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With increasing improvements in the time of flight (TOF) resolution of positron emission tomography (PET) scanners, an accurate model of the TOF measurements is becoming increasingly important. This work considers two parameters of the TOF kernel; the relative positioning of the timing data-bins and the timing resolution along each line of response (LOR). Similar to an existing data-driven method, we assume that any shifts of data-bins along lines of response can be modelled as differences between crystal timing offsets. Inspired by this, timing resolutions of all LORs are modelled as the hypotenuse of timing resolutions of the crystal-pairs in coincidence. Furthermore, in order to mitigate the influence of potential inaccuracies of detector-pair sensitivities on crystal timing resolutions, relative LOR sensitivities are modelled as the product of efficiency factors for the two crystals in coincidence. We validate estimating maps of crystal timing offsets, timing resolutions and efficiencies from the emission data using noisy simulations of a brain phantom. Results are shown for phantom and patient data scanned on clinically available TOF-PET scanners. We find that the estimation of crystal timing resolutions is more sensitive to the data statistics than the estimation of crystal timing offsets. As a result, estimation of crystal timing properties could either be limited to high count emission data, or be obtained utilizing additional regularizations on the estimates. Using a more accurate model of the TOF acquisition, improvements are observed in standard activity reconstructions as well as joint reconstructions of activity and attenuation. [ABSTRACT FROM AUTHOR]

Digital signal processing (DSP)-based system is a common architecture for high-speed communication links. One of the most important components for DSP-based architectures is the analog-to-digital convertor (ADC). Most of the high-speed ADCs are implemented as time interleaved ADC (TI-ADC). One of the major challenges in TI-ADC is the timing mismatch between the parallel sub-ADCs. The calibration of this mismatch increases system cost and complexity. In this article we propose a new background calibration method based on existing clock and data recovery (CDR) circuits. The timing mismatch can be calibrated using a simple and unique CDR per sub-ADC. Using the existing phase error detector and pulse gain estimator of the regular CDR, the calibration circuit becomes very low-cost, requiring only a first order loop, and a slow numerically controlled oscillator (NCO). VCSEL-based lab experiments are performed, which demonstrate the proposed method efficiency, performance and robustness. [ABSTRACT FROM AUTHOR]

Positron emission tomography (PET) relies on accurate timing information to pair two 511-keV photons into a coincidence event. Calibration of time delays between detectors becomes increasingly important as the timing resolution of detector technology improves, as a calibration error can quickly become a dominant source of error. Previous work has shown that the maximum likelihood estimate of these delays can be calculated by least squares estimation, but an approach is not tractable for complex systems and degrades in the presence of randoms. We demonstrate the original problem to be solvable iteratively using the LSMR algorithm. Using the LSMR, we solve for 60 030 delay parameters, including energy-dependent delays, in 4.5 s, using 1 000 000 coincidence events for a two-panel system dedicated to clinical locoregional imaging. We then extend the original least squares problem to be robust to random coincidences and low statistics by implementing \ell 1 -norm minimization using the alternating direction method of the multipliers (ADMM) algorithm. The ADMM algorithm converges after six iterations, or 20.6 s, and improves the timing resolution from 64.7 ± 0.1s full width at half maximum (FWHM) uncalibrated to 15.63 ± 0.02ns FWHM. We also demonstrate this algorithm’s applicability to commercial systems using a GE Discovery 690 PET/CT. We scan a rotating transmission source, and after subtracting the 511-keV photon time-of-flight due to the source position, we calculate 13 824 per-crystal delays using 5 000 000 coincidence events in 3.78 s with three iterations, while showing a timing resolution improvement that is significantly better than previous calibration methods in the literature. [ABSTRACT FROM PUBLISHER]

The COMET experiment at J-PARC aims to search for the charged lepton flavor violating process of neutrinoless muon-to-electron conversion with an improvement of a sensitivity by a factor of 10000 to the current limit. We plan to use a straw tube tracker with high momentum resolution as an electron detector. To read out the signal from the tracker precisely, optimal front-end electronics is needed, and we have developed the readout electronics board called ROESTI, which contains all the front-end processes; preamplification, pulse shaping, discrimination, and digitization. All the functionalities are controlled by FPGA. Using the prototype, we have constructed the calibration method and evaluated the fundamental performance. In this paper, we report the details of the design and performance for the ROESTI prototype. [ABSTRACT FROM AUTHOR]

Adding time-of-flight (TOF) technology has been proven to improve image quality in positron emission tomography (PET). In order for TOF information to significantly reduce the statistical noise in reconstructed PET images, good timing resolution is needed across the scanner field of view (FOV). This work proposes an accurate, robust, and practical crystal-based timing calibration method using ${}^{18}{\rm F} - {\rm FDG}$ positron-emitting sources together with a spatially separated annihilation target. We calibrated a prototype Toshiba TOF PET scanner using this method and then assessed its timing resolution at different locations in the scanner FOV. [ABSTRACT FROM PUBLISHER]

A time-interleaved ADC employs four pipelined time-interleaved channels along with a new timing mismatch detection algorithm and a high-resolution variable delay line. The digital background calibration technique suppresses the interchannel timing mismatches, achieving an SNDR of \44.4 dB and a figure of merit of 219 fJ/conversion-step in 65 nm CMOS technology. [ABSTRACT FROM AUTHOR]

Abstract: A general procedure for precision timing calibration of waveform digitizing systems is presented. Application specific integrated circuits (ASICs) implementing this functionality are increasingly used in high-energy physics as replacements for stand-alone time-to-digital and analog-to-digital modules. However, process variations cause such ASICs to have irregularly spaced timing intervals between samples, so careful calibration is required to improve the timing resolution of such systems. The procedure presented here exploits correlations between nearby samples of a sine wave of known frequency to obtain the time difference between them. As only the correlations are used, the procedure can be performed without knowledge of the phase of the input signal, and converges with smaller data samples than other common techniques. It also serves as a valuable diagnostic tool, allowing a fast, visual, qualitative check of gain mismatches between sampling cells and other ADC artifacts. Work is continuing to extend the procedure to fit for timing intervals in the face of such non-idealities. We present both the algorithm and example calibration results from a commercial oscilloscope and the PSEC-3 ASIC. For the latter, we have also applied the calibration to improve timing resolution in the readout of a prototype microchannel plate photomultiplier tube with a stripline anode configuration. [Copyright &y& Elsevier]

This paper presents a pilot-based clock and data recovery (CDR) technique for high-speed serial link applications where a low-amplitude clock signal, i.e., a pilot, is added to the transmit signal. The clock tone is extracted at the receiver using an injection-locked oscillator and is used to drive the receiver front-end samplers. The performance of the CDR technique is demonstrated using a 5 Gbps differential receiver fabricated in a 0.13 µm IBM CMOS technology. The clock and data recovery circuit implementation has an area of 0.171 mm² and consumes 11.75 mA from a 1.5 V supply voltage at 5 Gbps. The recovered clock peak-to-peak and rms jitter at 5 Gbps are less than 10 ps (5%UI) and 1.6 ps (0.8%UI), respectively with an effective CDR loop bandwidth of approximately 28 MHz at a bit-error rate (BER) of 10-12. The proposed technique simplifies the CDR design and provides data and inter-symbol interference (ISI) independent performance with a small ≈5% pilot voltage overhead to the transmitted data signal. [ABSTRACT FROM AUTHOR]

Abstract: The described system can be used in a sub-marine Very Large Volume neutrino Telescope where data are transported from Optical Modules (OM), arranged in vertical strings, into the on-shore data acquisition system using copper twisted pairs for the short runs and fiber optics for the long distance connection. All data communication, timing and timing calibration between the Shore Station and the OMs as well as the distribution of power is done via a single Master Module (MM) in the vertical string. VDSL2 provides more than 100Mbps bandwidth via a single copper twisted pair to transport all the data from an OM to the MM. The same twisted pair is also used to transport power and timing to the OM. A single channel of the long distance fiber optical Dense Wavelength Division Multiplexing (DWDM) system provides the data communication from a MM to the Shore Station. Reliability is a design issue; a large part of the system uses common infrastructure. Each vertical string has two separate paths to the Shore Station via separate junction boxes. Destructive single point failures in the common infrastructure divide the system into two parts, but each part is independently fully functional. [Copyright &y& Elsevier]

Abstract: The results of Monte Carlo simulation studies of the timing calibration accuracy required by the NEMO underwater neutrino telescope are presented. The NEMO Collaboration is conducting a long term R&D activity toward the installation of a apparatus in the Mediterranean Sea. An optimal site has been found and characterized at 3500m depth off the Sicilian coast. Monte Carlo simulation shows that the angular resolution of the telescope remains approximately unchanged if the offset errors of timing calibration are less than 1ns. This value is tolerable because the apparatus performance is not significantly changed when such inaccuracies are added to the other sources of error (e.g., the accuracy position of optical modules). We also discuss the optical background rate effect on the angular resolution of the apparatus and we compare the present version of the NEMO telescope with a different configuration. [Copyright &y& Elsevier]

Abstract: The ARGO-YBJ experiment is mainly devoted to search for astronomical gamma sources. The arrival direction of air showers is reconstructed thanks to the times measured by the pixels of the detector. Therefore, the timing calibration of the detector pixels is crucial in order to get the best angular resolution and pointing accuracy. Because of the large number of pixels a hardware timing calibration is practically impossible. Therefore an off-line software calibration has been adopted. Here, the details of the procedure and the results are presented. [Copyright &y& Elsevier]

Abstract: In extensive air shower (EAS) experiments, the primary direction is reconstructed by the space–time pattern of secondary particles. Thus the equalization of the transit time of signals coming from different parts of the detector is crucial in order to get the best angular resolution and pointing accuracy allowed by the detector. In this paper an off-line calibration method is proposed and studied by means of proper simulations. It allows to calibrate the array repeatedly just using the collected data without disturbing the standard acquisition. The calibration method is based on the definition of a Characteristic Plane introduced to analyze the effects of the time systematic offsets, such as the quasi-sinusoidal modulation on azimuth angle distribution. This calibration procedure works also when a pre-modulation on the primary azimuthal distribution is present. [Copyright &y& Elsevier]

A fundamental problem when locating sensors in a network is to estimate the distance between pairs of sensors. This paper considers a variety of time-of-arrival and phase-shift approaches that use bidirectional signaling to bypass the need for accurate synchronous clocking. The measurement techniques are simulated and analyzed to assess the accuracy of the distance estimation. The analysis demonstrates tradeoffs between the accuracy of the oscillators, the accuracy of the subsequent distance estimation, and the complexity of the methods. [ABSTRACT FROM AUTHOR]

Abstract: An electromagnetic calorimeter consisting of 576 undoped CsI crystals has been used to search for the decay at the KEK 12-GeV proton synchrotron (E391a). The calorimeter is placed in a vacuum of lower than 10−1 Pa. Special energy and timing calibrations have been performed. The energy calibration started from a check of the linearity for nine sample crystals using an electron beam. Then, after mounting all crystals in the E391a detector, we made an in situ calibration of the energy by using cosmic ray and punch-through muons. The gain constants obtained from both muons agree with each other with an accuracy of 2% . They were further refined by using γγ samples from π0''s produced off an aluminum plate (5-mm thick) hit by neutral beam particles. Using the final gain constants, we obtained a mass resolution of 4.3MeV/c 2 for the decay. Also, using the timing constants measured for cosmic rays, we obtained a resolution of 0.51ns for the timing difference among six γ''s in the decay. [Copyright &y& Elsevier]

In positron emission tomography (PET), improving time resolution is essential to ensure good scanner performance. Currently, most PET scanner scintillator-based designs, and they have limitations such as a constant delay in the analog circuitry, long conductive paths, or other elements in the detectors. In this study, a novel framework based on low-rank principles is proposed for timing calibration. We follow previous framework to formulate the timing calibration process as a linear problem; the linear equations are constructed using detected coincidence events. To verify the effectiveness, Monte Carlo simulation is performed, and data are generated by the point source experiment and cylinder source experiment. The results are based on the 2D configuration, and we compare performance of the proposed method with existing methods. [ABSTRACT FROM AUTHOR]

Integrated TOF-PET/MR is a multimodal imaging system which can acquire high-quality magnetic resonance (MR) and positron emission tomography (PET) images at the same time, and it has time of flight (TOF) function. The TOF-PET system usually features better image quality compared to traditional PET because it is capable of localizing the lesion on the line of response where annihilation takes place. TOF technology measures the time difference between the detectors on which the two 180-degrees-seperated photons generated from positron annihilation are received. Since every individual crystal might be prone to its timing bias, timing calibration is needed for a TOF-PET system to work properly. Three approaches of timing calibration are introduced in this article. The first one named as fan-beam method is an iterative method that measures the bias of the Gaussian distribution of timing offset created from a fan-beam area constructed using geometric techniques. The second one is to find solutions of the overdetermination equations set using L1 norm minimization and is called L1-norm method. The last one called L2-norm method is to build histogram of the TOF and find the peak, and uses L2 norm minimization to get the result. This article focuses on the comparison of the amount of the data and the calculation time needed by each of the three methods. To avoid location error of the cylinder radioactive source during data collection, we developed a location calibration algorithm which could calculate accurate position of the source and reduce image artifacts. The experiment results indicate that the three approaches introduced in this article could enhance the qualities of PET images and standardized uptake values of cancer regions, so the timing calibration of integrated TOF-PET/MR system was realized. The fan-beam method has the best image quality, especially in small lesions. In integrated TOF-PET/MR timing calibration, we recommend using fan-beam method.

Abstract: Measurement and control applications are increasingly using distributed system technologies. In such applications, which may be spread over large distances, it is often necessary to synchronize system timing and know with great precision the time offsets between parts of the system. Measuring the propagation delay over a coded serial communication channel using serializer/deserializer (SerDes) functionality in FPGAs is described. The propagation delay between transmitter and receiver is measured with a resolution of a single unit interval (i.e. a serial link running at 3.125Gbps provides a 320ps resolution). The technique has been demonstrated to work over 100km fibre to verify the feasibility for application in the future KM3NeT telescope. [ABSTRACT FROM AUTHOR]