Ricardo Martínez

xENoC - An eXperimental Network-On-Chip Environment for Parallel Distributed Computing on NoC-based MPSoC Architectures

This paper describes xENoC, an automatic and component re-use HW-SW environment to build simulatable and synthesizable Network-on-Chip-based MPSoC architectures. xENoC is based on a tool, named NoCWizard, which uses an eXtensible Markup Language (XML) specification, and a set of modularized components and templates to generate many types of NoC instances by using Verilog HDL. This NoC models can be customized in terms of topology, tile location/mapping, RNIs generation, different types of routers, FIFO and packet/flit sizes, by simply modifying the XML specifications. Furthermore, xENoC is also composed of software components, i.e. RNI drivers and a parallel programming model, embedded Message Passing Interface (eMPI), which let us to carry out a complete HW-SW co-design methodology to design distributed-memory NoC-based MPSoCs parallel applications. Through xENoC different distributed-memory NoC-based MPSoCs designs have been created simulated and prototyped in physical platforms (e.g. FPGA boards), and some parallel multiprocessor test traffic applications are running there as system level demonstrators.

Performance limits of a 55-/spl mu/m pixel CdTe detector

In this work, the results from simulation of a CdTe pixel detector with a pixel size of 45 mum and a pitch of 55 mum are presented. Simulation of charge sharing between neighboring pixels has been compared with experimental results obtained by the use of the Medipix2 photon counting chip by means of a unique read-out system developed for the Dear-Mama project. Electrical simulations have been performed using the commercial software package DESSIS (ISETCAD) and combined with the Monte Carlo code GEANT4 to simulate the process of interaction and subsequent charge transport of charges induced by radiation. This allowed the analysis of charge sharing between pixel elements, an important limiting factor in imaging applications. Simulation was compared with experimental results obtained by means of a 1 mm thick CdTe detector. Each of these pixel electrodes was connected to the corresponding readout pixel on the Medipix2 chip, via an indium bump-bond. The backside contact was biased at -100 V, so that the pixel electrodes were collecting electrons. The results obtained imply that using a detector 1 mm thick with a pixel size smaller than 55 mum in single photon counting mode is unrealistic, because such fine spatial resolution cannot be attained in the corresponding image due to charge sharing

Energy and coincidence time resolution measurements of CdTe detectors for PET

We report on the characterization of 2 mm thick CdTe diode detector with Schottky contacts to be employed in a novel conceptual design of PET scanner. Results at -8°C with an applied bias voltage of -1000 V/mm show a 1.2% FWHM energy resolution at 511 keV. Coincidence time resolution has been measured by triggering on the preamplifier output signal to improve the timing resolution of the detector. Results at the same bias and temperature conditions show a FWHM of 6 ns with a minimum acceptance energy of 500 keV. These results show that pixelated CdTe Schottky diode is an excellent candidate for the development of next generation nuclear medical imaging devices such as PET, Compton gamma cameras, and especially PET-MRI hybrid systems when used in a magnetic field immune configuration.

Toward VIP-PIX: A Low Noise Readout ASIC for Pixelated CdTe Gamma-Ray Detectors for Use in the Next Generation of PET Scanners

VIP-PIX will be a low noise and low power pixel readout electronics with digital output for pixelated Cadmium Telluride (CdTe) detectors. The proposed pixel will be part of a 2D pixel-array detector for various types of nuclear medicine imaging devices such as positron-emission tomography (PET) scanners, Compton gamma cameras, and positron-emission mammography (PEM) scanners. Each pixel will include a SAR ADC that provides the energy deposited with 10-bit resolution. Simultaneously, the self-triggered pixel which will be connected to a global time-to-digital converter (TDC) with 1 ns resolution will provide the events time stamp. The analog part of the readout chain and the ADC have been fabricated with TSMC 0.25 μm mixed-signal CMOS technology and characterized with an external test pulse. The power consumption of these parts is 200 μW from a 2.5 V supply. It offers 4 switchable gains from ± 10 mV/fC to ± 40 mV/fC and an input charge dynamic range of up to ± 70 fC for the minimum gain for both polarities. Based on noise measurements, the expected equivalent noise charge (ENC) is 65 e- RMS at room temperature.

Simulation of the Expected Performance of a Seamless Scanner for Brain PET Based on Highly Pixelated CdTe Detectors

The aim of this work is the evaluation of the design for a nonconventional PET scanner, the voxel imaging PET (VIP), based on pixelated room-temperature CdTe detectors yielding a true 3-D impact point with a density of 450 channels/cm3, for a total 6 336 000 channels in a seamless ring shaped volume. The system is simulated and evaluated following the prescriptions of the NEMA NU 2-2001 and the NEMA NU 4-2008 standards. Results show that the excellent energy resolution of the CdTe detectors (1.6% for 511 keV photons), together with the small voxel pitch (1 × 1 × 2 mm3), and the crack-free ring geometry, give the design the potential to overcome the current limitations of PET scanners and to approach the intrinsic image resolution limits set by physics. The VIP is expected to reach a competitive sensitivity and a superior signal purity with respect to values commonly quoted for state-of-the-art scintillating crystal PETs. The system can provide 14 cps/kBq with a scatter fraction of 3.95% and 21 cps/kBq with a scatter fraction of 0.73% according to NEMA NU 2-2001 and NEMA NU 4-2008, respectively. The calculated NEC curve has a peak value of 122 kcps at 5.3 kBq/mL for NEMA NU 2-2001 and 908 kcps at 1.6 MBq/mL for NEMA NU 4-2008. The proposed scanner can achieve an image resolution of ~ 1 mm full-width at half-maximum in all directions. The virtually noise-free data sample leads to direct positive impact on the quality of the reconstructed images. As a consequence, high-quality high-resolution images can be obtained with significantly lower number of events compared to conventional scanners. Overall, simulation results suggest the VIP scanner can be operated either at normal dose for fast scanning and high patient throughput, or at low dose to decrease the patient radioactivity exposure. The design evaluation presented in this work is driving the development and the optimization of a fully operative prototype to prove the feasibility of the VIP concept.

Inkjet printed antennas for NFC systems

Inkjet printing is one of the most promising techniques that could potentially revolutionize large area and organic electronics fabrication. At the moment, technology is still under development and some problems remain to be solved. Only few applications have been demonstrated with enough performance to be moved to industrial level. In this paper we present the study of a potentially successful inkjet printing application: a Near Field Communication Antenna. In our work we characterized an inkjet printing process and developed an antenna design to evaluate its potential. Fabricated antenna was tested on NFC systems and final results lead us to conclude that NFC antennas are a potentially successful inkjet printing application.

Characterization of CdTe detector for use in PET

CdTe diode detectors with Schottky contact have been characterized in terms of energy resolution and time of response. A resolution of 0.98% at 511keV has been achieved with a 4 mm × 4 mm × 2 mm detector at 900 V/mm and −7 °C. At the same bias and temperature conditions, two identical CdTe detectors show a coincidence time FWHM of 25 ns. Additionally, the effect of a strong magnetic field on the charge sharing has been studied for a 9-pixel array detector of 55 µm × 55 µm × 800 µm pixel size connected to MediPix2 front end electronics. No effect on the charge sharing distribution has been observed up to 4 T. These results show that CdTe Schottky diodes are excellent candidates for the development of next generation nuclear medical imaging devices such as PET, Compton gamma camera, and especially PET-MRI when used in a magnetic field immune configuration.

Modeling, simulation, and evaluation of a compton camera based on a pixelated solid-state detector

A novel Compton camera design based on pixelated solid-state detectors is proposed and evaluated via Monte Carlo simulation, using the Geant4-based Architecture for Medicine-Oriented Simulations GAMOS. For the image reconstruction, the Stochastic Origin Ensemble (SOE) method has been used. The efficiency of the reconstruction of Compton prompt events is constant up to activities of 107 Bq. The signal-to-noise ratio (SNR), i.e., the ratio between real coincidences and mis-reconstructed ones, was above 85% for photon energies ranging from 141 to 511 keV. For a 18F isotope source, a sensitivity of 12 cps/kBq has been obtained. For a 99mTc isotope source, a sensitivity of 15 cps/kBq has been obtained. Using the NEMA NU-4 2008 standard for the PSF estimation, values for the FWHM of 1.80 mm for the spatial resolution with a 18F radioactive source and 3.82 mm with a 99mTc source were obtained.

Simulation of pseudo-clinical conditions and image quality evaluation of PET scanner based on pixelated CdTe detector

A novel conceptual design of PET scanner, known as a Voxel Imaging PET (VIP) [1], based on pixelated solid state detector, has been proposed to overcome the intrinsic limitations of state-of-art PET devices based on scintillating crystals. For this study, the VIP scanner has been simulated in different pseudo-clinical conditions in order to assess its image quality performance. The evaluation of the PET image quality follows the NEMA prescriptions. Results are also presented for both analytic and iterative image reconstruction methods. The preliminary results from simulations show that the image reconstruction performance of the VIP scanner under realistic clinical conditions provides good images with low dose. The VIP scanner is able to detect down to 1 mm in diameter hot regions in small phantoms without background activity and down to 5 mm in diameter hot spheres in big phantoms in the presence of background activity. Moreover, good quality and high contrast images can be obtained with a considerably lower number of coincidences with respect to the usual crystal PETs.

A 2D

We present a 16-channel readout integrated circuit (ROIC) with nanosecond-resolution time to digital converter (TDC) for pixelated Cadmium Telluride (CdTe) gamma-ray detectors. The 4×4 pixel array ROIC is the proof of concept of the 10×10 pixel array readout ASIC for positron-emission tomography (PET) scanner, positron-emission mammography (PEM) scanner, and Compton gamma camera. The electronics of each individual pixel integrates an analog front-end with switchable gain, an analog to digital converter (ADC), configuration registers, and a 4-state digital controller. For every detected photon, the pixel electronics provides the energy deposited in the detector with 10-bit resolution, and a fast trigger signal for time stamp. The ASIC contains the 16-pixel matrix electronics, a digital controller, five global voltage references, a TDC, a temperature sensor, and a band-gap based current reference. The ASIC has been fabricated with TSMC 0. 25 μm mixed-signal CMOS technology and occupies an area of 5. 3 mm×6.8 mm. The TDC shows a resolution of 95.5 ps, a precision of 600 ps at full width half maximum (FWHM), and a power consumption of 130 μW. In acquisition mode, the total power consumption of every pixel is 200 μW. An equivalent noise charge (ENC) of 160 e- RMS at maximum gain and negative polarity conditions has been measured at room temperature.