Coincidence Imaging Research Articles

Microwave Coincidence Imaging with Phase-Coded Stochastic Radiation Field

Microwave coincidence imaging (MCI) represents a novel forward-looking radar imaging method with high-resolution capabilities. Most MCI methods rely on random frequency modulation to generate stochastic radiation fields, which introduces the complexity of radar systems and imposes limitations on imaging quality under noisy conditions. In this paper, microwave coincidence imaging with phase-coded stochastic radiation fields is proposed, which generates spatio-temporally uncorrelated stochastic radiation fields with phase coding. Firstly, the radiation field characteristics are analyzed, and the coding sequences are designed. Then, pulse compression is applied to achieve a one-dimensional range image. Furthermore, an azimuthal imaging model is built, and a reference matrix is derived from the frequency domain. Finally, sparse Bayesian learning (SBL) and alternating direction method of multipliers (ADMM)-based total variation are implemented to reconstruct targets. The methods have better imaging performance at low signal-to-noise ratios (SNRs), as shown by the imaging results and mean square error (MSE) curves. In addition, compared with the SBL and ADMM-based total variation methods based on the direct frequency-domain solution, the proposed method’s computational complexity is reduced, giving it great potential in forward-looking high-resolution scenarios, such as autonomous obstacle avoidance with vehicle-mounted radar and terminal guidance.

Analysis of the Grid Quantization for the Microwave Radar Coincidence Imaging Based on Basic Correlation Algorithm

In Microwave Radar Coincidence Imaging (MRCI), the imaging region is typically discretized into a fine grid. In other words, it assumes that the equivalent scatterers of the target are precisely located at the centers of these pre-discretized grids. However, this approach usually encounters the off-grid problem, which can significantly degrade the imaging performance. In this paper, to establish a criterion for grid quantization, the performance of the MRCI system related to the grid size and the distribution of imaging points is investigated. First, the discretization of the imaging scene is regarded as a random sampling problem, and the off-grid imaging model for MRCI is established. Then, the probability distribution function (PDF) of the imaging amplitude for a single point target is analyzed, and the mean first-order imaging error (MFE) for multiple point targets is derived based on the Basic Correlation Algorithm (BCA). Finally, the relationship between the grid quantization of the imaging area and the performance of the MRCI system is analyzed, providing a theoretical guidance for enhancing the performance of MRCI. The validity of the analyses is verified through simulation experiments.

Waveform design of radar coincidence imaging radiation field based on image entropy

AbstractRadar coincidence imaging (RCI) is a high‐resolution radar imaging mode which constructs a temporal spatial stochastic radiation field (TSSRF) and uses the correlation between reference signal and echoes for imaging. The correlation between the reference matrix and the echoes is the main factor affecting the imaging performance. In fact, radar target characteristics cause fluctuations in the radar cross section and variations in the scattering intensity of each resolution element. The latter degrades the correlation between the reference matrix and the echoes, seriously affecting the image reconstruction. This paper designs the waveform based on image entropy under fixed transmitting and receiving arrays. The targets with fluctuating scattering intensity at each resolution element are statistically modelled. Simulation results show this approach can improve the imaging performance and reduce the energy dissipation degree of the target grid.

An applied OFDM chirp waveform design scheme for radar coincidence imaging

An applied OFDM chirp waveform design scheme for radar coincidence imaging

Coincidence imaging for Jones matrix with a deep-learning approach

Coincidence measurement has become an emerging technique for optical imaging. Based on measuring the second-order coherence g2, sample features such as reflection/transmission amplitude and phase delay can be extracted with developed algorithms pixel-by-pixel. However, an accurate measurement of g2 requires a substantial number of collected photons which becomes difficult under low-light conditions. Here, we propose a deep-learning approach for Jones matrix imaging using photon arrival data directly. A variational autoencoder (β-VAE) is trained using numerical data in an unsupervised manner to obtain a minimal data representation, which can be transformed into an image with little effort. We demonstrate as few as 88 photons collected per pixel on average to extract a Jones matrix image, with accuracy surpassing previous semi-analytic algorithms derived from g2. Our approach not only automates formulating imaging algorithms but can also assess the sufficiency of information from a designed experimental procedure, which can be useful in equipment or algorithm designs for a wide range of imaging applications.

Imaging technology based on the interaction between muon and material

Muon imaging technology, as an emerging detection method, is widely used in various fields. Muons can be classified into cosmic ray muons and accelerator muons based on their origins. Cosmic ray muons stand out for wide energy range, strong penetrating power and no artificial radiation. These characteristics make cosmic ray muon imaging technology adept at achieving nondestructive imaging of target objects. Presently, the commonly used imaging methods include scattering and transmission imaging technologies that leverage muon information for imaging. Additionally, muon and muonic secondary particle coincidence imaging technology utilizes information from secondary particles generated during the interaction between muons and target objects for imaging. The accelerator muon, distinguished by its high flux, strong monochromaticity, and adjustable energy, enables rapid and multidimensional imaging of target objects at various depths. Furthermore, it facilitates the analysis of material elements through muonic X-rays. This article provides insights into the production process and physical characteristics of muons, the fundamental principles of muon imaging technology, and its diverse applications across disciplines. It also explores the current development status and emerging trends in fields such as mineral resource exploration, archaeological studies, and nuclear safety.

Spectroscopically resolved resonant interatomic Coulombic decay in photoexcited large He nanodroplets

Interatomic Coulombic decay (ICD) processes play a crucial role in weakly bound complexes exposed to intense or high-energy radiation. Using large helium nanodroplets, we demonstrate that ICD is efficient even when the droplets are irradiated by weak synchrotron radiation at relatively low photon energies. Below the ionization threshold, resonant excitation of multiple centers efficiently induces resonant ICD as previously observed for intense pulses [A. C. LaForge , ]. More surprisingly, we observe ICD even above the ionization threshold due to recombination of photoelectrons and ions into excited states which subsequently decay by ICD. This demonstrates the importance of secondary processes, in particular electron scattering and recombination, in inducing ICD in extended condensed phase systems. High-resolution ICD electron spectra in combination with coincidence imaging of electrons and ions reveal the relaxation dynamics of highly excited and ionized weakly bound nanosystems. Published by the American Physical Society 2024

Photonics-Based Broadband Single-Input-Multiple- Output-OAM Coincidence Imaging

Photonics-Based Broadband Single-Input-Multiple- Output-OAM Coincidence Imaging

Sidelobe Suppression of Scanning Synthetic Beams Based on Coincidence Imaging Array Radar

Sidelobe Suppression of Scanning Synthetic Beams Based on Coincidence Imaging Array Radar

Photonics-Based MIMO Radar With Broadband Digital Coincidence Imaging

Photonics-Based MIMO Radar With Broadband Digital Coincidence Imaging

Range-Azimuth Decouple Microwave Coincidence Imaging based on a Frequency-Diverse Bunching Metasurface Antenna

Range-Azimuth Decouple Microwave Coincidence Imaging based on a Frequency-Diverse Bunching Metasurface Antenna

Interferometric imaging of amplitude and phase of spatial biphoton states

High-dimensional biphoton states are promising resources for quantum applications, ranging from high-dimensional quantum communications to quantum imaging. A pivotal task is fully characterizing these states, which is generally time-consuming and not scalable when projective measurement approaches are adopted; however, new advances in coincidence imaging technologies allow for overcoming these limitations by parallelizing multiple measurements. Here we introduce biphoton digital holography, in analogy to off-axis digital holography, where coincidence imaging of the superposition of an unknown state with a reference state is used to perform quantum state tomography. We apply this approach to single photons emitted by spontaneous parametric down-conversion in a nonlinear crystal when the pump photons possess various quantum states. The proposed reconstruction technique allows for a more efficient (three orders of magnitude faster) and reliable (an average fidelity of 87%) characterization of states in arbitrary spatial modes bases, compared with previously performed experiments. Multiphoton digital holography may pave the route toward efficient and accurate computational ghost imaging and high-dimensional quantum information processing.

Metasurface modulator of frequency diverse multi-mode OAM beams with equal divergence angle for coincidence imaging

Traditional multi-mode orbital angular momentum (OAM) beams suffer from low energy efficiency in detection since the divergence angle tends to increase with increasing order of the OAM mode. Thus, OAM beams with equal divergence angle are highly desirable. In this paper, a frequency-diverse multi-mode (FDMM) OAM modulator with approximately equal divergence angle is proposed. The modulator is composed of an OAM modulation metasurface and a spatial filter (SF) with narrow passband. Firstly, the OAM modulation metasurface is designed based on multiple ring-like regions with different radii in the metasurface aperture. Each mode of OAM beam is generated at a corresponding frequency point in one region. Thus, the metasurface aperture can generate different modes of OAM beams at different frequencies (i.e., FDMM OAM beams) simultaneously. Then, the SF with narrow passband is proposed through synthesizing multi-layer frequency selective metasurfaces, aiming to reduce interferences between different modes of OAM beams. Finally, the FDMM OAM modulator is realized by superposing the SF on the OAM modulation metasurface. The FDMM OAM modulator can generate six modes of OAM beams (i.e., , and modes) at 12.5 GHz, 13.0 GHz and 13.6 GHz, respectively. A multi-mode OAM coincidence imaging model based on the FDMM OAM modulator is established. The simulation and experiment results show that the proposed FDMM OAM modulator can be used for target reconstruction and the coincidence imaging performance can be improved assisted by an optimization algorithm.

Quantum microscopy of cells at the Heisenberg limit

Entangled biphoton sources exhibit nonclassical characteristics and have been applied to imaging techniques such as ghost imaging, quantum holography, and quantum optical coherence tomography. The development of wide-field quantum imaging to date has been hindered by low spatial resolutions, speeds, and contrast-to-noise ratios (CNRs). Here, we present quantum microscopy by coincidence (QMC) with balanced pathlengths, which enables super-resolution imaging at the Heisenberg limit with substantially higher speeds and CNRs than existing wide-field quantum imaging methods. QMC benefits from a configuration with balanced pathlengths, where a pair of entangled photons traversing symmetric paths with balanced optical pathlengths in two arms behave like a single photon with half the wavelength, leading to a two-fold resolution improvement. Concurrently, QMC resists stray light up to 155 times stronger than classical signals. The low intensity and entanglement features of biphotons in QMC promise nondestructive bioimaging. QMC advances quantum imaging to the microscopic level with significant improvements in speed and CNR toward the bioimaging of cancer cells. We experimentally and theoretically prove that the configuration with balanced pathlengths illuminates an avenue for quantum-enhanced coincidence imaging at the Heisenberg limit.

Simultaneous multi-nuclide imaging via reconstruction-free double-photon emission coincidence imaging method with parallel hole collimator and slat collimator

Single-photon emission computed tomography is a widely used modality based on single-photon detection of radionuclides. However, research still needs to be conducted on further increasing the image contrast. We recently proposed a novel method called double-photon emission coincidence imaging (DPECI) using the coincidence detection of two cascade gamma photons emitted from a radionuclide, such as 111In or 177Lu. Compared with single-photon detection, the coincidence detection of two gamma photons can be used to theoretically identify the position at a single point free of detector rotation and image reconstruction. In this study, we demonstrate DPECI using parallel-hole and slat collimators to improve detection efficiency and verify the feasibility of simultaneous imaging using 67Cu and 111ln.

Towards product vibrational state resolution in the reaction

The title reaction has been the topic of a large body of research over many decades, but accurate quantum state information for the reaction product is not available up to now. Using a novel ion-molecule crossed-beam spectrometer we aim to resolve state-to-state differential cross sections by velocity map imaging. Here we present the design parameters for this setup as well as Monte Carlo simulations of the expected product energy resolution for two different assumed reaction mechanisms. The simulation results show that the product vibrational levels can be separated up to about 0.8 eV of internal excitation, which corresponds to two vibrational quanta in either the symmetric or the asymmetric stretching vibration. Using coincidence imaging of both products, even higher excitation may be imaged with vibrational resolution.

Resolution Analysis of Coincidence Imaging Based on OAM Beams With Equal Divergence Angle

The multi-mode orbital angular momentum (OAM) beams can be effectively applied in target detection when the divergence angles are equal. The resolution threshold of the coincidence imaging system with multi-mode OAM is analyzed assisted by the subspace projection method. First, the relationship between the imaging resolution and the correlation function (CF) of the measurement mode is obtained based on the first-order correlation algorithm for the multi-mode OAM-based coincidence imaging (MM-OAMCI). Then, the feature vector of each imaging unit is extracted to distinguish the imaging point in the discretized imaging plane. Finally, the resolution threshold is given based on three factors, i.e., the feature vector, the noise, and the reconstruction algorithm. Specifically, the resolution of the MM-OAMCI system is determined by the deployment of the transmitting array, the reconstruction algorithm and the noise caused by the system design, the imaging modeling, and the environment noise. The super-resolution capability of the multi-mode OAM coincidence imaging system is validated by the simulations and experiments. The imaging results show that the resolutions in elevation and azimuth of the reconstructed image can be improved largely compared with the traditional microwave coincidence imaging (TMCI) methods, which is consistent with the theoretical analysis results.

Characterization of Ethos therapy systems for adaptive radiation therapy: A multi-machine comparison.

The recently released Ethos therapy system (Varian Medical Systems) allows for online CBCT-guided adaptive radiation therapy (RT). The clinical introduction of multiple systems requires machine characterization and machine variation quantification to allow patient interchangeability between systems. Despite several clinical introductions, limited vendor-independent information on machine performance is available. Our aim was to determine the relevant dosimetric and mechanical characteristics of individual machines and to quantify machine variations. Six Ethos treatment machines, equipped with a 6-MV FFF beam including dual-layer MLC and kV-CBCT system, were recently introduced clinically after extensive machine characterization and pre-configured beam model verification. Point doses and profiles were measured and compared to vendor-provided reference data and dose calculations. Also, dose calculations were verified based on point measurements for non-standard fields and dose distributions for optimized treatment plans. Agreements between dose profiles (dose distributions) were quantified using 1D (3D) γ-analysis. Additionally, we quantified leaf transmission, dosimetric leaf gap (DLG) and couch attenuation, determined isocenter accuracy and kV-MV isocenter coincidence and verified the kV-CBCT system. Machine variations were quantified for all dosimetric and mechanical characteristics. For all machines, distinct agreements were found between measurements and vendor-provided reference data as well as measurements and dose calculations. Mean γ1%/1mm values for all profiles were below 0.30. All profiles, point measurements and dose distributions matched well among the six machines. Minimal machine variations were found in terms of DLG (0.05mm), leaf transmission (0.001%), isocenter accuracy (0.08mm), kV-MV isocenter coincidence (0.15mm), couch attenuation (0.69%), and CBCT imaging dose (0.29mGy). This study demonstrates excellent agreement between individual Ethos therapy systems and vendor-provided reference data as well as a pre-configured beam model. Furthermore, our results show good consistency among all machines and provide valuable insights on relevant machine characteristics. The systematically obtained results provide benchmark data for future clinical introduction of Ethos therapy systems.

Preparation and quality control of a new porphyrin complex labeled with 45Ti for PET imaging

This study aims to produce and quality control of a new porphyrin complex labeled with 45Ti for PET imaging, so at the first step, the cross-section of 45Sc(p,n)45Ti was investigated by TALYS-1.6 and the optimal target thickness and theoretical yield were calculated by SRIM code. The purified 45Ti was labeled with the anticancer agent of tetrakis (pentafluorophenyl) porphyrin (TFPP). The radiochemical purity and the percentage of labeling were evaluated by radiation layer chromatography then the division coefficient of [45Ti]-TFPP was calculated. The dual coincidence imaging system was used for imaging 1 and 2 h after injection [45Ti]-TFPP to rats. Immediately after imaging, the mean percent injected dose per gram and specific activity of different tissues including blood, heart, lungs, stomach, liver, bone, kidney, spleen, intestine, muscle, feces, and skin were measured. The yield of 45Ti production was measured 468 MBq/μAh and the labeling rate was observed more than 98%. The highest activity was observed in the liver (%ID/g = 2.27%, 1 h) and spleen (2.2%, 1 h), respectively, because of the high lipophilic of 45Ti-TFPP. SPECT images showed a significant uptake of radiopharmaceuticals in the abdomen. The labeling rate of 45Ti-TFPP was high and this compound has the potential for clinical application in different ways than PSMA, it can be joined with photodynamic therapy (Severin et al., 2015).

Synthetic Beam Scanning and Super-Resolution Coincidence Imaging Based on Randomly Excited Antenna Array

Nowadays, there is no good scheme for simultaneously achieving super-resolution imaging within a coherent beamwidth and beam scanning in microwave radar. In this paper, a synthetic beam scanning method based on a randomly excited antenna array, which possesses the ability of super-resolution coincidence imaging, is proposed. The beamwidth of the randomly excited array is comparable to that of the conventional phased array with the same size, and its steering angle can be adjusted by modulating the excitation signals. Firstly, the optimized covariance matrix of the proposed array to uniformly bunch the spatial radiation energy in a specific angle range is obtained by means of the sequential quadratic programming (SQP) algorithm. Accordingly, the partially correlated excitation signals restricted by the optimized covariance matrix are determined. Then, a secondary weighted modulation method is proposed to steer the main beam to the direction of interest. The excitation signals are weighted by the conjugated radiation fields in the direction of interest. Furthermore, the super-resolution ability of the proposed coincidence imaging system is analyzed based on the first-order statistical characteristics of the radiation fields. Simulations and experiments demonstrate that synthetic beam scanning can be realized by controlling the excitation signals. Besides, a 10 times super-resolution coincidence image can be reconstructed within a coherent beamwidth (3dB-beamwidth) when the signal-to-noise (SNR) is greater than 15 dB, assisted by the fast Bayesian learning (FBL) algorithm.