Development of a high bandwidth PET data acquisition system based on last generation FPGA architecture

Positron Emission tomography (PET) is a nuclear medical imaging technique which allows non-invasive quantitative assessment of biochemical and functional processes. Its purpose is to determine the distribution of radioactive tracers, chosen depending on the tissues and organs of interest, injected the patient body. The physical principle behind the PET is the detection of the two photons generated by electron positron annihilation due to a β+ decay. The PET is one of the most useful tools to investigate the biology for cancer and cardiac disorders, and to perform molecular imaging. Its best feature is sensitivity: it is the most sensitive technique for medical molecular imaging. This thesis aims at proposing a method for improve the count rate performance of the IRIS PET scanner, a new preclinical system developed on the Department of Physics at the University of Pisa. The IRIS scanner is a data acquisition system based on FPGA (Field Programmable Gate Array) developed with an high modularity and flexibility. It is composed by 16 detectors, 16 data acquisition boards (DAQ) and 1 motherboard. As of today, the detectors are able to count 0.8·106 single events per second, while the DAQ boards are able to transfer to the motherboard the data produced by 0.8 106 counts per second and the motherboard is able to transfer to the Host-PC the data produced by 1.1·106 counts per second. Thus, the maximum rate of photons that could be detected is 0.8·106 photons per second. For a PET scanner, this maximum rate is very important because place limits on the sensitivity and on the Noise Equivalent Count Rate (NECR) of the system and its performance when a tracer with a high activity is used. The bottleneck is given by the detectors and by the link between the DAQ boards and the motherboard. Research for improve the detectors are planned, thus my study has been focused on improve the link between the DAQ boards and the motherboard and the link between motherboard and Host-PC. In order to upgrade the first link, a new protocol for the data transfer has been investigate. This upgrade would be poorly invasive because does not require hardware changes. To implement this new protocol some firmware components have been developed. After a complete simulation, these components were integrated in the DAQ and the motherboard firmwares. Several tests were made for verify the data integrity and the data transfer performance. In order to upgrade the link between the motherboard and the Host-PC, the performance of a new family of FPGA was investigate. The main characteristic of this FPGA family is the integration of an Hard Processor System (HPS) in it. The combination of FPGA and HPS is very powerful because it allows to implement custom logic in the former and use the latter for high level control. High-throughput data paths between the HPS and FPGA fabric provide interconnect performance otherwise infeasible with dual-chip solutions. The board used for test the performance of this new platform is the general purpose prototyping board Arrow SoCkit. A separated set of firmware components has been developed to implement the communication interface between the FPGA and the HPS. Also, a separated set of driver has been developed to control these components through the HPS. Several test was made for verify the data transfer speed. The HPS-FPGA bridge was tested with a loop-back through two 64 bits FIFOs components. Eventually, a Ethernet test has been conducted to measure the data transfer speed between the HPS and the Host PC. The results obtained are: a 30% performance improvement on the link between the DAQ boards and the motherboard without any hardware changes; a potential 200% performance improvement reachable with the change of the FPGA family. The maximum count rate reachable with the firmware change is 1.1 Mcps, while the maximum count rate reachable with the change of the FPGA can potentially becomes 3.5 Mcps. Currently, with the implementation of the new firmware the bottleneck becomes the FPGA-Host link, but when a data acquisition system based on the new FPGA family will be developed the bottleneck will become the detectors. Thus, developments to improve the detectors speed will be necessary in the future

Evaluation of algorithms for photon depth of interaction estimation for the TRIMAGE PET component

The TRIMAGE consortium aims to develop a multimodal PET/MR/EEG brain scanner dedicated to the early diagnosis of schizophrenia and other mental health disorders. The PET component features a full ring made of 18 detectors, each one consisting of twelve 8x8 Silicon PhotoMultipliers (SiPMs) tiles coupled to two segmented LYSO crystal matrices with staggered layers. In each module, the crystals belonging to the bottom layer are coupled one to one to the SiPMs, while each crystal of the top layer is coupled to four crystals of the bottom layer. This configuration allows to increase the crystal thickness while reducing the depth of interaction uncertainty, as photons interacting in different layers are expected to produce different light patterns on the SiPMs. The PET scanner will implement the pixel/layer identification on a front-end FPGA. This will allow increasing the effective bandwidth, setting at the same time restrictions on the complexity of the algorithms to be implemented. In this work two algorithms whose implementation is feasible directly on an FPGA are presented and evaluated. The first algorithm implements a method based on adaptive thresholding, while the other uses a linear Support Vector Machine (SVM) trained to distinguish the light pattern coming from two different layers. The validation of the algorithm performance is carried out by using simulated data generated with the GAMOS Monte Carlo. The obtained results show that the achieved accuracy in layer and pixel identification is above the 90% for both the proposed approaches

The Digital Signal Processing Platform for the Low Frequency Aperture Array: Preliminary Results on the Data Acquisition Unit

A signal processing hardware platform has been developed for the Low Frequency Aperture Array component of the Square Kilometre Array (SKA). The processing board, called an Analog Digital Unit (ADU), is able to acquire and digitize broadband (up to 500MHz bandwidth) radio-frequency streams from 16 dual polarized antennas, channel the data streams and then combine them flexibly as part of a larger beamforming system. It is envisaged that there will be more than 8000 of these signal processing platforms in the first phase of the SKA, so particular attention has been devoted to ensure the design is low-cost and low-power. This paper describes the main features of the data acquisition unit of such a platform and presents preliminary results characterizing its performance

The Signal Processing Firmware for the Low Frequency Aperture Array

The signal processing firmware that has been developed for the Low Frequency Aperture Array component of the Square Kilometre Array is described. The firmware is implemented on a dual FPGA board, that is capable of processing the streams from 16 dual polarization antennas. Data processing includes channelization of the sampled data for each antenna, correction for instrumental response and for geometric delays and formation of one or more beams by combining the aligned streams. The channelizer uses an oversampling polyphase filterbank architecture, allowing a frequency continuous processing of the input signal without discontinuities between spectral channels. Each board processes the streams from 16 antennas, as part of larger beamforming system, linked by standard Ethernet interconnections. There are envisaged to be 8192 of these signal processing platforms in the first phase of the Square Kilometre array so particular attention has been devoted to ensure the design is low cost and low power

The TRIMAGE PET Data Acquisition System: Initial Results

We present the first results obtained with a prototype of the PET read-out electronics of the trimodal PET/MRI/EEG TRIMAGE scanner. The read-out is based on the 64-channel TRIROC ASIC and on an acquisition board that will control up to 12 ASICs. The output of each ASIC is processed in parallel and sent to a host system that in the final version will receive data from 18 acquisition boards. Blocks of 64 SiPMs are one-to-one coupled to a dual-layer staggered LYSO crystal matrix and read by a single ASIC. The FPGA reads the sparse output from the ASICs and reconstructs for each event a full image of the light pattern coming from the LYSO matrix. This pattern can be then processed on-line or sent to the host PC for post-processing. Early tests were conducted by using a prototype board with single LYSO crystals of 3.3mm×3.3mm×8mm and dual layer staggered LYSO matrices. Results show that the ASIC can sustain input rates above 58 kHz on all its channels, with small variations depending on the discriminating thresholds, being this limit due its digital output stage. With the single crystals setup, we obtained an energy resolution of 10.7% at 511 keV and a coincidence time resolution of 420 ps FWHM. With the staggered matrix the obtained mean energy resolution was 16% on the top layer and 18% on the bottom layer. The flood maps obtained with the LYSO matrix setup show that the pixels on both the staggered levels are clearly identifiable

In-treatment tests for the monitoring of proton and carbon-ion therapy with a large area PET system at CNAO

One of the most promising new radiotherapy techniques makes use of charged particles like protons and carbon ions, rather than photons. At present, there are more than 50 particle therapy centers operating worldwide, and many new centers are being constructed. Positron Emission Tomography (PET) is considered a well-established non-invasive technique to monitor range and delivered dose in patients treated with particle therapy. Nuclear interactions of the charged hadrons with the patient tissue lead to the production of β+ emitting isotopes (mainly 15O and 11C), that decay with a short lifetime producing a positron. The two 511 keV annihilation photons can be detected with a PET detector. In-beam PET is particularly interesting because it could allow monitoring the ions range also during dose delivery. A large area dual head PET prototype was built and tested. The system is based on an upgraded version of the previously developed DoPET prototype. Each head covers now 15×15 cm2 and is composed by 9 (3×3) independent modules. Each module consists of a 23×23 LYSO crystal matrix (2 mm pitch) coupled to H8500 PMT and is readout by custom front-end and a FPGA based data acquisition electronics. Data taken at the CNAO treatment facility in Pavia with proton and carbon beams impinging on heterogeneous phantoms demonstrate the DoPET capability to detect the presence of a small air cavity in the phantom

DoPET: An in-treatment monitoring system for proton therapy at 62 MeV

Proton beam radiotherapy is highly effective in treating cancer thanks to its conformal dose deposition. This superior capability in dose deposition has led to a massive growth of the treated patients around the world, raising the need of treatment monitoring systems. An in-treatment PET system, DoPET, was constructed and tested at CATANA beam-line, LNS-INFN in Catania, where 62 MeV protons are used to treat ocular melanoma. The PET technique profits from the beta+ emitters generated by the proton beam in the irradiated body, mainly 15-O and 11-C. The current DoPET prototype consists of two planar 15 cm × 15 cm LYSO-based detector heads. With respect to the previous versions, the system was enlarged and the DAQ up-graded during the years so now also anthropomorphic phantoms, can be fitted within the field of view of the system. To demonstrate the capability of DoPET to detect changes in the delivered treatment plan with respect to the planned one, various treatment plans were used delivering a standard 15 Gy fraction to an anthropomorphic phantom. Data were acquired during and after the treatment delivery up to 10 minutes. When the in-treatment phase was long enough (more than 1 minute), the corresponding activated volume was visible just after the treatment delivery, even if in presence of a noisy background. The after-treatment data, acquired for about 9 minutes, were segmented finding that few minutes are enough to be able to detect changes. These experiments will be presented together with the studies performed with PMMA phantoms where the DoPET response was characterized in terms of different dose rates and in presence of range shifters: the system response is linear up to 16.9 Gy/min and has the ability to see a 1 millimeter range shifter

Prognosis of Regenerative Endodontic Procedures in Mature Teeth: A Systematic Review and Meta-Analysis of Clinical and Radiographic Parameters

This work aimed to investigate the use of Regenerative Endodontic Procedures (REP) on the treatment of pulp necrosis in mature teeth through systematic review and meta-analysis of evidence on clinical and radiographic parameters before and after REP. A search was performed in different databases on 9 September 2020, including seven clinical studies and randomized controlled trials (RCT). The methodological quality was assessed using Revised Cochrane risk-of-bias (RoB 2) and Before-and-After tools. Meta-analyses were performed to evaluate the success incidences regarding the reduction of periapical lesion and recovery of sensitivity. The certainty of the evidence was assessed using GRADE. Meta-analysis showed a high overall success of 0.95 (0.92, 0.98) I2 = 6%, with high periapical lesion reduction at 12 months (0.93 (0.86, 0.96) I2 = 37%) and by the end of follow-up (0.91 (0.83, 0.96) I2 = 13%). Lower incidences of positive sensitivity response were identified for the electrical (0.58 (0.46, 0.70) I2 = 51%) and cold tests (0.70 (0.54, 0.84) I2 = 68%). The calculated levels of REP success were similar to those reported for immature teeth. With a very low certainty of evidence, the meta-analysis showed a high incidence of REP’s success for mature teeth with necrotic pulp evidenced by periapical lesion reduction and moderate positive responses to sensitivity tests