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ABSTRACT: We are developing a Time-of-Flight Positron Emission Tomography detector using flat panel micro-channel plate photomultiplier tubes (MCP PMT). The high-speed waveform sampling data acquisition is adopted to exploit the fast time response of MCP PMT efficiently by using transmission-line readout scheme. To demonstrate the feasibility of the proposed detector, prototype detector modules were built using Photonis XP85022 MCP PMT, transmission-line board (TL), and high-speed waveform sampling electronics equipped with DRS4 chips. The MCP/TL module was coupled to single LYSO crystal, and experimental tests have been conducted in a coincidence setup to measure the responses to 511 keV annihilation photon. The details of the prototype module, experimental setup, and the preliminary results are presented and discussed.
Physics procedia 01/2012; 37:1480-1487.
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ABSTRACT: We are developing a prototype PET detector module as an effort to demonstrate and investigate the feasibility of using large area flat panel (e.g. 8"×8") micro-channel plate photo-multiplier (MCP PMT) for PET instrumentation. The detector module consists of an array of LSO (or LYSO) crystals coupled to a commercially available MCP PMT (Photonis XP85022) with transmission-line strips and read-out by a waveform sampling electronics employing the DRS4 chips at the end of the strips. The details of building and testing of the prototype PET detector module is presented and the benefits of using waveform sampling in PET application also will be discussed.
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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ABSTRACT: A computer simulation study has been conducted to investigate the feasibility of a positron emission tomography (PET) detector design by using micro-channel plate (MCP) photomultiplier tubes (PMT) with transmission-line (TL) read-out and waveform sampling. The detector unit consisted of a 24×24 array of pixelated LSO crystals, each of which was 4×4×25 mm(3) in size, and two 102×102 mm(2) MCP-PMTs coupled to both sides of the scintillator array. The crystal (and TL) pitch was 4.25 mm and reflective medium was inserted between the crystals. The transport of the optical photons inside the scintillator were simulated by using the Geant4 package. The output pulses of the MCP-PMT/TL unit were formed by applying the measured single photo-electron response of the MCP-PMT/TL unit to each individual photon that interacts with the photo-cathode of the MCP-PMT. The waveforms of the pulses at both ends of the TL strips were measured and analyzed to produce energy and timing information for the detected event. An experimental setup was developed by employing a Photonis Planacon MCP-PMT (XP85022) and a prototype TL board for measuring the single photo-electron response of the MCP-PMT/TL. The simulation was validated by comparing the predicted output pulses to measurements obtained with a single MCP-PMT/TL coupled to an LSO crystal exposed to 511 keV gamma rays. The validated simulation was then used to investigate the performance of the proposed new detector design. Our simulation result indicates an energy resolution of ~11% at 511 keV. When using a 400-600 keV energy window, we obtain a coincidence timing resolution of ~323 ps FWHM and a coincidence detection efficiency of ~40% for normally-incident 511keV photons. For the positioning accuracy, it is determined by the pitch of the TLs (and crystals) in the direction normal to the TLs and measured to be ~2.5 mm in the direction parallel to the TLs. The energy and timing obtained at the front- and back-end of the scintillator array also show differences that are correlated with the depth of interaction of the event.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; 622(3):628-636. · 1.21 Impact Factor
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ABSTRACT: A computer simulation study has been conducted to investigate the design of a PET detector module. The detector unit consisted of a 24Ã24 array of pixelated LSO crystals, each was 4Ã4Ã25 mm<sup>3</sup> in size, and two 102Ã102 mm<sup>2</sup> microchannel plate (MCP) PMTs coupled to both sides of scintillators. The crystal pitch was 4.25 mm and reflective media was inserted between crystals. The signals from MCP were readout using a transmission-line scheme. The optical photon inside scintillator was simulated by using the Geant4 package and the output signals of the MCP was formed by applying the electrical responses measured of the MCP to each individual detected photon. A experimental setup was built using a Photonis planacon MCP(XP85022) and a Transmission line board to measure the characteristics of MCP/TL. The measured single photoelectron response(SER) was fed to the simulation of the electrical signal. The responses to 511 keV gamma of the test setup were compared to the simulation results for the validation. The simulation study results showed an energy resolution of ~11% at 511 keV for the detector module. When using a 400-600 keV energy window, we obtained a coincidence timing resolution of ~323 ps FWHM and a coincidence detection efficiency of ~40% for normally incident 511 keV photons. The position resolution was measured to be ~4.25 mm. The readout at both ends of scintillator made it possible to infer depth of interaction(DOI) based on the energy asymmetry and time differences. The simulation study showed that the design is suitable for Time of Flight(TOF) PET with DOI capability.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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ABSTRACT: A PET detector design using the continuous scintillator slab was investigated. The detector unit consists of two layers of LSO scintillator slab, each slab size of 102Ã102Ã5mm<sup>3</sup>, and two large area microchannel plate (MCP) PMTs, 102Ã102mm<sup>2</sup>, coupled to scintillator slabs. The optical photon inside scintillator was simulated using Geant4 package and the electrical signal of MCP was formed using the measured characteristics of MCP and Geant4 output. The signals from MCP were readout using the transmission line (TL) scheme with 4.25mm pitch. The multi-layers of structure enable us to extract the depth of interaction in addition to position, energy and timing in an event. The detector response was measured by impinging the pair of 511keV gamma upon the detector. As preliminary results, we obtained ~12% (FWHM) of energy resolution at 511keV and ~360ps (FWHM) coincidence timing resolution while keeping 14% detection efficiency at 511keV. The position resolution was measured ~2.3mm (RMS) at the center. Due to its simplified structure, the detector can be easily extendable to several layers of slab to increase the sensitivity. The fast timing characteristics of MCP combined with the high sensitivity of LSO makes this design reliable for TOF PET application.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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ABSTRACT: We investigate the potentials of digitally sampling scintillation pulses techniques for positron emission tomography (PET) in this paper, focusing on the determination of the event time. We have built, and continue building, a digital library of PET event waveforms generated with various combinations of photo-detectors and scintillator materials, with various crystal sizes. Events in this digital library are obtained at a high sampling of 20 GSps (Giga-samples per second) so that their waveforms are recorded with high accuracy. To explore the potential advantages of digitally sampling scintillation pulses, we employ a dataset in the above-mentioned library to evaluate two methods for digitizing the event pulses and linear interpolation techniques to analyze the resulting digital samples. Our results show that the two digitization methods that we studied can yield a coincidence timing resolution of about 300 ps FWHM when applied to events generated by a pair of LSO + PMT detector units. This timing resolution is comparable with that is achieved by the same detector pair with a constant fraction discriminator (CFD). As a benchmark, regular-time sampling (RTS) method, usually implemented with very fast traditional analog-to-digital converters (ADCs) for digitizing scintillation pulses, is not feasible for a multi-channel system like a PET system. Digitizing scintillation pulses with multi-voltage threshold (MVT) method could be implemented at a reasonable cost for a PET system. With digitized PET event samples, various digital signal processing (DSP) techniques can be implemented to determine event arrival time. Our results have therefore demonstrated the promising potentials of digitally sampling scintillation pulses techniques in PET imaging.
IEEE Transactions on Nuclear Science 11/2009; · 1.45 Impact Factor
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ABSTRACT: As an approach to realizing all-digital data acquisition for positron emission tomography (PET), we have previously proposed and studied a multi-threshold sampling method to generate samples of a PET event waveform with respect to a few user-defined amplitudes. In this sampling scheme, one can extract both the energy and timing information for an event. In this paper, we report our prototype implementation of this sampling method and the performance results obtained with this prototype. The prototype consists of two multi-threshold discriminator boards and a time-to-digital converter (TDC) board. Each of the multi-threshold discriminator boards takes one input and provides up to 8 threshold levels, which can be defined by users, for sampling the input signal. The TDC board employs the CERN HPTDC chip that determines the digitized times of the leading and falling edges of the discriminator output pulses. We connect our prototype electronics to the outputs of two Hamamatsu R9800 photomultiplier tubes (PMTs) that are individually coupled to a 6.25×6.25×25mm(3) LSO crystal. By analyzing waveform samples generated by using four thresholds, we obtain a coincidence timing resolution of about 340 ps and an ∼18% energy resolution at 511 keV. We are also able to estimate the decay-time constant from the resulting samples and obtain a mean value of 44ns with an ∼9 ns FWHM. In comparison, using digitized waveforms obtained at a 20 GSps sampling rate for the same LSO/PMT modules we obtain ∼300 ps coincidence timing resolution, ∼14% energy resolution at 511 keV, and ∼5 ns FWHM for the estimated decay-time constant. Details of the results on the timing and energy resolutions by using the multi-threshold method indicate that it is a promising approach for implementing digital PET data acquisition.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2009; 602(2):618-621. · 1.21 Impact Factor
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ABSTRACT: We investigate the use of digital signal processing (DSP) techniques for event processing in positron emission tomography (PET). In this work, we focus on the determination of the event time. We are building a digital library of pulse waveforms generated by using different photo-detectors, scintillator materials, crystal sizes, and read-out electronics of interest in PET. We employ a dataset from our library and investigate two methods for obtaining digital samples of an event pulse and several DSP algorithms for estimating the event time. Our first results, by using non-optimized DSP methods, are encouraging.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
