González Martínez, Antonio Javier
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- PublicaciónCalibration of Gamma Ray Impacts in Monolithic-Based Detectors Using Voronoi Diagrams(Institute of Electrical and Electronics Engineers, 2020-05) Freire, Marta; Gonzalez-Montoro, Andrea; Sánchez Martínez, Filomeno; Benlloch Baviera, Jose María; González Martínez, Antonio Javier; Instituto de Instrumentación para Imagen Molecular; European Commission; Ministerio de Economía y Competitividad[EN] Molecular imaging systems, such as positron emission tomography (PET), use detectors providing energy and a 3-D interaction position of a gamma ray within a scintillation block. Monolithic crystals are becoming an alternative to crystal arrays in PET. However, calibration processes are required to correct for nonuniformities, mainly produced by the truncation of the scintillation light distribution at the edges. We propose a calibration method based on the Voronoi diagrams. We have used $50 \times 50 \times 15$ mm(3) LYSO blocks coupled to a $12\times 12$ SiPMs array. We have first studied two different interpolation algorithms: 1) weighted average method (WAM) and 2) natural neighbor (NN). We have compared them with an existing calibration based on 1-D monomials. Here, the crystal was laterally black painted and a retroreflector (RR) layer added to the entrance face. The NN exhibited the best results in terms of XY impact position, depth of Interaction, and energy, allowing us to calibrate the whole scintillation volume. Later, the NN interpolation has been tested against different crystal surface treatments, allowing always to correct edge effects. Best energy resolutions were observed when using the reflective layers (12%-14%). However, better linearity was observed with the treatments using black paint. In particular, we obtained the best overall performance when lateral black paint is combined with the RR.
- PublicaciónA proof-of-concept of cross-luminescent metascintillators: testing results on a BGO: BaF2metapixel(IOP Publishing, 2023-01-21) Konstantinou, G.; Latella, Riccardo; Moliner Martínez, Laura; Zhang, L.; Benlloch Baviera, Jose María; González Martínez, Antonio Javier; Lecoq, Paul; Instituto de Instrumentación para Imagen Molecular; European Commission[EN] Objective: Time-of-flight positron emission tomography (PET)is the next frontier in improving the effective sensitivity. To achieve superior timing for time-of-flight PET, combined with high detection efficiency and cost-effectiveness, we have studied the applicability of BaF2 in metascintillators driven by the timing of cross-luminescence photon production. Approach: Based on previous simulation studies of energy sharing and analytic multi-exponential scintillation pulse, as well as sensitivity characteristics, we have experimentally tested a pixel of 3 × 3 × 15 mm3 based on 300 ¿m BGO and 300 ¿m BaF2 layers. To harness the deep ultraviolet cross-luminescent light component, which carries improved timing, we use the FBK VUV SiPM. Metascintillator energy sharing is addressed through a double integration approach. Main results: We reach an energy resolution of 22%, comparable to an 18% resolution of simple BGO pixels using the same readout, through the optimized use of the integrals of the metascintillator pulse in energy sharing calculation. We measure the energy sharing extent of each pulse with a resolution of 25% and demonstrate that experimental and simulation results agree well. Based on the energy sharing, a timewalk correction is applied, exhibiting significant improvements for both the coincidence time resolution (CTR) and the shape of the timing histogram. We reach 242 ps CTR for the entire photopeak, while for a subset of 13% of the most shared events, the CTR value improves to 108 ps, comparable to the 3 × 3 × 5 mm3 LYSO:Ce:Ca reference crystal. Significance: While we are considering different ways to improve further these results, this proof-ofconcept demonstrates the applicability of cross-luminescence for metascintillator designs through the application of VUV compatible SiPM coupling, and easily implementable digital algorithms. This is the first test of BaF2-based metascintillators of sufficient stoppng power to be included in a PET scanner, demonstrating the industrial applicability of such cross-luminescent metascintillators.
- PublicaciónDevelopments in Dedicated Prostate PET Instrumentation(2024-01) González Martínez, Antonio Javier; González-Montoro, Andrea; Instituto de Instrumentación para Imagen Molecular; Generalitat Valenciana[EN] Some specific MI designs assessing early detection and staging of PCa have been proposed. It can be differentiated between systems (dedicated-, WB-and TB-PET), and inserts or probes that are placed much closer to the prostate with the aim to boost spatial resolution (magnification effect) and eventually sensitivity in the area under observation. Fully prostate-dedicated systems have not yet reached an optimum of performance to be transferred to the clinics or industry, most likely due to the lack of precise detectors able to include DOI and TOF capabilities simultaneously at an affordable cost. Moreover, several attempts have been carried out in a variety of probe technologies such as PET alone, US combined, with TOF capabilities and even MRI compatible, reporting promising results.It seems very likely that using images provided by prostate dedicated-PET scanners for biopsy guidance would help in diagnosis. As reviewed in the present article, this may be accomplished with dedicated prostate PET using for instance TransRectal PET imaging probes resulting in a high sensitivity.As an alternative to dedicated PET and the combination PET probe, currently available PET scanners could be technologically upgraded by designing more precise detectors or/and by including AI techniques. To accomplish these goals, advancements in the detection technology are required. There have been several encouraging attempts during the last years on these lines, and it seems feasible that enhanced PET and TB PET technology may become a reality soon, and thus, their use could be extended for PCa.
- PublicaciónIn-depth evaluation of TOF-PET detectors based on crystal arrays and the TOFPET2 ASIC(Elsevier, 2020-10-11) Lamprou, Efthymios; Sánchez Martínez, Filomeno; Benlloch Baviera, Jose María; González Martínez, Antonio Javier; Instituto de Instrumentación para Imagen Molecular; European Commission; Generalitat Valenciana; Ministerio de Economía y Competitividad[EN] In recent years high efforts have been devoted to enhance spatial and temporal resolutions of PET detectors. However, accurately combining these two main features is, in most of the cases, challenging. Typically, a compromise has to be made between the number of readout channels, scintillator type and size, and photosensors arrangement if aiming for a good system performance, while keeping a moderate cost. In this work, we have studied several detector configurations for PET based on a set of 8x8 Silicon Photomultiplier (SiPMs) of 3x3 mm(2) active area, and LYSO crystal arrays with different pixel sizes. An exhaustive evaluation in terms of spatial, energy and timing resolution was made for all detector configurations. In some cases, when using pixel sizes different than SiPM active area, a significant amount of scintillation light may spread among several SiPMs. Therefore, we made use of a calibration method considering the different SiPM timing contributions. Best Detector Time Resolution (DTR) of 156 ps FWHM was measured when using 3x3 mm(2) crystal pixels directly coupled to the 3x3 mm(2) SiPMs. However, when using 1.5 mm crystal pixels with the same photosensor array, although we could clearly resolve all crystal pixels, an average DTR of 250 ps FWHM was achieved. We also shed light in this work on the timing dependency of the crystal pixel and photosensor alignment.
- PublicaciónPilot performance of a dedicated prostate PET suitable for diagnosis and biopsy guidance(SpringerOpen (part of Springer Nature), 2020-06-05) Cañizares-Ledo, Gabriel; Gonzalez-Montoro, Andrea; Freire, Marta; Lamprou, Efthymios; Barrio, John; Sánchez Martínez, Filomeno; Benlloch Baviera, Jose María; Hernandez, Liczandro; Moliner Martínez, Laura; Vidal San Sebastián, Luis Fernando; Torres, Irene; Sopena, Pablo; Vera-Donoso, Cesar D.; Bello, Pilar; Barbera, Julio; González Martínez, Antonio Javier; Instituto de Instrumentación para Imagen Molecular; European Commission; Generalitat Valenciana; European Regional Development Fund; Ministerio de Economía y Competitividad[EN] Background: Prostate cancer (PCa) represents one of the most common types of cancers facing the male population. Nowadays, to confirm PCa, systematic or multiparametric MRI-targeted transrectal or transperineal biopsies of the prostate are required. However, due to the lack of an accurate imaging technique capable to precisely locate cancerous cells in the prostate, ultrasound biopsies sample random parts of the prostate and, therefore, it is possible to miss regions where those cancerous cells are present. In spite of the improvement with multiparametric MRI, the low reproducibility of its reading undermines the specificity of the method. Recent development of prostatespecific radiotracers has grown the interest on using positron emission tomography (PET) scanners for this purpose, but technological improvements are still required (current scanners have resolutions in the range of 4¿5 mm). Results: The main goal of this work is to improve state-of-the-art PCa imaging and diagnosis. We have focused our efforts on the design of a novel prostate-dedicated PET scanner, named ProsPET. This system has small scanner dimensions defined by a ring of just 41 cm inner diameter. In this work, we report the design, implementation, and evaluation (both through simulations and real data) of the ProsPET scanner. We have been able to achieve < 2 mm resolution in reconstructed images and high sensitivity. In addition, we have included a comparison with the Philips Gemini-TF scanner, which is used for routine imaging of PCa patients. The ProsPET exhibits better contrast, especially for rod sizes as small as 4.5 mm in diameter. Finally, we also show the first reconstructed image of a PCa patient acquired with the ProsPET. Conclusions: We have designed and built a prostate specific PET system, with a small footprint and improved spatial resolution when compared to conventional whole-body PET scanners. The gamma ray impact within each detector block includes accurate DOI determination, correcting for the parallax error. The potential role of combined organdedicated prostate-specific membrane antigen (PSMA) PET and ultrasound devices, as a prebiopsy diagnostic tool, could be used to guide sampling of the most aggressive sites in the prostate.
- PublicaciónCharacterization of a preclinical PET insert in a 7 tesla MRI scanner: beyond NEMA testing(IOP Publishing, 2020-12-21) Gsell, Willy; Molinos, Cesar; Correcher, Carlos; Belderbos, Sarah; Wouters, Jens; Junge, Sven; Heidenreich, Michael; Vande Velde, Greetje; Rezaei, Ahmadreza; Nuyts, Johan; Cawthorne, Christopher; Cleeren, Frederik; Nannan, Lise; Deroose, Christophe M.; Himmelreich, Uwe; González Martínez, Antonio Javier; Instituto de Instrumentación para Imagen Molecular; European Commission; Hercules Foundation; Stichting Tegen Kanker[EN] This study evaluates the performance of the Bruker positron emission tomograph (PET) insert combined with a BioSpec 70/30 USR magnetic resonance imaging (MRI) scanner using the manufacturer acceptance protocol and the NEMA NU 4-2008 for small animal PET. The PET insert is made of 3 rings of 8 monolithic LYSO crystals (50 x 50 x 10 mm(3)) coupled to silicon photomultipliers (SiPM) arrays, conferring an axial and transaxial FOV of 15 cm and 8 cm. The MRI performance was evaluated with and without the insert for the following radiofrequency noise, magnetic field homogeneity and image quality. For the PET performance, we extended the NEMA protocol featuring system sensitivity, count rates, spatial resolution and image quality to homogeneity and accuracy for quantification using several MRI sequences (RARE, FLASH, EPI and UTE). The PET insert does not show any adverse effect on the MRI performances. The MR field homogeneity is well preserved (Diameter Spherical Volume, for 20 mm of 1.98 +/- 4.78 without and -0.96 +/- 5.16 Hz with the PET insert). The PET insert has no major effect on the radiofrequency field. The signal-to-noise ratio measurements also do not show major differences. Image ghosting is well within the manufacturer specifications (<2.5%) and no RF noise is visible. Maximum sensitivity of the PET insert is 11.0% at the center of the FOV even with simultaneous acquisition of EPI and RARE. PET MLEM resolution is 0.87 mm (FWHM) at 5 mm off-center of the FOV and 0.97 mm at 25 mm radial offset. The peaks for true/noise equivalent count rates are 410/240 and 628/486 kcps for the rat and mouse phantoms, and are reached at 30.34/22.85 and 27.94/22.58 MBq. PET image quality is minimally altered by the different MRI sequences. The Bruker PET insert shows no adverse effect on the MRI performance and demonstrated a high sensitivity, sub-millimeter resolution and good image quality even during simultaneous MRI acquisition.
- PublicaciónExploiting Cherenkov Radiation With BGO-Based Metascintillators(Institute of Electrical and Electronics Engineers, 2023-11) Latella, Riccardo; González Martínez, Antonio Javier; Bonifacio, Daniel A. B.; Kovylina Zabyako, Miroslavna; Griol Barres, Amadeu; Benlloch Baviera, Jose María; Lecoq, Paul; Konstantinou, Georgios; Instituto Universitario de Telecomunicación y Aplicaciones Multimedia; Instituto Universitario de Tecnología Nanofotónica; Instituto de Instrumentación para Imagen Molecular; European Commission; European Research Council; Universitat Politècnica de València; Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brasil[EN] In time-of-flight positron emission tomography (TOF-PET), the timing capabilities of the scintillation-based detector play an important role. An approach for fast timing is using the so-called metascintillators, which combine two materials leading to the synergistic blending of their favorable characteristics. An added effect for BGO-based metascintillators is taking advantage of better transportation of Cherenkov photons through UV-transparent materials such as plastic (type EJ232). To prove this, we use an optimized Coincidence Time Resolution (CTR) setup based on electronic boards with two output signals (timing and energy) and near-ultraviolet (NUV) and vacuum-ultraviolet (VUV) silicon photomultipliers (SiPMs) from Fondazione Bruno Kessler (FBK), along with different coupling materials. As a reference detector, we employed a 3x3x5-mm(3) LYSO:Ce,Ca crystal pixel coupled with optical grease to an NUV-HD SiPM. The evaluation is based on low-threshold rise time, energy and time of arrival of event datasets. Timing results of a BGO/EJ232 3x3x15-mm(3) metapixel show detector time resolutions (DTRs) of 159 ps for the full photopeak. We demonstrate the possibility of event discrimination using subsets with different DTR from the rise time distributions (RTDs). Finally, we present the synergistic capability of metascintillators to enhance Cherenkov photons detection when used along with VUV-sensitive SiPMs.
- PublicaciónMetascintillators: New Results for TOF-PET Applications(Institute of Electrical and Electronics Engineers, 2022-05) Lecoq, Paul; Konstantinou, Georgios; Latella, Riccardo; Moliner Martínez, Laura; Nuyts, Johan; Zhang, Lei; Barrio Toala, John; Benlloch Baviera, Jose María; González Martínez, Antonio Javier; Departamento de Ingeniería Electrónica; Escuela Técnica Superior de Ingeniería de Telecomunicación; Instituto de Instrumentación para Imagen Molecular; European Commission; European Research Council[EN] We report on the progress on a first generation of realistic size metascintillators for time-of-flight PET. These heterostructures combine dense LYSO or BGO plates, interleaved with fast scintillator layers producing a bunch of prompt photons from the energy leakage of the recoil photoelectric electron. From a Geant4 simulation of the energy sharing distribution between the dense and the fast scintillator on 42 LYSO-based and 42 BGO-based configurations, a detailed study of the timing performance has been performed on a selection of the most promising 12 LYSO-based and 14 BGO-based metascintillators. A Monte Carlo simulation was first performed to extrapolate from direct measurements of the performance of the metascintillator components, the detector time resolution (DTR), and sensitivity on the basis of the simulated amount of energy leakage to the fast scintillator. An analytic algorithm was then applied to determine an equivalent coincidence time resolution (CTR) from the random association of the DTR distributions from two metapixels in coincidence. This equivalent CTR is calculated in order to obtain the same variance in the reconstructed image as the combination of the DTR distributions of 2 metapixels. Preliminary results confirm that with these simple and still nonoptimized configurations, an equivalent CTR of 150 ps for BGO-based and 140 ps for LYSO-based metapixels of realistic size can be obtained
- PublicaciónSimulation Study of Clinical PET Scanners With Different Geometries, Including TOF and DOI Capabilities.(Institute of Electrical and Electronics Engineers, 2024-07) Cañizares-Ledo, Gabriel; Jiménez Serrano, Santiago; Lucero-Ruiz, Alejandro; Morera-Ballester, Constantino; Muñoz, Enrique; Benlloch Baviera, Jose María; González Martínez, Antonio Javier; Departamento de Sistemas Informáticos y Computación; Escuela Técnica Superior de Ingeniería Informática; Instituto de Instrumentación para Imagen Molecular; European Research Council; European Regional Development Fund; Universitat Politècnica de València; Conselleria de Sanitat Universal i Salut Pública de la Generalitat Valenciana[EN] Total Body Positron Emission Tomography (TB-PET) scanners provide high-quality images due to the large sensitivity. Our motivation is to design a TB-PET system with up to 70 cm axial coverage that mitigates the parallax error degradation by using a detector concept based on semi-monolithic LYSO crystals. Furthermore, this detector approach allows to simultaneously reach an accurate Coincidence Time Resolution (CTR) to enhance the image quality by means of Time of Flight (TOF) reconstruction algorithms. We have simulated and compared two Positron Emission Tomography (PET) prototypes with about 70 cm but a different number of detector rings (7 vs. 5). The NEMA NU 2 2018 protocol has been implemented. By correcting the parallax error with the Depth of Interaction (DOI) information, the spatial resolution remains homogeneous and below 3 mm in the entire Field of View (FOV), differently from designs based on pixelated crystals. The sensitivity reaches values of 58 and 115 cps/kBq, for the 5 and 7 rings configurations, respectively. The Noise Equivalent Count Rate (NECR) was found at 563 kcps/mL. This value is lower than other systems, most likely due to the requirement to process a larger number of channels to characterize the DOI. Percent contrasts obtained for two different phantoms are in general beyond 80% for the largest spheres, nearly 100% for the 7 rings configuration once TOF is applied during the reconstruction process. In conclusion, although the sensitivity and NECR results for the 5-rings configuration are lower compared to the 7-rings approach, its overall performance is enhanced by the addition of TOF and parallax error correction, improving that of conventional Whole Body PET scanners (axial length: 20 ¿ 30 cm) in terms of image quality.
- PublicaciónSemi-Monolithic Meta-Scintillator Simulation Proof-of-Concept, Combining Accurate DOI and TOF(Institute of Electrical and Electronics Engineers, 2024-05) Konstantinou, Georgios; Zhang, Lei; Bonifacio, Daniel; Latella, Riccardo; Benlloch Baviera, Jose María; González Martínez, Antonio Javier; Lecoq, Paul; Instituto de Instrumentación para Imagen Molecular; European Commission[EN] In this study, we propose and examine a unique semimonolithic metascintillator (SMMS) detector design, where slow scintillators (BGO or LYSO) are split into thin slabs and read by an array of SiPM, offering depth-of-interaction (DOI) information. These are alternated with thin segmented fast scintillators (plastic EJ232 or EJ232Q), also read by single SiPMs, which provides pixel-level coincidence time resolution (CTR). The structure combines layers of slow scintillators of size 0.3 x 25.5 x (15 or 24) mm(3) with fast scintillators of size 0.1 x 3.1 x (15 or 24) mm(3). We use a Monte Carlo Gate simulation to gauge this novel semimonolithic detector's performance. We found that the time resolution of SMMS is comparable to pixelated metascintillator designs with the same materials. For example, a 15-mm deep LYSO-based SMMS yielded a CTR of 121 ps before applying timewalk correction (after correction, 107-ps CTR). The equivalent BGO-based SMMS presented a CTR of 241 ps, which is a 15% divergence from metascintillator pixel experimental findings from previous works. We also applied neural networks to the photon distributions and timestamps recorded at the SiPM array, following guidelines on semimonolithic detectors. This led to determining the DOI with less than 3-mm precision and a confidence level of 0.85 in the best case, plus more than 2 standard deviations accuracy in reconstructing energy sharing and interaction energy. In summary, neural network prediction capabilities outperform standard energy calculation methods or any analytical approach on energy sharing, thanks to the improved understanding of photon distribution.