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We have developed a scalable detector readout design for a 100 ps coincidence time resolution (CTR) time of flight (TOF) positron emission tomography (PET) detector technology. The basic scintillation detectors studied in this paper are based on 2 × 4 arrays of 3 × 3 × 10 mm3 ‘fast-LGSO:Ce’ scintillation crystals side-coupled to 6 × 4 arrays of 3 × 3 mm2 silicon photomultipliers (SiPMs). We employed a novel mixed-signal front-end electronic configuration and a low timing jitter Field Programming Gate Array-based time to digital converter for data acquisition. Using a 22Na point source, >10 000 coincidence events were experimentally acquired for several SiPM bias voltages, leading edge time-pickoff thresholds, and timing channels. CTR of 102.03 ± 1.9 ps full-width-at-half-maximum (FWHM) was achieved using single 3 × 3 × 10 mm3 ‘fast-LGSO’ crystal elements, wrapped in Teflon tape and side coupled to a linear array of 3 SiPMs. In addition, the measured average CTR was 113.4 ± 0.7 ps for the side-coupled 2 × 4 crystal array. The readout architecture presented in this work is designed to be scalable to large area module detectors with a goal to create the first TOF-PET system with 100 ps FWHM CTR.

We present a nonuniform multiphase (NUMP) method to construct a high-resolution time-to-digital converter (TDC) for low-cost field-programmable gate array (FPGA) devices. The NUMP method involves a system clock being passed through a series of delay elements to generate multiple clocks with different phase shifts. The phases of the rising and falling edges of all the clocks are sorted in order and the states of all the clocks are latched when a hit signal arrives. The sizes of the time bins (and precision) of the NUMP method are not limited by the uniformity and minimum value of the time delays of the delay lines. In theory, any delay sources with small jitters in an FPGA, not just very fine carry chains, can be used in the NUMP method to delay and randomize the clocks. Thus, the NUMP method can achieve excellent TDC timing resolutions in low-cost FPGAs without very fine delay lines. We implemented four NUMP TDC channels in a low-cost FPGA device (an Altera Cyclone V 5CEBA4F23C7N). The performance of the four NUMP TDCs was evaluated using both internal and external pulses. The root mean square (rms) for the timing resolution measured using the internal and the external pulses with short-time intervals (less than 1 ns) was 2.3 and 5.2 ps, respectively. A 14.1-ps rms timing resolution was measured at a time interval of 517 ns. The NUMP method is suitable for applications that require a number of high-performance TDC channels in a low-cost FPGA.

We have developed a scalable detector readout design for a 100 ps coincidence time resolution (CTR) TOF- PET system. The basic PET detector elements are based on 3×3×10 mm3“LGSO” scintillation crystals sidecoupled to arrays of three 3×3 mm2SiPMs. We employed a novel mixed-signal front-end electronic configuration and a low timing jitter FPGA-based TDC for data acquisition. Coincidence data were experimentally acquired for several SiPM bias voltages, comparator thresholds, and timing channels. Before final optimizations, the measured CTR was 103.3 ± 1.5 ps for 3×3×10 mm3 fast LGSO crystals. Furthermore, this readout architecture is scalable to modules and eventually a clinical system with a goal to achieve 100 ps CTR.

To achieve 2 - fold improvement in reconstructed image Signal to Noise Ratio (SNR) compared to state-of-the-art TOF-PET scanners, we have evaluated CTR performance of three different mixed-signal front-end electronic configurations. The proposed TOF-PET detector elements are based on two 3×3×10 mm3 “LGSO” crystal segments for a 20 mm effective length and side-coupled to arrays of 3×3 mm2 SiPMs. The front-end readouts were based on: a) high speed RF amplifiers; b) NINO ASIC as discriminator, and; c) combination of both RF+NINO. Coincidence data were experimentally acquired using the 10 mm length crystals, a low jitter FPGA-based TDC, several SiPM bias voltages, and NINO thresholds, achieving CTR value of 103.3 ± 1.5 ps FWHM using configuration (c). This value is much improved compared to the results achieved using configurations (a) and (b).

In order to improve the accuracy of the proposed algorithm in collaborative filtering recommendation system, an Improved Pearson collaborative filtering (IP-CF) algorithm is proposed in this paper. The algorithm uses the user portrait, item characteristics and data of user behavior to compute the baseline predictors model. Instead of the traditional algorithm’s similarity calculation, the prediction model is used to improve the accuracy of the recommendation algorithm. Experimental results on Moivelens dataset show that the IP-CF algorithm significantly improves the accuracy of the recommended results, and the RMSE and MAE evaluation results are better than the traditional algorithms.

The conventional front-end electronics for PET imaging consist of an energy circuit and a timing circuit. A single channel in front-end electronics typically requires several amplifiers, an ADC and a TDC. In this paper, we present a novel front-end electronic design using 1-bit sigma-delta ( $\boldsymbol {\Sigma }$ - $\boldsymbol {\Delta }$ ) modulation and an FPGA. The new design requires only one analog amplifier per channel. The output of the analog amplifier is read directly by the FPGA. Both the energy and timing calculation are implemented in FPGA firmware. The scope of this paper is to introduce the novel design in detail and to evaluate its performance in energy and dark current measurements. Simulink simulations were performed to validate the design with ideal components. A one-channel prototype circuit was built to assess the design with real components. The prototype circuit was tested with different input signals, including test pulses, pulse signals from a PMT detector, DC current signals and dark current signals from an SiPM sensor. Both the simulation and experimental results show that the method is inherently stable and has excellent accuracy and linearity in energy and dark current measurements. The prototype analog board was built with discrete components cost about $ 0.5 in total. The power consumption was about 20 mW. We conclude that the new method provides a cost-efficient and power-efficient way to accurately measure the energies of analog pulses and dark currents from detectors. The timing performance of this method is currently under evaluation.

This paper presents a unique preclinical positron emission tomography (PET) detector constructed with a monolithic scintillator ring (MSR) and two rings of silicon photomultipliers (SiPM). The inner diameter, outer diameter and length of the MSR were 48.5 mm, 58.5 mm, and 25.1 mm, respectively. The two SiPM rings, constructed with 46 SiPMs, were air-coupled to the two ends of the MSR detector. The center of gravity (COG) and artificial neural network (ANN) methods were adapted to decode the positions of the gamma interactions in the circumferential (θ) and axial (Z) directions, respectively. Collimating systems, consisting of a tungsten collimator and a high-precision displacement and rotating platform, were constructed to assess the decoding accuracies of the MSR detector in both θ and Z directions. The average intrinsic full-width half maximums (FWHMs) and mean absolute errors (MAEs) of the decoding accuracies were 0.94 mm and 0.33 mm in the circumferential direction, 2.45 mm and 1.08 mm in the axial direction. An energy resolution of 10.7% was measured at 511 keV. The scintillating photons generated by a pair of coincidence gamma photons overlap with each other, and cause circumferential parallax errors in the lines of response (LOR). The experimental results show that the average FWHM errors in the θ direction increased slightly from 0.94 mm to 1.14 mm when Δθ of the two single events was larger than 70°. The imaging performance of the MSR detector was also initially assessed with a Derenzo phantom filled with 18F-FDG. The rods with a diameter larger than 1.2 mm can be resolved. The energy resolutions were 12.3% at 511 keV (single events), and 11.4% at 1022 keV (coincidence events). We concluded that it is feasible to construct the high-performance preclinical PET scanners using one or multiple MSR detectors.

Preclinical positron emission tomography (PET) is a sensitive and quantitative molecule imaging modality widely used in characterizing the biological processes and diseases in small animals. The purpose of this study is to investigate the methods to optimize a PET detector for high-resolution preclinical imaging. The PET detector proposed in this study consists of a 28 × 28 array of LYSO crystals 0.5 × 0.5 × 6.25 mm3in size, a wedged lightguide, and a 6 × 6 array of SiPMs 3 × 3 mm2in size. The simulation results showed that the most uniform flood map was achieved when the thickness of the lightguide was 2.35 mm. The quality of the flood map was significantly improved by suppressing the electronics noises using the simple threshold method with a best threshold. The peak-to-valley ratio of flood map improved 25.4% when the algorithm of ICS rejection was applied. An energy resolution (12.96% ± 1.03%) was measured on the prototype scanner constructed with 12 proposed detectors. Lastly, a prototype preclinic PET imager was constructed with 12 optimized detectors. The point source experiment was performed and an excellent spatial resolution (axial: 0.56 mm, tangential: 0.46 mm, radial: 0.42 mm) was achieved with the proposed high-performance PET detectors.

We present a preclinical PET scanner constructed with a single piece of monolithic scintillator ring (MSR) and two rings of silicon photomultipliers (SiPM). The two SiPM rings, constructed with 46 SiPMs 3 mm× 3mm in size, were air-coupled to the two ends of the MSR. A Tungsten collimator was fabricated to characterize the decoding accuracies in circumferential (θ) and axial (Z) directions. The center of gravity (COG) method and an artificial neural network (ANN) method were used to decode the positions of gamma interactions in θ and Z directions, respectively. The experimental results show excellent energy resolution (10.7%) and decoding accuracies in θ directions. The measured average mean absolute error (MAE) spatial resolutions in the θ and Z directions were 0.33 mm and 1.08 mm respectively. Phantom imaging studies with 18F-FDG were performed. We have also designed and constructed the 2nd generation PET scanner with twelve semi-monolithic rings (SMR) to improve the spatial resolution in Z directions.

The purpose of the study is to assess the performance of different methods in correcting the inter-crystal Compton scatters in one-to-one coupled PET detectors. A experimental system was constructed with 10 x 10 LYSO crystal arrays, 10 x 10 SiPM arrays and read-out circuits. The SiPMs were one-to-one air-coupled with the crystals, and then connected to the read-out circuit though the cable. Two detector modules were placed face to face. When a coincidence events were detected, the energy signals from all 200 SiPMs (two detectors) were read and sent to the host PC for data analysis off-line. Signals from one of the two detectors were used as references for electronic collimation. Four different practical methods to decode the crystal ID were implemented on the second detector. We compared the performance of different methods by calculating and comparing the MAE error of their energy distribution. In the end, we drew a conclusion to support our further work.

This work modified the commonly used Monte Carlo tool package GATE by developing a new 'multiPatchPET' system so that GATE users can easily simulate PET systems with irregular geometries. The motivation was to design a brain PET scanner with high sensitivity. It is known that compact PET scanners with a large solid coverage angle can achieve high sensitivity with fewer scintillation detectors, and thus have the potential to provide better image quality in brain PET imaging than conventional ring PET scanners. However, considering a straightforward example with the largest possible solid angle, a spherical PET scanner is hard to manufacture. A more practical alternative would be a sphere-like polyhedral PET scanner with flat detector patches. Moreover, when monolithic scintillators are chosen to construct these flat detector modules, detection efficiency is further improved. Thus, we plan to design a sphere-like polyhedral PET scanner made up of monolithic scintillators. Unfortunately, in our design study, we found that simulating such a scanner with the latest GATE version (8.0) was not trivial, since no predefined systems could be used. In this work we introduced a 'multiPatchPET' system to GATE, which we and other GATE users will be able to use to develop PET scanners with any irregular geometry and any shape of patch. To validate our modification, a single block detector and an mCT scanner were simulated via both the original 'ecat' system and the new 'multiPatchPET' system. The results show no difference in terms of the detecting efficiency and reconstruction image. Then we used the 'multiPatchPET' system to simulate an 86 surface polyhedral brain PET scanner. Compared with two cylindrical brain scanners, the polyhedral brain scanner shows a higher sensitivity and has fewer noisy images. Thus, it was proved that our modification, which is accessible to the nuclear imaging research community, equipped GATE with a powerful and user-friendly tool to simulate complex scanners with irregular patches easily.

Conventional PET cameras are constructed with detectors which consist of arrays of discrete scintillators and photosesnsors. Arrays of very fine discrete crystals have been used in high-resolution small animal imaging. However, it is very challenging to machine and assemble discrete crystals with a size smaller than 1 mm. Thus, the arrays of fine crystals are usually very expensive. And the quality of these arrays, which is heavily depended on the vendor’s skills, does not always meet the requirements. Reflectors with a thickness of 0.1 mm ~ 0.2mm are necessary to separate the individual crystals in an array. The smaller the size of the discrete crystals, the smaller the filling factor of the crystals in the array, and the smaller the sensitivity of the system. In this paper, we present a novel PET system constructed with a monolithic scintillator ring. This PET system is very different from any PET systems which have been constructed so far. It is constructed from a single piece of monolithic crystal. And the lines of response (LOR) are calculated directly from the light distribution around the crystal ring, instead of being calculated from the measurement of the positions of interaction (POI) of the two gammas. Thus, we name it LOR-PET. We have designed and constructed the first LOR-PET with a monolithic LYSO scintillator ring. The inner and outer diameters of the ring are 48.5 mm and 58.5 mm respectively. The length and thickness of the ring are 25.12mm and 5 mm respectively. Twenty-three 4x1 SiPM arrays are fabricated and mounted inside of the monolithic LYSO crystal ring. A low-cost highperformance electronics system (named Pico-PET electronics) was built to read out the 92 channels of SiPM in parallel. The results of initial tests shows that the electronics system works very well. We conclude that the LOR-PET system is a unique low-cost PET system that has the potential to achieve good sensitivity and spatial resolution in small animal or organ specific imaging. We are performing system characterization and phantom study to further assess the performance of the LORPET system.

The conventional PET cameras, consisting of rings of gamma detectors which may block the paths of radiation beams, are not ideal for in-beam monitoring. In this paper, we presented a novel PET design with adjustable field-of-view (FOV), axial field-of-view (AFOV) and sensitivity, like the pupil of the human eye. Thus, we named it Pupil-PET. The sensitivity of a Pupil-PET is no fixed and depends on the system configuration. We designed a 16-module prototypic pupil-PET system which has two planes with Archimedean spiral tracks on both of them. Four step motors are used to adjust the aperture and the AFOV automatically with a precision of 1 mm per step. The system can automatically transform into a two-ring system with a 100 mm aperture and a 72 mm AFOV, a two-ring system with an aperture ranged from 100 mm to 200 mm and an AFOV ranged from 72 mm to 100 mm, or a two-ring system with a 200 mm aperture and a 38 mm AFOV. The sensitivity of the smallaperture two-ring configuration is about 8 times higher than that in a large-aperture one-ring configuration. Sixteen detector modules have been fabricated and tested for the prototypic PupilPET system. The detector module consists of a 10 x 10 LYSO crystal array (3 mm x 3 mm x 20 mm), a 10 x 10 SiPM array (3 mm), and a high performance readout board (call Pico-PET electronics) which are able to read out all 100 SiPMs in parallel. In conclusion, our Pupil-PET has two unique features: (1) It is able to transform to adapt objects with different sizes. The largeaperture one-ring configuration can be adapted to achieve a large FOV for objects large in size, such as big animal and whole-body human. Small-aperture two-ring configuration can be adapted to achieve an 8 times higher sensitivity for objects small in size, such as small animal, human brain or breast. (2) The gaps between the detectors and between the rings in a Pupil-PET system provide omnidirectional paths for radiation beams.

The purposes of this study is to investigate the Lightsharing-window (LSW) method for DOI measurement by optic simulation. When a gamma interaction happens in a crystal, most of the scintillating photons will be detected by the photo sensors directly coupled with it. However, some scintillating photons will pass through light-sharing windows, enter the adjacent crystals and be detected by the photo sensors coupled to them. DOI can be derived from the percentages of the photons detected by the photo sensors. Different light-sharing window designs (single window vs. dual windows; rectangular vs. triangle window) were simulated and compared. The effects of surface finish were assessed. The simulation results show: (1) the relations between DOI and energy differences between photo sensors are monotonic. Thus, they can be used to calculate the DOI; (2) When using single window, the DOI vs. Diff. Energy curves have two segments which are not desired for DOI measurement; (3) Crystals with rough surfaces are more desired since the qualities of their DOI vs. Diff. Energy curves are better. (4) The dual-window method has the best DOI vs. Diff. Energy curves in term of linearity. We conclude that dual-window LSW method is a very promising method for accurate DOI measurements. The LSW method didn’t catch enough attentions before for two practical reasons. Firstly, it is very challenging to accurately fabricate the designed light-sharing windows on discrete scintillators. Secondly, LSW method requires to read out the light output from every single crystals accurately. In our previous studies, we have developed an anti-reflection coating technology which can ’’print’’ any designed light-sharing windows on a crystal. We have also developed an advanced read out electronics (called Pico-PET electronics), which is able to read out energy signals from hundreds of individual photo sensors accurately. Our next step is to apply those two technologies to fabricate dual-window LSW detectors to validate this simulation study.

The increased statistical efficiency gained with TOF information can be used to decrease acquisition time, decrease injected dose, or improve image quality of a PET system. We are designing Tachyon TOF PET cameras (Tachyon I, II and III) to: (1) Construct “demonstration” single-ring TOF PET cameras that achieve significantly improved timing resolution; (2) Quantitatively measure the benefit for clinically relevant tasks as a function of timing resolution; (3) Design practical multiple-ring PET cameras with excellent timing performances for clinic applications. Tachyon I is a single-ring TOF PET scanner constructed with LYSO crystals and Hamamatsu R-9800 PMTs. The ring diameter of the scanner is 76.6 cm. Time resolution of the system (defined as of each crystal-crystal combination) is 314ps ±20ps. Tachyon I is currently in clinical test stage. Tachyon II is a single-ring SiPM-based TOF PET scanner currently under construction. The ring diameter of the scanner is still 76.6 cm. LaBr3 scintillator crystals will be used in Tachyon II. The target system-level CRT timing resolution is 100ps or better. Tachyon III is a practical multiple-ring SiPM-based TOF PET scanner for real clinic applications. Tachyon III is currently in conceptual design stage.

The Silicon photomultiplier (SiPM) becomes a choice of photon sensors for advanced radiation detector development. However, reading out large-scale SiPM arrays is still a fundamental technical obstacle. We present a new method (named π-PET electronics) to address this issue. Very different from conventional front-end electronics design, the key innovation of the new electronics is to include almost all functions of front-end readout electronics inside a low-cost FPGA. That not only simplifies the analog components and reduce the cost (with only one linear amplifier) but also provides powerful and flexible signal processes to enable applying different algorithms to both enhance the performance and add new real-time dark current measurement and calibration features.

Dedicated brain PET has the potential to achieve better sensitivity, spatial resolution and image quality than conventional whole body PET cameras in brain tomography. Spherical PET (S-PET), that can achieve a higher geometrical sensitivity and a lower parallax error than conventional cylindrical ring PET scanners, is a good candidate for high performance dedicated brain imaging. Our simulation studies show that the S-PET has a local geometric efficiency 2.7 times higher than the 30cm cylinder PET, and 19 times higher than the 76cm cylinder PET in the zones around the cerebral cortex. However, it is very challenging to design detectors with curved surface for S-PET. Convex polyhedron PETs, such as dodecahedral PET, is easier to build and has the potential to achieve performances equivalent to those of S-PETs. We are building a high-sensitivity dodecahedron PET for brain imaging. In this paper, we report our progresses in: (1) sensitivity simulation studies, (2) design, simulation and fabrication of a pentagon-shaped detector module, (3) design and fabrication of the mechanic gantry, and (4) image reconstruction.

The conceptual study on the accelerator driven system (ADS) that lasted for about five years ended in 1999 in China. As one project of the National Basic Research Program of China (973 Program) in the energy domain, which is sponsored by the China Ministry of Science and Technology (MOST), a five-year-program of fundamental research of ADS physics and related technology was launched in 2000 and passed national review at the end of 2005. The China Institute of Atomic Energy (CIAE), the Institute of High Energy Physics (IHEP), the Institute of Heavy Ion Physics in Peking University (PKU-IHIP) and other institutions jointly carried out the research. The research activities were focused on HPPA physics and technology, reactor physics of external source driven sub-critical assembly, nuclear data base and material study. For HPPA, a high current injector consisting of an ECR ion source, LEBT and an RFQ accelerating structure of 3.5 MeV was built. In reactor physics study, a series of neutron multiplication experimental study has been carried out and still being done. The VENUS facility has been constructed as the basic experimental platform for neutronics study in ADS blanket. It’s a zero power sub-critical neutron multiplying assembly driven by external neutron produced by a pulsed neutron generator. The theoretical, experimental and simulation study on nuclear data, material properties and nuclear fuel circulation related to ADS is carrying on to provide the database for ADS system analysis. The main results on ADS related researches will be reported.

We present a novel front-end electronic design using sigma-delta (Σ-Δ) modulation. The new design needs only one analog amplifier, one differential digital input port and one digital output port from a FPGA. Both the energy and timing calculation are implemented in FPGA firmware. A Simulink model is established to simulate and evaluate the circuit design and the sample data processing. The energy is calculated directly by summing the sequences of 0 and 1 generated by the 1-bit Σ-Δ ADC module. The simulation disclosed the non-linear transfer function of the amplitudes of the input pulse and the calculated energy, which can be corrected using LUT(s). The timing is determined either directly by measuring the timing of first pulse generated by the 500MHz Σ-Δ ADC (timing resolution: 2ns), or by measuring the leading edge of the first pulse generated by FPGA differential input using a FPGA-based TDC.

Chinese Evaluated Nuclear Data Library third version (CENDL-3.1) contains the nuclear data evaluated works which were performed during the period of 1995-2005 at China Nuclear Data Center (CNDC) in cooperation with the China Nuclear Data Coordination Network (CNDCN), including the neutron data for about 200 nuclides in ENDF/B-6 format in energy region of 10 −5 eV - 20MeV. For the most important nuclei the comparisons with other nuclear data libraries (ENDF, JENDL, BROND, JEFF...) have been performed, and the benchmark testing for the most important nuclei also have been done. CNDC and CNDCN also have got a lot of progress in the fields of nuclear data theory study, model and code developments, and nuclear database establishment, etc. The status of CENDL-3 and some progress of the nuclear data evaluation studies in the past several years will be introduced in this presentation.