225 research outputs found

    고양자효율 다양극 광전자증배관을 이용한 비정시간 측정 가능 PET

    Get PDF
    학위논문 (박사)-- 서울대학교 대학원 : 의과대학 의과학과, 2019. 2. 이재성.In vivo imaging of physiological activities in molecular level has proven to be useful for diagnosing diseases in early stage. Positron emission tomography (PET) is a widely used molecular imaging technique that provides three-dimensional images of functional changes with high sensitivity by estimating the distribution of injected radiotracers. The advent of time-of-flight (TOF) PET scanners has dramatically improved the quality of generated images, which led to enhanced diagnostic power and/or reduced scan time or patient radiation dose. Herein, a prototype TOF PET scanner based on advanced high-quantum-efficiency multianode photomultiplier tubes (PMTs) is presented. Superior time performance of the scanner was demonstrated and improvement of reconstructed images was confirmed from various phantom studies. Finally, our system was verified to be capable of serving as a demonstration system that provides experimental evidences of the benefits of excellent time performance and to be useful for validating the feasibility of new PET applications that have been traditionally challenging.생체 내의 생리적 현상을 분자 수준으로 촬영하는 것이 가능해짐에 따라 질병의 조기 진단이 가능해지고 있다. 양전자 방출 단층촬영기법(PET)은 이와 같은 분자 영상 기법 중 하나로, 체내에 주사한 방사성 의약품의 체내 분포를 추정함으로써 생리적 기능의 변화를 높은 민감도로 촬영하여 3차원 영상으로 제공한다. 비정 시간 측정 가능 PET 장치는 영상의 품질을 향상시킴으로써 질병을 진단할 확률을 높이거나 환자의 촬영 시간 또는 방사선 피폭 정도를 감소시키는 효과를 나타내는 것으로 알려져 있다. 이에 본 연구에서는 고양자효율 다양극 광전자증배관을 이용하여 고성능의 비정 시간 측정 PET 프로토타입을 개발하였다. 다양한 팬텀 촬영을 수행한 결과 이 프로토타입은 우수한 시간 성능과 향상된 영상을 제공함을 확인하였다. 본 시스템을 활용하여 우수한 시간 성능이 갖는 장점을 실험적으로 입증할 수 있음과 기술적인 한계로 적용이 불가능했던 새로운 PET 응용 분야의 실현 가능성 평가가 가능함을 확인하였다.Contents Abstract i Contents iii List of Figures v List of Tables vii General Introduction 1 Chapter 1. Development of TOF PET detectors 3 1.1. Background 3 1.2. Materials and Methods 4 1.2.1. Photomultiplier Tube 4 1.2.2. Detector Design 6 1.2.3. Front-end Electronics 7 1.2.4. Data Acquisition 9 1.2.5. Experimental Setup 10 1.2.6. Analysis 12 1.2.7. Timing Resolution Optimization 13 1.3. Results 14 1.3.1. Optimal Setup 14 1.3.2. Detector Performance 16 1.3.3. Verification of the Optimized Timing Resolution 19 1.4. Discussion 21 Chapter 2. Proof-of-concept prototype TOF PET system 23 2.1. Background 23 2.2. Materials and Methods 24 2.2.1. Prototype TOF PET Scanner 24 2.2.2. System Performance Measurement 26 2.2.3. Image Quality Measurement 27 2.2.4. Robustness to Errors in Data Correction 29 2.2.5. Partial Ring Geometry and Limited Angle Tomography 30 2.2.6. Joint Estimation of Activity and Attenuation 32 2.2.7. Comparison to Conventional 600-ps TOF PET 34 2.3. Results 35 2.3.1. System Performance Measurement 35 2.3.2. Image Quality Measurement 40 2.3.3. Robustness to Errors in Data Correction 44 2.3.4. Partial Ring Geometry and Limited Angle Tomography 47 2.3.5. Joint Estimation of Activity and Attenuation 49 2.4. Discussion 51 General Discussion 55 Reference 57 국문 초록 64Docto

    Evaluation of Single-Chip, Real-Time Tomographic Data Processing on FPGA - SoC Devices

    Get PDF
    A novel approach to tomographic data processing has been developed and evaluated using the Jagiellonian PET (J-PET) scanner as an example. We propose a system in which there is no need for powerful, local to the scanner processing facility, capable to reconstruct images on the fly. Instead we introduce a Field Programmable Gate Array (FPGA) System-on-Chip (SoC) platform connected directly to data streams coming from the scanner, which can perform event building, filtering, coincidence search and Region-Of-Response (ROR) reconstruction by the programmable logic and visualization by the integrated processors. The platform significantly reduces data volume converting raw data to a list-mode representation, while generating visualization on the fly.Comment: IEEE Transactions on Medical Imaging, 17 May 201

    Estudio, diseño e integración de un sistema basado en FPGA para el cálculo del tiempo de vuelo aplicado a equipos PET

    Get PDF
    La Medicina Nuclear ha experimentado avances significativos en los últimos años debido a la mejora en materiales, sistemas electrónicos, técnicas de algoritmia, de procesado etc., que han permitido que su aplicación se haya extendido considerablemente. Una de las técnicas que más ha progresado en este ámbito ha sido la Tomografía por Emisión de Positrones (PET, del inglés Positron Emission Tomography), consistente en un método no invasivo y muy útil para la evaluación de anomalías de tipo cancerosas. Este sistema está basado en un principio de toma de datos y procesado mediante el cual se obtienen imágenes de la distribución espacial y temporal de los procesos metabólicos que se generan en el interior del organismo. Los sistemas PET están formados por un conjunto de detectores, colocados habitualmente en anillo, de forma que cada uno de ellos proporciona información acerca de los eventos que se han producido en su interior. Uno de los motivos por el cual los sistemas PET han evolucionado de forma tan significativa, ha sido la aparición de técnicas que permiten determinar el Tiempo de Vuelo (TOF, del inglés Time of Flight) de los fotones que se generan a causa de la aniquilación de los positrones con su antipartícula, los electrones. La determinación del TOF permite establecer con mayor precisión la ubicación de los eventos que se generan y, por tanto, facilita la labor de reconstrucción de la imagen que, en última instancia, utilizará el equipo médico para el diagnóstico y/o tratamiento. En esta Tesis se parte de la hipótesis de desarrollar un sistema basado en Dispositivos Lógicos Reconfigurables (FPGAs, del inglés Field Programmable Gate Arrays) para la integración de un Convertidor Digital de Tiempo (TDC, del inglés Time-to-Digital Converter) para la medida precisa de tiempos con capacidad para el cálculo de la diferencia temporal de las partículas gamma para su posterior aplicación en sistemas PET. Inicialmente, se describe el entorno dentro del cual surge la necesidad de la implementación de tal sistema y se formula una premisa de partida. A continuación, se exponen los principios básicos del PET así como el estado del arte de los sistemas similares. Seguidamente, se plantean los principios del cálculo del TOF con FPGAs y se justifica el esquema adoptado, entrando en detalle en cada una de sus partes. Tras la implementación, se presentan los primeros resultados de medida de tiempos, obteniendo resoluciones menores de 100 ps para múltiples canales y caracterizando el sistema ante variaciones de temperatura. Una vez caracterizado el sistema, se presentan las pruebas realizadas con un prototipo PET de mama y con tecnología de detectores FotoMultiplicadores Sensibles a la Posición (PSPMTs, del inglés, Position Sensitive PhotoMultiplier Tubes), haciendo medidas de TOF para distintos supuestos. Tras esta primera prueba, se pasa a la implementación de dos módulos de FotoMultiplicadores basados en Silicio (SiPMs, del inglés Silicon PhotoMultipliers), detectores que presentan con respecto a los PSPMTs, entre otras ventajas, inmunidad a elevados campos magnéticos. Esto es de vital importancia si se pretende que el PET trabaje en combinación con una Resonancia Magnética (MR, del inglés Magnetic Resonance), como es el caso. Los dos módulos detectores se componen de un solo píxel y, para cada uno, se diseña su electrónica de acondicionamiento, teniendo en cuenta los parámetros más influyentes en la resolución temporal. Tras estos resultados, se pasa a probar el sistema en una matriz de 144 SiPMs, optimizando además diversos parámetros de impacto directo en el funcionamiento del sistema y, por tanto, en la resolución temporal alcanzada (hasta 700 ps). Por último, demostradas las capacidades del sistema, se lleva a cabo un proceso de optimización, tanto del TDC, que permite mejorar la resolución a valores menores de 40 ps, como de un algoritmo de coincidencias, el cual se encarga de identificar pares de detectores que han registrado un evento dentro de cierta ventana temporal. Finalmente, se recogen las conclusiones de la Tesis y las líneas futuras en las que se va a trabajar. Asimismo, se presentan las diversas participaciones, tanto en revistas de impacto como en congresos.Nuclear Medicine has undergone significant advances in recent years due to improvements in materials, electronics, software techniques, processing etc., which has allowed to considerably extend its application. One technique that has progressed in this area has been the Positron Emission Tomography (PET) based on a non-invasive method with its especial relevance in the evaluation of cancer diagnosis and assessment, among others. This system is based on the principle of data collection and processing from which images of the spatial and temporal distribution of the metabolic processes that are generated inside the body are obtained. The imaging system consists of a set of detectors, normally placed in a ring geometry, so that each one provides information about events that have occurred inside. One of the reasons that have significantly evolved in PET systems is the development of techniques to determine the Time-of-Flight (TOF) of the photons that are generated due to the annihilation of positrons with their antiparticle, the electron. Determining TOF allows one for a more precise location of the events that are generated inside the ring and, therefore, facilitates the task of image reconstruction that ultimately use the medical equipment for the diagnosis and/or treatment. This Thesis begins with the assumption of developing a system based on Field Programmable Gate Arrays (FPGAs) for the integration of a Time- to-Digital Converter (TDC) in order to precisely carry out time measurements. This would permit the estimation of the TOF of the gamma particles for subsequent application in PET systems. First of all, the environment for the application is introduced, justifying the need of the purposed system. Following, the basic principles of PET and the state-of-the-art of similar systems are introduced. Then, the principles of Time-of-Flight based on FPGAs are discussed, and the adopted scheme explained, going into detail in each of its parts. After the development, the initial time measurement results are presented, achieving time resolutions below 100 ps for multiple channels. Once characterized, the system is tested with a breast PET prototype, whose technology detectors are based on Position Sensitive PhotoMultiplier Tubes (PSPMTs), performing TOF measurements for different scenarios. After this point, tests based on two Silicon Photomultipliers (SiPMs) modules were carried out. SiPMs are immune to magnetic fields, among other advantages. This is an important feature since there is a significant interest in combining PET and Magnetic Resonances (MR). Each of the two detector modules used are composed of a single crystal pixel. The electronic conditioning circuits are designed, taking into account the most influential parameters in time resolution. After these results, an array of 144 SiPMs is tested, optimizing several parameters, which directly impact on the system performance. Having demonstrated the system capabilities, an optimization process is devised. On the one hand, TDC measurements are enhanced up to 40 ps of precision. On the other hand, a coincidence algorithm is developed, which is responsible of identifying detector pairs that have registered an event within certain time window. Finally, the Thesis conclusions and the future work are presented, followed by the references. A list of publications and attended congresses are also provided

    Recent developments in time-of-flight PET

    Get PDF
    While the first time-of-flight (TOF)-positron emission tomography (PET) systems were already built in the early 1980s, limited clinical studies were acquired on these scanners. PET was still a research tool, and the available TOF-PET systems were experimental. Due to a combination of low stopping power and limited spatial resolution (caused by limited light output of the scintillators), these systems could not compete with bismuth germanate (BGO)-based PET scanners. Developments on TOF system were limited for about a decade but started again around 2000. The combination of fast photomultipliers, scintillators with high density, modern electronics, and faster computing power for image reconstruction have made it possible to introduce this principle in clinical TOF-PET systems. This paper reviews recent developments in system design, image reconstruction, corrections, and the potential in new applications for TOF-PET. After explaining the basic principles of time-of-flight, the difficulties in detector technology and electronics to obtain a good and stable timing resolution are shortly explained. The available clinical systems and prototypes under development are described in detail. The development of this type of PET scanner also requires modified image reconstruction with accurate modeling and correction methods. The additional dimension introduced by the time difference motivates a shift from sinogram- to listmode-based reconstruction. This reconstruction is however rather slow and therefore rebinning techniques specific for TOF data have been proposed. The main motivation for TOF-PET remains the large potential for image quality improvement and more accurate quantification for a given number of counts. The gain is related to the ratio of object size and spatial extent of the TOF kernel and is therefore particularly relevant for heavy patients, where image quality degrades significantly due to increased attenuation (low counts) and high scatter fractions. The original calculations for the gain were based on analytical methods. Recent publications for iterative reconstruction have shown that it is difficult to quantify TOF gain into one factor. The gain depends on the measured distribution, the location within the object, and the count rate. In a clinical situation, the gain can be used to either increase the standardized uptake value (SUV) or reduce the image acquisition time or administered dose. The localized nature of the TOF kernel makes it possible to utilize local tomography reconstruction or to separate emission from transmission data. The introduction of TOF also improves the joint estimation of transmission and emission images from emission data only. TOF is also interesting for new applications of PET-like isotopes with low branching ratio for positron fraction. The local nature also reduces the need for fine angular sampling, which makes TOF interesting for limited angle situations like breast PET and online dose imaging in proton or hadron therapy. The aim of this review is to introduce the reader in an educational way into the topic of TOF-PET and to give an overview of the benefits and new opportunities in using this additional information

    Optimized PET module for both pixelated and monolithic scintillator crystals

    Get PDF
    [eng] Time-of-Flight Positron Emission Tomography (TOF-PET) scanners demand fast and efficient photo-sensors and scintillators coupled to fast readout electronics. Nowadays, there are two main configurations regarding the scintillator crystal geometry: the segmented or pixelated and the monolithic approach. Depending on the cost, spatial resolution and time requirements of the PET module, one can choose between one or another. The pixelated crystal is the most extensive configuration on TOF-PET scanners as the coincidence time resolution is better compared to the monolithic. On the contrary, monolithic scintillator crystals for Time-of-Flight Positron Emission Tomography (ToF-PET) are increasing in popularity this last years due to their performance potential and price in front of the commonly used segmented crystals. On one hand, monolithic blocks allows to determine 3D information of the gamma-ray interaction inside the crystal, which enables the possibility to correct the parallax error (radial astigmatism) at off-center positions within a PET scanner, resulting in an improvement of the spatial resolution of the device. On the other hand, due to the simplicity during the crystal manufacturing process as well as for the detector design, the price is reduced compared to a regular pixelated detector. The thesis starts with the use of HRFlexToT, an ASIC developed in this group, as the readout electronics for measurements with single pixelated crystals coupled to different SiPMs. These measurements show an energy linearity error of 3% and an energy resolution below 10% of the 511 keV photopeak. Single Photon Time Resolution (SPTR) measurements performed using an FBK SiPM NUV-HD (4 mm x 4 mm pixel size) and a Hamamatsu SiPM S13360-3050CS gave a 141 ps and 167 ps FWHM respectively. Coincidence Time Resolution (CTR) measurements with small cross-section pixelated crystals (LFS crystal, 3 m x 3 mm x 20 mm ) coupled to a single Hamamatsu SiPM S13360-3050CS provides a CTR of 180 ps FWHM. Shorter crystals (LSO:Ce Ca 0.4%) coupled to a Hamamatsu S13360-3050CS SiPM or FBK-NUVHD yields a CTR of 117 ps and 119 ps respectively. Then, the results with different monolithic crystals and SiPM sensors using HRFlexToT ASIC will be presented. A Lutetium Fine Silicate (LFS) of 25 mm x 25 mm x 20 mm, a small LSO:Ce Ca 0.2% of 8 mm x 8 mm x 5 mm and a Lutetium-Yttrium Oxyorthosilicate (LYSO) of 25 mm x 25 mm x 10 mm has been experimentally tested. After subtracting the TDC contribution (82 ps FWHM), a coincidence time resolution of 244 ps FWHM for the small LFS crystal and 333 ps FWHM for the largest LFS one is reported. Additionally, a novel time calibration correction method for CTR improvement that involves a pico-second pulsed laser will be detailed. In the last part of the dissertation, a new developed simulation framework that will enable the cross-optimization of the whole PET system will be explained. It takes into consideration the photon physics interaction in the scintillator crystal, the sensor response (sensor size, pixel pitch, dead area, capacitance) and the readout electronics behavior (input impedance, noise, bandwidth, summation). This framework has allowed us to study a new promising approach that will help reducing the CTR parameter by segmenting a large area SiPM into "m" smaller SiPMs and then summing them to recover all the signal spread along these smaller sensors. A 15% improvement on time resolution is expected by segmenting a 4 mm x 4 mm single sensor into 9 sensors of 1.3 mm x 1.3 mm with respect to the case where no segmentation is applied.[cat] Aquesta tesi tenia com a objectiu la fabricació i avaluació d'un prototip per a detecció de fotons gamma en aplicació per imatge mèdica, més concretament en Tomografia per Emissió de Positrons amb mesura de temps de vol (TOF-PET). L'avaluació del mòdul va començar fent una caracterització completa del chip (ASIC) anomenat HRFlexToT, una versió nova i millorada de l'antic chip FlexToT, desenvolupat i fabricat pel grup de la Unitat Tecnològica del ICC de la Universitat de Barcelona. Aquesta avaluació inicial del chip compren des de la comprovació de les funcionalitats bàsiques fins a la generació d'un test automàtic per generar les gràfiques de linealitat corresponents durant el test elèctric. Un cop donat per bo, es va muntar en una placa demostrada, també ideada per l'equip d'enginyers del grup, i ja quedava llesta per realitzar les mesures pertinents. Tot seguit, es varen realitzar les mesures òptiques, que incloïa mesures de Singe Photon Time Resolution (SPTR) i de Coincidence Time Resolution (CTR). Aquest valors actuen com a figures de mèrit a l'hora de comparar les prestacions amb d'altres ASICs competidors del HRFlexToT. Es van obtenir valors de 60 ps de resposta pel que respecta al SPTR i de 115 ps de CTR en cristalls segmentats, una millora entorn del 20-30% respecte a la versió predecessora del chip. Aquests valors mostren ser el límit de l'estat de l'art actual i amb aquesta idea es van començar a fer altres mesures, en aquest cas amb cristall monolítics, blocs grans llegits per diversos fotosensors de les empreses Hamamatsu i FBK. Per altra banda, es va provar el funcionament del ASIC en configuració anomenada monolítica, on el cristall centellejador s'utilitza en blocs grans en coptes d’emprar cristalls segmentats, això abarateix el cost total del detector. Aquesta configuració degrada les propietats de CTR, un paràmetre crític a l'hora de tenir un producte bo i eficient. S’han obtingut mesures de 250 ps de CTR amb aquesta configuració, d’on es pot dir que l’HRFlexToT es trobar a l’estat de l’art de la tecnologia electrònica dedicada a TOF-PET amb cristalls segmentats i monolítics. Finalment, es va desenvolupar una nova eina simulació que consisteix en un sistema híbrid entre un simulador físic i un electrònic per tal de tenir una idea del comportament complet del mòdul detector. Una solució que ningú havia provat fins ara o que no es pot trobar en la literatura

    Development and Performance Evaluation of High Resolution TOF-PET Detectors Suitable for Novel PET Scanners

    Full text link
    Tesis por compendio[ES] La Tomografía por Emisión de Positrones (PET) es una de las técnicas más importantes en la medicina de diagnóstico actual y la más representativa en el campo de la Imagen Molecular. Esta modalidad de imagen es capaz de producir información funcional única, que permite la visualización en detalle, cuantificación y conocimiento de una variedad de enfermedades y patologías. Áreas como la oncología, neurología o la cardiología, entre otras, se han beneficiado en gran medida de esta técnica. A pesar de que un elevado número de avances han ocurrido durante el desarrollo del PET, existen otros que son de gran interés para futuras investigaciones. Uno de los principales pilares actualmente en PET, tanto en investigación como en desarrollo, es la obtención de la información del tiempo de vuelo (TOF) de los rayos gamma detectados. Cuando esto ocurre, aumenta la sensibilidad efectiva del PET, mejorando la calidad señal-ruido de las imágenes. Sin embargo, la obtención precisa de la marca temporal de los rayos gamma es un reto que requiere, además de técnicas y métodos específicos, compromisos entre coste y rendimiento. Una de las características que siempre se ve afectada es la resolución espacial. Como discutiremos, la resolución espacial está directamente relacionada con el tipo de centellador y, por lo tanto, con el coste del sistema y su complejidad. En esta tesis, motivada por los conocidos beneficios en imagen clínica de una medida precisa del tiempo y de la posición de los rayos gamma, proponemos configuraciones de detectores TOF- PET novedosos capaces de proveer de ambas características. Sugerimos el uso de lo que se conoce como métodos de "light-sharing", tanto basado en cristales monolíticos como pixelados de tamaño diferente al del fotosensor. Estas propuestas hacen que la resolución espacial sea muy alta. Sin embargo, sus capacidades temporales han sido muy poco abordadas hasta ahora. En esta tesis, a través de varios artículos revisados, pretendemos mostrar los retos encontrados en esta dirección, proponer determinadas configuraciones y, además, indagar en los límites temporales de éstas. Hemos puesto un gran énfasis en estudiar y analizar las distribuciones de la luz centellante, así como su impacto en la determinación temporal. Hasta nuestro conocimiento, este es el primer trabajo en el que se estudia la relación de la determinación temporal y la distribución de luz de centelleo, en particular usando SiPM analógicos y ASICs. Esperamos que esta tesis motive y permita otros muchos trabajos orientados en nuevos diseños, útiles para instrumentación PET, así como referencia para otros trabajos. Esta tesis esta organizada como se describe a continuación. Hay una introducción compuesta por tres capítulos donde se resumen los conocimientos sobre imagen PET, y especialmente aquellos relacionados con la técnica TOF-PET. Algunos trabajos recientes, pero aún no publicados se muestran también, con el objetivo de corroborar ciertas ideas. En la segunda parte se incluyen las cuatro contribuciones que el candidato sugiere para el compendio de artículos.[CA] La Tomografia per Emissió de Positrons (PET) és una de les tècniques més importants en la medicina de diagnòstic actual i la més representativa en el camp de la Imatge Molecular. Esta modalitat d'imatge és capaç de produir informació funcional única, que permet la visualització en detall, quantificació i coneixement d'una varietat de malalties i patologies. Àrees com l'oncologia, neurologia o la cardiologia, entre altres, s'han beneficiat en gran manera d'aquesta tècnica. Tot i que un elevat nombre d'avanços han ocorregut durant el desenvolupament del PET, hi ha altres que són de gran interés per a futures investigacions. Un dels principals pilars actuals en PET, tant en investigació com en desenvolupament, és l'obtenció de la informació del temps de vol (TOF en anglès) dels raigs gamma detectats. Quan açò ocorre, augmenta la sensibilitat efectiva del PET, millorant la qualitat senyal-soroll de les imatges. No obstant això, l'obtenció precisa de la marca temporal dels raigs gamma és un repte que requerix, a més de tècniques i mètodes específics, compromisos entre cost i rendiment. Una de les característiques que sempre es veu afectada és la resolució espacial. Com discutirem, la resolució espacial està directament relacionada amb el tipus de centellador, i per tant, amb el cost del sistema i la seua complexitat. En aquesta tesi, motivada pels coneguts beneficis en imatge clínica d'una mesura precisa del temps i de la posició dels raigs gamma, proposem nouves configuracions de detectors TOF-PET capaços de proveir d'ambduess característiques. Suggerim l'ús del que es coneix com a mètodes de "light-sharing", tant basat en cristalls monolítics com pixelats de diferent tamany del fotosensor. Aquestes propostes fan que la resolució espacial siga molt alta. No obstant això, les seues capacitats temporals han sigut molt poc abordades fins ara. En aquesta tesi, a través de diversos articles revisats, pretenem mostrar els reptes trobats en aquesta direcció, proposar determinades configuracions i, a més, indagar en els límits temporals d'aquestes. Hem posat un gran èmfasi a estudiar i analitzar les distribucions de la llum centellejant, així com el seu impacte en la determinació temporal. Fins al nostre coneixement, aquest és el primer treball en què s'estudia la relació de la determinació temporal i la distribució de llum de centelleig, en particular utilitzant SiPM analògics i ASICs. Esperem que aquesta tesi motive i permeta molts altres treballs orientats en nous dissenys, útils per a instrumentació PET, així com referència per a altres treballs. Aquesta tesi esta organitzada com es descriu a continuació. Hi ha una introducció composta per tres capítols on es resumeixen els coneixements sobre imatge PET i, especialmente, aquells relacionats amb la tècnica TOF-PET. Alguns treballs recents, però encara no publicats es mostren també, amb l'objectiu de corroborar certes idees. La segona part de la tesi conté els quatre articles revisats que el candidat suggereix.[EN] Positron Emission Tomography (PET) is one of the greatest tools of modern diagnostic medicine and the most representative in the field of molecular imaging. This imaging modality, is capable of providing a unique type of functional information which permits a deep visualization, quantification and understanding of a variety of diseases and pathologies. Areas like oncology, neurology, or cardiology, among others, have been well benefited by this technique. Although numerous important advances have already been achieved in PET, some other individual aspects still seem to have a great potential for further investigation. One of the main trends in modern PET research and development, is based in the extrapolation of the Time- Of-Flight (TOF) information from the gamma-ray detectors. In such case, an increase in the effective sensitivity of PET is accomplished, resulting in an improved image signal-to-noise ratio. However, the direction towards a precise decoding of the photons time arrival is a challenging task that requires, besides specific approaches and techniques, tradeoffs between cost and performance. A performance characteristic very habitually compromised in TOF-PET detector configurations is the spatial resolution. As it will be discussed, this feature is directly related to the scintillation materials and types, and consequently, with system cost and complexity. In this thesis, motivated by the well-known benefits in clinical imaging of a precise time and spatial resolution, we propose novel TOF-PET detector configurations capable of inferring both characteristics. Our suggestions are based in light sharing approaches, either using monolithic detectors or crystal arrays with different pixel-to-photosensor sizes. These approaches, make it possible to reach a precise impact position determination. However, their TOF capabilities have not yet been explored in depth. In the present thesis, through a series of peer-reviewed publications we attempt to demonstrate the challenges encountered in these kinds of configurations, propose specific approaches improving their performance and eventually reveal their limits in terms of timing. High emphasis is given in analyzing and studying the scintillation light distributions and their impact to the timing determination. To the best of our knowledge, this is one of the first works in which such detailed study of the relation between light distribution and timing capabilities is carried out, especially when using analog SiPMs and ASICs. Hopefully, this thesis will motivate and enable many other novel design concepts, useful in PET instrumentation as well as it will serve as a helpful reference for similar attempts. The present PhD thesis is organized as follows. There is an introduction part composed by three detailed sections. We attempt to summarize here some of the knowledge related to PET imaging and especially with the technique of TOF-PET. Some very recent but still unpublished results are also presented and included in this part, aiming to support statements and theories. The second part of this thesis lists the four peer-reviewed papers that the candidate is including.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 Economía, Industria y Competitividad under Grants No. FIS2014-62341-EXP and TEC2016-79884-C2-1-R. Efthymios Lamprou has also been supported by Generalitat Valenciana under grant agreement GRISOLIAP-2018-026.Lamprou, E. (2021). Development and Performance Evaluation of High Resolution TOF-PET Detectors Suitable for Novel PET Scanners [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/162991TESISCompendi

    Implementation and characterisation of radiation detectors based on SIPM for medical imaging

    Get PDF
    In the last decades, medical imaging techniques have revolutionized medicine facilitating the work to the clinicians, favouring the earlier diagnosis of diseases such as cancer, and reducing the time required for surgical procedures. Among these techniques, one of the most promising is Positron Emission Tomography (PET) due to its constant evolution, the functional information it provides and the possibility of combining it with other structural techniques such as CT or MRI. Recently, new generations of PET detectors have been developed leaving behind the conventionally used photomultiplier tubes (PMTs) for the state-of-the-art digital silicone photomultipliers (d-SiPM). In this work, the last generation of radiation detectors, Philips Digital Photon Counting’s (PDPC) d-SiPMs, was studied and characterized. These detectors are used in the commercial Philips Vereos time-of-flight PET/CT scanner, as well as in the Hyperion-IID preclinical PET scanner. The main objective of this work was to learn how to operate this new system in optimum conditions for small-animal imaging, how to design a precise centre of gravity (COG) algorithm for the localization of the scintillator pixels in a scintillator array, and to characterize the energy and spatial resolutions obtained with this PDPC module. Different COG algorithms were tested, and the final one was designed in such a way that only valid events were considered. This algorithm focuses on the main pixel of each event and the eight pixels surrounding it, discarding scatter and noise as much as possible. The energy resolution was measured by studying the full width half maximum (FWHM) of the photopeak, whereas the spatial resolution was measured by computing the valley-to-peak ratio (V/P) and the resolvability index (RI) of a profile taken from the flood field images acquired. In this project, we used a 30×30 scintillator matrix of LYSO crystals of 1.3×1.3×12 mm3, coupled to a 50×50×2 mm3 light guide in order to spread the scintillation photons among 36 of the 64 die sensors integrated in the PDPC DPC 3200-22 module. A study of how the temperature affects the performance of the system and which acquisition parameters, light guide and time window gives better results was performed. As a final check, we compared the initial and final images obtained, considering their spatial and energy resolution.Ingeniería Biomédic

    Positron Emission Tomography: Current Challenges and Opportunities for Technological Advances in Clinical and Preclinical Imaging Systems

    Get PDF
    Positron emission tomography (PET) imaging is based on detecting two time-coincident high-energy photons from the emission of a positronemitting radioisotope. The physics of the emission, and the detection of the coincident photons, give PET imaging unique capabilities for both very high sensitivity and accurate estimation of the in vivo concentration of the radiotracer. PET imaging has been widely adopted as an important clinical modality for oncological, cardiovascular, and neurological applications. PET imaging has also become an important tool in preclinical studies, particularly for investigating murine models of disease and other small-animal models. However, there are several challenges to using PET imaging systems. These include the fundamental trade-offs between resolution and noise, the quantitative accuracy of the measurements, and integration with X-ray computed tomography and magnetic resonance imaging. In this article, we review how researchers and industry are addressing these challenges.This work was supported in part by National Institutes of Health grants R01-CA042593, U01-CA148131, R01CA160253, R01CA169072, and R01CA164371; by Human Frontier Science Program grant RGP0004/2013; and by the Innovative Medicines Initiative under grant agreement 115337, which comprises financial contributions from the European Union’s Seventh Framework Program (FP7/2007–2013
    corecore