High resolution and sensitivity gamma camera with active septa. A first Monte Carlo study

[EN] Gamma cameras are of great interest due to their high potential in the field of Nuclear Medicine Imaging. They allow for an early diagnosis of reduced size tumors, and also for a wide variety of preclinical studies with the aim of designing more effective treatments against cancer. In this work we propose a significantly improved multi-pinhole collimator gamma camera and perform a first Monte Carlo analysis of its characteristics. Maintaining the configuration of a multi-pinhole collimator with a high degree of overlapping (thus with a high sensitivity), we add a new element, an active septa, that besides acting as a collimator, is able to measure the impact coordinates of the incident photon. This way one is able to unambiguously identify through which pinhole any gamma ray passes before being detected. The result is a high sensitivity and resolution multi-pinhole gamma camera with an arbitrarily large field of view. As a consequence, the final reconstructed image does not suffer from the undesired artifacts or truncation associated to the multiplexing phenomenon. In this study we focus on the development of a system able to visualize in 3D tumors, nodes and metastasis in real time in the operating room with very low dose. We also briefly analyse and propose a novel design for a Single Photon Emission Computed Tomography system.This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 695536). This work was supported in part by the Spanish Government Grants Generalitat Valenciana, APOSTD/2019/086 and TEC2016-79884-C2 and RTC-2016-5186-1.Ilisie, V.; Moliner, L.; Oliver-Gil, S.; Sánchez Martínez, F.; González Martínez, AJ.; Seimetz, M.; Rodríguez Álvarez, MJ.... (2019). High resolution and sensitivity gamma camera with active septa. A first Monte Carlo study. Scientific Reports. 9:1-9. https://doi.org/10.1038/s41598-019-54934-0S199Mok, G. S. P., Tsui, B. M. W. & Beekman, F. J. The effects of object activity distribution on multiplexing multi-pinhole SPECT. Phys. Med. Biol. 56, 2635–2650 (2011).Johnson, C., Shokouhi, S. & Peterson, T. E. Reducing Multiplexing artifacts in Multi-Pinhole SPECT with a Stacked Silicon-Germanium System: a Simulation Study. IEEE Trans Med Imaging. 33(12), 2342–2351 (2014).Mok, G. S. P., Wang, Y. & Tsui, B. M. W. Quantification of the Multiplexing Effects in Multi-Pinhole Small Animal SPECT: A Simulation Study. IEEE Trans Nucl Sci. 56(5), 2636–2643 (2009).Vunckx, K., Suetens, P. & Nuyts, J. Effect of Overlapping Projections on Reconstruction Image Quality in Multipinhole SPECT. IEEE Transactions on Medical Imaging. 27(7) (2008).Ivashchenko, O. et al. Quarter-Millimeter-Resolution Molecular Mouse Imaging with U-SPECT+. Mol Imaging. 2014. 13 (2014).Gal, O. et al. Development of a portable gamma camera with coded apertura. Nuclear Instruments and Methods in Phys. Res. A. 563, 233–237 (2006).Accorsi, R., Gasparini, F. & Lanza, R. C. A Coded Aperture for High-Resolution Nuclear Medicine Planar Imaging With a Conventional Anger Camera: Experimental Results. IEEE Transactions on Nuclear Science. 48, 2411–2417 (2001).Fuji, H. et al. Optimization of Coded Aperture Radioscintigraphy for Sentinel Lymph Node Mapping. Mol. Imaging Biol. 14, 173–182 (2012).Accorsi, R., Gasparini, F. & Lanza, R. C. Optimal coded aperture patterns for improved SNR in nuclear medicine imaging. Nucl. Instrum. Methods Phys. Res. A. 474, 273–284 (2001).Lee, T. & Lee, W. Portable Active Collimation Imager Using URA Patterned Scintillator. IEEE Transactions on Nuclear Science. 61, 654–662 (2014).Lee, T. & Lee, W. A cubic gamma camera with an active collimator. Applied Radiation and Isotopes. 90, 102–108 (2014).Accorsi, R. & Lanza, R. C. Near-field artifact reduction in coded aperture imaging. Appl. Opt. 40, 4697–4705 (2001).Ilisie, V., Sánchez, F., González, A. J. & Benlloch, J. M. Dispositivo Para la Detección de Rayos Gamma con Tabiques Activos (Device for Gamma Ray Detection with Active Septa), Patent application Ref. P201831058/PT-018004.González, A. J. et al. Detector block based on arrays of 144 SiPMs and monolithic scintillators: A performance study. Nuclear Instruments and Methods in Physics Research A. 787, 42–45 (2015).Pani, R. et al. Preliminary evaluation of a monolithic detector module for integrated PET/MRI scanner with high spatial resolution. JINST. 10, C06006 (2015).Pani, R. et al. Continuous DOI determination by Gaussian modelling of linear and non-linear scintillation light distributions. Proc. IEEE NSS-MIC. 3386–3389 (2011).Shepp, L. A. & Vardi, Y. Maximum likelihood reconstruction for emission tomography. IEEE Transactions on Medical Imaging. 2, 113 (1982).Hudson, H. M. & Larkin, R. S. Accelerated Image Reconstruction Using Ordered Subsets of projection Data. IEEE Transactions on Medical Imaging. 13, 601 (1994).Reader, A. J. et al. Accelerated list-mode EM algorithm. IEEE Transactions on Nuclear Science. 49, 42 (2002).Rahmim, A., Ruth, T. & Sossi, V. Study of a convergent subsetized list-mode EM reconstruction algorithm. FILTR SEP. 6. 3978–3982. 6, 10.1109 (2004).Siddon, R. L. Fast calculation of the exact radiological path for a three-dimensional CT array. Medical Physics. 12, 252 (1985).Sundermann, E., Jacobs, F., Christiaens, M., De Sutter, B. & Lemahieu, I. A Fast Algorithm to Calculate the Exact Radiological Path Through a Pixel Or Voxel Space. Journal of Computing and Information Technology. 6 (1998).Reader, A. J. et al. One-pass list-mode EM algorithm for high-resolution 3-D PET image reconstruction into large arrays. IEEE Transactions on Nuclear Science. 49(3), 693–699 (2002).Agostinelli, S. et al. Geant4 - a simulation toolkit. Nuclear Instruments and Methods in Physics Research A. 506, 250–303 (2003).Jan, S. et al. GATE - Geant4 Application for Tomographic Emission: a simulation toolkit for PET and SPECT. Phys. Med. Biol. 49(19), 4543–4561 (2004)

Sistema compacto, híbrido e integrado GAMMA/RF para la formación de imágenes simultáneas PETSPECT/MR

Sistema compacto, híbrido e integrado GAMMA/RF para la formación de imágenes simultáneas PET-SPECT/MR. El sistema compacto, híbrido e integrado GAMMA-RF para la formación de imágenes simultáneas PET-SPECT/MR de la invención comprende un dispositivo GAMMA-RF que integra una bobina RF, del tipo empleado en sistemas MR convencionales, con unos módulos detectores de radiación GAMMA del tipo utilizado en sistemas PET o SPECT, de modo que se obtienen imágenes combinadas de las técnicas PET o SPECT y MR.Peer reviewedConsejo Superior de Investigaciones Científicas (España), Universidad de Valencia, Universidad Politécnica de Valencia, General Equipment for Medical Imaging SA, Exploraciones Radiológicas Especiales SA (ERESA)A1 Solicitud de patente con informe sobre el estado de la técnic

TOF studies for dedicated PET with open geometries

[EN] Recently, two novel PET devices have been developed with open geometries, namely: breast and prostate-dedicated scanners. The breast-dedicated system comprises two detector rings of twelve modules with a field of view of 170 mm x 170 mm x 94 mm. Each module consists of a continuous trapezoidal LYSO crystal and a PSPMT. The system has the capability to vary the opening of the rings up to 60 mm in order to allow the insertion of a needle to perform a biopsy procedure. The prostate system has an open geometry consisting on two parallel plates separated 28 cm. One panel includes 18 detectors organized in a 6 x 3 matrix while the second one comprises 6 detectors organized in a 3 x 2 matrix. All detectors are formed by continuous LYSO crystals of 50 mm x 50 mm x15 mm, and a SiPM array of 12 x 12 individual photo-detectors. The system geometry is asymmetric maximizing the sensitivity of the system at the prostate location, located at about 2/3 in the abdomen-anus distance. The reconstructed images for PET scanners with open geometries present severe artifacts due to this peculiarity. These artifacts can be minimized using Time Of Flight information (TOF). In this work we present a TOF resolution study for open geometries. With this aim, the dedicated breast and prostate systems have been simulated using GATE (8.1 version) with different TOF resolutions in order to determine the image quality improvements that can be achieved with the existing TOF-dedicated electronics currently present in the market. The images have been reconstructed using the LMOS algorithm including TOF modeling in the calculation of the voxel-Line Of Response emission probabilities.This work was supported in part by the Spanish Government Grants TEC2016-79884-C2 and RTC-2016-5186-1 and by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 695536).Moliner, L.; Ilisie, V.; González Martínez, AJ.; Oliver-Gil, S.; Gonzalez, A.; Giménez-Alventosa, V.; Cañizares, G.... (2019). TOF studies for dedicated PET with open geometries. Journal of Instrumentation. 14:1-8. https://doi.org/10.1088/1748-0221/14/02/C02006S181

Prepolarized MRI of Hard Tissues and Solid-State Matter

[EN] Prepolarized MRI (PMRI) is a long-established technique conceived to counteract the loss in signal-to-noise ratio (SNR) inherent to low-field MRI systems. When it comes to hard biological tissues and solid-state matter, PMRI is severely restricted by their ultra-short characteristic relaxation times. Here we demonstrate that efficient hard-tissue prepolarization is within reach with a special-purpose 0.26 T scanner designed for ex vivo dental MRI and equipped with suitable high-power electronics. We have characterized the performance of a 0.5 T prepolarizer module, which can be switched on and off in 200 mu s. To this end, we have used resin, dental and bone samples, all with T1$${\mathbf{T}}_{\mathbf{1}}$$ times of the order of 20 ms at our field strength. The measured SNR enhancement is in good agreement with a simple theoretical model, and deviations in extreme regimes can be attributed to mechanical vibrations due to the magnetic interaction between the prepolarization and main magnets.Agencia Valenciana de la Innovaci~o; European Regional Development Fund; Ministerio de Ciencia e Innovacion; This work was supported by the Ministerio de Ciencia e Innovaci~on of Spain through research grant PID2019-111436RBC21. Action co-financed by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022). JMG and JB acknowledge support from the Innodocto program of the Agencia Valenciana de la Innovacion (INNTA3/2020/22 and INNTA3/2021/17); Ministerio de Ciencia e Innovaci~on of Spain, Grant/Award Number: PID2019-111436RB-C21; Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana, Grant/Award Number: IDIFEDER/2018/022; Innodocto program of the Agencia Valenciana de la Innovacion, Grant/Award Numbers: INNTA3/2020/22, INNTA3/2021/17Borreguero-Morata, J.; González Hernández, JM.; Pallás Lodeiro, E.; Rigla, JP.; Algarín-Guisado, JM.; Bosch-Esteve, R.; Galve, F.... (2022). Prepolarized MRI of Hard Tissues and Solid-State Matter. NMR in Biomedicine. 35(8):1-10. https://doi.org/10.1002/nbm.473711035

Simultaneous imaging of hard and soft biological tissues in a low-field dental MRI scanner

[EN] Magnetic Resonance Imaging (MRI) of hard biological tissues is challenging due to the fleeting lifetime and low strength of their response to resonant stimuli, especially at low magnetic fields. Consequently, the impact of MRI on some medical applications, such as dentistry, continues to be limited. Here, we present three-dimensional reconstructions of ex-vivo human teeth, as well as a rabbit head and part of a cow femur, all obtained at a field strength of 260 mT. These images are the first featuring soft and hard tissues simultaneously at sub-Tesla fields, and they have been acquired in a home-made, special-purpose, pre-medical MRI scanner designed with the goal of demonstrating dental imaging at low field settings. We encode spatial information with two pulse sequences: Pointwise-Encoding Time reduction with Radial Acquisition and a new sequence we have called Double Radial Non-Stop Spin Echo, which we find to perform better than the former. For image reconstruction we employ Algebraic Reconstruction Techniques (ART) as well as standard Fourier methods. An analysis of the resulting images shows that ART reconstructions exhibit a higher signal-to-noise ratio with a more homogeneous noise distribution.We thank anonymous donors for their tooth samples, Andrew Webb and Thomas O'Reilly (LUMC) for discussions on hardware and pulse sequences, and Antonio Tristan (UVa) for information on reconstruction techniques. This work was supported by the European Commission under Grants 737180 (FET-OPEN: HISTO-MRI) and 481 (ATTRACT: DentMRI). Action co-financed by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022). Santiago Aja-Fernandez acknowledges Ministerio de Ciencia e Innovacion of Spain for research grant RTI2018-094569-B-I00.Algarín-Guisado, JM.; Díaz-Caballero, E.; Borreguero-Morata, J.; Galve, F.; Grau-Ruiz, D.; Rigla, JP.; Bosch-Esteve, R.... (2020). Simultaneous imaging of hard and soft biological tissues in a low-field dental MRI scanner. Scientific Reports. 10(1):1-14. https://doi.org/10.1038/s41598-020-78456-2S114101Haacke, E. M. et al. Magnetic Resonance Imaging: Physical Principles and Sequence Design Vol. 82 (Wiley-liss, New York, 1999).Bercovich, E. & Javitt, M. C. Medical imaging: from roentgen to the digital revolution, and beyond. Rambam Maimonides Med. J. 9, e0034. https://doi.org/10.5041/rmmj.10355 (2018).Mastrogiacomo, S., Dou, W., Jansen, J. A. & Walboomers, X. F. Magnetic resonance imaging of hard tissues and hard tissue engineered bio-substitutes. Mol. Imag. Biol. 21, 1003–1019. https://doi.org/10.1007/s11307-019-01345-2 (2019).Duer, M. J. Introduction to Solid-State NMR Spectroscopy (Blackwell, Oxford, 2004).Oatridge, A. et al. Magnetic resonance: magic angle imaging of the achilles tendon. Lancet 358, 1610–1611. https://doi.org/10.1016/S0140-6736(01)06661-2 (2001).Funduk, N. et al. Composition and relaxation of the proton magnetization of human enamel and its contribution to the tooth NMR image. Magnetic Resonance Med.1, 66–75. https://doi.org/10.1002/mrm.1910010108 (1984).Schreiner, L. J. et al. Proton NMR spin grouping and exchange in dentin. Biophys. J . 59, 629–639. https://doi.org/10.1016/S0006-3495(91)82278-0 (1991).Niraj, L. K. et al. MRI in dentistry–a future towards radiation free imaging-systematic review. JCDRhttps://doi.org/10.7860/JCDR/2016/19435.8658 (2016).Shah, N. Recent advances in imaging technologies in dentistry. World J. Radiol. 6, 794. https://doi.org/10.4329/wjr.v6.i10.794 (2014).Newton, C. W., Hoen, M. M., Goodis, H. E., Johnson, B. R. & McClanahan, S. B. Identify and determine the metrics, hierarchy, and predictive value of all the parameters and/or methods used during endodontic diagnosis. J. Endodontics 35, 1635–1644. https://doi.org/10.1016/j.joen.2009.09.033 (2009).Brady, E., Mannocci, F., Brown, J., Wilson, R. & Patel, S. A comparison of cone beam computed tomography and periapical radiography for the detection of vertical root fractures in nonendodontically treated teeth. Int. Endod. J. 47, 735–746. https://doi.org/10.1111/iej.12209 (2014).Idiyatullin, D., Garwood, M., Gaalaas, L. & Nixdorf, D. R. Role of MRI for detecting micro cracks in teeth. Dentomaxillofac. Radiol. 45, 20160150. https://doi.org/10.1259/dmfr.20160150 (2016).Idiyatullin, D. et al. Dental magnetic resonance imaging: making the invisible visible. J. Endodontics 37, 745–752 (2011).Marques, J. P., Simonis, F. F. & Webb, A. G. Low-field MRI: an MR physics perspective. J. Magn. Reson. Imaging 49, 1528–1542. https://doi.org/10.1002/jmri.26637 (2019).Sarracanie, M. et al. Low-cost high-performance MRI. Sci. Rep. 5, 15177. https://doi.org/10.1038/srep15177 (2015).Weiger, M. et al. High-resolution ZTE imaging of human teeth. NMR Biomed. 25, 1144–1151. https://doi.org/10.5041/rmmj.103552 (2012).Grodzki, D. M., Jakob, P. M. & Heismann, B. Ultrashort echo time imaging using pointwise encoding time reduction with radial acquisition (PETRA). Magn. Reson. Med. 67, 510–518. https://doi.org/10.5041/rmmj.103553 (2012).Kaczmarz, S. Angenäherte auflösung von systemen linearer gleichungen. Bull. Int. Acad. Pol. Sci. Let., Cl. Sci. Math. Nat. 35, 355–357 (1937).Gordon, R., Bender, R. & Herman, G. T. Algebraic reconstruction techniques (ART) for three-dimensional electron microscopy and X-ray photography. J. Theor. Biol. 29, 471–481. https://doi.org/10.1016/0022-5193(70)90109-8 (1970).Gower, R. M. & Richtarik, P. Randomized iterative methods for linear systems. SIAM J. Matrix Anal. Appl.36, 1660–1690. 10.1137/15M1025487 (2015). arXiv:1506.03296.Ludwig, U. et al. Dental MRI using wireless intraoral coils. Sci. Rep.6, https://doi.org/10.1038/srep23301 (2016).Maggioni, M., Katkovnik, V., Egiazarian, K. & Foi, A. Nonlocal transform-domain filter for volumetric data denoising and reconstruction. IEEE Trans. Image Process. 22, 119–133. https://doi.org/10.5041/rmmj.103555 (2013).Weiger, M. & Pruessmann, K. P. Short-t2 mri: principles and recent advances. Prog. Nucl. Magn. Reson. Spectrosc. 114–115, 237–270 (2019).Jang, H., Wiens, C. N. & McMillan, A. B. Ramped hybrid encoding for improved ultrashort echo time imaging. Magn. Resonance Med. 76, 814–825 (2016).Wu, Y. et al. Water- and fat-suppressed proton projection mri (waspi) of rat femur bone. Magn. Reson. Med. 57, 554–567 (2007).Carr, H. Y. Steady-state free precession in nuclear magnetic resonance. Phys. Rev. 112, 1693–1701. https://doi.org/10.5041/rmmj.103556 (1958).Waugh, J. S., Huber, L. M. & Haeberlen, U. Approach to high-resolution NMR in solids. Phys. Rev. Lett. 20, 180–182. https://doi.org/10.5041/rmmj.103557 (1968).Waeber, A. M. et al. Pulse control protocols for preserving coherence in dipolar-coupled nuclear spin baths. Nat. Commun. 10, 1–9. https://doi.org/10.1038/s41467-019-11160-6 (2019).Frey, M. A. et al. Phosphorus-31 MRI of hard and soft solids using quadratic echo line-narrowing. Proc. Natl. Acad. Sci. U.S.A. 109, 5190–5195. https://doi.org/10.1073/pnas.1117293109 (2012).Galve, F., Alonso, J., Algarín, J. M. & Benlloch, J. M. Magnetic resonance imaging method with zero echo time and slice selection. ESP202030504 (2020).Cooley, C. Z. et al. A portable brain mri scanner for underserved settings and point-of-care imaging. arXiv2004.13183 (2020).Hills, B. P. & Clark, C. J. Quality Assessment of Horticultural Products by NMRhttps://doi.org/10.1016/S0066-4103(03)50002-3 (2003).Somers, A. E., Bastow, T. J., Burgar, M. I., Forsyth, M. & Hill, A. J. Quantifying rubber degradation using NMR. Polym. Degrad. Stab. 70, 31–37. https://doi.org/10.1007/s11307-019-01345-21 (2000).Tyler, D. J., Robson, M. D., Henkelman, R. M., Young, I. R. & Bydder, G. M. Magnetic resonance imaging with ultrashort TE (UTE) PULSE sequences: technical considerations. J. Magn. Reson. Imaging 25, 279–289. https://doi.org/10.1002/jmri.20851 (2007).Weiger, M., Pruessmann, K. P. & Hennel, F. MRI with zero echo time: hard versus sweep pulse excitation. Magn. Reson. Med. 66, 379–389. https://doi.org/10.1002/mrm.22799 (2011).Rahmer, J., Blume, U. & Börnert, P. Selective 3D ultrashort TE imaging: comparison of “dual-echo” acquisition and magnetization preparation for improving short-T2 contrast. Magn. Resonance Mater. Phys. Biol. Med.20, 83–92. https://doi.org/10.1007/s10334-007-0070-6 (2007).Rasche, V., Holz, D. & Schepper, W. Radial turbo spin echo imaging. Magn. Reson. Med. 32, 629–638 (1994).Fessler, J. A. On NUFFT-based gridding for non-Cartesian MRI. J. Magn. Reson. 188, 191–195. https://doi.org/10.1007/s11307-019-01345-24 (2007).Fessler, J. Model-based image reconstruction for MRI. In IEEE Signal Processing Magazine, vol. 27, 81–89, https://doi.org/10.1109/MSP.2010.936726(Institute of Electrical and Electronics Engineers Inc., 2010).Aja-Fernández, S. & Vegas-Sánchez-Ferrero, G. Statistical Analysis of Noise in MRI (Springer, Berlin, 2016).Aja-Fernández, S., Pieciak, T. & Vegas-Sánchez-Ferrero, G. Spatially variant noise estimation in MRI: a homomorphic approach. Med. Image Anal. 20, 184–197 (2015)

PET detector block with accurate 4D capabilities

[EN] In this contribution, large SiPM arrays (8 x 8 elements of 6 x 6 mm(2) each) are processed with an ASIC-based readout and coupled to a monolithic LYSO crystal to explore their potential use for TOF-PET applications. The aim of this work is to study the integration of this technology in the development of clinical PET systems reaching sub-300 ps coincidence resolving time (CRT). The SiPM and readout electronics have been evaluated first, using a small size 1.6 mm (6 mm height) crystal array (32 x 32 elements). All pixels were well resolved and they exhibited an energy resolution of about 20% (using Time-over-Threshold methods) for the 511 keV photons. Several parameters have been scanned to achieve the optimum readout system performance, obtaining a CRT as good as 330 +/- 5 ps FWHM. When using a black-painted monolithic block, the spatial resolution was measured to be on average 2.6 +/- 0.5 mm, without correcting for the source size. Energy resolution appears to be slightly above 20%. CRT measurements with the monolithic crystal detector were also carried out. Preliminary results as well as calibration methods specifically designed to improve timing performance, are being analyzed in the present manuscript.This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No 695536). It has also been supported by the Spanish Ministerio de Economia, Industria y Competitividad under Grants No. FIS2014-62341-EXP and TEC2016-79884-C2-1-R.Lamprou, E.; Aguilar -Talens, A.; Gonzalez-Montoro, A.; Monzó Ferrer, JM.; Cañizares-Ledo, G.; Iranzo-Egea, S.; Vidal San Sebastian, LF.... (2018). PET detector block with accurate 4D capabilities. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment. 912:132-136. https://doi.org/10.1016/j.nima.2017.11.002S13213691

Simulation study of resistor networks applied to an array of 256 SiPMs

[EN] In this work we describe a procedure to reduce the number of signals detected by an array of 256 Silicon Photo-multipliers (SiPMs) using a resistor network to divide the signal charge into few readout channels. Several configurations were modeled, and the pulsed signal at the readout contacts were simulated. These simulation results were experimentally tested on a specifically designed and manufactured set of printed circuit boards. Three network configurations were modeled. The modeling provided encouraging results for all three configurations. The measurements on the prototypes constructed for this study, however, provided useful position-sensitivity for only one of the network configurations. The lack of input signal amplification into the networks, the SiPM dark current, as well as the complexity of an eight layers board with parasitic capacitances, could have caused the degradation of resolving the impact photon position. This is hard to overcome with external printed circuit boards and components.This work was supported by the Spanish Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica (I+D+I) under Grant FIS2010-21216-CO2-01, the Valencian Local Government under Grant PROMETEO 2008/114 and through the JAE-Predoc grant from CSIC (BOE 29/01/2010).Gonzalez, A. J., Moreno, M., Barbera, J., Conde, P., Hernandez, L., Moliner, L., . . . Benlloch, J. M. (2013). Simulation study of resistor networks applied to an array of 256 SiPMs. IEEE Transactions on Nuclear Science, 60(2), 592-598. doi:10.1109/TNS.2012.2226051S59259860

Calibration and performance tests of detectors for laser-accelerated protons

We present the calibration and performance tests carried out with two detectors for intense proton pulses accelerated by lasers. Most of the procedures were realized with proton beams of 0.46-5.60 MeV from a tandem accelerator. One approach made use of radiochromic films, for which we calibrated the relation between optical density and energy deposition over more than three orders of magnitude. The validity of these results and of our analysis algorithms has been confirmed by controlled irradiation of film stacks and reconstruction of the total beam charge for strongly non-uniform beam profiles. For the spectral analysis of protons from repeated laser shots, we have designed an online monitor based on a plastic scintillator. The resulting signal from a photomultiplier directly measured on a fast oscilloscope is especially useful for time-of-flight applications. Variable optical filters allow for suppression of saturation and an extension of the dynamic range. With pulsed proton beams we have tested the detector response to a wide range of beam intensities from single particles to 3 ×105 protons per 100 ns time interval.Project funded by the Spanish Ministry of Economy and Competitiveness and co-funded with FEDER's funds within the INNPACTO 2011 program under Grant No. IPT-2011-0862-900000. This work was supported by the Spanish Plan Nacional de Investigacion Cientifica, Desarrollo e Innovacion Tecnologica (I+D+i) under Grant No. TEC 2013-48036-C3-1-R and the Valencian Local Government under Grants PROMETEOII/2013/010 and ISIC 2011/013. The work of A. J. Gonzalez is financed by CSIC with a JAE-Doc contract under Junta de Ampliacion de Estudios program, cofinanced by the European Social Fund.Peer Reviewe

Results of a combined monolithic crystal and an array of ASICs controlled SiPMs

[EN] In this work we present the energy and spatial resolutions we have obtained for a γ ray detector based on a monolithic LYSO crystal coupled to an array of 256 SiPMs. Two crystal configurations of the same trapezoidal shape have been tried. In one approach all surfaces were black painted but the exit one facing the photosensor array which was polished. The other approach included a retroreflector (RR) layer coupled to the entrance face of the crystal powering the amount of transmitted light to the photosensors. Two coupling media between the scintillator and the SiPM array were used, namely direct coupling by means of optical grease and coupling through an array of light guides. Since the same operational voltage was supplied to the entire array, it was needed to equalize their gains before feeding their signals to the Data Acquisition system. Such a job was performed by means of 4 scalable Application Specific Circuits (ASICs). An energy resolution of about 24.4% has been achieved for the direct coupling with the RR layer together with a spatial resolution of approximately 2.9 mm at the detector center. With the light guides coupling the effects of image compression at the edges are significantly minimized, but worsening the energy resolution to about 33.1% with a spatial resolution nearing 4 mm at the detector center. & 2013 Elsevier B.V. All rights reserved.cknowledgments This work was supported by the Centre for Industrial Technological Development co-funded by FEDER through the Technology Fund (DREAM Project, IDI-20110718), the Spanish Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica (IþDþI) under Grant no. FIS2010-21216-CO2-01 and the Valencian Local Government under Grant PROMETEO 2008/114Conde Castellanos, PE.; González Martínez, AJ.; Hernández Hernández, L.; Bellido, P.; Iborra Carreres, A.; Crespo Navarro, E.; Moliner Martínez, L.... (2014). Results of a combined monolithic crystal and an array of ASICs controlled SiPMs. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 734:132-136. https://doi.org/10.1016/j.nima.2013.08.079S13213673

EM tomographic image reconstruction using polarvoxels

[EN] The splitting of the field of view (FOV) in polar voxels is proposed in this work in order to obtain an efficient description of a cone-beam computed tomography (CT) scanner. The proposed symmetric-polar pixelation makes it possible to deal with the 3D iterative reconstruction considering a number of projections and voxel sizes typical in CT preclinical imaging. The performance comparison, between the filtered backprojection (FBP) and 3D maximum likelihood expectation maximization (MLEM) reconstruction algorithm for CT, is presented. It is feasible to achieve the hardware spatial resolution limit with the considered pixelation. The image quality achieved with MLEM and FBP have been analyzed. The results obtained with both algorithms in clinical images have been compared too. Although the polar-symmetric pixelation is presented in the context of CT imaging, it can be applied to any other tomographic technique as long as the scan comprises the measurement of an object under several projection angles.This work was supported by the Spanish Plan Nacional de Investigaci´on Cient´ıfica, Desarrollo e Innovaci´on Tecnol´ogica (I+D+I) under Grant No. FIS2010-21216-CO2-01 and Valencian Local Government under Grants PROMETEO/2008/114, ISIC/2012/013 and APOSTD/2010/012.Soriano Asensi, A.; Rodríguez Álvarez, MJ.; Iborra Carreres, A.; Sánchez Martínez, F.; Carles Fariña, M.; Conde Castellanos, PE.; González Martínez, AJ.... (2013). EM tomographic image reconstruction using polarvoxels. Journal of Instrumentation. 8(12):1-7. https://doi.org/10.1088/1748-0221/8/01/C01004S1781