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Bandos I.A.,University of the Basque Country | Bandos I.A.,Ikerbasque | de Azcarraga J.A.,IFIC CSIC UVEG | Meliveo C.,University of the Basque Country
Fortschritte der Physik | Year: 2012

We discuss the formulation of free conformal higher spin theories with extended N{script} = 2, 4, 8 supersymmetry in N{script}-extended tensorial superspaces. The superfield higher spin equations can be obtained by quantizing a superparticle model in N{script}-extended tensorial superspace. The N{script}-extended higher spin supermultiplets just contain scalar and 'spinor' fields in tensorial space so that, in contrast with the standard (super)space approach, no nontrivial generalizations of the Maxwell or Einstein equations to tensorial space appear when N{script} > 2. For N{script} = 4, 8, the higher spin-tensorial components of the extended tensorial superfields are expressed through additional scalar and spinor fields in tensorial space which obey the same free higher spin equations, but that are axion-like in the sense that they possess Peccei-Quinn-like symmetries. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Studen A.,Jozef Stefan Institute | Brzezinski K.,IFIC CSIC UVEG | Chesi E.,Ohio State University | Cindro V.,Jozef Stefan Institute | And 13 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

Silicon based devices can extend PET-MR and SPECT-MR imaging to applications, where their advantages in performance outweigh benefits of high statistical counts. Silicon is in many ways an excellent detector material with numerous advantages, among others: excellent energy and spatial resolution, mature processing technology, large signal to noise ratio, relatively low price, availability, versatility and malleability. The signal in silicon is also immune to effects of magnetic field at the level normally used in MR devices. Tests in fields up to 7 T were performed in a study to determine effects of magnetic field on positron range in a silicon PET device. The curvature of positron tracks in direction perpendicular to the field's orientation shortens the distance between emission and annihilation point of the positron. The effect can be fully appreciated for a rotation of the sample for a fixed field direction, compressing range in all dimensions. A popular Ga-68 source was used showing a factor of 2 improvement in image noise compared to zero field operation. There was also a little increase in noise as the reconstructed resolution varied between 2.5 and 1.5 mm. A speculative applications can be recognized in both emission modalities, SPECT and PET. Compton camera is a subspecies of SPECT, where a silicon based scatter as a MR compatible part could inserted into the MR bore and the secondary detector could operate in less constrained environment away from the magnet. Introducing a Compton camera also relaxes requirements of the radiotracers used, extending the range of conceivable photon energies beyond 140.5 keV of the Tc-99m. In PET, one could exploit the compressed sub-millimeter range of positrons in the magnetic field. To exploit the advantage, detectors with spatial resolution commensurate to the effect must be used with silicon being an excellent candidate. Measurements performed outside of the MR achieving spatial resolution below 1 mm are reported. © 2012 Elsevier B.V. All rights reserved. Source


Studen A.,Jozef Stefan Institute | Chesi E.,Ohio State University | Cindro V.,Jozef Stefan Institute | Clinthorne N.H.,University of Michigan | And 12 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

PET scanners with high spatial resolution offer a great potential in improving diagnosis, therapy monitoring and treatment validation for several severe diseases. One way to improve resolution of a PET scanner is to extend a conventional PET ring with a small probe with excellent spatial resolution. The probe is intended to be placed close to the area of interest. The coincidences of interactions within the probe and the external ring provide a subset of data which combined with data from external ring, greatly improve resolution in the area viewed by the probe. Our collaboration is developing a prototype of a PET probe, composed of high-resolution silicon pad detectors. The detectors are 1 mm thick, measuring 40 by 26 mm2, and several such sensors are envisaged to either compensate for low stopping power of silicon or increase the area covered by the probe. The sensors are segmented into 1 mm3 cubic voxels, giving 1040 readout pads per sensor. A module is composed of two sensors placed in a back-to-back configuration, allowing for stacking fraction of up to 70% within a module. The pads are coupled to a set of 16 ASICs (VaTaGP7.1 by IDEAS) per module and read out through a custom designed data acquisition board, allowing for trigger and data interfacing with the external ring. This paper presents an overview of probe requirements and expected performance parameters. It will focus on the characteristics of the silicon modules and their impact on overall probe performance, including spatial resolution, energy resolution and timing resolution. We will show that 1 mm 3 voxels will significantly extend the spatial resolution of conventional PET rings, and that broadening of timing resolution related to varying depth of photon interactions can be compensated to match the timing resolution of the external ring. The initial test results of the probe will also be presented. © 2010 Elsevier B.V. All rights reserved. Source


Stankova V.,IFIC CSIC UVEG | Barrio J.,IFIC CSIC UVEG | Brzezinski K.,IFIC CSIC UVEG | Chesi E.,Ohio State University | And 14 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2012

High resistivity silicon is a competitive material for photon detectors. Its excellent spatial and energy resolution make them attractive to be used as second detector in medical physics applications. A stack of several detector layers would significantly improve the low stopping power of a single detector. This however, increases considerably the number of channels to be read-out. A Data acquisition system (DAQ) has been developed at IFIC - Valencia to cope with a stack of such detectors. The system is based on the 128 channels VATAGP7 application specific integrated circuit (ASIC) from Gamma Medica - Ideas. A dedicated electronic board (MADDAQ) is in charge of the ASIC control and the administration of the whole readout process. Collected data is processed and sent to a computer trough Ethernet connection. Several MADDAQ boards can work in parallel independently or in coincidence mode. Measurements with the system are presented and characterization of the system is described. © 2012 IEEE. Source


Stankova V.,IFIC CSIC UVEG | Chesi E.,Ohio State University | Cindro V.,Jozef Stefan Institute | Clinthorne N.H.,University of Michigan | And 14 more authors.
IEEE Nuclear Science Symposium Conference Record | Year: 2012

We have developed a data acquisition system for the parallel read-out of silicon pixel detector modules. The front-end electronics of the system is based on the VATAGP7, a Gamma Medica - Ideas application specific integrated circuit (ASIC). The acquisition board (MADDAQ) has an FPGA chip that controls the ASIC configuration and the readout process. Collected data is stored into internal memory and sent to a PC through an Ethernet connection. Several MADDAQ boards can work together independently or in coincidence mode. The system has the option to be synchronized with another setup like in a conventional PET scanner. The full characterization of the system is presented. © 2011 IEEE. Source

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