Next-generation PET capability with lutetium fine silicate and multi-pixel photon counter

Currently, positron emission tomography (PET) systems are rapidly developing owing to the invention of new scintillators and photosensors, which contribute to construction of clearer and high-resolution images in cancer diagnosis. In this study, we used a Lutetium Fine Silicate (LFS) inorganic scintillator and multi-pixel photon counter (MPPC) as a photosensor. This combination is realistic for next-generation PET systems. These devices were directly coupled to form a unit detector. A pair of detector units was placed face-to-face, and they simultaneously detected annihilation gamma rays, assuming a pair detector in the PET system. A timing resolution of 96 ps in full width at half maximum (FWHM) was obtained. This result is almost the fastest timing resolution ever achieved. A good timing resolution contributes to noise reduction that leads to clear images. Furthermore, a spatial resolution of 1.9 mm in FWHM was obtained, which is sufficient to meet the spatial resolution requirements for next-generation PET systems.ArticleJOURNAL OF INSTRUMENTATION. 7:P10014 (2012)journal articl

Measurement on properties of MPPC for TOF-PET system

A large number of techniques are rapidly being developed for the diagnosis of cancer, including time-of-flight positron-emission tomography (TOF- PET). To construct an effective TOF-PET system, we introduced lutetium fine silicate (LFS) as a scintillator and a multi-pixel photon counter (MPPC) as a photosensor that exhibits a rapid response. In this study, we investigated four types of MPPCs with a sensitive area of 1 x 1 mm(2) sensitive area and different pitch sizes. All MPPCs showed a timing resolution of 72 ps at the full-width at half-maximum with operating voltages of dV similar to 3 V (with the exception of the 100-pixels MPPC).ArticleJOURNAL OF INSTRUMENTATION. 8:P02018 (2013)journal articl

Design and validation of key components for the readout electronics of future PET scanners

This thesis work discusses the design and validation of two circuit components used in the electronic readout of positron emission tomography (PET) scanners for biomedical applications: a constant fraction discriminator (CFD) and an integrated CMOS time to digital converter (TDC). The former is used in the read out of a double-head PET scanner already developed by the group of medical physics at INFN Pisa for non-invasive dose delivery monitoring in hadrontherapy. The goal of the work has been the optimization of the front-end PCB in terms of timing performances so as to reduce the dead time and resolution at system level. A new CFD board has been implemented and experimental results have shown a significant enhancement of the timing characteristics which have enabled performing in-beam PET data acquisition which is fundamental in hadrontherapy treatment. The design of an integrated CMOS TDC to be used for the time of flight measurement in a magnetic field-compatible PET block detector is the second topic of the thesis. The required time resolutions, linear behaviour as well as the communication with other readout elements have been taken into account in the definition of the circuit topology. Cadence and Verilog simulations have shown that a bin size of 100 ps can be obtained with the combination of a submicron technology (UMC 65 nm LLLVT) and a pipeline approach where a 10 bit systolic counter coupled to a 4 stage delay locked loop (DLL) are exploited. This translates into a nominal resolution of 29 ps. In addition, the use of a short DLL leads to a high linearity which is an issue in PET measurements. Despite lower resolutions are obtained in literature with different TDC topologies, achieving good performances in terms of both time resolution and linearity is not straightforward. The converter also features a real-time validation algorithm which is capable to reject noise inputs generated by the photodetector without impairing the acquisition capability of the system. A standard-cell unit has been also designed which is in charge of data buffering and serial communication with external readout boards. A 47 bit output word is provided by the semi-custom stage at a measurement rate which is selectable between 31.25 MHz and 62.5 MHz with a double hit resolution of 170 ns. An 8 channel prototype of 1.875 x 1.875 mm2 has been submitted in March 2013 in order to validate simulated data with experimental results

Investigation of YAG:Ce Scintillating Fiber Properties Using Silicon Photomultipliers

The properties of thin, cerium activated, yttrium aluminum garnet (YAG:Ce), scintillating fiber-shaped crystals were investigated for particle tracking and calorimetric applications such as Compton imaging of Special Nuclear Material from remote platforms at standoff ranges. Silicon photomultipliers (SiPMs) are relatively new, efficient, single photon sensitive, solid-state photodiode arrays which are well suited for the readout of scintillating fibers. Using SiPMs, the scintillation decay time profiles of six 400 micrometers YAG:Ce fiber crystals were measured under alpha and gamma irradiation. Interestingly, the observed decay times in the thin fibers were substantially slower than values for bulk single crystal YAG:Ce reported in open scientific literature; possible explanations are explored. Both laser induced photoluminescence and alpha scintillation measurements were conducted to estimate the effective attenuation length of the YAG:Ce fibers. Using the measured attenuation lengths, position-of-interaction measurements were conducted to determine the achievable position resolution in YAG:Ce fibers using dual fiber end SiPM readouts. The measured results are compared to theoretical calculations and Monte Carlo simulations. Finally, improvements to the detector concept, including a formula to determine the best SiPM model based on device parameters and the Birks\u27 figure of merit of the scintillating material, are presented

Optimized PET module for both pixelated and monolithic scintillator crystals

[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

Design and Characterisation of an MRI Compatible Human Brain PET Insert by Means of Simulation and Experimental Studies

Positron emission tomography (PET) is a widely used in-vivo imaging technique to visualise metabolism, allowing for a broad spectrum of applications in oncology, cardiology and neuroscience. At present, an MRI compatible human brain PET scanner for applications in neuroscience is being constructed in the scope of a Helmholtz Validation Fund project. In this thesis, a detector for this novel PET device was designed. The detector concept combined three scintillator layers with a lightguide and digital silicon photomultipliers (dSiPMs). Monte Carlo simulations were used to optimise the dimensions of the scintillator arrays, so that the new scanner design yielded the maximum possible sensitivity. The benefit from the additional depth information, which can be acquired with three scintillator layers, was evaluated and proven to be higher compared to a less expensive two layer geometry. Since a more homogeneous spatial resolution was achieved in the whole field of view, this finding had a high relevance for the envisaged neuroscientific applications. In order to accurately acquire the depth information, new strategies for decoding the flood map during the calibration of a detector module were developed. This required realistic simulation data with ground truth information, so that the simulation toolkit GATE was extended to model the electronic readout of the dSiPMs. To overcome extended simulation times and to provide simulations on a statistically sound basis, the GATE studies were executed on the supercomputer JURECA. The simulated data were matched to measured data from test detectors. This allowed the determination of an optimum thickness of a lightguide between the scintillators and the dSiPMs. Moreover, the number of correctly identified scintillation events was evaluated by means of different event positioning approaches and different clustering methods during the calibration step. The highest amount of correctly identified events in a single detector block was achieved with model-based clustering and Maximum Likelihood positioning (61.5 %). By simulating the whole propagation and detection of scintillation photons including ground truth information, this study provides the opportunity to improve the positioning approaches and to enhance this number in future. The gained insights were further applied to select a surface finish of the scintillators. Measurements with crystal samples of the final detector dimensions showed that rough lateral crystal surfaces yielded the best signal separation in the calibration flood map. The experimental and simulation studies presented in this thesis had a major influence on the final detector design of the novel brain PET. The detailed simulations including the propagation and detection of scintillation photons were in good agreement with measured data, and could be a promising approach for future detector design studies

Microfabrication of photonic devices for mid-infrared optical applications

This thesis details research into the microfabrication of photonic devices for mid-infrared optical applications using the technique of ultrafast laser inscription. A diverse range of devices and materials is explored, including the first fabrication and development of an ultrafast laser inscribed mid-infrared waveguide laser source in thulium-doped sesquioxide ceramic gain media. The source produced 81 mW of output power at 1942 nm with a maximum slope efficiency of 9.5% demonstrating progress towards compact, low-threshold and efficient ultrafast laser written waveguide laser sources near 2 μm with the potential for high pulse repetition rate and ultrashort pulse operation. Also shown is the first demonstration of ultrafast laser inscription enabled selective chemical etching of chalcogenide glass. Investigations into the etching of modified regions in gallium lanthanum sulphide glass showed they could be etched at a rate ~13.3 times greater than the un-modified bulk. This result was explored further as a potential route to the production of optofluidic sensors for gas, liquid chemical or biomedical samples. The first demonstration and characterisation of ultrafast laser written waveguides in the chalcogenide glass GASIR-1 is also described. The waveguides were employed for chip scale supercontinuum generation producing the broadest and deepest Infrared supercontinuum from an ultrafast laser inscribed waveguide to-date, spanning ~4 μm from 2.5 to 6.5 μm, which has applications in remote sensing. Finally, the design, build and commissioning of an advanced laser processing setup suitable for ultrafast laser inscription is also detailed

Development of a data acquisition system using silicon detectors for PET applications

Este trabajo describe el desarrollo de parte de la electr´onica elaborada para el diseño de un escáner de Tomografíıa de Emisión de Positrones (PET) denominado Petete. Dicho escáner debe identificar offline los eventos de coincidencia y utilizar la técnica de ToF (Time of Flight) para descartar el ruido de fondo, lo cual permite contribuir a la mejora de la relación señal-ruido (SNR) y por lo tanto al aumento de la calidad de las imágenes médicas. El principal uso del escáner PET será en la investigación para el estudio y prueba de diferentes detectores para la mejora de las prestaciones del escáner PET en términos de resolución espacial, tiempo de adquisición (lo cual implica la reducción del tiempo de exposición del paciente a la radiación), la sensibilidad y calidad de imagen. El escáner conste en 16 módulos de detectores, basados en fotomultiplicadores de silicio, contando con un total de 1024 canales. Para poder recoger la información de ToF, la electrónica de proximidad (Front-end) debe registrar el tiempo de llegada de los eventos válidos detectados con una precisión del orden de cientos de picosegundos. Dado el número no despreciable de canales, y el reducido espacio disponible, la electrónica Front-end debe estar basada en un circuito integrado de aplicación específica (ASIC). Cada módulo de detectores se ubica en una tarjeta denominada tarjeta híbrida, que contiene al menos un ASIC para el registro del tiempo de llegada. Para el presente trabajo se han identificado y trabajado con dos ASICs que se adecúan a las necesidades del escáner: el Vata64hdr16 y el STiC. La electrónica desarrollada consta de dos partes: Por una parte se ha desarrollado completamente el sistema de adquisición de datos que realiza la lectura de los detectores de silicio, incluyendo tanto el hardware como el firmware necesario. Esta tarjeta de adquisición es la encargada de controlar los ASICs, realizar proceso de adquisición de datos, gestionar la comunicación con el ordenador y llevar a cabo la transferencia de datos. Para cubrir el escáner completo, son necesarias en total cuatro tarjetas de adquisición de datos que deben trabajar en paralelo, cubriendo cada una un total de 256 canales. El sistema se controla por un programa software diseñado para esta aplicación e instalado en un ordenador. El sistema de adquisici´on de datos está diseñado para que sea compacto, flexible, rápido y adaptable a las ASICs mencionadas. Por otra parte, es importante destacar que una parte del presente trabajo se ha dedicado al desarrollo de parte de la electrónica digital de STiC. Este trabajo se ha desarrollado en la Universidad de Heidelberg (Alemania) y ha permitido profundizar en el desarrollo de un sistema de adquisici´on de datos en este caso desde el punto de vista de la síntesis de un ASIC. La electrónica y el software implementado en el sistema satisfacen completamente las necesidades del escáner Petete, lo que constituye un sistema multi-configurable con transmisión de datos rápida a través de Gigabit Ethernet. El diseño se ha realizado de forma que se pueden seleccionar diferentes configuraciones, tales como diferentes modos de lectura, diferentes opciones de prueba y configuraci´on separada para cada tarjeta híbrida. Las pruebas experimentales llevadas a cabo verifican el comportamiento funcional correcto de todos los sub-sistemas, tales como ADC, DAC, TDC, triggers, señales de control, comunicación y otros, como se explica en la memoria presentada. Está previsto que el sistema sea utilizado para la investigación en el laboratorio de diferentes sensores de silicio y centelladores, dado que el sistema se ha diseñado de formare configurable y fácil de adaptar con los nuevos detectores. Hasta este momento la tarjera HDRDAQ se ha testado con dos tarjetas híbridas con 64 canales cada uno. En un futuro próximo están previstas las pruebas del sistema completo con cuatro tarjetas hibridas y con cuatro módulos detectores. Otras pruebas planeadas son el uso de varias tarjetas HDRDAQ en paralelo trabajando de modo sincronizado para cubrir el número de módulos detectores del scanner completo. La estructura del presente trabajo es la siguiente: En el primer capítulo se han estudiado las características de los detectores, además de describir el escáner Petete y definir los requerimientos del sistema de adquisición de datos. En el capítulo dos se ha dado una introducción a los fotomultiplicadores de silicio y a las características de los ASICs con los que se ha trabajado: el Vata64hdr16 y el STiC. Además también se ha llevado a cabo el desarrollo de las tarjetas hibridas que forman los módulos del escáner PET. El capítulo 3 se centra en el chip STiC y en el desarrollo de la electrónica digital del diseño ASIC que se ha llevado a cabo. En el capítulo 4 se desarrolla de forma detallada la electrónica de adquisición que lleva a cabo el proceso de control de los chips y la comunicación con el ordenador. Para el diseño de tarjeta de adquisición se ha tenido en cuenta la geometría del escáner, el número de las tarjetas hibridas necesarias que hay que controlar y los requisitos específicos de los ASICs. Para controlar el escáner y la electrónica desde el ordenador se ha desarrollado un programa específico. El capítulo 5 est´a dedicado al desarrollo firmware realizado, y el cap´ıtulo 6 se describe brevemente el software. El ultimo capitulo se ha dedicado al desarrollo de las pruebas en el laboratorio para verificar la funcionalidad de sistema con sus diferentes partes como el software, electrónica y detectores. Finalmente se incluyen las conclusiones del trabajo completo

Technical Design Report for PANDA Electromagnetic Calorimeter (EMC)

This document presents the technical layout and the envisaged performance of the Electromagnetic Calorimeter (EMC) for the PANDA target spectrometer. The EMC has been designed to meet the physics goals of the PANDA experiment. The performance figures are based on extensive prototype tests and radiation hardness studies. The document shows that the EMC is ready for construction up to the front-end electronics interface