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Vascular Streak Dieback (VSD) disease caused by Ceratobasidium theobromae is the most severe emerging cocoa disease in Southeast Asia. Once the tree is infected, tree defoliation will occur as leaf senescence followed by leaf falls. VSD to have associated with endophytes. However, a fundamental question is whether a similar microbe inhabiting vascular tissue of branch and petiole is entire or patchy? The aim of research was to track and quantify microbial diversity associated with VSD symptoms occupying branches and petiole throughout the stem in different clones. The study focused on VSD symptoms expressing in local (Sulawesi 02), susceptible (RCC 70), and resistant (MCC 02) clones to VSD disease. Sample collection was conducted in Lili Riaja, Soppeng District. The 30 cm-branch with the attached petiole of interest was cut into small pieces 1 cm and transferred into water agar medium before submersion into 2.5% NaOCl for 3 minutes, 70% alcohol for 2 minutes and sterilized water for 1 minute. Morphological characterization followed by microscope check was determined to microbial genera. Eight different fungal communities occupying branch and/or petiole consisted of Cladosporium sp., Fusarium sp., Colletotrichum sp., Penicillium sp., Aspergillus sp., Moniliophthora sp., Lasiodiplodia sp., Curvularia sp. and one Oomycete Phytophthora palmivora. Among occupants in branch and petiole, Fusarium sp. and Colletotrichum sp. were the most frequent. Only one Oomycete Phytophthora palmivora occupying clone samples was found. The most diverse microbes were found to associate with Sulawesi 02 and RCC 70 clones, while fewer microbes were detected with MCC 02 clone.

Four dimensional cone-beam computed tomography (4D-CBCT) has great potential clinical value because of its ability to describe tumor and organ motion. But the challenge in 4D-CBCT reconstruction is the limited number of projections at each phase, which result in a reconstruction full of noise and streak artifacts with the conventional analytical algorithms. To address this problem, in this paper, we propose a motion compensated total variation regularization approach which tries to fully explore the temporal coherence of the spatial structures among the 4D-CBCT phases. In this work, we additionally conduct motion estimation/motion compensation (ME/MC) on the 4D-CBCT volume by using inter-phase deformation vector fields (DVFs). The motion compensated 4D-CBCT volume is then viewed as a pseudo-static sequence, of which the regularization function was imposed on. The regularization used in this work is the 3D spatial total variation minimization combined with 1D temporal total variation minimization. We subsequently construct a cost function for a reconstruction pass, and minimize this cost function using a variable splitting algorithm. Simulation and real patient data were used to evaluate the proposed algorithm. Results show that the introduction of additional temporal correlation along the phase direction can improve the 4D-CBCT image quality.

We improve the system of multi-slit streak tube imaging lidar (MS-STIL) for occluded target detection. To solve the contradiction between high range resolution and deep depth of field, a fiber-optic beam, called ‘beam shunting’, is designed. In addition, we combine the deep-learning-based image inpainting algorithm with the MS-STIL to solve the problem of ineffective imaging when the target is obscured by a large area. Finally, the results of the simulated contrast experiments show that the range resolution is increased from 0.4 m to 0.1 m, and the new system is effective in detecting occluded targets.

In order to study the impacts of the non-uniform conditions of the combustor exit on the flow loss of the turbine guide blade and the cooling performance of the leading edge film, a hot streak and swirl distribution generation program has been developed to implement the parameterization specification of the non-uniform flow state. In addition, the calculation of this paper is based on GE-E3, the numerical simulation analysis is conducted for the swirl/hot streak of the positive blade on the leading edge of the film cooling guide blade. The results showed that the presence of hot streak increased the non-uniformity of vane heat load and had no effect on vane wall pressure distribution. The presence of swirl changes the pressure distribution on the vane wall, affects the migration form of hot streak in the passage, and reduces the cooling effect of the film cooling on the vane. The temperature at the outlet section of the guide vane is uniform.

When a high-current relativistic electron beam interacts with the polymer surface, plasma forms. The results of a plasma dynamics study in vacuum diode using laser shadow photography, including the effect of atypically rapid propagation of the glow, are presented. Experiments were carried out on the high current generator «Calamary». Series of the experiments to study the plasma propagation along the diode axis and in the transverse direction in different cross sections were performed. The results were discussed and possible ways to continue research were considered.

The suppression of streak artifacts in computed tomography with a limited-angle configuration is challenging. Conventional analytical algorithms, such as filtered backprojection (FBP), are not successful due to incomplete projection data. Moreover, model-based iterative total variation algorithms effectively reduce small streaks but do not work well at eliminating large streaks. In contrast, FBP mapping networks and deep-learning-based postprocessing networks are outstanding at removing large streak artifacts; however, these methods perform processing in separate domains, and the advantages of multiple deep learning algorithms operating in different domains have not been simultaneously explored. In this paper, we present a hybrid-domain convolutional neural network (hdNet) for the reduction of streak artifacts in limited-angle computed tomography. The network consists of three components: the first component is a convolutional neural network operating in the sinogram domain, the second is a domain transformation operation, and the last is a convolutional neural network operating in the CT image domain. After training the network, we can obtain artifact-suppressed CT images directly from the sinogram domain. Verification results based on numerical, experimental and clinical data confirm that the proposed method can significantly reduce serious artifacts.

Trichoderma asperellum is a potential biocontrol agent against vascular streak dieback disease (VSD) on cocoa. In this research, we evaluated the suppress capacity of the fungus combined with composted plant residues against the VSD disease on five cocoa clones: S1, MCC 02, AP, THR, and RB. According to VSD development observed in six months, Sulawesi 1 was considered as less sensitive, MCC 02 was moderate resistant, AP was resistant, THR was susceptible, and RB was moderate resistant. The disease incidence on these five clones was 32.9%, 31.0%, 27.9%, 39.9%, and 26.6%, respectively three months post-application and each of this incidence were significantly different (p ≤ 0.05) with the control. While, the efficacy of application was 60.1%, 55.2%, 49.9%, 75.6%, and 37,6%, respectively. These data indicated that capability of T. asperellum in suppressing VSD disease depends on the clone and lowest on the resistant clone.

This paper propose a dilated residual spatial attentive generative adversarial network for single image de-raining. The improved spatial attentive mechanism is combined with the dilated convolution residual module to optimize the Condition Generative Adversarial Network(CGAN) structure, to solve two problems still exist in the task of removing rain from a single image: First, the rain streaks contained in the dataset we can use are limited, and in the case of real rainy days, the rain streak density is diverse, it is impossible to simulate them completely and accurately. Then, the existing rain removal models cannot remove rain streaks properly for images with different rain streak density which attend to over or under rain removal. In our methods, Firstly, the dilated convolution module is used to enhance the feature extraction of rain streaks, and then an attention map is generated by the spatial attention mechanism module to accurately locate the position of rain streaks, and the rain streaks are extracted as the foreground information by combining the two parts of the network to guide the subsequent rain removal operation; Then the rain streaks is removed through the Contextual auto-encoder, combining with PatchGAN discriminator. The experimental results on two synthetic dataset and real-world rain image show that the network model proposed in this paper has high generalization ability under different rainfall conditions. it improves the rain removal effect of the model on the most realistic public dataset, and improves the recovery ability of image details while effectively removing rain on other public datasets, which verifies the effectiveness of the model in improving the generalization ability and improving the image quality after rain removal. At the same time, the effect of rain removal is better than other methods on the real rain images, which proves that the method proposed in this paper has high practical application value.

To promote high-speed boundary layer transition, this paper proposes an active self-sustaining dual jets (SDJ) actuator utilizing the energy of supersonic mainflow. Employing the nanoparticle-based planar laser scattering (NPLS), supersonic flat-plate boundary layer transition induced by SDJ is experimentally investigated in an Ma-2.95 low-turbulence wind tunnel. Streamwise and spanwise NPLS images are obtained to analyze fine flow structures of the whole transition process. The results reveal the transition control mechanisms that on the one hand, the jet-induced shear layer produces unstable Kelvin–Helmholtz instabilities in the wake flow, on the other hand, the jets also generates an adverse pressure gradient in the boundary layer and induce unstable streak structures, which gradually break down into turbulence downstream. The paper provides a new method for transition control of high-speed boundary layer, and have prospect both in theory and engineering application.

Numerical modelling is used to analyse some effects restricting the enhancement of temporal resolution into the area better than 100 fs in streak image tubes and photoelectron guns. A particular attention is paid to broadening of an electron bunch as a result of Coulomb interaction. Possible ways to overcome the limitations under consideration are discussed.

Ebony has a beautiful heartwood with black and brown streaks alternately. Each site has various streak pattern in which the industry classified it into two streak types namely batang macis (BM) and sarang laba-laba/bendera (SL). This research was conducted to investigate the influence of site on streak patterns and several physical properties of the heartwood of ebony. Ebony from Parigi has BM streaks pattern and meet the grade B-A, meanwhile ebony from Poso has SL streaks pattern, qualified for grade C only. On the basis of t-test, only L* (lightness-darkness) was differed between the two streak patterns, while wood density and initial moisture content were not differed significantly. The BM streaks pattern has a darker of heartwood color, higher density but lower initial moisture content.

Limited-angle computed tomography is a very challenging problem in applications. Due to a high degree of ill-posedness, conventional reconstruction algorithms will introduce blurring along the directions perpendicular to the missing projection lines, as well as streak artifacts when applied on limited-angle data. Various models and algorithms have been proposed to improve the reconstruction quality by incorporating priors, among which the total variation, i.e. l 1 norm of gradient, and l 0 norm of the gradient are the most popular ones. These models and algorithms partially solve the blurring problem under certain situations. However, the fundamental difficulty remains. In this paper, we propose a reconstruction model for limited-angle computed tomography, which incorporates two regularization terms that play the role of edge-preserving diffusion and smoothing along the x-direction and y -direction respectively. Then, an alternating minimization algorithm is proposed to solve the model approximately. The proposed model is inspired by the theory of visible and invisible singularities of limited-angle data, developed by Quinto et al. By incorporating visible singularities as priors into an iterative procedure, the proposed algorithm could produce promising results and outperforms state-of-the-art algorithms for certain limited-angle computed tomography applications. Extensive experiments on both simulated data and real data are provided to validate our model and algorithm.

International audience; The image quality in low dose computed tomography (LDCT) can be severely degraded by amplified mottle noise and streak artifacts. Although the iterative reconstruction (IR) algorithms bring sound improvements, their high computation cost remains a major inconvenient. In this work, a deep iterative reconstruction estimation (DIRE) strategy is developed to estimate IR images from LDCT analytic reconstructions images. Within this DIRE strategy, a 3D residual convolutional network (3D ResNet) architecture is proposed. Experiments on several simulated and real datasets as well as comparisons with state-of-the-art methods demonstrate that the proposed approach is effective in providing improved LDCT images.

The aim of this study was to evaluate the application of monoenergetic (ME) extrapolation technique of dual-energy computed tomography (DECT) for metal artefact reduction using phantom study. This study involved phantom study with a customized phantom consisting different types of metal implant such as titanium and stainless steel. The phantom was scanned using a single-source DECT scanner (SOMATOM Definition AS+, Siemens Healthcare, Germany) with dual-energy mode of 140/80 kV spectrum. The commercially available post-processing software (Syngo DE, Siemens) was applied to generate ME image datasets with different extrapolated energies ranged from 55 to 160 keV. The reduction of artefacts was measured qualitatively and quantitatively using region of interests (ROIs) statistical analysis. The results show 60% of metal streak regions were reduced significantly at higher extrapolated energy which is 160 keV. Quantitative analysis also resulted in lower HU readings within the region of artefact for 160 keV. However, higher extrapolated energy resulted in higher noise and lower signal-to-noise (SNR) value. ME images at 160 keV appear noisier while ME images at 64, 70 and 80 keV appear smoother. Metal artefacts induced by both metal implants were reduced significantly using DECT ME extrapolation and diagnostic quality of CT images also improved. It can be achieved by using higher ME of DECT. However, image noise is higher, and SNR is reduced with higher ME extrapolated energy.

Streak Cameras are an essential diagnostic tool used in shock physics and high energy density physics experiments. Such experiments require well calibrated temporally resolving diagnostics for studying events that occur on the nanosecond to microsecond time scales. The Nevada National Security Site (NNSS) and Sandia National Laboratories (SNL) have built a 42-channel solid state streak camera (SSSC) prototype as a proof of concept for use as a streak camera replacement. This work is part of an ongoing project to develop the technology to a level competitive with analog streak cameras. The device concept, results from electronic and laser testing, along with recent improvements to increase the device's dynamic range will be discussed in this manuscript.

Sea surface wind is of great importance for weather forecasts, oil spill monitoring, etc. Currently, sea surface wind by using reversion techniques from synthetic aperture radar (SAR) images has become emerging means to get more fine-grained wind products. In general case, the retrieval of wind speeds from synthetic aperture radar (SAR) images requires the input of wind directions. There are two conventional methods of retrieving wind directions from SAR images, namely, two-dimensional fast Fourier transform (2D FFT) method in the spectral domain and local gradients (LG) method in the spatial domain. However, the spectral method works fine only on open oceans and large image areas, such as 20 × 20km and the spatial method is likely aligned with wind streak. To improve the accuracy and resolution of 2D FFT-retrieved wind directions, a new approach by combining the wind directions retrieved from 2D FFT and LG with a modified cycle median filter (CMF) is proposed in this paper. In our experiment, the proposed method is validated at different spatial resolutions, and the resolution of FFT-retrieved wind directions can be improved to 3km × 3km.

A new optical emission spectroscopy (OES) system using a streak camera (streak-OES) is developed to obtain highly time-resolved OES measurements of nanosecond-duration pulsed air-plasmas at atmospheric pressure. The newly developed system is used to measure the time evolution of the emission of N2(C), a critical species in the two-step mechanism of rapid heating characteristic of nanosecond pulsed discharges. Time resolution of less than 400 ps is achieved in the current system, a significant improvement over conventional OES measurements with ICCD cameras or photomultiplier tubes. In addition, as long as the driving voltage pulse lies within the streak camera sweep window, the entire plasma emission spectrum for a single discharge is acquired. This capability is in contrast to prior studies where the time-dependent emission is obtained by plotting measurements at single steps from separate discharges. The effect of pulse repetition frequency (PRF) on the N2(C) decay is investigated by recording emission spectra for single discharges at 5–100 kHz. The streak images clearly show that the decay time of the N2(C–B, 0–0) transition increases as the PRF is increased. The emission decay exhibits two distinct phases with significantly different decay rates, consistent with prior measurements. The 1/e lifetimes of the two decay regimes are found using exponential fits to the emission decay curves. In addition, joint statistics relating the decay times and energy deposited in the plasma were also obtained.

The Zwicky Transient Facility (ZTF) is a new robotic time-domain survey currently in progress using the Palomar 48-inch Schmidt Telescope. ZTF uses a 47 square degree field with a 600 megapixel camera to scan the entire northern visible sky at rates of ~3760 square degrees/hour to median depths of g ~ 20.8 and r ~ 20.6 mag (AB, 5sigma in 30 sec). We describe the Science Data System that is housed at IPAC, Caltech. This comprises the data-processing pipelines, alert production system, data archive, and user interfaces for accessing and analyzing the products. The realtime pipeline employs a novel image-differencing algorithm, optimized for the detection of point source transient events. These events are vetted for reliability using a machine-learned classifier and combined with contextual information to generate data-rich alert packets. The packets become available for distribution typically within 13 minutes (95th percentile) of observation. Detected events are also linked to generate candidate moving-object tracks using a novel algorithm. Objects that move fast enough to streak in the individual exposures are also extracted and vetted. The reconstructed astrometric accuracy per science image with respect to Gaia is typically 45 to 85 milliarcsec. This is the RMS per axis on the sky for sources extracted with photometric S/N >= 10. The derived photometric precision (repeatability) at bright unsaturated fluxes varies between 8 and 25 millimag. Photometric calibration accuracy with respect to Pan-STARRS1 is generally better than 2%. The products support a broad range of scientific applications: fast and young supernovae, rare flux transients, variable stars, eclipsing binaries, variability from active galactic nuclei, counterparts to gravitational wave sources, a more complete census of Type Ia supernovae, and Solar System objects., 30 pages, 16 figures, Published in PASP Focus Issue on the Zwicky Transient Facility (doi: 10.1088/1538-3873/aae8ac)

Proton beam range is of major concern, in particular, when images used for dose computations are artifacted (for example in patients with surgically treated bone tumors). We investigated several conditions and methods for determination of computed tomography Hounsfield unit (CT-HU) calibration curves, using two different conversion schemes. A stoichiometric methodology was used on either kilovoltage (kV) or megavoltage (MV) CT images and the accuracy of the calibration methods was evaluated. We then studied the effects of metal artifacts on proton dose distributions using metallic implants in rigid phantom mimicking clinical conditions. MV-CT images were used to evaluate relative proton stopping power in certain high density implants, and a methodology is proposed for accurate delineation and dose calculation, using a combined set of kV- and MV-CT images. Our results show good agreement between measurements and dose calculations or relative proton stopping power determination (

International audience; The x-ray exposure to patients has become a major concern in computed tomography (CT) and minimizing the radiation exposure has been one of the major efforts in the CT field. Due to plenty high-attenuation tissues in the human chest, under low-dose scan protocols, thoracic low-dose CT (LDCT) images tend to be severely degraded by excessive mottled noise and non-stationary streak artifacts. Their removal is rather a challenging task because the streak artifacts with directional prominence are often hard to discriminate from the attenuation information of normal tissues. This paper describes a two-step processing scheme called 'artifact suppressed large-scale nonlocal means' for suppressing both noise and artifacts in thoracic LDCT images. Specific scale and direction properties were exploited to discriminate the noise and artifacts from image structures. Parallel implementation has been introduced to speed up the whole processing by more than 100 times. Phantom and patient CT images were both acquired for evaluation purpose. Comparative qualitative and quantitative analyses were both performed that allows conclusion on the efficacy of our method in improving thoracic LDCT data.

A high energy digital radiography (DR) testing system has generated diverse scientific and technological interest in the field of industrial non-destructive testing. However, due to the limitations of manufacturing technology for accelerators, an energy fluctuation of the X-ray beam exists and leads to bright and dark streak artifacts in the DR image. Here we report the utilization of a new software-based method to correct the fluctuation artifacts. The correction method is performed using a high pass filtering operation to extract the high frequency information that reflects the X-ray beam energy fluctuation, and then subtracting it from the original image. Our experimental results show that this method is able to rule out the artifacts effectively and is readily implemented on a practical scanning system.

In this paper, we present a beam hardening correction (BHC) method in three-dimension space for a cone-beam computed tomography (CBCT) system in a mono-material case and investigate its effect on the spatial resolution. Due to the polychromatic character of the X-ray spectrum used, cupping and streak artifacts called beam hardening artifacts arise in the reconstructed CT images, causing reduced image quality. In addition, enhanced edges are introduced in the reconstructed CT images because of the beam hardening effect. The spatial resolution of the CBCT system is calculated from the edge response function (ERF) on different planes in space. Thus, in the CT images with beam hardening artifacts, enhanced ERFs will be extracted to calculate the modulation transfer function (MTF), obtaining a better spatial resolution that deviates from the real value. Reasonable spatial resolution can be obtained after reducing the artifacts. The 10% MTF value and the full width at half maximum (FWHM) of the point spread function with and without BHC are presented.

Micro-CT is commonly used in preclinical studies to provide anatomical information. There is growing interest in obtaining functional measurements from 4D micro-CT. We report here strategies for 4D micro-CT with a focus on two applications: (i) cardiac imaging based on retrospective gating and (ii) pulmonary perfusion using multiple contrast injections/rotations paradigm. A dual source micro-CT system is used for image acquisition with a sampling rate of 20 projections per second. The cardiac micro-CT protocol involves the use of a liposomal blood pool contrast agent. Fast scanning of free breathing mice is achieved using retrospective gating. The ECG and respiratory signals are used to sort projections into ten cardiac phases. The pulmonary perfusion protocol uses a conventional contrast agent (Isovue 370) delivered by a micro-injector in four injections separated by 2 min intervals to allow for clearance. Each injection is synchronized with the rotation of the animal, and each of the four rotations is started with an angular offset of 22.5 from the starting angle of the previous rotation. Both cardiac and perfusion protocols result in an irregular angular distribution of projections that causes significant streaking artifacts in reconstructions when using traditional filtered backprojection (FBP) algorithms. The reconstruction involves the use of the point spread function of the micro-CT system for each time point, and the analysis of the distribution of the reconstructed data in the Fourier domain. This enables us to correct for angular inconsistencies via deconvolution and identify regions where data is missing. The missing regions are filled with data from a high quality but temporally averaged prior image reconstructed with all available projections. Simulations indicate that deconvolution successfully removes the streaking artifacts while preserving temporal information. 4D cardiac micro-CT in a mouse was performed with adequate image quality at isotropic voxel size of 88 µm and 10 ms temporal resolution. 4D pulmonary perfusion images were obtained in a mouse at 176 µm and 687 ms temporal resolution. Compared with FBP reconstruction, the streak reduction ratio is 70% and the contrast to noise ratio is 2.5 times greater in the deconvolved images. The radiation dose associated with the proposed methods is in the range of a typical micro-CT dose (0.17 Gy for the cardiac study and 0.21 Gy for the perfusion study). The low dose 4D micro-CT imaging presented here can be applied in high-throughput longitudinal studies in a wide range of applications, including drug safety and cardiopulmonary phenotyping.

On the Laser Integration Line (LIL) facility at Commissariat a l'Energie Atomique (CEA) near Bordeaux (France), streak cameras (SCs) are extensively used as x-ray detectors by plasma physicists for the recording of transient phenomena as short as 100 ps. For proper interpretation of the experimental results measurements of the SC yield are carried out before each experimental campaign. The yield is actually an indirect measurement that depends on several other measured quantities. The uncertainty associated with the yield is evaluated using the analytical GUM approach and the Monte Carlo (MC) approach using GUM Supplement 1. It is shown in particular that in the assessment process the standard uncertainty and the probability density function of some input quantities propagate through polynomial fitting functions and integrals. A sensitivity analysis is also performed to identify the critical input quantities. The study shows that after correction of the manufacturer's fact sheet the GUM evaluation converges to MC evaluation when the uncertainties associated with non-linear input quantities become small. When propagating uncertainties through integrals it is observed that the uncertainty of the output quantity is mainly dominated by strong correlation effects with the covariance components adding up to produce large uncertainties. Finally, by comparing the experimental yield with a theoretical model good agreement is found.

Iterative reconstruction (IR) methods that can incorporate filtering or regularization techniques have received widespread attention in many situations. Total variation (TV) regularization has proven to be a powerful tool to suppress streak artifacts and noise for sparse-view computed tomography (CT) reconstruction over 360°. However, with under-sampled projection data from limited-view (e.g. half-view) CT scanning, where the projections are further reduced, the edge structures are partly blurred, and some artifacts (such as blocky artifacts) are not effectively suppressed in TV-based results. To further improve the quality of the reconstructed image, a sparsity-induced dynamic guided image filtering reconstruction (SIDGIFR) method is proposed. Intermediate reconstruction results constrained by total difference (TD) minimization are taken as the guidance image to filter the results of projection onto convex sets (POCS) by guided image filtering (GIF). In the SIDGIFR algorithm, the guidance image is dynamically updated, which can transfer the important features (such as edge and small details) to the filtered image during the iterative process. To confirm the efficiency and feasibility of the SIDGIFR algorithm, simulated experiments and real data studies are performed. The quantitative evaluation shows that the proposed SIDGIFR method has better performance than other classical IR methods. What's more, the proposed SIDGIFR algorithm can better preserve the edge structures, and suppress noise and artifacts, than the existing IR methods.

Image-guided radiation therapy using implanted fiducial markers is a common solution for prostate localization to improve targeting accuracy. However, fiducials that are typically used for conventional photon radiotherapy cause large dose perturbations in patients who receive proton radiotherapy. A proposed solution has been to use fiducials of lower atomic number (Z) materials to minimize this effect in tissue, but the effects of these fiducials on dose distributions have not been quantified. The objective of this study was to analyze the magnitude of the dose perturbations caused by select lower-Z fiducials (a carbon-coated zirconium dioxide fiducial and a plastic-coated stainless steel fiducial) and compare them to perturbations caused by conventional gold fiducials. Sets of phantoms were used to assess select components of the effects on dose. First, the fiducials were assessed for radiographic visibility using both conventional computed tomography (CT) and an on-board kilovoltage imaging device at our proton therapy center. CT streak artifacts from the fiducials were also measured in a separate phantom. Second, dose perturbations were measured downstream of the fiducials using radiochromic film. The magnitude of dose perturbation was characterized as a function of marker material, implantation depth and orientation with respect to the beam axis. The radiographic visibility of the markers was deemed to be acceptable for clinical use. The dose measurements showed that the perpendicularly oriented zirconium dioxide and stainless steel fiducials located near the center of modulation of the proton beam perturbed the dose by less than 10%, but that the same fiducials in a parallel orientation near the end of the range of the beam could perturb the dose by as much as 38%. This suggests that carbon-coated and stainless steel fiducials could be used in proton therapy if they are located far from the end of the range of the beam and if they are oriented perpendicular to the beam axis.

Radiation exposure and the associated risk of cancer for patients in computed tomography (CT) scans have been major clinical concerns. The radiation exposure can be reduced effectively via lowering the x-ray tube current (mA). However, this strategy may lead to excessive noise and streak artifacts in the conventional filtered back-projection reconstructed images. To address this issue, some deep convolutional neural network (ConvNet) based approaches have been developed for low-dose CT imaging inspired by the recent development of machine learning. Nevertheless, some of the image textures reconstructed by the ConvNet could be corrupted by the severe streaks, especially in ultra-low-dose cases, which could be close to prostheses and hamper diagnosis. Therefore, in this work, we propose an iterative residual-artifact learning ConvNet (IRLNet) approach to improve the reconstruction performance over the ConvNet based approaches. Specifically, the proposed IRLNet estimates the high-frequency details within the noise and then removes them iteratively; after eliminating severe streaks in the low-dose CT images, the residual low-frequency details can be processed through the conventional network. Moreover, the proposed IRLNet scheme can be extended for robust handling of quantitative dual energy CT/cerebral perfusion CT imaging, and statistical iterative reconstruction. Real patient data are used to evaluate the proposed IRLNet, and the experimental results demonstrate that the proposed IRLNet approach outperforms the previous ConvNet based approaches in reducing the image noise and streak artifacts efficiently at the same time as preserving edge details well, suggesting that the proposed IRLNet approach can be used to improve the CT image quality, especially in ultra-low-dose cases.

Imaging ultrafast dynamic scenes has been long pursued by scientists. As a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP) provides the fastest receive-only camera to capture transient events. This technique is based on three-dimensional image reconstruction by combining streak imaging with compressed sensing (CS). However, the image quality and the frame rate of CUP are limited by the CS-based image reconstruction algorithms and the inherent temporal and spatial resolutions of the streak camera. Here, we report a new method to improve the temporal and spatial resolutions of CUP. Our numerical simulation and experimental verification show that by using a multi-encoding imaging method, both the image quality and the frame rate of CUP can be significantly improved beyond the intrinsic technical parameters. Importantly, the temporal resolution by our scheme can break the limitation of the streak camera. Therefore, this new technology has potential benefits in many applications that require the ultrafast dynamic scene image with high temporal and spatial resolutions.

A hybrid lidar system design using the complementarity streak tube imaging lidar (STIL) and time-correlated single-photon counting (TCSPC) lidar is proposed. The new scheme is proposed for the issue that the low sensitivity of STIL system when detecting weak echo signals, and the range walk error of TCSPC lidar system when detecting strong echo signals. The hybrid system is validated by an indoor experiment. The 3D range image of the target made by a 3D printer is obtained, and the makers on the target with a height of 1 cm is clearly identified. The range data have a root mean square error of 2.9 mm. The results show that the applicability for dynamic range of echo signal intensity is improved by the hybrid lidar system.

The objective of this study was to develop an oscillating sweeping gap test for volumetric modulated arc therapy (VMAT) quality assurance (QA). A novel test was designed and used to simultaneously determine uncertainties associated with linac performance, dose calculation and dosimetric MLC parameters during VMAT delivery. Delivered doses were measured with Matrixx, ionization chamber A12 and EDR2 films, and compared to calculations from the treatment planning system (TPS) Eclipse. A new gantry and MLC motion pattern, called here 'oscillating sweeping gap', is developed as an extension of the standard sweeping gap MLC pattern developed for IMRT QA. Specifically, in the oscillating sweeping gap test, a uniform MLC gap is moving repeatedly back and forth across the field at a constant speed during a full rotation of the gantry. The dose distribution generated by the combined gantry and MLC motion pattern is designed to be quasi-uniform within a cylindrical target volume with a sharp penumbra. The test design allows for an easy detection of dose errors as deviations from the uniform background. MLC gap sizes, gantry and MLC speeds and monitor units (MU) are selected according to a formula determining the magnitude of dose delivered to the target. Both measured and calculated dose distributions were analyzed as a function of the number of control points in the TPS, MLC gap size and magnitude of the gantry angle error. Dose calculation errors due to the insufficient number of control points in the gantry and MLC motion pattern appear as streak artifacts. The magnitude of these artifacts is increasing with the decreased number of control points, and with the decreased MLC gap size. The spatial distribution of dose errors due to the gantry angle errors (unsteady rocking motion) appears as high-frequency noise for higher wobble frequencies and as large hot/cold spots for lower wobble frequencies. The actual MLC leaf position as a function of time (or the gantry angle), determined from the Matrixx snaps (dose images measured per time interval) of the moving gap and compared to the ideal leaf positions, reveal discrepancies in agreement with theoretical calculations. The MLC parameters determined for VMAT with the oscillating sweeping gap test, their uncertainties and the associated dose errors are similar to those determined for IMRT with the standard sweeping gap test. The oscillating sweeping gap test has been developed for the gantry and MLC QA. Applications include commissioning of the planning system for VMAT and performing routine linac QA. The test is sensitive to several errors in dose calculation and delivery.

For multi-camera volumetric flow measurement techniques like tomographic PIV or shake-the-box, volume self-calibration (VSC) has become the standard procedure to correct remaining calibration errors using actual recorded images with particles. For high seeding densities and large allowed triangulation errors necessary to detect large camera shifts, the number of triangulated ghost particles can exceed the number of true particles by orders of magnitude, which makes the detection of the true disparity peaks more difficult. VSC has been improved here using the distinction between true particles with disparities always inside the true disparity peak in the disparity map for all cameras, while ghost particles are distributed over random position. This VSC with ghost particle suppression (VSC-GPS) makes VSC significantly more robust with many orders of magnitude fewer ghost particles and enables detection of disparities even larger than 10 pixels. In addition, an alternative volume self-calibration method is presented based on standard image correlation (VSC-IC) between dewarped images of two cameras similar to Stereo-PIV self-calibration without the need of particle detection and triangulation. For each camera combination, a correlation streak becomes visible in the correlation map, where the position of the streak is used for correcting the camera mapping functions. VSC-IC can easily detect very large camera shifts >10–30 pixels. For inline camera configurations, VSC-IC needs to be modified by some slower triple-image correlation technique. As a useful side-benefit, the intensity along the correlation streak provides directly the intensity profile across the measurement volume depth. Both methods, VSC-GPS and VSC-IC, have been tested on many experiments, and in particular for the most difficult case of vibrations where each camera image needs a modified calibration function. Guidelines are given to detect and correct vibrations.

Myocardial perfusion computed tomography (MPCT) imaging is commonly used to detect myocardial ischemia quantitatively. A limitation in MPCT is that an additional radiation dose is required compared to unenhanced CT due to its repeated dynamic data acquisition. Meanwhile, noise and streak artifacts in low-dose cases are the main factors that degrade the accuracy of quantifying myocardial ischemia and hamper the diagnostic utility of the filtered backprojection reconstructed MPCT images. Moreover, it is noted that the MPCT images are composed of a series of 2/3D images, which can be naturally regarded as a 3/4-order tensor, and the MPCT images are globally correlated along time and are sparse across space. To obtain higher fidelity ischemia from low-dose MPCT acquisitions quantitatively, we propose a robust statistical iterative MPCT image reconstruction algorithm by incorporating tensor total generalized variation (TTGV) regularization into a penalized weighted least-squares framework. Specifically, the TTGV regularization fuses the spatial correlation of the myocardial structure and the temporal continuation of the contrast agent intake during the perfusion. Then, an efficient iterative strategy is developed for the objective function optimization. Comprehensive evaluations have been conducted on a digital XCAT phantom and a preclinical porcine dataset regarding the accuracy of the reconstructed MPCT images, the quantitative differentiation of ischemia and the algorithm's robustness and efficiency.

Endophytic fungi are one of the agents to control phytopathogen both bacterial or fungi including dieback disease on cacao such as Vascular Streak Dieback (VSD). Ten fungal isolates that associated with a healthy branch of VSD resistant clone was applied to cacao seedling, the fungi were a Curvularia-like colony, a Fusarium-like colony, a Geotrichum-like colony, an Aspergillus-like colony, a Gliocladium-like colony, a Colletotrichum-like colony and four isolates indicates as mycelia sterilia fungi. Those fungi were applied at 2.5-old months cacao seedling of moderate to susceptible clone against VSD, and 30 days after inoculation of those fungi, the seedling was applied with a bunch of mycelia emerged from infected branch that mix with water using mixer appliance and then the seedling was exposed at open area surrounded by infested cacao tree. The disease incidence was recorded started at 30 and then 60, 90 and 120 days after inoculation of the pathogen and exposed. The result of study shows that the disease appeared increasing gradually and 120 days fungus Curvularia-like colony exhibited lower incidence followed by Copper fungicide, Mycelia sterilia 1, Gliocladium-like colony, Fusarium-like colony, Geotrichum-like colony, Mycelia sterilia 3, Colletotrichum-like colony, Aspergillus-like colony, control (no application), Mycelia sterilia 2, Mycelia sterilia 4 with percentage of 3.0, 8.3, 9.5, 11.3, 15.8, 18.0, 19.0, 19.3, 21.3, 26.5, 30.5, respectively. The result indicates that some fungi associated with VSD resistant clone were able to prevent VSD to develop and causing symptoms.

Compton scatter poses a significant threat to volumetric x-ray computed tomography, bringing cupping and streak artefacts thus impacting qualitative and quantitative imaging procedures. To perform appropriate scatter compensation, it is necessary to estimate the magnitude and spatial distribution of x-ray scatter. The aim of this study is to compare three experimental methods for measurement of the scattered radiation profile in a 64-slice CT scanner. The explored techniques involve the use of collimator shadow, a single blocker (a lead bar that suppresses the primary radiation) and an array blocker. The latter was recently proposed and validated by our group. The collimator shadow technique was used as reference for comparison since it established itself as the most accurate experimental procedure available today. The mean relative error of measurements in all tube voltages was 3.9 +/- 5.5% (with a maximum value of 20%) for the single blocker method whereas it was 1.4 +/- 1.1% (with a maximum value of 5%) for the proposed blocker array method. The calculated scatter-to-primary ratio (SPR) using the blocker array method for the tube voltages of 140 kVp and 80 kVp was 0.148 and 1.034, respectively. For a larger polypropylene phantom, the maximum SPR achieved was 0.803 and 6.458 at 140 kVp and 80 kVp, respectively. Although the three compared methods present a reasonable accuracy for calculation of the scattered profile in the region corresponding to the object, the collimator shadow method is by far the most accurate empirical technique. Nevertheless, the blocker array method is relatively straightforward for scatter estimation providing minor additional radiation exposure to the patient.

Cone-beam computed tomography (CBCT) has been clinically used to verify patient position and to localize the target of treatment in image-guided radiation therapy (IGRT). However, when the chest and the upper abdomen are scanned, respiratory-induced motion blurring limits the utility of CBCT. In order to mitigate this blurring, respiratory-gated CBCT, i.e. 4D CBCT, was introduced. In 4D CBCT, the cone-beam projection data sets acquired during a gantry rotation are sorted into several respiratory phases. In these gated reconstructions, the number of projections for each respiratory phase is significantly reduced. Consequently, undersampling streaking artifacts are present in the reconstructed images, and the image contrast resolution is also significantly compromised. In this paper, we present a new method to simultaneously achieve both high temporal resolution ( approximately 100 ms) and streaking artifact-free image volumes in 4D CBCT. The enabling technique is a newly proposed image reconstruction method, i.e. prior image constrained compressed sensing (PICCS), which enables accurate image reconstruction using vastly undersampled cone-beam projections and a fully sampled prior image. Using PICCS, a streak-free image can be reconstructed from 10-20 cone-beam projections while the signal-to-noise ratio is determined by a denoising feature of the selected objective function and by the prior image, which is reconstructed using all of the acquired cone-beam projections. This feature of PICCS breaks the connection between the temporal resolution and streaking artifacts' level in 4D CBCT. Numerical simulations and experimental phantom studies have been conducted to validate the method.

The temporal evolutions of small, streamwise elongated disturbances in the asymptotic suction boundary layer (ASBL) and the Blasius boundary layer (BBL) are compared. In particular, initial perturbations localized (δ-functions) in the wall-normal direction are studied, corresponding to an axi-symmetric jet coming out of a plane parallel to the flat plate. Analytical solutions are presented for the wall-normal and streamwise velocities in the ASBL case whereas both analytical and numerical methods are used for the BBL case. The initial position of the perturbation and its spanwise wave number are varied in a parameter study. We present results of maximum amplitudes obtained, the time to reach them, their position and optimal spanwise scales. Free-stream disturbances are shown to migrate towards the wall and reach their (negative) optimum inside the boundary layer. The migration is faster for the ASBL case and a larger amplitude is reached than for the BBL. For perturbations originating inside the boundary layer the amplitudes are overall larger and show the phenomenon of overshoot, i.e. positive amplitudes moving out of the boundary layer. The overall largest amplitudes are obtained for the BBL case, as in other studies, but it is shown that for free-stream disturbances initiated somewhere downstream the leading edge streak growth may be amplified due to suction since in the BBL the disturbance mainly advects above the boundary layer.

Work in the field of electron-optical diagnostics of laser-induced rapid processes performed for almost half a century at the Photoelectronics Department at the General Physics Institute, RAS, is summed up. New femtosecond image-converter tubes have been developed, which provide the time resolution no worse than 100 fs in the slit scan (streak) regime, and photoelectron guns have been built for time-resolved studies of electron diffraction. The results of recent studies on manifold (up to fifty-fold) compression of picosecond electron bunches in nonstationary focusing fields are demonstrated.

The lattice undulation of a silicon-on-insulator (SOI) layer in bonded SOI wafers was observed by synchrotron white and monochromatic X-ray topographies. Pattern formation for white X-ray topography was discussed using the geometric relation among the Bragg streak and diffracted X-rays in reciprocal space. The diffraction images in white X-ray topographs were simulated using the angular distributions of the lattice inclination in SOI layers obtained by the analysis of monochromatic X-ray topographs. The results of this simulation were in very good agreement with observations including the dependences on camera distance and SOI layer thickness, indicating that the contrast is mainly formed by the divergence/convergence effect of the diffracted X-rays.

The evolutions of the electron temperatures of aluminum plasmas produced with 0.351 ?m laser are simulated by means of one-dimensional hydrodynamic code. The simulations show that the plasma geometry has strong influence on the electron temperature's evolution while the effect of the flux limiter is not so significant. The simulations are in good agreement with the experiments only at some spatial points. A full comparison between the simulations and experiments indicates that the one-dimensional code is not accurate enough to characterize the laser-produced plasmas. A post-processor code based on the hydro code is developed to generate the streak image of the Thomson scattering spectra, which can be directly compared with the experimental data.

Collision of fast plasma streams in vacuum is investigated. Plasma streams were produced by irradiation of thin foils with a powerful pulsed electron beam. Interaction of the plasma flows was studied by using frame and streak cameras. One-dimensional numerical simulation was carried out. Application of this method for porous ICF targets and high-energy physics is discussed.

Free-electron lasers will change the way we carry out time-resolved X-ray experiments. At present date, we use laser-produced plasma sources or synchrotron radiation. Laser-produced plasma sources have short pulses, but unfortunately large pulse-to-pulse fluctuations and large divergence. Synchrotron radiation from third generation source provide collimated and stable beams, but unfortunately long pulses. This means that either the time-resolution is limited to 100 ps or rather complex set-ups involving slicing or streak cameras are needed. Hard X-ray free-electron lasers will combine the best properties of present-day sources and increase the number of photons by many orders of magnitude. Already today, a precursor to the free-electron lasers has been built at Stanford Linear Accelerator Centre (SLAC). The Sub-Picosecond Photon Source (SPPS) has already shown the opportunities and challenges of using short-pulse X-ray sources. (Less)

Interactions of the laser beam of iodine laser 'PALS' with low-density foam targets and acceleration of Al foils by the pressure of heated foam matter are investigated here, both experimentally and theoretically. An x-ray streak camera was used for the evaluation of the speed of energy transfer through the porous foam material. X-ray streak records show no noticeable emission near the Al foil at the rear side of a 400 µm thick foam and, thus, Al foil is most likely accelerated without significant heating and expansion. Accelerated foil velocities, measured by three-frame optical shadowgraphy, reach up to 107 cm s−1. Experimental results compare well with our two-dimensional hydrodynamics simulations and with an approximate analytical model.

The streak instability is examined experimentally by artificially generating spanwise-periodic low-speed streaks in a laminar boundary layer on a flat plate. Fundamental and subharmonic modes are excited for each of the sinuous and varicose instabilities and their development is compared with the corresponding result of a single low-speed streak. The development of subharmonic sinuous mode does not strongly depend on the streak spacing and it grows with almost the same growth rate as that for the single streak. By contrast, the development of fundamental sinuous mode is very sensitive to the streak spacing and is completely suppressed when the streak spacing is smaller than a critical value, about 2.5 times the streak width for the low-speed streaks examined. On the varicose instability, the fundamental mode is less amplified than the subharmonic mode, but the growth of both modes is weak compared with the case of the single streak.

The electro-dynamical properties and the mutual influence of several simultaneously propagating streamers are investigated in a point-to-plane configuration in air at atmospheric pressure under impulse voltage. When a fast and short high voltage pulse is applied to the point, a bunch of streamer branches develops into the interval. Since no previous ionized path has been traced before in the gap, streamers spread in the whole gap, branching while propagating. This behaviour is quite different from streamers under DC voltage conditions, which successively extend on the point–plane axis. The aim of this work is an attempt to distinguish the properties of an individual streamer simultaneously propagating with the others, by means of fast techniques based on simultaneous streak and still photographs and space-time decoupled currents measurements. Especially, their mean velocity can be estimated. In most cases, an axial streamer is observed, propagating faster than the others. This result can be interpreted in terms of the electric field space distribution by means of a three-dimensional electrostatic solver. This analysis shows that a mutual electro-dynamical influence is exerted from one streamer on another.

Attenuation correction in positron emission tomography (PET) is an essential part of clinical and research studies. However, correction using noisy transmission data acquired over short scan durations has been a problem as the noise is introduced into emission images. This study investigates the effect of smoothing the two-dimensional projections of the attenuation maps (mu-map) using the nonlinear anisotropic diffusion filtering method. Experiments are presented on a whole-body study to qualitatively evaluate the efficacy of the method in reducing the random noise and streak artefacts. The results show that image quality is significantly improved with minimal resolution loss. A reduction in statistical noise was quantitatively demonstrated when the same approach was applied to a cylindrical phantom dataset.

A femtosecond synchroscan streak tube has been developed. In order to achieve femtosecond time resolution, the following conditions were adopted in the tube design: high electric field application near the photocathode, high positive voltage application to the focusing electrode to reduce photoelectron transit time spread in the focusing region, and setting the anode electric potential as low as possible to obtain a very high deflection sensitivity for sweep due to low photoelectron drift velocity between the anode and the sweeping screen. The electrode structure and the applied voltages were designed by computer simulation of electron trajectory, and the theoretical time resolution obtained is ~520 fs. Based on the above design parameters, a prototype tube was fabricated and evaluated. A time resolution of ~660 fs was experimentally obtained at the synchroscan frequency of ~80 MHz.