P.R. Mendes

Bio: P.R. Mendes is an academic researcher. The author has contributed to research in topics: Detector & Iterative reconstruction. The author has an hindex of 2, co-authored 3 publications receiving 16 citations.

Clear-PEM: Monte Carlo performance and image reconstruction studies

Abstract: The Clear-PEM prototype under development aims to improve early stage breast cancer diagnostics. The proposed device is based on cerium doped lutetium crystal matrices developed by the Crystal Clear Collaboration, as well as on modern data acquisition techniques. A series of Monte Carlo studies were performed to evaluate detection sensitivity, background rate and intrinsic spatial resolution in order to optimize the final detector concept. A description of the developed GEANT4 based simulation framework and PEM image reconstruction software is also presented in this paper. First simulation results indicates that Clear-PEM design significantly increases detection sensitivity in comparison with conventional PET cameras for breast cancer diagnostics. Count-rate simulation results are within operation limits for the data acquisition system, able to read 1 MHz event rate, allowing to take full profit of the large detector acceptance.

First experimental results with the Clear-PEM detector

Abstract: First experimental results of the imaging system Clear-PEM for positron emission mammography, under development within the framework of the Crystal Clear Collaboration at CERN, are presented. The quality control procedures of crystal pixels, APD arrays and assembled detector modules are described. The detector module performance was characterized in detail. Results on measurements of light yield, energy resolution, depth-of-interaction and inter-channel cross-talk are discussed. The status of the development of the front-end electronics and of the data acquisition boards is reported.

Further readout electronics development for the ISPA gamma camera

Abstract: The ISPA (Imaging Silicon Pixel Array)-tube is a position sensitive photon detector based on the hybrid technology. It detects light via a photocathode and an appropriate electric field accelerates the emitted photoelectrons towards a silicon pixel anode. This anode, finely segmented into pixel detectors provides binary images and allows for the self-triggering of the tube. Coupled to scintillating crystals, ISPA-tubes have been successfully tested in the field of gamma ray imaging, demonstrating real capabilities in both space and energy resolution. Recently, we have concentrated our efforts on the development of a compact and portable readout system based on new electronics and able to provide full control and real-time processing of ISPA-tubes. The system overview and the dedicated interface are presented in this paper.

Geant4 applications and developments for medical physics experiments

Abstract: The GEANT4 Monte Carlo radiation transport toolkit provides the basic services and infrastructure required for the development of flexible simulation frameworks and applications which have found generalized use in high energy physics, nuclear physics, astrophysics and medical physics research. GEANT4 object-oriented design provides the possibility to implement or modify any physics process in GEANT4 without changing other parts of the software. This feature makes GEANT4 open to extension of its physics modeling capabilities and to the implementation of alternative physics models. In this paper, the development a simulation platform for performance studies and detector optimization of the Clear-PEM scanner, a high-performance positron emission mammography prototype, and the implementation of precise low energy bremsstrahlung angular generators for the GEANT4 low energy electromagnetic physics category are described.

Experimental characterization of the 192 channel Clear-PEM frontend ASIC coupled to a multi-pixel APD readout of LYSO:Ce crystals

Abstract: In the framework of the Clear-PEM project for the construction of a high-resolution scanner for breast cancer imaging, a very compact and dense frontend electronics system has been developed for readout of multi-pixel S8550 Hamamatsu APDs. The frontend electronics are instrumented with a mixed-signal Application-Specific Integrated Circuit (ASIC), which incorporates 192 low-noise charge pre-amplifiers, shapers, analog memory cells and digital control blocks. Pulses are continuously stored in memory cells at clock frequency. Channels above a common threshold voltage are readout for digitization by off-chip free-sampling ADCs. The ASIC has a size of 7.3 × 9.8 mm 2 and was implemented in a AMS 0.35 μ m CMOS technology. In this paper the experimental characterization of the Clear-PEM frontend ASIC, reading out multi-pixel APDs coupled to LYSO:Ce crystal matrices, is presented. The chips were mounted on a custom test board connected to six APD arrays and to the data acquisition system. Six 32-pixel LYSO:Ce crystal matrices coupled on both sides to APD arrays were readout by two test boards. All 384 channels were operational. The chip power consumption is 660 mW (3.4 mW per channel). A very stable behavior of the chip was observed, with an estimated ENC of 1200 – 1300 e - at APD gain 100. The inter-channel noise dispersion and mean baseline variation is less than 8% and 0.5%, respectively. The spread in the gain between different channels is found to be 1.5%. Energy resolution of 16.5% at 511 keV and 12.8% at 662 keV has been measured. Timing measurements between the two APDs that readout the same crystal is extracted and compared with detailed Monte Carlo simulations. At 511 keV the measured single photon time RMS resolution is 1.30 ns, in very good agreement with the expected value of 1.34 ns.

Whole-Body Single-Bed Time-of-Flight RPC-PET: Simulation of Axial and Planar Sensitivities With NEMA and Anthropomorphic Phantoms

Abstract: A single-bed, whole-body positron emission tomograph based on resistive plate chambers has been proposed (RPC-PET). An RPC-PET system with an axial field-of-view (AFOV) of 2.4 m has been shown in simulation to have higher system sensitivity using the NEMA NU2-1994 protocol than commercial PET scanners. However, that protocol does not correlate directly with lesion detectability. The latter is better correlated with the planar (slice) sensitivity, obtained with a NEMA NU2-2001 line-source phantom. After validation with published data for the GE Advance, Siemens TruePoint and TrueV, we study by simulation their axial sensitivity profiles, comparing results with RPC-PET. Planar sensitivities indicate that RPC-PET is expected to outperform 16-cm (22-cm) AFOV scanners by a factor 5.8 (3.0) for 70-cm-long scans. For 1.5-m scans (head to mid-legs), the sensitivity gain increases to 11.7 (6.7). Yet, PET systems with large AFOV provide larger coverage but also larger attenuation in the object. We studied these competing effects with both spherical- and line-sources immersed in a 27-cm-diameter water cylinder. For 1.5-m-long scans, the planar sensitivity drops one order of magnitude in all scanners, with RPC-PET outperforming 16-cm (22-cm) AFOV scanners by a factor 9.2 (5.3) without considering the TOF benefit. A gain in the effective sensitivity is expected with TOF iterative reconstruction. Finally, object scatter in an anthropomorphic phantom is similar for RPC-PET and modern, scintillator-based scanners, although RPC-PET benefits further if its TOF information is utilized to exclude scatter events occurring outside the anthropomorphic phantom.

Performance Simulation Studies of the Clear-PEM DAQ/Trigger System

Abstract: The Clear-PEM detector is a positron emission mammography scanner based on a high-granularity avalanche photodiode readout with 12 288 channels. The front-end sub-system is instrumented with low-noise 192:2 channel amplifier-multiplexer ASICs and free-running sampling ADCs. The off-detector trigger, implemented in a FPGA based architecture, computes the pulses amplitude and timing required for coincidence validation from the front-end data streams. A high-level C++ simulation tool was developed for data acquisition performance analysis and validated at bit-level against FPGA VHDL testbenches. In this work, simulation studies concerning the performance of the on-line/off-line energy and time extraction algorithms and the foreseen detector energy and time resolution are presented. Time calibration and trigger efficiency are also discussed

Performance simulation studies of the clear-PEM DAQ/trigger system

Abstract: The clear-PEM detector is a positron emission mammography scanner based on high-granularity avalanche photodiodes readout with 12 288 channels. The front-end sub-system is instrumented with low-noise 192:2 channel amplifier-multiplexer ASICs and free-running sampling ADCs. The off-detector trigger, implemented in a FPGA based architecture, computes the pulses amplitude and timing required for coincidence validation from the front-end data streams. A high-level C++ simulation tool was developed for data acquisition performance analysis and validated at bit level against FPGA VHDL testbenches. In this work, simulation studies concerning the performance of the on-line/off-line energy and time extraction algorithms and the foreseen detector energy and time resolution are presented. Time calibration, trigger efficiency and ghosting are also discussed