Imaging Cherenkov Research Articles

Performance study of the aerogel RICH at the Belle II experiment

The Belle II experiment at the SuperKEKB asymmetric e+e− collider in High Energy Accelerator Research Organization (KEK, Tsukuba, Japan) is searching for CP asymmetries in different rare decays in the Standard Model. We will collect a large data sample to improve precision of Standard Model measurements (of which CP asymmetries are one example) and search for New Physics. We study the Aerogel Ring Imaging Cherenkov (ARICH) detector response in terms of loglikelihood functions using decay samples of D∗+→D0π+ and D∗−→D̄0π− resonances. The particle identification efficiencies and mis-identification probabilities are presented in 2D momentum and polar angle bins.

Status and perspectives of vacuum-based photon detectors

In this overview article vacuum-based photon detectors are reviewed emphasizing their applications in Cherenkov imaging devices. After the discussion of the basic detector stages such as photo cathode, electron multiplication, and (anode) readout, the status and recent progress with single- and multi-anode dynode photomultipliers (PMTs), hybrid (avalanche) photodetectors and microchannel-plate PMTs are presented. For all of these devices selected examples of their current and planned applications in neutrino, astroparticle, and high energy physics experiments are given. Possible future developments and innovations are also debated. The last part of this review is dedicated to a comparison of important performance parameters like particle detection efficiency, gain inside a magnetic field, rate capability, aging and lifetime issues, and radiation tolerance.

Development of an integrated housing for Silicon Photomultipliers for future Ring Imaging Cherenkov photo-detectors

The housing of the photo-detectors for future Ring Imaging Cherenkov detectors is a complex task, regardless of the sensor choice, due to the many requirements. The sensor housing for LHCb Upgrade II will be an evolution of the one developed for Upgrade I where a totally modular solution, based on fully autonomous functional units called Elementary Cells has been adopted. The main challenge of the new Elementary Cell will be to include active cooling. With SiPM, cooling well below zero degrees centigrade is required. Two different cooling strategies are considered and the status of the design for the Upgrade II Elementary Cell is presented.

Lepto-hadronic Interpretation of 2021 RS Ophiuchi Nova Outburst

Very-high-energy (VHE; 100 GeV < E ≤ 100 TeV) and high-energy (HE; 100 MeV < E ≤ 100 GeV) gamma rays were observed from the symbiotic recurrent nova RS Ophiuchi (RS Oph) during its outburst in 2021 August by various observatories, such as the High Energy Stereoscopic System (HESS), Major Atmospheric Gamma Imaging Cherenkov (MAGIC), and Fermi-Large Area Telescope (LAT). The models that have been explored so far tend to favor a hadronic scenario of particle acceleration over an alternative leptonic scenario. This paper explores a time-dependent lepto-hadronic scenario to explain the emission from the RS Oph source region. We have used simultaneous low-frequency radio data observed by various observatories along with the data provided by HESS, MAGIC, and Fermi-LAT to explain the multiwavelength spectral energy distributions corresponding to 4 days after the outburst. Our results show that a lepto-hadronic interpretation of the source not only explains the observed HE-VHE gamma-ray data but the corresponding model synchrotron component is also consistent with the first 4 days of low-radio-frequency data, indicating the presence of nonthermal radio emission at the initial stage of the nova outburst. We have also calculated the expected neutrino flux from the source region and discuss the possibility of detecting neutrinos.

Optical systems for future Ring Imaging Cherenkov detectors

Optical systems for Ring Imaging Cherenkov (RICH) detectors have historically taken a variety of designs. Nowadays, technological developments allow more flexibility in the design and construction than was possible in the past, such as lightweight secondary mirrors that can be placed in the acceptance of an experiment, widespread use of non-spherical optical surfaces, flexible and fast tools for parametric optimisation of the optical systems before feeding into a full detector simulation. Within this context, the design of the LHCb RICH optical system for the current Run-3 data-taking of the LHC will be presented and compared to the parametric design of the proposed optics for the Upgrade II for the future HL-LHC phase.

Highlights of the very-high-energy gamma-ray sky as seen by MAGIC

MAGIC (Major Atmospheric Gamma Imaging Cherenkov) is a system of two 17-m diameter Cherenkov telescopes operating at the Observatorio del Roque de Los Muchachos in La Palma (Canary Islands, Spain) since 2009. The telescopes detect very-high-energy (VHE, E > 100 GeV) gamma rays ranging from few tens of GeV to few tens of TeV. In this contribution I will present a selection of the latest scientific results obtained by the MAGIC telescopes, regarding Gamma-Ray Bursts observations, multi-messenger and multi-wavelength astronomy, and the discovery of VHE gamma-ray emission from the first VHE nova, RS Ophiuchi.

Abstract 5046: Cerenkov luminescence imaging of interscapular brown adipose tissue using TSPO-targeting probe to overcome off-target effect of [18F]FDG

Abstract Aim/Introduction: [18F]fluorodeoxyglucose-positron emission tomography ([18F]FDG-PET) has been used as an imaging methods for measuring interscapular brown adipose tissue (iBAT) activity. However, [18F]FDG-PET has limitations for obtaining iBAT-specific images due to off-target effects with high uptake in skeletal muscle, tumors, and inflamed tissue. Uncoupling protein 1 (UCP1), a well-known biomarker for BAT, located in mitochondria also has been suggested as BAT imaging marker. Recently, UCP1 ThermoMouse was established as a reporter mouse for monitoring UCP1 expression. Translocator protein-18 kDa (TSPO) located in the mitochondria outer membrane along with UCP1 is overexpressed in BAT. TSPO targeting probe has been proposed as a potential imaging marker for iBAT imaging. To date, there have been no studies for BAT imaging using TSPO-targeting probe in UCP1 ThermoMouse reflecting UCP1 expression. Moreover, Cerenkov luminescence imaging (CLI) which captures Cerenkov radiation emitted from PET probes has been suggested as an alternative option for PET. In this study, we aim to evaluate [18F]fm-PBR28-d2 as a TSPO-targeting probe for iBAT imaging using PET and CLI in the UCP1 ThermoMouse. Materials and Methods: UCP1 ThermoMouse with insertion of a Luc2-T2A-tdTomato cassette into the initiation of codon of the Ucp1-coding sequence exon 1 were used to monitor UCP1 expression. UCP1 ThermoMouse were characterized with Western blotting and immunohistochemistry to measure the levels of UCP1 expression. PET images were acquired with SimPET, and optical images such as bioluminescence imaging (BLI), fluorescence imaging (FLI) and Cerenkov luminescence imaging (CLI) were acquired with IVIS 100. Results: BLI or FLI reflecting UCP1 expression were clearly showed iBAT in UCP1 ThermoMouse. Also, UCP1 and TSPO expression were correlated in iBAT. TSPO-targeting PET probe with [18F]fm-PBR28-d2 showed iBAT-specific signals without off-target effect in brain or heart. In addition, [18F]fm-PBR28-d2 better reflected individual variation in different UCP1 expression than [18F]FDG. In particular, higher molar activity of [18F]fm-PBR28-d2 was required to obtain better imaging quality of CLI as well as PET. In physiological changes such as cold stimulation and isoflurane exposure, we observed increased imaging signals with cold exposure and decreased imaging signals with prolonged isoflurane exposure. Conclusions: We showed that the TSPO-targeting probe is superior to [18F]FDG as a reliable imaging probe reflecting UCP1 expression in iBAT imaging. Probes with higher molar activity provide better images and are required for quantitative analysis of TSPO-CLI and PET. Our data suggest that CLI with TSPO-targeting probe could be an alternative option for PET. Citation Format: Seok-Yong Lee, Ho Rim Oh, Young-Hwa Kim, Sung-Hwan Bae, Yongseok Lee, Yun-Sang Lee, Byung Chul Lee, Gi Jeong Cheon, Keon Wook Kang, Hyewon Youn. Cerenkov luminescence imaging of interscapular brown adipose tissue using TSPO-targeting probe to overcome off-target effect of [18F]FDG. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5046.

Study of hybrid micropattern gaseous detector with CsI photocathode for Super Tau-Charm facility RICH

Super τ-Charm facility (STCF) is a future electron-positron collider operating in the τ-Charm energy region with the aim of studying hadron structure and spectroscopy. The baseline design of the STCF barrel particle identification (PID) detector, which covers momentum up to 2 GeV/c, is provided by a Ring Imaging Cherenkov Counter (RICH). The RICH features an approximately focusing design with liquid perfluorohexane sealed in a quartz container as the radiator and a hybrid combination of CsI-coated THGEMs and Micromegas as the photo-electron detector. A 16×16 cm2 prototype with a quartz radiator has been built and tested at DESY and stably operated with an effective gain of 105. In this paper, the design, performance, and reconstruction algorithm of RICH detectors are discussed.

Photon-limited Cherenkov imaging of radiation therapy dose.

Cherenkov imaging is a unique verification tool that could provide both dosimetric and tissue functional information during radiation therapy. However, the number of interrogated Cherenkov photons in tissue is always limited and tangled with stray radiation photons, severely frustrating the measurement the signal-to-noise ratio (SNR). As such, here, a noise-robust photon-limited imaging technique is proposed by comprehensively exploiting the physical rationale of low-flux Cherenkov measurements together with the spatial correlations of the objects. Validation experiments confirmed that the Cherenkov signal could be promisingly recovered with high SNR by irradiating at as few as one x ray pulse from a linear accelerator (10 mGy dose), and the Cherenkov excited luminescence imaging depth can be extended by >100% on average, for most concentrations of phosphorescent probe. This approach demonstrates that improved applications in radiation oncology could be seen when signal amplitude, noise robustness, and temporal resolution are comprehensively considered in the image recovery process.

Color-resolved Cherenkov imaging allows for differential signal detection in blood and melanin content.

High-energy x-ray delivery from a linear accelerator results in the production of spectrally continuous broadband Cherenkov light inside tissue. In the absence of attenuation, there is a linear relationship between Cherenkov emission and deposited dose; however, scattering and absorption result in the distortion of this linear relationship. As Cherenkov emission exits the absorption by tissue dominates the observed Cherenkov emission spectrum. Spectroscopic interpretation of this effects may help to better relate Cherenkov emission to ionizing radiation dose delivered during radiotherapy. In this study, we examined how color Cherenkov imaging intensity variations are caused by absorption from both melanin and hemoglobin level variations, so that future Cherenkov emission imaging might be corrected for linearity to delivered dose. A custom, time-gated, three-channel intensified camera was used to image the red, green, and blue wavelengths of Cherenkov emission from tissue phantoms with synthetic melanin layers and varying blood concentrations. Our hypothesis was that spectroscopic separation of Cherenkov emission would allow for the identification of attenuated signals that varied in response to changes in blood content versus melanin content, because of their different characteristic absorption spectra. Cherenkov emission scaled with dose linearly in all channels. Absorption in the blue and green channels increased with increasing oxy-hemoglobin in the blood to a greater extent than in the red channel. Melanin was found to absorb with only slight differences between all channels. These spectral differences can be used to derive dose from measured Cherenkov emission. Color Cherenkov emission imaging may be used to improve the optical measurement and determination of dose delivered in tissues. Calibration for these factors to minimize the influence of the tissue types and skin tones may be possible using color camera system information based upon the linearity of the observed signals.

Comparison of surface dose during whole breast radiation therapy on Halcyon and TrueBeam using Cherenkov imaging.

The emergence of the Halcyon linear accelerator has allowed for increased patient throughput and improved treatment times for common treatment sites in radiation oncology. However, it has been shown that this can lead to increased surface dose in sites like breast cancer compared with treatments on conventional machines with flattened radiation beams. Cherenkov imaging can be used to estimate surface dose by detection of Cherenkov photons emitted in proportion to energy deposition from high energy electrons in tissue. Phantom studies were performed with both square beams in reference conditions and with clinical treatments, and dosimeter readings and Cherenkov images report higher surface dose (25% for flat phantom entrance dose, 5.9% for breast phantom treatment) from Halcyon beam deliveries than for equivalent deliveries from a TrueBeam linac. Additionally, the first Cherenkov images of a patient treated with Halcyon were acquired, and superficial dose was estimated.

Novel Biophotonic Techniques for Phototherapy Enhancement: Cerenkov Radiation as a Bridge between Ionizing and Non-Ionizing Radiation Treatment

In oncology, tremendous research has been conducted on the use of alternative minimally invasive techniques for cancer treatment and diagnosis. The use of biophotonic techniques as a standalone treatment or together with conventional imaging techniques has gained interest among researchers in recent years, while biophotonic therapies such as photothermal and photodynamic therapies tend to bring the use of non-ionizing radiation in therapy back into the spotlight due to the progressive development of optical instrumentation, enhancement agents, molecular probes, light sources and nanocarriers. Thus, the coupling of non-ionizing with ionizing radiation (IR) and the combination of nanomedicine with nuclear medicine procedures are considered to be revolutionary strategies to optimize the therapeutic efficacy of biophotonic modalities and to develop theranostic applications for the better diagnosis and treatment of cancer. Recently, the low-intensity Cerenkov light emitted by tissues as a byproduct of the IR–biostructure interaction has been suggested as an effective internal light source that can trigger phototherapy and guide radiotherapy dosimetry using Cerenkov imaging. This review also provides an overview of in vitro and in vivo studies regarding the use of Cerenkov radiation produced by X-rays or radionucleotides and combined with nanoparticles as a hybrid method to induce enhanced photothermal and photodynamic therapies.

Robust reconstruction of fluorescence molecular tomography based on adaptive adversarial learning strategy

Objective. Fluorescence molecular tomography (FMT) is a promising molecular imaging modality for quantifying the three-dimensional (3D) distribution of tumor probes in small animals. However, traditional deep learning reconstruction methods that aim to minimize the mean squared error (MSE) and iterative regularization algorithms that rely on optimal parameters are typically influenced by strong noise, resulting in poor FMT reconstruction robustness. Approach. In this letter, we propose an adaptive adversarial learning strategy (3D-UR-WGAN) to achieve robust FMT reconstructions. Unlike the pixel-based MSE criterion in traditional CNNs or the regularization strategy in iterative solving schemes, the reconstruction strategy can greatly facilitate the performance of the network models through alternating loop training of the generator and the discriminator. Second, the reconstruction strategy combines the adversarial loss in GANs with the L1 loss to significantly enhance the robustness and preserve image details and textual information. Main results. Both numerical simulations and physical phantom experiments demonstrate that the 3D-UR-WGAN method can adaptively eliminate the effects of different noise levels on the reconstruction results, resulting in robust reconstructed images with reduced artifacts and enhanced image contrast. Compared with the state-of-the-art methods, the proposed method achieves better reconstruction performance in terms of target shape recovery and localization accuracy. Significance. This adaptive adversarial learning reconstruction strategy can provide a possible paradigm for robust reconstruction in complex environments, and also has great potential to provide an alternative solution for solving the problem of poor robustness encountered in other optical imaging modalities such as diffuse optical tomography, bioluminescence imaging, and Cherenkov luminescence imaging.

Practical Guidance for Developing Small-Molecule Optical Probes for In Vivo Imaging.

The WMIS Education Committee (2019-2022) reached a consensus that white papers on molecular imaging could be beneficial for practitioners of molecular imaging at their early career stages and other scientists who are interested in molecular imaging. With this consensus, the committee plans to publish a series of white papers on topics related to the daily practice of molecular imaging. In this white paper, we aim to provide practical guidance that could be helpful for optical molecular imaging, particularly for small molecule probe development and validation in vitro and in vivo. The focus of this paper is preclinical animal studies with small-molecule optical probes. Near-infrared fluorescence imaging, bioluminescence imaging, chemiluminescence imaging, image-guided surgery, and Cerenkov luminescence imaging are discussed in this white paper.

Deep learning particle identification in LHCb RICH

The use of Ring Imaging Cherenkov detectors (RICH) offers a powerful technique for identifying the particle species in particle physics. These detectors produce 2D images formed by rings of individual photons superimposed on a background of photon rings from other particles.The RICH particle identification (PID) is essential to the LHCb experiment at CERN. While the current PID algorithm has performed well during LHC data-taking periods between 2010 to 2018, its complexity poses a challenge for LHCb computing infrastructure upgrades towards multi-core architectures. The high particle multiplicity environment of future LHC runs strongly motivates shifting towards high-throughput computing for the online event reconstruction.In this contribution, we introduce a convolutional neural network (CNN) approach to particle identification in LHCb RICH. The CNN takes binary input images from the two RICH detectors to classify particle species. The input images are polar-transformed sub-sections of the RICH photon-detection planes. The model is hyperparameter-optimised and trained on classification accuracy with simulated collision data for the upcoming LHC operation starting in 2022. The PID performance of the CNN is comparable to the conventional algorithm, and its simplicity renders it suitable for fast online reconstruction through parallel processing.We show that under conditions of reduced combinatorial background, as expected from the introduction of timing resolution to the RICH detectors in future upgrades, the network achieves a particle identification performance close to 100 %, with simultaneous misclassification of the most prevalent particle species approaching 0 %.

Grimoire1 of the MAGIC telescopes

The MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes are a system of two Cherenkov telescopes located on the Canary island of La Palma (Spain), at the Roque de Los Muchachos Observatory, and operating in stereo mode since 2009. Their design and dedicated trigger system allows to reach an energy threshold of 50 GeV, which can be lowered to 15 GeV when using the Sum-Trigger-II. This made it possible to observe sources at the limit of detection for imaging atmospheric Cherenkov telescopes (z∼1) and to deeply study the Geminga pulsar tail emission. A strategy of alert follow-ups from other facilities and the fast repositioning of the telescopes made possible the detection of the first neutrino associated with a blazar and of gamma-ray bursts in the very-high-energy (VHE, E>100 GeV) gamma-ray band, respectively. Moreover, the discovery of GRB190114C allowed a test of general relativity through the study of the Lorentz Invariant Violation. Recently MAGIC observed the first VHE gamma-ray nova, RS Ophiuchi, revealing that protons are accelerated to hundreds of gigaelectronvolts in the nova shock. In this talk we will go through the MAGIC recent highlights in the study of galactic and extragalactic sources, spanning from multimessenger astronomy to astroparticle and fundamental physics.

High performance cross strip imaging readout Planacon sealed tubes

Sealed tube microchannel plate (MCP) detectors have provided a valuable platform for high time resolution photon counting detectors. Specifically, electronic readout MCP based sensors have been used as photon counting, imaging, event time tagging detectors for astronomy, time resolved biological imaging, imaging LIDAR, Cherenkov (RICH), scintillation detection, and neutron imaging. For future initiatives we have been developing novel atomic layer deposited MCPs, UV photocathodes and cross strip (XS) readouts for sealed tube detectors. Novel, atomic layer deposited MCPs can replace standard MCPs, providing enhanced gain stability with reduced intrinsic background and lower gamma ray sensitivity. Additionally, XS readouts provide a compact package to achieve high resolution imaging of single photon positions at low MCP gain. The Photonis Planacon is a commercial sealed tube detector (∼50 mm area) which we have modified to incorporate these novel technologies and demonstrate their performance and robustness.

VTSCat: The VERITAS Catalog of Gamma-Ray Observations

The ground-based gamma-ray observatory Very Energetic Radiation Imaging Telescope Array System (VERITAS, https://veritas.sao.arizona.edu/) is sensitive to photons of astrophysical origin with energies in the range between ≈85 GeV and ≈30 TeV. The instrument consists of four 12 m diameter imaging Cherenkov telescopes operating at the Fred Lawrence Whipple Observatory in southern Arizona. VERITAS started four-telescope operations in 2007 and collects about 1100 hr of good-weather data per year. The VERITAS collaboration has published over 100 journal articles since 2008 reporting on gamma-ray observations of a large variety of objects: Galactic sources like supernova remnants, pulsar wind nebulae, and binary systems; extragalactic sources like star-forming galaxies, dwarf-spheroidal galaxies, and highly variable active galactic nuclei. This note presents VTSCat: the catalog of high-level data products from all VERITAS publications.

Study of nanodiamond photocathodes for MPGD-based detectors of single photons

The proposed new Electron–Ion Collider poses a technical and intellectual challenge for the detector design to accommodate the long-term diverse physics goals envisaged by the program. This requires a 4π detector system capable of reconstructing the energy and momentum of final state particles with high precision. The Electron-Ion Collider also requires identification of particles of different masses over a wide momentum range.A diverse spectrum of Particle IDentification detectors has been proposed. Of the four types of detectors for hadron identification, three are based on Ring Imaging Cherenkov Counter technologies, and one is realized by the Time of Flight method. The quest for a novel photocathode, sensitive in the far vacuum ultraviolet wavelength range and more robust than cesium iodide, motivated an R&D programme to explore nano-diamond (ND) based photocathodes, started by a collaboration between INFN and CNR Bari and INFN Trieste. Systematic measurements of the photoemission in different Ar:CH4 and Ar:CO2 gas mixtures with various types of ND powders and Hydrogenated ND (H-ND) powders are reported. A first study of the response of THGEMs coated with different photocathode materials is presented.The progress of this R&D programme and the results obtained so far by these exploratory studies are described.

Prospective study on observations of gamma-ray emission from active galactic nuclei using the HADAR experiment

The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It is a hybrid array consisting of four water-lens telescopes and a surrounding scintillation detector array for observing Cherenkov light induced by 10 GeV–10 TeV cosmic rays and gamma rays in the atmosphere. The water-lens telescope mainly consists of a hemispherical lens with a diameter of 5 m acting as a Cherenkov light collector, a cylindrical metal tank with a 4 m radius and 7 m height, and an imaging system at the bottom of the tank. The sky region covered by HADAR is much larger than the current generation of Imaging Atmospheric Cherenkov Telescopes, and even the CTA. The field-of-view (FOV) of HADAR can reach up to 60 degrees. The HADAR experiment possesses the advantages of a large field-of-view and low energy threshold, so it can continuously scan wide portions of the sky and easily observe extragalactic gamma-ray sources. The majority of the extragalactic gamma-ray sources detected at very high energy (VHE) energies are active galactic nuclei (AGNs). In this study, we present the potential of using the HADAR experiment for detecting AGN. Based on the AGN catalog sources of the Fermi Large Area Telescope (Fermi-LAT), the observed energy is extrapolated to the VHE range. The VHE gamma rays propagating over cosmological distances can interact with the low-energy of the extragalactic background light (EBL) and produce electron-positron pairs. Therefore, we consider the absorption effects of different EBL models when calculating the expected gamma ray spectra of the AGN sample. We select the sample with redshift measurements and locations inside the FOV of HADAR from 4LAC catalog. In total, there are 375 BL Lacertae objects (BL Lacs) and 289 flat-spectrum radio quasars (FSRQs) satisfying the selection conditions. The integral gamma ray spectra are derived and compared with the sensitivity curve of HADAR, the number of sources with fluxes above the sensitivity of HADAR is counted. Further, we calculate the statistical significance of HADAR for AGN source observation based on the equi-zenith angle sky scanning analysis method. The simulation results reveal that a total of 31 sources of Fermi-LAT AGN can be detected by HADAR with a significance greater than five standard deviations over a one-year survey period, most of which are BL Lacs.