Browsing by Author "Loureiro, Custódio F. M."
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- An easy procedure for calibrating data acquisition systems using interleavingPublication . Clemêncio, Filomena; Loureiro, Custódio F. M.; Correia, Carlos M. B. A.Interleaving data acquisition channels is a well-known and interesting technique to achieve higher acquisition rates. However, to obtain the expected benefits, a careful look at the interleaving technique and to mismatches that can lead to unwanted harmonic distortion and noise is essential. In this paper we discuss the methods used to interleave existing high-speed, 250 MSPS 8-bit acquisition channels, and the results obtained. The methods presented allowed a good relative channel calibration in amplitude (amplitude mismatch under 0.1 lsb) and in time (time mismatch between acquisition channels in the ps range, under the specified maximum jitter for the ADC used). A dynamic, by software, amplitude level signal-dependent adjustment procedure is also suggested for signals with rich frequency content that can substantially improve the quality of the acquired signal when using interleaved channels. The techniques presented provide good results even in the presence of noise.
- An easy procedure for calibrating data systems using interleavingPublication . Clemêncio, Filomena; Loureiro, Custódio F. M.; Correia, Carlos M. B. A.Interleaving data acquisition channels is a well-known and interesting technique to achieve higher acquisition rates. However, to obtain the expected benefits, a careful look at the interleaving technique and to mismatches that can lead to unwanted harmonic distortion and noise is essential. In this paper we discuss the methods used to interleave existing high-speed, 250 MSPS 8-bit acquisition channels, and the results obtained. The methods presented allowed a good channel calibration in amplitude (amplitude mismatch under 0.1 lsb) and in time (time mismatch between acquisition channels in the ps range, under the specified maximum jitter for the ADC used). A dynamic, by software, amplitude level signal-dependent adjustment procedure is also suggested for signals with reach frequency content that can substantially improve the quality of the acquired signal when using interleaved channels. The techniques presented provide good results even in the presence of noise.
- A data acquisition architecture for a RPC-based small animal petPublication . Clemêncio, Filomena; Loureiro, Custódio F. M.; Correia, Carlos M. B. A.On-going work suggests that a RPC-based small animal pet camera can be built with a FWHM resolution below 0.5 mm and at a very competitive cost. The camera being developed demands a high-resolution data acquisition system along with very good trigger coincidence detection and on-line data reduction. In this paper the actual system specifications are given and a solution is discussed. The elected solution includes the development of four similar data acquisition modules, each with 16 channels based on 12-bit, 70 MSPS ADCs with LVDS outputs, dedicated memory, trigger logic, processing unit, and a USB 2.0 interface. The trigger and data processing logic of each module were placed inside a Xilinx-4 Virtex FGPA. The proposed solution allows a cheap and efficient system to be constructed in a PC-centric way.
- Online trigger processing for a small-animal RPC-PET cameraPublication . Clemêncio, Filomena M. C.; Loureiro, Custódio F. M.; Landeck, JorgeA complex task for positron emission tomography (PET) cameras is the design of an appropriate coincidence-detec tion trigger system as it usually encompasses coincidences in a large number of channels and requires tight time specifications. Those requirements are even greater for a resistive plate chamber (RPC)-based detector technology since the time window specifica tion is quite small (in the order of a few hundred picoseconds) and the number of coincidence-channels can be quite large. Previous work showed that the time resolution for gamma photon pairs of a detector based on resistive plate chamber technology is under 300 ps full width at half maximum. This allows for a very tight time window for coincidence detection, with the corresponding benefits in reducing the number of random coincidences observed and, hence, the overall noise on the acquired image. In this paper, we first show experimental results of a coincidence-detection algo rithm implemented inside a Xilinx Virtex-5 field-programmable gate array for a small-animal RPC-PET camera being built.
- The design of a digital coincidence-detection trigger system for a RPC-based petPublication . Clemêncio, Filomena M. C.; Loureiro, Custódio F. M.; Correia, Carlos M. B. A.A complex task for PET cameras is the design of an appropriate coincidence-detection trigger as it usually encompasses coincidences in a large number of channels and tight time specifications. Those requirements are even greater for a resistive plate chamber (RPC)-based detector technology as the time window specification is quite small (in the order of a few hundred picoseconds) and the number of coincidence-channels can be quite large (more than 100 in a large camera). In this work we discuss on-going work aimed at implementing the coincidence-detection algorithm inside a FPGA along with the necessary TDCs. The use of the developed solution in a first prototype of an RPC-based small animal PET and its scalability to the case of a human, all-body, PET, is discussed.