A new elastographic technique using acoustic vortices

[EN] We present a novel method of elastography based on acoustic vortices to transfer angular momentum to tissue in addition to linear momentum. Focused vortex beams can push and twist tissue, and the rotation direction of the applied torque can be dynamically controlled by the modulation of the topological charge of the vortex. The technique results in a robust excitation of shear waves with quasi-omnidirectional radiation pattern and arbitrary waveform, which may have a great impact in imaging performance for elastography.This research has been supported by the Spanish Ministry of Science, Innovation and Universities through grants Juan de la Cierva - Incorporacion¿ IJC2018-037897-I and PID2019-111436RBC22, and by the Agencia Valenciana de la Innovacio through grants INNVA1/2020/92 and INNCON/2020/009. Action cofinanced by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022).Jimenez, N.; Benlloch Baviera, JM.; Camarena Femenia, F. (2020). A new elastographic technique using acoustic vortices. IEEE. 1-4. https://doi.org/10.1109/IUS46767.2020.9251417S1

Organ-Dedicated Molecular Imaging Systems

[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 (DTS15/00152) funded by the Ministerio de Economia y Competitividad under Grant TEC2016-79884-C2-1-R.González Martínez, AJ.; Sánchez, F.; Benlloch Baviera, JM. (2018). Organ-Dedicated Molecular Imaging Systems. IEEE Transactions on Radiation and Plasma Medical Sciences. 2(5):388-403. https://doi.org/10.1109/TRPMS.2018.2846745S3884032

Transcranial acoustic holograms for arbitrary fields generation using focused ultrasound into the brain

[EN] We present 3D printed holographic lenses that correct the aberrations of the skull and, simultaneously, produce arbitrary ultrasonic fields with the geometry of brain structures. Using experimental techniques on a human skull phantom (HSP), a multiple-point focusing lens is designed to focus at both human hippocampi at once; a beam following an arbitrary curved trajectory, i.e., a self-bending beam; and a holographic plate producing a broad focus that overlaps with the left hippocampus (LH). Skull and LH geometries and acoustic properties are obtained from CT-scans and MRI, respectively. Time-reversal (TR) method is used to obtain the magnitude and phase of the back-propagated field from the target shape towards the lens surface. The holographic lenses are designed assuming each pixel of the lens vibrates as a Fabry-Pérot resonator. The resulting lenses are 3D printed using SLA techniques. The three studied cases show similar results in simulation and experiment with and without the HSP: for the bi-focal beam, the reconstructed field accurately matches the target foci; for the curved trajectory beam, the target acoustic image is reconstructed by the designed holographic lens; for the broad focus beam, results present the same qualitative performance providing a similar overall covering of the LH. The reported holographic lenses can be used to control the spatial features of ultrasonic beams inside the skull in an unprecedented manner using single-element ultrasonic sources.This work was supported by Generalitat Valenciana through grants APOSTD/2017/042, ACIF/2017/045 and GV/2018/11. FC acknowledges financial support from Agencia Valenciana de la Innovacio through grant INNCON00/18/9 and European Regional Development Fund (IDIFEDER/2018/022).Jiménez-Gambín, S.; Jimenez, N.; Benlloch Baviera, JM.; Camarena Femenia, F. (2019). Transcranial acoustic holograms for arbitrary fields generation using focused ultrasound into the brain. Acoustical Society of America. 1-6. https://doi.org/10.1121/2.0001195S1

In-depth evaluation of TOF-PET detectors based on crystal arrays and the TOFPET2 ASIC

[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 Accelerators Spectrometers Detectors and Associated Equipment. 977:1-8. https://doi.org/10.1016/j.nima.2020.164295S18977Jones, T., & Townsend, D. (2017). History and future technical innovation in positron emission tomography. Journal of Medical Imaging, 4(1), 011013. doi:10.1117/1.jmi.4.1.011013Surti, S. (2014). Update on Time-of-Flight PET Imaging. Journal of Nuclear Medicine, 56(1), 98-105. doi:10.2967/jnumed.114.145029Lecoq, P. (2017). Pushing the Limits in Time-of-Flight PET Imaging. IEEE Transactions on Radiation and Plasma Medical Sciences, 1(6), 473-485. doi:10.1109/trpms.2017.2756674Surti, S., & Karp, J. S. (2016). Advances in time-of-flight PET. Physica Medica, 32(1), 12-22. doi:10.1016/j.ejmp.2015.12.007Gundacker, S., Auffray, E., Pauwels, K., & Lecoq, P. (2016). Measurement of intrinsic rise times for various L(Y)SO and LuAG scintillators with a general study of prompt photons to achieve 10 ps in TOF-PET. Physics in Medicine and Biology, 61(7), 2802-2837. doi:10.1088/0031-9155/61/7/2802González-Montoro, A., Sánchez, F., Bruyndonckx, P., Cañizares, G., Benlloch, J. M., & González, A. J. (2019). Novel method to measure the intrinsic spatial resolution in PET detectors based on monolithic crystals. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 920, 58-67. doi:10.1016/j.nima.2018.12.056Moses, W. W. (2011). Fundamental limits of spatial resolution in PET. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 648, S236-S240. doi:10.1016/j.nima.2010.11.092Lamprou, E., Gonzalez, A. J., Sanchez, F., & Benlloch, J. M. (2020). Exploring TOF capabilities of PET detector blocks based on large monolithic crystals and analog SiPMs. Physica Medica, 70, 10-18. doi:10.1016/j.ejmp.2019.12.004Lamprou, E., Aguilar, A., González-Montoro, A., Monzó, J. M., Cañizares, G., Iranzo, S., … Benlloch, J. M. (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. doi:10.1016/j.nima.2017.11.002A. Di Francesco, R. Bugalho, L. Oliveira, L. Pacher, A. Rivetti, M. Rolo, et al. TOFPET2: A high-performance ASIC for time and amplitude measurements of SiPM signals in time-of-flight applications, J. Instrum. 11 (03) C03042.Van Dam, H. T., Borghi, G., Seifert, S., & Schaart, D. R. (2013). Sub-200 ps CRT in monolithic scintillator PET detectors using digital SiPM arrays and maximum likelihood interaction time estimation. Physics in Medicine and Biology, 58(10), 3243-3257. doi:10.1088/0031-9155/58/10/3243V. Nadig, D. Schug, B. Weissler, V. Schulz, Evaluation Of The PETsys TOFPET2 ASIC In Multi-Channel Coincidence Experiments, arXiv:1911.08156.Gundacker, S., Turtos, R. M., Auffray, E., Paganoni, M., & Lecoq, P. (2019). High-frequency SiPM readout advances measured coincidence time resolution limits in TOF-PET. Physics in Medicine & Biology, 64(5), 055012. doi:10.1088/1361-6560/aafd52Gundacker, S., Acerbi, F., Auffray, E., Ferri, A., Gola, A., Nemallapudi, M. V., … Lecoq, P. (2016). State of the art timing in TOF-PET detectors with LuAG, GAGG and L(Y)SO scintillators of various sizes coupled to FBK-SiPMs. Journal of Instrumentation, 11(08), P08008-P08008. doi:10.1088/1748-0221/11/08/p0800

Exploring TOF Capabilities of PET Detector Blocks Based on Large Monolithic Crystals and Analog SiPMs

[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 Based on Large Monolithic Crystals and Analog SiPMs. Physica Medica. 70:10-18. https://doi.org/10.1016/j.ejmp.2019.12.004101870Surti, S. (2014). Update on Time-of-Flight PET Imaging. Journal of Nuclear Medicine, 56(1), 98-105. doi:10.2967/jnumed.114.145029Spanoudaki, V. C., & Levin, C. S. (2010). Photo-Detectors for Time of Flight Positron Emission Tomography (ToF-PET). Sensors, 10(11), 10484-10505. doi:10.3390/s101110484Szczesniak, T., Moszynski, M., Swiderski, L., Nassalski, A., Lavoute, P., & Kapusta, M. (2009). Fast Photomultipliers for TOF PET. IEEE Transactions on Nuclear Science, 56(1), 173-181. doi:10.1109/tns.2008.2008992Renker, D. (2007). New trends on photodetectors. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 571(1-2), 1-6. doi:10.1016/j.nima.2006.10.016Kim, C. L., Wang, G.-C., & Dolinsky, S. (2009). Multi-Pixel Photon Counters for TOF PET Detector and Its Challenges. IEEE Transactions on Nuclear Science, 56(5), 2580-2585. doi:10.1109/tns.2009.2028075Moses, W. W. (2002). Current trends in scintillator detectors and materials. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 487(1-2), 123-128. doi:10.1016/s0168-9002(02)00955-5Gundacker, S., Auffray, E., Pauwels, K., & Lecoq, P. (2016). Measurement of intrinsic rise times for various L(Y)SO and LuAG scintillators with a general study of prompt photons to achieve 10 ps in TOF-PET. Physics in Medicine and Biology, 61(7), 2802-2837. doi:10.1088/0031-9155/61/7/2802Gundacker, S., Acerbi, F., Auffray, E., Ferri, A., Gola, A., Nemallapudi, M. V., … Lecoq, P. (2016). State of the art timing in TOF-PET detectors with LuAG, GAGG and L(Y)SO scintillators of various sizes coupled to FBK-SiPMs. Journal of Instrumentation, 11(08), P08008-P08008. doi:10.1088/1748-0221/11/08/p08008Surti, S., & Karp, J. S. (2016). Advances in time-of-flight PET. Physica Medica, 32(1), 12-22. doi:10.1016/j.ejmp.2015.12.007Gundacker, S., Knapitsch, A., Auffray, E., Jarron, P., Meyer, T., & Lecoq, P. (2014). Time resolution deterioration with increasing crystal length in a TOF-PET system. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 737, 92-100. doi:10.1016/j.nima.2013.11.025Marcinkowski, R., España, S., Van Holen, R., & Vandenberghe, S. (2014). Optimized light sharing for high-resolution TOF PET detector based on digital silicon photomultipliers. Physics in Medicine and Biology, 59(23), 7125-7139. doi:10.1088/0031-9155/59/23/7125González-Montoro, A., Sánchez, F., Martí, R., Hernández, L., Aguilar, A., Barberá, J., … González, A. J. (2018). Detector block performance based on a monolithic LYSO crystal using a novel signal multiplexing method. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 912, 372-377. doi:10.1016/j.nima.2017.10.098Xi, D., Xie, Q., Zhu, J., Lin, L., Niu, M., Xiao, P., … Kao, C.-M. (2012). Optimization of the SiPM Pixel Size for a Monolithic PET Detector. Physics Procedia, 37, 1497-1503. doi:10.1016/j.phpro.2012.04.101Gonzalez-Montoro A, Aguilar A, Canizares G, Conde P, Hernandez L, Vidal LF, et al. Performance Study of a Large Monolithic LYSO PET Detector With Accurate Photon DOI Using Retroreflector Layers. IEEE Trans Rad Plasma Med Sci. PP. 1-1. DOI: 10.1109/TRPMS.2017.2692819.Krishnamoorthy, S., Blankemeyer, E., Mollet, P., Surti, S., Van Holen, R., & Karp, J. S. (2018). Performance evaluation of the MOLECUBES β-CUBE—a high spatial resolution and high sensitivity small animal PET scanner utilizing monolithic LYSO scintillation detectors. Physics in Medicine & Biology, 63(15), 155013. doi:10.1088/1361-6560/aacec3González-Montoro, A., Sánchez, F., Bruyndonckx, P., Cañizares, G., Benlloch, J. M., & González, A. J. (2019). Novel method to measure the intrinsic spatial resolution in PET detectors based on monolithic crystals. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 920, 58-67. doi:10.1016/j.nima.2018.12.056Van Dam, H. T., Borghi, G., Seifert, S., & Schaart, D. R. (2013). Sub-200 ps CRT in monolithic scintillator PET detectors using digital SiPM arrays and maximum likelihood interaction time estimation. Physics in Medicine and Biology, 58(10), 3243-3257. doi:10.1088/0031-9155/58/10/3243Di Francesco A, Bugalho R, Oliveira L, Pacher L, Rivetti A, Rolo M, et al. TOFPET2: A high-performance ASIC for time and amplitude measurements of SiPM signals in time-of-flight applications. Journal of Instrumentation, vol. 11, no. 03, p. C03042.TOFPET2 ASIC Evaluation kit - Hardware User Guide (v1.2), v1.2, PETsys Electronics SA., 2018.Lamprou, E., Aguilar, A., González-Montoro, A., Monzó, J. M., Cañizares, G., Iranzo, S., … Benlloch, J. M. (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. doi:10.1016/j.nima.2017.11.002Acerbi, F., & Gundacker, S. (2019). Understanding and simulating SiPMs. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 926, 16-35. doi:10.1016/j.nima.2018.11.118Schug D, Nadig V, Weissler B, Gebhardt P, Schulz V. Initial Measurements with the PETsys TOFPET2 ASIC Evaluation Kit and a Characterization of the ASIC TDC IEEE Trans Rad Plasma Med Sci. PP. 1-1. DOI: 10.1109/TRPMS.2018.2884564.Seifert, S., van Dam, H. T., Vinke, R., Dendooven, P., Lohner, H., Beekman, F. J., & Schaart, D. R. (2012). A Comprehensive Model to Predict the Timing Resolution of SiPM-Based Scintillation Detectors: Theory and Experimental Validation. IEEE Transactions on Nuclear Science, 59(1), 190-204. doi:10.1109/tns.2011.2179314Vinke R, Olcott PD, Cates JW, Levin CS. The lower timing resolution bound for scintillators with non-negligible optical photon transport time in time-of-flight PET. Phys. Med. Phys. Med. Biol. 59 6215. Phys Med Biol. 2014; 59(20): 6215–29.Gonzalez AJ, Sanchez F, Benlloch JM. 2018 Organ-Dedicated Molecular Imaging Systems. IEEE Trans Ratiat Plasma Med Sci. 2017; 2(5): 388–403

Magnetic force induced vibration on a ferromagnetic sphere for viscoelastic media characterization

[EN] A new method that combines transient magnetic forces with ultrasonic imaging and allows the local experimental characterization of the complex shear modulus of a viscoelastic medium is presented. By measuring the dynamics of a ferromagnetic inclusion under the application of a magnetic force, the viscoelastic properties of the medium are extracted. The system is composed of a coil, which creates a magnetic field that induces displacement on a ferromagnetic particle located inside a test phantom, and an ultrasound transducer operating in pulsed-echo mode, utilized to track the displacement of the particle with spatial resolution of several um. Experiments were conducted embedding a ferromagnetic sphere on test phantoms with different compositions and at different temperatures. The obtained results are in good agreement with the theoretical estimation of the dynamical response of a sphere and show robustness on the estimation of the viscoelastic parameters. Moreover, temperature dependent results show asymptotic elasticity values which are physically consistent for soft-solid media.This work is funded by the Spanish Ministerio de Economía e lnnovación (MlNECO) Generalitat Valenciana (GVA) through the projects TEC2016-80976-R and AlCO2016-108. N.J. and A. C acknowledge the support of GVA through the contracts APOSTD/2017/042 and APOSTD/2018/A/229.Cebrecos, A.; Company, M.; Jimenez, N.; Benlloch Baviera, JM.; Camarena Femenia, F. (2019). Magnetic force induced vibration on a ferromagnetic sphere for viscoelastic media characterization. Acoustical Society of America. 1-5. https://doi.org/10.1121/2.0001200S1

Simulation Study for Designing a Dedicated Cardiac TOF-PET System

[EN] The development of dedicated positron emission tomography scanners is an active area of research, especially aiming at the improvement of lesion detection and in support of cancer treatment and management. Recently, dedicated Positron Emission Tomography (PET) systems with different configurations for specific organs have been developed for improving detection effectiveness. Open geometries are always subject to distortion and artifacts in the reconstructed images. Therefore, the aim of this work is to determine the optimal geometry for a novel cardiac PET system that will be developed by our team, and determine the time resolution needed to achieve reasonable image quality for the chosen geometry. The proposed geometries consist of 36 modules. These modules are arranged in two sets of two plates, each one with different configurations. We performed Monte Carlo simulations with different TOF resolutions, in order to test the image quality improvement in each case. Our results show, as expected, that increasing TOF resolution reduces distortion and artifact effects. We can conclude that a TOF resolution of the order of 200 ps is needed to reduce the artifacts, to acceptable levels, generated in the simulated cardiac-PET open geometries.This project has been co-financed by the Spanish Government Grants TEC2016-79884-C2 and RTC-2016-5186-1, by the European Union through the European Regional Development Fund (ERDF) and by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 695536). The work of V.I. was supported by the Generalitat Valenciana APOSTD/2019/086 fellowship.Oliver-Gil, S.; Moliner, L.; Ilisie, V.; Benlloch Baviera, JM.; Rodríguez-Álvarez, M. (2020). Simulation Study for Designing a Dedicated Cardiac TOF-PET System. Sensors. 20(5):1-16. https://doi.org/10.3390/s20051311S116205Gaemperli, O., & Kaufmann, P. A. (2011). PET and PET/CT in cardiovascular disease. Annals of the New York Academy of Sciences, 1228(1), 109-136. doi:10.1111/j.1749-6632.2011.06030.xThackeray, J. T., & Bengel, F. M. (2018). Molecular Imaging of Myocardial Inflammation With Positron Emission Tomography Post-Ischemia. JACC: Cardiovascular Imaging, 11(9), 1340-1355. doi:10.1016/j.jcmg.2018.05.026Li, Z., Gupte, A. A., Zhang, A., & Hamilton, D. J. (2017). Pet Imaging and its Application in Cardiovascular Diseases. Methodist DeBakey Cardiovascular Journal, 13(1), 29. doi:10.14797/mdcj-13-1-29Juárez-Orozco, L. E., Tio, R. A., Alexanderson, E., Dweck, M., Vliegenthart, R., El Moumni, M., … Slart, R. H. J. A. (2017). Quantitative myocardial perfusion evaluation with positron emission tomography and the risk of cardiovascular events in patients with coronary artery disease: a systematic review of prognostic studies. European Heart Journal - Cardiovascular Imaging, 19(10), 1179-1187. doi:10.1093/ehjci/jex331Schelbert, H. R. (2009). Quantification of Myocardial Blood Flow: What is the Clinical Role? Cardiology Clinics, 27(2), 277-289. doi:10.1016/j.ccl.2008.12.009Knuuti, J., Kajander, S., Mäki, M., & Ukkonen, H. (2009). Quantification of myocardial blood flow will reform the detection of CAD. Journal of Nuclear Cardiology, 16(4), 497-506. doi:10.1007/s12350-009-9101-1Peng, H. (2015). Design study of a cardiac-dedicated PET system. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 779, 39-46. doi:10.1016/j.nima.2015.01.042Gonzalez, A. J., Sanchez, F., & Benlloch, J. M. (2018). Organ-Dedicated Molecular Imaging Systems. IEEE Transactions on Radiation and Plasma Medical Sciences, 2(5), 388-403. doi:10.1109/trpms.2018.2846745Moliner, L., Rodríguez-Alvarez, M. J., Catret, J. V., González, A., Ilisie, V., & Benlloch, J. M. (2019). NEMA Performance Evaluation of CareMiBrain dedicated brain PET and Comparison with the whole-body and dedicated brain PET systems. Scientific Reports, 9(1). doi:10.1038/s41598-019-51898-zAhmed, A. M., Tashima, H., Yoshida, E., Nishikido, F., & Yamaya, T. (2017). Simulation study comparing the helmet-chin PET with a cylindrical PET of the same number of detectors. Physics in Medicine and Biology, 62(11), 4541-4550. doi:10.1088/1361-6560/aa685cCho, Z.-H., Son, Y.-D., Kim, H.-K., Kwon, D.-H., Joo, Y.-H., Ra, J. B., … Kim, Y.-B. (2019). Development of Positron Emission Tomography With Wobbling and Zooming for High Sensitivity and High-Resolution Molecular Imaging. IEEE Transactions on Medical Imaging, 38(12), 2875-2882. doi:10.1109/tmi.2019.2916326Surti, S., & Karp, J. S. (2008). Design considerations for a limited angle, dedicated breast, TOF PET scanner. Physics in Medicine and Biology, 53(11), 2911-2921. doi:10.1088/0031-9155/53/11/010Surti, S., & Karp, J. S. (2016). Advances in time-of-flight PET. Physica Medica, 32(1), 12-22. doi:10.1016/j.ejmp.2015.12.007Grant, A. M., Deller, T. W., Khalighi, M. M., Maramraju, S. H., Delso, G., & Levin, C. S. (2016). NEMA NU 2-2012 performance studies for the SiPM-based ToF-PET component of the GE SIGNA PET/MR system. Medical Physics, 43(5), 2334-2343. doi:10.1118/1.4945416Van Sluis, J., de Jong, J., Schaar, J., Noordzij, W., van Snick, P., Dierckx, R., … Boellaard, R. (2019). Performance Characteristics of the Digital Biograph Vision PET/CT System. Journal of Nuclear Medicine, 60(7), 1031-1036. doi:10.2967/jnumed.118.215418Ito, M., Lee, M. S., & Lee, J. S. (2013). Continuous depth-of-interaction measurement in a single-layer pixelated crystal array using a single-ended readout. Physics in Medicine and Biology, 58(5), 1269-1282. doi:10.1088/0031-9155/58/5/1269Bugalho, R., Di Francesco, A., Ferramacho, L., Leong, C., Niknejad, T., Oliveira, L., … Varela, J. (2018). Experimental results with TOFPET2 ASIC for time-of-flight applications. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 912, 195-198. doi:10.1016/j.nima.2017.11.034Gundacker, S., Auffray, E., Frisch, B., Jarron, P., Knapitsch, A., Meyer, T., … Lecoq, P. (2013). Time of flight positron emission tomography towards 100ps resolution with L(Y)SO: an experimental and theoretical analysis. Journal of Instrumentation, 8(07), P07014-P07014. doi:10.1088/1748-0221/8/07/p07014A Code System for Monte Carlo Simulation of Electron and Photon Transporthttp://www.oecd-nea.org/lists/penelope.htmlStrydhorst, J., & Buvat, I. (2016). Redesign of the GATE PET coincidence sorter. Physics in Medicine and Biology, 61(18), N522-N531. doi:10.1088/0031-9155/61/18/n522Baró, J., Sempau, J., Fernández-Varea, J. M., & Salvat, F. (1995). 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Calibration of Gamma Ray Impacts in Monolithic-Based Detectors Using Voronoi Diagrams

[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.2019.2947716S3503604

Characterization of a High-Aspect Ratio Detector With Lateral Sides Readout for Compton PET

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.2020.3006862S5465544

Progress report on the MEDAMI 2019 and CTR research at the DMIL in i3M

[EN] This contribution reports on the recently held MEDAMI 2019 workshop in Valencia (15-17th May 2019). This workshop is about advanced molecular imaging and the main topic of this last edition was Imaging in Immunotherapy. Around 70 attenders met together during three days. This meeting made it possible to join medical doctors and instrumentalists. In MEDAMI 2019 it was exposed the new immunotherapies from a clinical and research point of view. It was shown the already observed improvements when using these therapies. At the same time, we heard about the difficulties and limitations of current molecular imaging in this particular field. It was clear that improvements in system sensitivity and resolution are demanded. Timing information can be utilized in different ways to improve the image quality in PET systems. Precise Coincidence Time Resolution (CTR) improves the signal-to-noise ratio and, therefore, the image contrast, allowing for instance to distinguish low uptake tumors, multicentric lesions, or tumor heterogeneity, to name but a few. Both high time resolution and angular coverage in a PET system can improve the effective sensitivity. An example of a system benchmarking the timing resolution is the Siemens Biograph Vision with 214 ps FWHM, enhancing the detectability. The Explorer total-body PET from UC Davis improves the system sensitivity by having a 2 meters long PET scanner. Deep investigations, from different research groups, are being carried out to further push the limits of timing resolution. This work also describes some of the projects on high timing performance that are being carried out at the Detector for Molecular Imaging Lab (DMIL) at the Institute for Instrumentation in Molecular Imaging (i3M) in Valencia. The DMIL group has extensively worked on detectors and implementation of PET systems enabling the use of accurate timing information. In this progress report we describe the results obtained at the DMIL regarding timing determination in gamma-ray detectors both based on monolithic and pixelated crystals. Although with 15 min thick LYSO blocks it was tough to obtain values of CTR below 500 ps when using analog SiPMs and ASIC-based readout, this was improved down to 250 ps if small 3 mm size and 6 mm height pixels under the one-to-one coupling approach were enabled. This type of approach, the one-to-one coupling, seems to benefit from the light collection in a single photosensor element and, therefore, to improve the timing properties. Monolithic blocks offer, on the contrary, advantages such as photon depth of interaction. In order to separate Compton and photoelectric events we have thought of a detector block design with a high aspect ratio, using LYSO crystals of 51 mm size vs. 3 mm thickness, read-out by the four lateral sides. We have demonstrated the possibility to reach below 2 mm FWHM spatial resolution with an energy resolution of 12%.The DMIL work presented in this paper 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. The author would like to thank all current and former members of the DMIL at i3M for their continuous contributions to this work.González Martínez, AJ.; Barrio, J.; Lamprou, E.; Ilisie, V.; Sánchez Martínez, F.; Benlloch Baviera, JM. (2020). Progress report on the MEDAMI 2019 and CTR research at the DMIL in i3M. Il Nuovo cimento C. 43(1):1-10. https://doi.org/10.1393/ncc/i2020-20005-8S11043