-to-digi-tal converter implemented in field-programmable-gate-arrays[J].IEEE Transactions on Nuclear Science,2006,53(1):236-241.
[46]Kang X,Wang S,Liu Y,et al.A simple smart time-to-digital convertor based on vernier method for a highresolution LYSO microPET[C].IEEE Nuclear Sci-ence Symposium Conference Record,2007:2892-2896.
[47]Gao W,Fang X,Hu-Guo C,et al.A low-noise front-end readout chip integrated with a high-resolutionTDC for APD-based small-animal PET[C].Proceed-ings of First International Conference on Advance-ments in Nuclear Instrumentation Measurement Meth-ods and their Applications,2009:1-6.
[48]Gao W,Hu-Guo C,Wei T,et al.A 12-bit 2.5 MS/smulti-channel ramp analog-to-digital Converter forimaging detectors[C].IEEE International Workshopon in Imaging Systems and Techniques,2009:183-186.
[49]Gao W,Gao D,Wei T,et al.A high-resolution mul-ti-channel time-to-digital converter(TDC)for high-energy physics and biomedical imaging applications[C].4th IEEE Conference on Industrial Electronicsand Applications,2009:1133-1138.
[50]Tai Y C,Chatziioannou A F,Silverman R W,et al.MicroPET II:an ultra-high resolution small animalPET system[C].IEEE Nuclear Science SymposiumConference Record,2002,3:1848-1852.
[51]Martinez J D,Benlloch J W,Cerda J,et al.High-speed data acquisition and digital signal processingsystem for PET imaging techniques applied to mam-mography[J].IEEE Transactions on Nuclear Science,2004,51(3):407-412.
[52]Guerra P,Espinosa J,Ortun~o J E,et al.New em-bedded digital front-end for high resolution PET scan-ner[J].IEEE Transactions on Nuclear Science,2006,53(3):770-775.
[53]Junnarkar S S,Fried J,Southekal S,et al.New timeto digital converter,signal processing,data acquisi-tion,calibration and test hardware for RatCAP[C].IEEE Nuclear Science Symposium Conference Record,2007:4597-4601.
[54]Nadeski M,Gatherer A.DSPs in medical imaging.http:∥focus.ti.com/general/docs/gencontent.tsp?contentId=51435,White paper,Texas Instruments,2008.
[55]Xie Q,Kao C M,Hsiau Z,et al.A new approach forpulse processing in positron emission tomography[J].IEEE Transactions on Nuclear Science,2005,52(4):988-995.
[2]Melcher C L.Scintillation crystals for PET[J].Jour-nal of Nuclear Medicine,2000,41(6):1051-1055.
[3]Spieler H.Semiconductor Detector Systems[M].Ox-ford Univ Press,2005:43-102.
[4]Koli K.CMOS current amplifier:Speed versus non-linearity[D].Helsinki University of Technology,2000.
[5]Chang Z Y,Sansen W M C.Low-noise Wide-bandAmplifier in Bipolar and CMOS Technologies[M].Dordrecht:Kluwer Press,1991:20-100.
[6]Sansen W,Chang Z Y.Limits of low noise perfor-mance of detector readout front ends in CMOS tech-nology[J].IEEE Transactions on Circuits and Sys-tems,1990,37(11):1375-1381.
[7]Gramegna G,Connor P O,Rehak P,et al.CMOSpreamplifier for low capacitance detectors[J].NuclearInstruments and Methods in Physics Research SectionA:Accelerators,Spectrometers,Detectors and Asso-ciated Equipment,1997,390:241-245.
[8]Oo K T Z,Mandelli E,Moses W W,et al.A high-speed low-noise 16-channel CSA with automatic leak-age compensation in 0.35-μm CMOS process for APD-based PET detectors[J].IEEE Transactions on Nu-clear Science,2007,54(3):444-453.
[9]Razavi B,Wooley B A.Design techniques for high-speed,high-resolution comparators[J].IEEE Journalof Solid-state Circuits,1992,27(12):1916-1926.
[10]Degerli Y,Fourches N,Rouger M,et al.Low-powerautozeroed high-speed comparator for the readoutchain of a CMOS monolithic active pixel sensor basedvertex detector[J].IEEE Transactions on NuclearScience,2003,50(5):1709-1717.
[11]Delagnes E,Breton D,Lugiez F,et al.A low powermulti-channel single ramp ADC with up to 3.2 GHzvirtual clock[J].IEEE Transactions on Nuclear Sci-ence,2007,54(5):1735-1742.
[12]Banks D,Toumazou C.Low-power high-speed cur-rent comparator design[J].Electronics Letters,2008,44(3):171-172.
[13]Ollivier-Henry N,Berst J D,Colledani C,et al.Afront-end readout mixed chip for high-efficiency smallanimal PET imaging[J].Nuclear Instruments andMethods in Physics Research Section A:Accelera-tors,Spectrometers,Detectors and Associated Equip-ment,2007,571(1-2):312-316.
[14]Geronimo G D,Connor P O,Kandasamy A.AnalogCMOS peak detect and hold circuits:Parts I.analysisof the classical configuation[J].IEEE Transactionson Nuclear Science,2002,484:533-543.
[15]Vert P E,Lecoq J,Montarou G,et al.InnovativeElectronics Architecture for PET Imaging[C].Nucle-ar Science Symposium Conference Record,2006:3057-3059.
[16]Le B,Rondeau T W,Reed J H,et al.Analog-to-digi-tal converters[J].IEEE Signal Processing Magazine,2005,11:69-77.
[17]Tanaka M,Ikeda H,Ikeda M,et al.Development ofmonolithic time-to-amplitude converter for high preci-sion TOF measurement[J].IEEE Transactions onNuclear Science,1991,38(2):301-305.
[18]Bogdan M,Frisch H,Heintz M,et al.A 96-channelFPGA-based time-to-digital converter(TDC)and fasttrigger processor module with multi-hit capability andpipeline[J].Nuclear Instruments and Methods inPhysics Research Section A:Accelerators,Spectrom-eters,Detectors and Associated Equipment,2005,554:444-457.
[19]Mota M,Christiansen J.A four-channel self-calibrat-ing high-resolution time to digital converter,in elec-tronics[C].Proceedings of IEEE International Con-ference on Circuits and Systems,1998,1:409-412.
[20]Poki C,Liu S I,Wu J.Highly accurate cyclic CMOStime-to-digital converter with extremely low powerconsumption[J].Electronics Letters,1997,33(10):858-860.
[21]Straayer M Z,Perrott M H.A multi-path gated ringoscillator TDC with first-order noise shaping[J].IEEE Journal of Solid-state Circuits,2009,44(4):1089-1098.
[22]Minjae L,Abidi A A.A 9 b,1.25 ps resolutioncoarse-fine time-to-digital converter in 90 nm CMOSthat amplifies a time residue[J].IEEE Journal of Sol-id-state Circuits,2008,43(4):769-777.
[23]Jones W F,Byars L G,Casey M E,et al.Positron e-mission tomographic images and expectation maxi-mization:a VLSI architecture for multiple iterationsper second[J].IEEE Transactions on Nuclear Sci-ence,1988,35(1):620-624.
[24]Newport D F,Young J W.An ASIC implementationof digital front-end electronics for a high resolutionPET scanner[J].IEEE Transactions on Nuclear Sci-ence,1993,40:1017-1019.
[25]Wai-Hoi W,Hu G,Zhang N,et al.Front end elec-tronics for a variable field PET camera using thePMT-quadrant-sharing detector array design[J].IEEE Transactions on Nuclear Science,1997,44(4):1291-1296.
[26]Swann B K,Rochelle J M,Binkley D M,et al.Acustom mixed signal CMOS integrated circuit for highperformance PET tomograph front-end applications[C].IEEE Nuclear Science Symposium ConferenceRecord,2002,1:24-28.
[27]Musrock M S,Young J W,Moyers J C,et al.Per-formance characteristics of a new generation of pro-cessing circuits for PET applications[J].IEEE Trans-actions on Nuclear Science,2003,50(4):974-978.
[28]Saoudi A,Lecomte R.A novel APD-based detectormodule for multi-modality PET/SPECT/CT scanners[J].IEEE Transactions on Nuclear Science,1999,46(3):479-484.
[29]Woodring M L,Christian J F,Shah K S,et al.De-velopment of an ASIC for APD-based small animalPET[C].IEEE Nuclear Science Symposium Confer-ence Record,2001,2:737-741.
[30]Deng Z,Yeom J Y,Ishitsu T,et al.Design of newfront-end electronics for animal PET[C].IEEE Nu-clear Science Symposium Conference Record,2002,3:1543-1546.
[31]Lewellen T K,Laymon C M,Miyaoka R S,et al.Development of a data acquisition system for theMiCES small animal PET scanner[C].IEEE NuclearScience Symposium Conference Record,2002,2:1066-1070.
[32]Habte F,Levin C S.Study of low noise multichannelreadout electronics for high sensitivity PET systemsbased on avalanche photodiode arrays[J].IEEETransactions on Nuclear Science,2004,51(3):764-769.
[33]Pratte J F,De Geronimo G,Junnarkar S,et al.Front-end electronics for the RatCAP mobile animalPET scanner[J].IEEE Transactions on Nuclear Sci-ence,2004,51(4):1318-1323.
[34]Shah K S,Grazioso R,Farrell R,et al.Position sen-sitive APDs for small Animal PET imaging[J].IEEETransactions on Nuclear Science,2004,51(1):91-95.
[35]Pratte J F,Robert S,De Geronimo G,et al.Designand performance of 0.18μm CMOS charge preampli-fiers for APD-based PET scanners[J].IEEE Transac-tions on Nuclear Science,2004,51(5):1979-1985.
[36]Moses W W.Recent advances and future advances intime-of-flight PET[J].Nuclear Instruments andMethods in Physics Research Section A:Accelera-tors,Spectrometers,Detectors and Associated Equip-ment,2007,580(2):919-924.
[37]Conti M.State of the art and challenges of time-of-ight PET[J].Physica Medica,2009,25(1):1-11.
[38]Fischer P,Peric I,Ritzert M,et al.Multi-channelreadout ASIC for ToF-PET[C].IEEE Nuclear Sci-ence Symposium Conference Record,2006:2523-2527.
[39]Pedrali-Noy M,Gruber G,Krieger B,et al.PET-RIC-a positron emission tomography readout integrat-ed circuit[J].IEEE Transactions on Nuclear Science,2001,48(3):479-484.
[40]Pratte J F,Pepin C M,Rouleau D,et al.Design of afast shaping amplifier for PET/CT APD detectorswith depth-of-interaction[C].IEEE Nuclear ScienceSymposium Conference Record,2001,2:807-811.
[41]刘力.正电子断层扫描仪与PET图像重建概述[J].CT理论与应用研究,2003,12(1):47-50.
[42]东软集团.东软PET研制成功并获得美国FDA.http:∥www.neusoft.com/news/html∥20090526/2174061627.html,2009.
[43]中国教育网.华中科技大学成功研制首台全数字化平板PET.http:∥www.edu.cn/cheng-guo-zhan-shi-1085/20101221/t20101221-556657.shtml,2010.
[44]王永纲.基于A PD阵列的PET探测器模块电子学[J].核电子学与探测技术,2002,22(5):399-400.
[45]Jian S,An Q,Liu S.A high-resolution time-to-digi-tal converter implemented in field-programmable-gate-arrays[J].IEEE Transactions on Nuclear Science,2006,53(1):236-241.
[46]Kang X,Wang S,Liu Y,et al.A simple smart time-to-digital convertor based on vernier method for a highresolution LYSO microPET[C].IEEE Nuclear Sci-ence Symposium Conference Record,2007:2892-2896.
[47]Gao W,Fang X,Hu-Guo C,et al.A low-noise front-end readout chip integrated with a high-resolutionTDC for APD-based small-animal PET[C].Proceed-ings of First International Conference on Advance-ments in Nuclear Instrumentation Measurement Meth-ods and their Applications,2009:1-6.
[48]Gao W,Hu-Guo C,Wei T,et al.A 12-bit 2.5 MS/smulti-channel ramp analog-to-digital Converter forimaging detectors[C].IEEE International Workshopon in Imaging Systems and Techniques,2009:183-186.
[49]Gao W,Gao D,Wei T,et al.A high-resolution mul-ti-channel time-to-digital converter(TDC)for high-energy physics and biomedical imaging applications[C].4th IEEE Conference on Industrial Electronicsand Applications,2009:1133-1138.
[50]Tai Y C,Chatziioannou A F,Silverman R W,et al.MicroPET II:an ultra-high resolution small animalPET system[C].IEEE Nuclear Science SymposiumConference Record,2002,3:1848-1852.
[51]Martinez J D,Benlloch J W,Cerda J,et al.High-speed data acquisition and digital signal processingsystem for PET imaging techniques applied to mam-mography[J].IEEE Transactions on Nuclear Science,2004,51(3):407-412.
[52]Guerra P,Espinosa J,Ortun~o J E,et al.New em-bedded digital front-end for high resolution PET scan-ner[J].IEEE Transactions on Nuclear Science,2006,53(3):770-775.
[53]Junnarkar S S,Fried J,Southekal S,et al.New timeto digital converter,signal processing,data acquisi-tion,calibration and test hardware for RatCAP[C].IEEE Nuclear Science Symposium Conference Record,2007:4597-4601.
[54]Nadeski M,Gatherer A.DSPs in medical imaging.http:∥focus.ti.com/general/docs/gencontent.tsp?contentId=51435,White paper,Texas Instruments,2008.
[55]Xie Q,Kao C M,Hsiau Z,et al.A new approach forpulse processing in positron emission tomography[J].IEEE Transactions on Nuclear Science,2005,52(4):988-995.