Charged Particle Imaging Research Articles

A Wireless, Battery-Powered Probe Based on a Dual-Tier CMOS SPAD Array for Charged Particle Sensing

A compact probe for charged particle imaging, with potential applications in source activity mapping and radio-guided surgery was designed and tested. The development of this technology holds significant implications for medical imaging, offering healthcare professionals accurate and efficient tools for diagnoses and treatments. To fulfill the portability requirements of these applications, the probe was designed for battery operation and wireless communication with a PC. The core sensor is a dual-layer CMOS SPAD detector, fabricated using 150 nm technology, which uses overlapping cells to produce a coincidence signal and reduce the dark count rate (DCR). The sensor is managed and interfaced with a microcontroller, and custom firmware was developed to facilitate communication with the sensor. The performance of the probe was evaluated by characterizing the on-board SPAD detector in terms of the DCR, and the results were consistent with the characterization measurements taken on the same chip samples using a purposely developed benchtop setup.

Arbitrary image reinflation: A deep learning technique for recovering 3D photoproduct distributions from a single 2D projection.

Many charged particle imaging measurements rely on the inverse Abel transform (or related methods) to reconstruct three-dimensional (3D) photoproduct distributions from a single two-dimensional (2D) projection image. This technique allows for both energy- and angle-resolved information to be recorded in a relatively inexpensive experimental setup, and its use is now widespread within the field of photochemical dynamics. There are restrictions, however, as cylindrical symmetry constraints on the overall form of the distribution mean that it can only be used with a limited range of laser polarization geometries. The more general problem of reconstructing arbitrary 3D distributions from a single 2D projection remains open. Here, we demonstrate how artificial neural networks can be used as a replacement for the inverse Abel transform and-more importantly-how they can be used to directly "reinflate" 2D projections into their original 3D distributions, even in cases where no cylindrical symmetry is present. This is subject to the simulation of appropriate training data based on known analytical expressions describing the general functional form of the overall anisotropy. Using both simulated and real experimental data, we show how our arbitrary image reinflation (AIR) neural network can be utilized for a range of different examples, potentially offering a simple and flexible alternative to more expensive and complicated 3D imaging techniques.

Trends in angle-resolved molecular photoelectron spectroscopy.

The field of angle-resolved molecular photoelectron spectroscopy is reviewed, with emphasis on foundations and most recent applications in different regimes of light-matter interaction. The basic formalism underlying one-photon electron angular distributions is presented, from the primary molecular frame (MF) photoemission i.e. emission from fully oriented molecules to laboratory frame (LF) observables produced from randomly oriented targets, extensions to multiphoton and strong field processes being briefly described, followed by a survey of current quantum mechanical computational approaches. The description of experimental developments is focused on the advancements in two major instrumentation fields for angle-resolved PES of molecules in the last two decades, namely charged-particle imaging spectrometers and adiabatically or impulsively laser-induced molecular alignment, together with their interplay with the remarkable characteristics achieved nowadays by the ionizing light sources and the challenging control of complex molecules in the gas phase. Aspects and applications of LF angular observables from unoriented targets are presented, with contemporary applications, especially as probes of the target electronic structure, including higher angular observables, in particular photoelectron circular dichroism (PECD) from chiral molecules, which is confirmed as a powerful chiral technique, and higher terms arising from multiphoton or non-dipole terms. Molecular frame photoelectron angular distributions (MFPADs), which stand out as the most complete observables of molecular photoionization stereodynamics in different excitation regimes, now broadly extended to characterize molecular structure and dynamics, are then discussed stemming from fully oriented molecules tackled by electron-ion momentum coincidence techniques, or from laser aligned samples. Finally, novel developments and challenging perspectives, notably the implementation of PAD in time-resolved schemes at ultrashort time scales, high energy, and high intensity regimes are drawn.

Artificial Neural Networks for Noise Removal in Data-Sparse Charged Particle Imaging Experiments.

We present the first demonstration of artificial neural networks (ANNs) for the removal of Poissonian noise in charged particle imaging measurements with very low overall counts. The approach is successfully applied to both simulated and real experimental image data relating to the detection of photoions/photoelectrons in unimolecular photochemical dynamics studies. Specific examples consider the multiphoton ionization of pyrrole and (S)-camphor. Our results reveal an extremely high level of performance, with the ANNs transforming images that are unusable for any form of quantitative analysis into statistically reliable data with an impressive similarity to benchmark references. Given the widespread use of charged particle imaging methods within the chemical dynamics community, we anticipate that the use of ANNs has significant potential impact - particularly, for example, when working in the limit of very low absorption/photoionization cross-sections, or when attempting to reliably extract subtle image features originating from phenomena such as photofragment vector correlations or photoelectron circular dichroism.

Thermal characterization of resistance and gain of microchannel plate (MCP) detectors for the JENI experiment

The microchannel plate (MCP) has been used for decades as a photon, electron and atoms detector in most of the space instruments dedicated for X-rays, energetic neutral atoms and charged particle imaging. The deep-space missions, as near-future ESA Jupiter Icy moon Explorer (JUICE) mission, expect very low temperature conditions on the destination orbit. Since instruments are usually calibrated on the ground under the “room” temperature, it is very important to know the variation of the detectors’ properties with temperature. The resistance and the gain of MCP detectors, dedicated for the Jovian Energetic Neutrals and Ions (JENI) sensor as part of the Particle Environment Package (PEP) instrument onboard JUICE, were measured as a function of temperature at INTRASPEC TECHNOLOGIES, Toulouse, France over the temperature range of − 50 to + 50 °C and at the CALIPSO-3 facility of the Institut de Recherche en Astrophysique et Planetologie (IRAP), Toulouse, France over the temperature range of − 25 to + 25 °C using samples from PHOTONIS France and PHOTONIS USA. Depending on how the resistance of an MCP detector behaves with temperature, it is possible to properly size a high voltage source or, conversely, to choose a glass technology according to the resistance range required for the MCP detector or their minimum operational bias strip current in relation to the extracted current due to the particle counts. Moreover, since the environment of Jupiter is very severe, the sensors of the PEP package instrument onboard JUICE will operate in the presence of high-energy particles which represent a noise source for them despite the shielding of the instrument against radiation. In particular, the background radiation in the Jovian environment represents a crucial issue for the JENI MCP detectors whose gain can be degraded prematurely if too much of charge is extracted from them. Our measurements show that the gain variation of JENI MCP detectors depends on their characteristics, which is an important result that can be used to optimize their gain performance and lifetime. We also show that the resistance of the JENI MCP detectors increases when the temperature decreases and is influenced by the MCP-resistive heating.

Multidimensional Analysis of Time-Resolved Charged Particle Imaging Experiments

We present a tutorial to realize a multidimensional fitting procedure capable of extracting all the relevant information contained in a sequence of charged particle images acquired as a function of time in femtosecond pump–probe experiments. The images are reproduced using a 3D fitting method, which provides the velocity (or center-of-mass kinetic energy) and angular distributions contained in the images and their time evolution. A detailed example of the method is shown through the analysis of the time-resolved predissociation dynamics of CH3I on the B-band origin (Gitzinger et al., J. Chem. Phys.2010, 133, 234313). We show that the multidimensional approach is essential for the analysis of complex images that contain several overlapping contributions where reduced dimensionality analyses cannot provide a reliable description of the features present in the image sequence. This methodology can be generalized to many types of multidimensional data analysis.

Stopping power accuracy and achievable spatial resolution of helium ion imaging using a prototype particle CT detector system.

A precise relative stopping power map of the patient is crucial for accurate particle therapy. Charged particle imaging determines the stopping power either tomographically – particle computed tomography (pCT) – or by combining prior knowledge from particle radiography (pRad) and x-ray CT. Generally, multiple Coulomb scattering limits the spatial resolution. Compared to protons, heavier particles scatter less due to their lower charge/mass ratio. A theoretical framework to predict the most likely trajectory of particles in matter was developed for light ions up to carbon and was found to be the most accurate for helium comparing for fixed initial velocity. To further investigate the potential of helium in particle imaging, helium computed tomography (HeCT) and radiography (HeRad) were studied at the Heidelberg Ion-Beam Therapy Centre (HIT) using a prototype pCT detector system registering individual particles, originally developed by the U.S. pCT collaboration. Several phantoms were investigated: modules of the Catphan QA phantom for analysis of spatial resolution and achievable stopping power accuracy, a paediatric head phantom (CIRS) and a custommade phantom comprised of animal meat enclosed in a 2 % agarose mixture representing human tissue. The pCT images were reconstructed applying the CARP iterative reconstruction algorithm. The MTF10% was investigated using a sharp edge gradient technique. HeRad provides a spatial resolution above that of protons (MTF1010%=6.07 lp/cm for HeRad versus MTF10%=3.35 lp/cm for proton radiography). For HeCT, the spatial resolution was limited by the number of projections acquired (90 projections for a full scan). The RSP accuracy for all inserts of the Catphan CTP404 module was found to be 2.5% or better and is subject to further optimisation. In conclusion, helium imaging appears to offer higher spatial resolution compared to proton imaging. In future studies, the advantage of helium imaging compared to other imaging modalities in clinical applications will be further explored.

Charged-particle emission tomography.

PurposeConventional charged-particle imaging techniques —such as autoradiography —provide only two-dimensional (2D) black ex vivo images of thin tissue slices. In order to get volumetric information, images of multiple thin slices are stacked. This process is time consuming and prone to distortions, as registration of 2D images is required. We propose a direct three-dimensional (3D) autoradiography technique, which we call charged-particle emission tomography (CPET). This 3D imaging technique enables imaging of thick tissue sections, thus increasing laboratory throughput and eliminating distortions due to registration. CPET also has the potential to enable in vivo charged-particle imaging with a window chamber or an endoscope.MethodsOur approach to charged-particle emission tomography uses particle-processing detectors (PPDs) to estimate attributes of each detected particle. The attributes we estimate include location, direction of propagation, and/or the energy deposited in the detector. Estimated attributes are then fed into a reconstruction algorithm to reconstruct the 3D distribution of charged-particle-emitting radionuclides. Several setups to realize PPDs are designed. Reconstruction algorithms for CPET are developed.ResultsReconstruction results from simulated data showed that a PPD enables CPET if the PPD measures more attributes than just the position from each detected particle. Experiments showed that a two-foil charged-particle detector is able to measure the position and direction of incident alpha particles.ConclusionsWe proposed a new volumetric imaging technique for charged-particle-emitting radionuclides, which we have called charged-particle emission tomography (CPET). We also proposed a new class of charged-particle detectors, which we have called particle-processing detectors (PPDs). When a PPD is used to measure the direction and/or energy attributes along with the position attributes, CPET is feasible.

Time-resolved multi-mass ion imaging: Femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera.

The Pixel-Imaging Mass Spectrometry (PImMS) camera allows for 3D charged particle imaging measurements, in which the particle time-of-flight is recorded along with (x, y) position. Coupling the PImMS camera to an ultrafast pump-probe velocity-map imaging spectroscopy apparatus therefore provides a route to time-resolved multi-mass ion imaging, with both high count rates and large dynamic range, thus allowing for rapid measurements of complex photofragmentation dynamics. Furthermore, the use of vacuum ultraviolet wavelengths for the probe pulse allows for an enhanced observation window for the study of excited state molecular dynamics in small polyatomic molecules having relatively high ionization potentials. Herein, preliminary time-resolved multi-mass imaging results from C2F3I photolysis are presented. The experiments utilized femtosecond VUV and UV (160.8 nm and 267 nm) pump and probe laser pulses in order to demonstrate and explore this new time-resolved experimental ion imaging configuration. The data indicate the depth and power of this measurement modality, with a range of photofragments readily observed, and many indications of complex underlying wavepacket dynamics on the excited state(s) prepared.

INSIDE in-beam positron emission tomography system for particle range monitoring in hadrontherapy.

The quality assurance of particle therapy treatment is a fundamental issue that can be addressed by developing reliable monitoring techniques and indicators of the treatment plan correctness. Among the available imaging techniques, positron emission tomography (PET) has long been investigated and then clinically applied to proton and carbon beams. In 2013, the Innovative Solutions for Dosimetry in Hadrontherapy (INSIDE) collaboration proposed an innovative bimodal imaging concept that combines an in-beam PET scanner with a tracking system for charged particle imaging. This paper presents the general architecture of the INSIDE project but focuses on the in-beam PET scanner that has been designed to reconstruct the particles range with millimetric resolution within a fraction of the dose delivered in a treatment of head and neck tumors. The in-beam PET scanner has been recently installed at the Italian National Center of Oncologic Hadrontherapy (CNAO) in Pavia, Italy, and the commissioning phase has just started. The results of the first beam test with clinical proton beams on phantoms clearly show the capability of the in-beam PET to operate during the irradiation delivery and to reconstruct on-line the beam-induced activity map. The accuracy in the activity distal fall-off determination is millimetric for therapeutic doses.

Charged Particle Imaging of the Deprotonated Octatrienoic Acid Anion: Evidence for a Photoinduced Cyclization Reaction.

Photoelectron spectroscopy of the deprotonated octatrienoic acid anion, [C7H9-CO2]-, shows the formation of [C7H9]- and loss of H- at hν = 4.13 eV. Using velocity map imaging, the H- fragment was characterized to have a Boltzmann-like kinetic energy distribution consistent with dissociation on a ground electronic state. Similar dynamics were not observed at hν = 4.66 eV even though there is clear evidence for recovery of the ground electronic state of [C7H9-CO2]-. In accord with supporting electronic structure calculations, the production of H- at hν = 4.13 eV is explained by excited-state dissociation of CO2 to form [C7H9]-, which subsequently undergoes a ring-closure isomerization reaction to yield toluene and H-. These data represent the first evidence for a photoinduced ring-closing isomerization reaction in an anionic polyene and provides an interesting example of the rich anion dynamics that can occur in the detachment continuum and that can influence photochemistry.

Design and characterisation of a real time proton and carbon ion radiography system based on scintillating optical fibres

This paper describes the design and characterization of a charged particle imaging system composed of a position sensitive detector and residual range detector. The position detector consists of two identical overlying and orthogonal planes each of which consists of two layers of pre-aligned and juxtaposed scintillating fibres. The 500μm square section fibres are optically coupled to two Silicon Photomultiplier arrays using a channel reduction system patented by the Istituto Nazionale di Fisica Nucleare. The residual range detector consists of sixty parallel layers of the same fibres used in the position detector each of which is optically coupled to a Silicon Photomultiplier array by wavelength shifting fibres. The sensitive area of the two detectors is 9×9cm2. Characterising the position sensitive and the residual range detectors to reconstruct the radiography, is fundamental to validating the detectors’ designs. The proton radiography of a calibrated target in imaging conditions is presented. The spatial resolution of the position sensitive detector is about 150μm and the range resolution is about 170μm. The performance of the prototypes were tested at CATANA proton therapy facility (Laboratori Nazionali del Sud, INFN, Catania) with energy up to 58MeV and rate of about 106 particles per second. The comparison between the simulations and measurements confirms the validity of this system.

Design and characterization of a real time particle radiography system based on scintillating optical fibers

The fabrication and characterization of a charged particle imaging system composed of a tracker and a residual range detector (RRD) is described. The tracker is composed of four layers of scintillating fibers (SciFi), 500μm side square section, arranged to form two planes orthogonal to each other. The fibers are coupled to two Multi-Pixel Photon Counter (MPPC) arrays by means of a channel reduction system patented by the Istituto Nazionale di Fisica Nucleare (INFN) (Presti, 2015) [1]. Sixty parallel layers of the same fibers used in the tracker compose the RRD. The various layers are optically coupled to a MPPC array by means of wavelength shifting (WLS) fibers. The sensitive area of the two detectors is 9×9cm2. The results of the measurements, acquired by the prototypes with CATANA (Cirrone, 2008) [2] proton beam, and a comparison with the simulations of the detectors are presented.

Correction of image drift and distortion in a scanning electron microscopy.

Continuous research on small-scale mechanical structures and systems has attracted strong demand for ultrafine deformation and strain measurements. Conventional optical microscope cannot meet such requirements owing to its lower spatial resolution. Therefore, high-resolution scanning electron microscope has become the preferred system for high spatial resolution imaging and measurements. However, scanning electron microscope usually is contaminated by distortion and drift aberrations which cause serious errors to precise imaging and measurements of tiny structures. This paper develops a new method to correct drift and distortion aberrations of scanning electron microscope images, and evaluates the effect of correction by comparing corrected images with scanning electron microscope image of a standard sample. The drift correction is based on the interpolation scheme, where a series of images are captured at one location of the sample and perform image correlation between the first image and the consequent images to interpolate the drift-time relationship of scanning electron microscope images. The distortion correction employs the axial symmetry model of charged particle imaging theory to two images sharing with the same location of one object under different imaging fields of view. The difference apart from rigid displacement between the mentioned two images will give distortion parameters. Three-order precision is considered in the model and experiment shows that one pixel maximum correction is obtained for the employed high-resolution electron microscopic system.

Precise 3D Track Reconstruction Algorithm for the ICARUS T600 Liquid Argon Time Projection Chamber Detector

Liquid Argon Time Projection Chamber (LAr TPC) detectors offer charged particle imaging capability with remarkable spatial resolution. Precise event reconstruction procedures are critical in order to fully exploit the potential of this technology. In this paper we present a new, general approach to 3D reconstruction for the LAr TPC with a practical application to the track reconstruction. The efficiency of the method is evaluated on a sample of simulated tracks. We present also the application of the method to the analysis of stopping particle tracks collected during the ICARUS T600 detector operation with the CNGS neutrino beam.

SP-0021 TREATMENT PLANNING: INTEGRATING ROBUSTNESS IN OPTIMIZATION

irradiation. Due to the nuclear reaction characteristics, most of the resulting light charged particles have a larger range than the primaries, i.e. they can leave the patient, whereas the primary projectiles are completely stopped inside. Measuring the trajectories of the escaped particles and calculating their intersection points with the pencil beam results in a depth distribution of the nuclear reaction probability, which is correlated to the primary particle range. It should be noticed that for prompt gamma-ray as well as charged particle imaging proof-of-principle experiments have been performed. Clinically applicable systems are not available at present. However, their development is in progress at several institutions worldwide.

Characterization of a two-color pump–probe setup at FLASH using a velocity map imaging spectrometer

We report on the implementation of a high-count-rate charged particle imaging detector for two-color pump-probe experiments at the free electron laser in Hamburg (FLASH). In doing so, we have developed a procedure for finding the spatial and temporal overlap between the extreme UV free electron laser (FEL) pulses and the IR pulses, which allows for complete alignment of the setup in situations where the region of overlap between the FEL and the IR is not easily accessible by means of imaging optics.

Direct Charged-Particle Imaging System Using an Ultra-Thin Phosphor: Physical Characterization and Dynamic Applications

Imaging β rays in vivo will help to advance microdosimetry and radiopharmaceutical development. In an earlier paper [1], we reported a newly developed system capable of directly imaging high-energy electron emissions in small animals in vivo. In this paper, we have thoroughly characterized the performance of the system. We have measured the sensitivity and detectability and the spatial resolution at various magnifications, as well as the linearity of the system. The system has also demonstrated the capability of directly detecting conversion electrons and positrons as well as β rays. The system has been applied to dynamically image spatiotemporal (18)F-Fluorodeoxyglucose (FDG) uptake distributions in xenograft small tumors in dorsal window chambers on mice in vivo. Heterogeneity in FDG uptake in millimeter-sized tumors has been observed.

Integrated Sensors for Charged-Particle Imaging Using Per-Pixel Correlated Double Sampling

Monolithic CMOS cameras for direct imaging in electron microscopy and other radiation imaging applications have been developed and have been used to capture images with high signal to noise and resolution. Based on CMOS Active Pixel Sensor (APS) technology, the arrays use an 8 to 20 mum epitaxial layer that acts as a thicker sensitive region for the liberation and collection of ionization electrons resulting from impinging charged particles. This results in a 100% fill factor and a far larger signal per incident charged particle than a typical CMOS photodiode could provide. The per-pixel CDS scheme discussed in this paper has demonstrated reductions in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">kT</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> noise by a factor of four, to 11 electrons RMS at room temperature. The CDS scheme requires only one read instead of the two reads plus pre- and post-integration subtraction required by traditional CDS, and is hence faster than alternate schemes. In addition, the test device was used in the observation of Random Telegraph Signal noise (RTS) in small-capacitance pixels under different <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> conditions.

Modeling and Analysis of Charged-Particle CMOS Image Sensor Arrays

Direct-detection CMOS image sensors optimized for charged-particle imaging applications, such as electron microscopy and particle physics, have been designed, fabricated and characterized. Based on standard silicon CMOS active pixel sensor (APS) technology, the sensor arrays uses an 8 to 20 mum epitaxial layer that acts as a thicker sensitive region in the generation and collection of ionization electrons resulting from impinging high-energy particles. A range of optimizations to this technology have been developed via simulation and experimental device design. These include the simulation and measurement of charge collection efficiency versus recombination, effect of diode size and stray capacitance versus signal gain and noise, and the effect of different epitaxial silicon depths and the energy of incident electrons. Results from several experimental devices are presented and compared with simulations, including measurements from two prototypes that systematically and independently vary pixel pitch and diode area.