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[EN] The use of photosensors of the type Silicon Photomultpliers (SiPM) has widely been extended in recent years for multiple applications in both research and industry. However, there is a lack of comparative studies of different SiPMs under the same conditions, making it difficult to choose the most appropriate one for a specific application. SiPM arrays are suitable for gamma rays detectors, especially when covering large active areas. They are used either in clinical or pre-clinical scenarios, constituting Single-Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) scanners, or just gamma cameras. The current work presents, for the first time, a comparative study between SensL, Hamamatsu Photonics and KETEK arrays of 12 x 12 SiPMs, with individual active areas of 3 mm x 3 mm, thus covering a total active area of about 5 cm x 5 cm. In this study, we have first evaluated their bias and temperature dependencies, resulting in a very similar behaviour with just a slightly larger dependency of the tested Hamamatsu parts. We also report the performance of detector blocks based on these three SiPM arrays, when coupled to pixelated crystal arrays and monolithic scintillators, in terms of photon impact estimation accuracy, as well as energy resolution. In the case of the monolithic crystals, also the depth of interaction resolution was determined. Both monolithic and pixelated blocks are nowadays widely used in academia or are commercially available for molecular imaging systems. The results obtained for the three SiPM arrays when using those crystals, are comparable, without observing any significant different among them. ; 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 Grant TEC2016-79884-C2-1-R. ; Gonzalez-Montoro, A.; González Martínez, AJ. (2019). Performance ...

388 403 2 5 ; S ; [EN] In this review, we will cover both clinical and technical aspects of the advantages and disadvantages of organ specific (dedicated) molecular imaging (MI) systems, namely positron emission tomography (PET) and single photon emission computed tomography, including gamma cameras. This review will start with the introduction to the organ-dedicated MI systems. Thereafter, we will describe the differences and their advantages/disadvantages when compared with the standard large size scanners. We will review time evolution of dedicated systems, from first attempts to current scanners, and the ones that ended in clinical use. We will review later the state of the art of these systems for different organs, namely: breast, brain, heart, and prostate. We will also present the advantages offered by these systems as a function of the special application or field, such as in surgery, therapy assistance and assessment, etc. Their technological evolution will be introduced for each organ-based imager. Some of the advantages of dedicated devices are: higher sensitivity by placing the detectors closer to the organ, improved spatial resolution, better image contrast recovery (by reducing the noise from other organs), and also lower cost. Designing a complete ring-shaped dedicated PET scanner is sometimes difficult and limited angle tomography systems are preferable as they have more flexibility in placing the detectors around the body/organ. Examples of these geometries will be presented for breast, prostate and heart imaging. Recently achievable excellent time of flight capabilities below 300-ps full width at half of the maximum reduce significantly the impact of missing angles on the reconstructed images. This work was supported in part by the European Research Council through the European Union's Horizon 2020 Research and Innovation Program under Grant 695536, in part by the EU through the FP7 Program under Grant 603002, and in part by the Spanish Ministerio de Economia, Industria y Competitividad through ...

[EN] In this review, we will cover both clinical and technical aspects of the advantages and disadvantages of organ specific (dedicated) molecular imaging (MI) systems, namely positron emission tomography (PET) and single photon emission computed tomography, including gamma cameras. This review will start with the introduction to the organ-dedicated MI systems. Thereafter, we will describe the differences and their advantages/disadvantages when compared with the standard large size scanners. We will review time evolution of dedicated systems, from first attempts to current scanners, and the ones that ended in clinical use. We will review later the state of the art of these systems for different organs, namely: breast, brain, heart, and prostate. We will also present the advantages offered by these systems as a function of the special application or field, such as in surgery, therapy assistance and assessment, etc. Their technological evolution will be introduced for each organ-based imager. Some of the advantages of dedicated devices are: higher sensitivity by placing the detectors closer to the organ, improved spatial resolution, better image contrast recovery (by reducing the noise from other organs), and also lower cost. Designing a complete ring-shaped dedicated PET scanner is sometimes difficult and limited angle tomography systems are preferable as they have more flexibility in placing the detectors around the body/organ. Examples of these geometries will be presented for breast, prostate and heart imaging. Recently achievable excellent time of flight capabilities below 300-ps full width at half of the maximum reduce significantly the impact of missing angles on the reconstructed images. ; This work was supported in part by the European Research Council through the European Union's Horizon 2020 Research and Innovation Program under Grant 695536, in part by the EU through the FP7 Program under Grant 603002, and in part by the Spanish Ministerio de Economia, Industria y Competitividad through PROSPET ...

[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. ; 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) and by the Spanish Ministerio de Economia, Industria y Competitividad under Grant TEC2016-79884-C2-1-R. The first author has also been supported by Generalitat Valenciana, Spain under grant agreement GRISOLIAP-2018-026. ; Lamprou, E.; Sánchez Martínez, F.; Benlloch Baviera, JM.; González Martínez, AJ. (2020). In-depth evaluation of TOF-PET detectors based on crystal arrays and the TOFPET2 ASIC. Nuclear Instruments and Methods in Physics Research Section A ...

[EN] Monolithic scintillators are more frequently used in PET instrumentation due to their advantages in terms of accurate position estimation of the impinging gamma rays both planar and depth of interaction, their increased efficiency, and expected timing capabilities. Such timing performance has been studied when those blocks are coupled to digital photosensors showing an excellent timing resolution. In this work we study the timing behaviour of detectors composed by monolithic crystals and analog SiPMs read out by an ASIC. The scintillation light spreads across the crystal towards the photosensors, resulting in a high number of SiPMs and ASIC channels fired. This has been studied in relation with the Coincidence Timing Resolution (CTR). We have used LYSO monolithic blocks with dimensions of 50 x 50 x 15 mm(3) coupled to SiPM arrays (8 x 8 elements with 6 x 6 mm(2) area) which compose detectors suitable for clinical applications. While a CTR as good as 186 ps FWHM was achieved for a pair of 3 x 3 x 5 mm(3) LYSO crystals, when using the monolithic block and the SiPM arrays, a raw CTR over 1 ns was observed. An optimal timestamp assignment was studied as well as compensation methods for the time-skew and time-walk errors. This work describes all steps followed to improve the CTR. Eventually, an average detector time resolution of 497 ps FWHM was measured for the whole thick monolithic block. This improves to 380 ps FWHM for a central volume of interest near the photosensors. The timing dependency with the photon depth of interaction and planar position are also included. ; 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 Grant TEC2016-79884-C2-1-R. ; Lamprou, E.; González Martínez, AJ.; Sánchez Martínez, F.; Benlloch Baviera, JM. (2020). Exploring TOF Capabilities of PET Detector Blocks ...

This work was supported by the European Research Council through the European Union's Horizon 2020 Research and Innovation Program under Grant 695536. ; Barrio, J.; Cucarella, N.; González Martínez, AJ.; Freire, M.; Ilisie, V.; Benlloch Baviera, JM. (2020). Characterization of a High-Aspect Ratio Detector With Lateral Sides Readout for Compton PET. IEEE Transactions on Radiation and Plasma Medical Sciences. 4(5):546-554. https://doi.org/10.1109/TRPMS.2020.3006862 ; S ; 546 ; 554 ; 4 ; 5

[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. ; This work was supported in part by the European Research Council through the European Union's Horizon 2020 Research and Innovation Program under Grant 695536, and in part by the Spanish Ministerio de Economia, Industria y Competitividad under Grant TEC2016-79884-C2-1-R. ; Freire, M.; Gonzalez-Montoro, A.; Sánchez Martínez, F.; Benlloch Baviera, JM.; González Martínez, AJ. (2020). Calibration of Gamma Ray Impacts in Monolithic-Based Detectors Using Voronoi Diagrams. IEEE Transactions on Radiation and Plasma Medical Sciences. 4(3):350-360. https://doi.org/10.1109/TRPMS.2019.2947716 ; S ; 350 ; 360 ...

546 554 4 5 ; S ; This work was supported by the European Research Council through the European Union's Horizon 2020 Research and Innovation Program under Grant 695536. Barrio, J.; Cucarella, N.; González Martínez, AJ.; Freire, M.; Ilisie, V.; Benlloch Baviera, JM. (2020). Characterization of a High-Aspect Ratio Detector With Lateral Sides Readout for Compton PET. IEEE Transactions on Radiation and Plasma Medical Sciences. 4(5):546-554. https://doi.org/10.1109/TRPMS.2020.3006862

[EN] This article presents system performance studies of the CareMiBrain dedicated brain PET according to NEMA NU 2-2012 (for whole-body PETS) and NU 4-2008 (for preclinical PETs). This scanner is based on monolithic LYSO crystals coupled to silicon photomultipliers. The results obtained for both protocols are compared with current commercial whole body PETs and dedicated brain PETs found in the literature. Spatial resolution, sensitivity, NECR and scatter-fraction are characterized with NEMA standards, as well as an image quality study. A customized image quality phantom is proposed as NEMA phantoms do not fulfil the necessities of dedicated brain PETs. The full-width half maximum of the radial/tangential/ axial spatial resolution of CareMiBrain reconstructed with FBP at 10 and 100 mm from the system center were, respectively, 1.87/1.68/1.39 mm and 1.86/1.91/1.40 mm (NU 2-2012) and 1.58/1.45/1.40 mm and 1.64/1.66/1.44 mm (NU 4-2008). Peak NECR was 49 kcps@287 MBq with a scatter fraction of 48% using NU 2-2012 phantom. The sensitivity was 13.82 cps/kBq at the center of the FOV (NU 2-2012) and 10% (NU 4-2008). Contrast recovery coefficients for customizing image quality phantom were 0.73/0.78/1.14/1.01 for the 4.5/6/9/12 mm diameter rods. The performance characteristics of CareMiBrain are at the top of the current technologies for PET systems. Dedicated brain PET systems significantly improve spatial resolution and sensitivity, but present worse results in count rate measurements and scatter-fraction tests. As for the comparison of preclinical and clinical standards, the results obtained for solid and liquid sources were similar. ; This study was funded by the Spanish Ministry of Science, Innovation and University under grant RTC-2016-5186-1, a project co-financed by the European Union through the European Regional Development Fund (ERDF). CareMiBrain system was funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 711323. Author Dr. Jose Maria Benlloch owns a ...

[EN] Current PET detectors have a very low sensitivity, of the order of a few percent. One of the reasons is the fact that Compton interactions are rejected. If an event involves multiple Compton scattering and the total deposited energy lays within the photoelectric peak, then an energy-weighted centroid is the given output for the coordinates of the reconstructed interaction point. This introduces distortion in the final reconstructed image. The aim of our work is to prove that Compton events are a very rich source of additional information as one can improve the resolution of the detector and implicitly the final reconstructed image. This could be a real breakthrough for PET detector technology as one should be able to obtain better results with less patient radiation. Using a PET as a double Compton camera, by means of Compton cone matching i.e., Compton cones coming from the same event should be compatible, is applied to discard randoms, patient scattered events and also, to perform a correct matching among events with multiple coincidences. In order to fully benefit experimentally from Compton events using monolithic scintillators a multi-layer configuration is needed and a good time-of-flight resolution. ; 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 TEC2016-79884-C2 and RTC-2016-5186-1. ; Ilisie, V.; Giménez-Alventosa, V.; Moliner Martínez, L.; Sánchez, F.; González Martínez, AJ.; Rodríguez-Álvarez, M.; Benlloch Baviera, JM. (2018). Building blocks of a multi-layer PET with time sequence photon interaction discrimination and double Compton camera. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment. 895:74-83. https://doi.org/10.1016/j.nima.2018.03.076 ; S ; 74 ; 83 ; 895

This work was supported by the Spanish Ministerio de Economia, Industria y Competitividad under Grants No. FIS2014-62341-EXP and TEC2016-79884-C2-1-R. 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). ; González Martínez, AJ.; Gonzalez-Montoro, A.; Aguilar, A.; Cañizares, G.; Martí, R.; Iranzo, S.; Lamprou, E. (2017). A scintillator geometry suitable for very small PET gantries. Journal of Instrumentation. 12. https://doi.org/10.1088/1748-0221/12/12/C12018 ; S ; 12

[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/s41598-019-54934-0 ; S ; 1 ; 9 ; 9 ; Mok, G. S. P., Tsui, B. M. W. & Beekman, F. J. ...

[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. ...

[EN] There are drawbacks with using a Positron Emission Tomography (PET) scanner design employing the traditional arrangement of multiple detectors in an array format. Typically PET systems are constructed with many regular gaps between the detector modules in a ring or box configuration, with additional axial gaps between the rings. Although this has been significantly reduced with the use of the compact high granularity SiPM photodetector technology, such a scanner design leads to a decrease in the number of annihilation photons that are detected causing lower scanner sensitivity. Moreover, the ability to precisely determine the line of response (LOR) along which the positron annihilated is diminished closer to the detector edges because the spatial resolution there is degraded due to edge effects. This happens for both monolithic based designs, caused by the truncation of the scintillation light distribution, but also for detector blocks that use crystal arrays with a number of elements that are larger than the number of photosensors and, therefore, make use of the light sharing principle. In this report we present a design for a small-animal PET scanner based on a single monolithic annulus-like scintillator that can be used as a PET insert in high-field Magnetic Resonance systems. We provide real data showing the performance improvement when edge-less modules are used. We also describe the specific proposed design for a rodent scanner that employs facetted outside faces in a single LYSO tube. In a further step, in order to support and prove the proposed edgeless geometry, simulations of that scanner have been performed and lately reconstructed showing the advantages of the design. ; This project was funded in part by 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 Grant TEC2016-79884-C2-1-R and through PROSPET (DTS15/00152) ...

[Otros] Monolithic scintillation crystals offer the possibility to preserve the scintillation light distribution, specially when black painted. Furthermore, the statistical moments of that distribution can provide accurate information about the three spatial components. Nevertheless, for monolithic crystal the moments estimation has an associated error due to the symmetry truncation of the light distribution towards the crystal borders. For the 2-D impact coordinates determination, this error is called compression as it is accentuated near the edges. The computation of all centered moments is, therefore, affected by this error. Digital SiPMs (dSiPMs) can offer complete information about the light distribution, since all cells are purely digital detectors, so that other ways to obtain ¿-impact coordinates can be performed. In this work, a comparison between the statistical moments analysis and an alternative fitting the light distribution for each event to a theoretical distribution has been made. With the fitted approach, compression is avoided and an approximately constant spatial resolution is obtained for the entire photodetection area. Moreover, DOI information is improved and preserved all over the crystal. ; This work was supported by the Spanish Plan Nacional de Investigacion Científica, Desarrollo e Innovación Tecnologica (I+D+I) under Grant No. FIS2010-21216-CO2-01 and Valencian Local Government under Grants PROMETEOII/2013/010 and ISIC 2011/013 ; Conde, P.; González Martínez, AJ.; Hernández, L.; Bellido, P.; Crespo, E.; Iborra, A.; Moliner, L. (2013). Statistical moments of scintillation light distribution analysis with dSiPMs and monolithic crystals. IEEE. 10-13. https://doi.org/10.1109/NSSMIC.2013.6829086 ; S ; 10 ; 13