High Field Of View Research Articles

High-Speed Imaging of the Ultrasonic Deagglomeration of Carbon Nanotubes in Water

Ultrasonic treatment is effective in deagglomerating and dispersing nanoparticles in various liquids. However, the exact deagglomeration mechanisms vary for different nanoparticle clusters, owing to different particle geometries and inter-particle adhesion forces. Here, the deagglomeration mechanisms and the influence of sonotrode amplitude during ultrasonication of multiwall carbon nanotubes in de-ionized water were studied by a combination of high-speed imaging and numerical modeling. Particle image velocimetry was applied to images with a higher field of view to calculate the average streaming speeds distribution. These data allowed direct comparison with modeling results. For images captured at higher frame rates and magnification, different patterns of deagglomeration were identified and categorized based on different stages of cavitation zone development and for regions inside or outside the cavitation zone. The results obtained and discussed in this paper can also be relevant to a wide range of carbonaceous and other high aspect ratio nanomaterials.

Detection and Mosaicing Techniques for Low-Quality Retinal Videos.

Ideally, to carry out screening for eye diseases, it is expected to use specialized medical equipment to capture retinal fundus images. However, since this kind of equipment is generally expensive and has low portability, and with the development of technology and the emergence of smartphones, new portable and cheaper screening options have emerged, one of them being the D-Eye device. When compared to specialized equipment, this equipment and other similar devices associated with a smartphone present lower quality and less field-of-view in the retinal video captured, yet with sufficient quality to perform a medical pre-screening. Individuals can be referred for specialized screening to obtain a medical diagnosis if necessary. Two methods were proposed to extract the relevant regions from these lower-quality videos (the retinal zone). The first one is based on classical image processing approaches such as thresholds and Hough Circle transform. The other performs the extraction of the retinal location by applying a neural network, which is one of the methods reported in the literature with good performance for object detection, the YOLO v4, which was demonstrated to be the preferred method to apply. A mosaicing technique was implemented from the relevant retina regions to obtain a more informative single image with a higher field of view. It was divided into two stages: the GLAMpoints neural network was applied to extract relevant points in the first stage. Some homography transformations are carried out to have in the same referential the overlap of common regions of the images. In the second stage, a smoothing process was performed in the transition between images.

Image mosaicking using improved auto-sorting algorithm and local difference-based harris features

Image mosaicking is an image processing technique which is useful for tiling images. Image Mosaicing stitches many correlated images to get a picture of a greater field of view. General-purpose cameras, which have a low field of view, can not create images with a higher field of view while mosaicking can help us achieve it. One important step in an image mosaicking framework is the auto-sorting algorithm, which is to be performed to minimize registration errors in the mosaic image. Another step in mosaicking is the detection of interest points for matching of the source images obtained after auto-sorting. However, in the presence of noisy and pseudo-periodic structures in the source images, the existing auto-sorting methods generally produce distortions in the final mosaic image. Secondly, most of the popular interest point detection algorithms do not specifically consider computational issues. So, this work mainly addresses the above-mentioned problems which are generally encountered during image mosaicking. The problem of image auto-sorting can be partially solved by adopting a phase correlation strategy. In our method, the sorting procedure is further improved by deploying the structural similarity index (SSIM) measure instead of using the phase correlation. The issue of high time complexity of conventional corner detectors is reduced by using our proposed local difference operation in place of standard Sobel edge detector. Experimental results show the efficacy of the proposed method.

Detection of minor compounds in complex mineral samples from millions of spectra: A new data analysis strategy in LIBS imaging

Today, Laser-Induced Breakdown Spectroscopy (LIBS) imaging is in full change. Indeed, always more stable instrumentations are developed, which significantly increases the signal quality and naturally the analytical potential of the technique for the characterization of complex and heterogeneous samples at the micro-scale level. Obviously, other intrinsic features such as a limit of detection in the order of ppm, a high field of view and high acquisition rate make it one of the most complete chemical imaging techniques to date. It is thus possible in these conditions to acquire several million spectra from one single sample in just hours. Managing big data in LIBS imaging is the challenge ahead. In this paper, we put forward a new spectral analysis strategy, called embedded k-means clustering, for simultaneous detection of major and minor compounds and the generation of associated localization maps. A complex rock section with different phases and traces will be explored to demonstrate the value of this approach.

Holographically customized optical combiner for eye-box extended near-eye display.

We propose a customizing method of a holographic optical element (HOE) by using a holographic printer, which extends the eye-box with high field of view (FOV) for a holographic augmented reality near-eye display (AR NED). The holographic printer setup to manufacture HOE is presented and a prototype of the AR NED is implemented. To make a simple AR NED system, we propose a total internal reflection holographic printing method using an index-matching optical frame. As a result, the eye-box of the AR NED is extended in both vertical and horizontal directions and FOV of 50° is achieved at the center of the eye-box. Through the simulations and the experimental results, the feasibility of the proposed method is verified.

Evaluating the potential of post-processing kinematic (PPK) georeferencing for UAV-based structure- from-motion (SfM) photogrammetry and surface change detection

Abstract. Images captured by unmanned aerial vehicles (UAVs) and processed by structure-from-motion (SfM) photogrammetry are increasingly used in geomorphology to obtain high-resolution topography data. Conventional georeferencing using ground control points (GCPs) provides reliable positioning, but the geometrical accuracy critically depends on the number and spatial layout of the GCPs. This limits the time and cost effectiveness. Direct georeferencing of the UAV images with differential GNSS, such as PPK (post-processing kinematic), may overcome these limitations by providing accurate and directly georeferenced surveys. To investigate the positional accuracy, repeatability and reproducibility of digital surface models (DSMs) generated by a UAV–PPK–SfM workflow, we carried out multiple flight missions with two different camera–UAV systems: a small-form low-cost micro-UAV equipped with a high field of view (FOV) action camera and a professional UAV equipped with a digital single lens reflex (DSLR) camera. Our analysis showed that the PPK solution provides the same accuracy (MAE: ca. 0.02 m, RMSE: ca. 0.03 m) as the GCP method for both UAV systems. Our study demonstrated that a UAV–PPK–SfM workflow can provide consistent, repeatable 4-D data with an accuracy of a few centimeters. However, a few flights showed vertical bias and this could be corrected using one single GCP. We further evaluated different methods to estimate DSM uncertainty and show that this has a large impact on centimeter-level topographical change detection. The DSM reconstruction and surface change detection based on a DSLR and action camera were reproducible: the main difference lies in the level of detail of the surface representations. The PPK–SfM workflow in the context of 4-D Earth surface monitoring should be considered an efficient tool to monitor geomorphic processes accurately and quickly at a very high spatial and temporal resolution.

Analysis of bone density in a group of patients with dental inclusion

Background/Aim: Genetic and environmental etiologic factors have been described for maxillary canine impaction, except for the trabecular bone characteristics in the impacted area. The aim of this study was to evaluate the surface area and bone density using cone-beam computed tomography (CBCT) images of patients with maxillary impacted canines. Material and Methods: The sample comprised preorthodontic treatment, CBCT images of 24 participants with unilateral maxillary impacted canines, using the impacted side as study group and the non-impacted side as control group. CBCT images were acquired in portrait mode (17 x 23 cm high field of view) at 120 kV, 5 mA, 8.9 seconds exposure time, and 0.3 mm voxel size. Each root was divided into three levels (cervical, intermediate, and apical) to determine whether the bone density change varied with the tooth level. Moreover, each level was divided into four regions (palatal, distal, mesial, and buccal sides). Bone density was measured using Hounsfield Units. Comparisons were made using paired t tests and linear regression. Repeated measurements were obtained randomly from about 20% of the sample. Results: In subjects with unilateral impactions, the maxillary bone density was higher in the impacted side, with a mean difference of 350 HU. Bone density increases in the corono-apical direction of about 100 HU in the impaction site and about 50 HU in the site of the erupted canine. The repeated measurements showed similar results. Conclusions: The maxillary alveolar bone area and bone density are increased in the impacted side compared with the nonimpacted side.

Alternative cone-beam computed tomography method for the analysis of bone density around impacted maxillary canines.

Genetic and environmental etiologic factors have been described for maxillary canine impaction, except for the trabecular bone characteristics in the impacted area. The aim of this study was to evaluate the surface area and fractal dimension of the alveolar bone on cone-beam computed tomography (CBCT) images of patients with maxillary impacted canines. The sample comprised preorthodontic treatment CBCT images of 49 participants with maxillary impacted canines (31 unilateral and 18 bilateral). CBCT images were acquired in portrait mode (17×23cm high field of view) at 120kV, 5mA, 8.9-seconds exposure time, and 0.3-mm voxel size. Coronal slices (0.3mm) were obtained from the right and left alveolar processes between the first and second maxillary premolars. We collected 64×64-pixel regions of interest between the premolars to assess maxillary bone area and fractal dimension using ImageJ software (National Institutes of Health, Bethesda, Md). Comparisons were made using paired t tests and linear regression. Repeated measurements were obtained randomly from about 20% of the sample. In subjects with unilateral impactions, the maxillary bone area (P=0.0227) was higher in the impacted side, with a mean difference of 245.5 pixels (SD, 569.2), but the fractal dimension (P=0.9822) was not, -0.0003 pixels (SD, 0.082). Comparisons of unilateral and bilateral subjects using a general linear mixed model test confirmed the increased bone area in the impacted side (P=0.1062). The repeated measurements showed similar results. The maxillary alveolar bone area is increased in the impacted side compared with the nonimpacted side.

Optimisation of pulsed and pseudo-continuous arterial spin labeling MRI techniques: A phantom study

Arterial Spin Labeling (ASL) MRI is a non-invasive technique using a freely diffusible intrinsic tracer. The main objective of this study is to evaluate two different techniques of ASL MRI; pulsed ASL (PASL) and pseudo-continuous ASL (PCASL) in obtaining the best signal by manipulating the different imaging parameters. We used a fabricated Perspex flow phantom that is magnetically susceptible. The phantom has a straight tube that mimics carotid artery in adult patients and a U-shaped tube with 75% stenosis. We used a mixture of 60:40 distilled water and glycerol respectively as a substitute to blood. The fabricated phantom was scanned with 1.5T and 3T MRI Scanner using PCASL technique and PASL respectively. Two main imaging parameters were studied which were the field of view (FOV) and slice thickness (ST) to obtain the signal-to-noise ratio (SNR) of the region of interests. The 1.5 T PCASL technique gave SNR values of (13, 22, 30.1) for ST (5, 7, 9 mm) and FOV 240. When higher FOV = 320 was selected, the SNR values were (26.8, 15, 37) for different ST (5, 7, 9 mm). The 3.0 T PASL technique gave the SNR values of (9, 9.3, 11) for ST (5, 7, 9mm) and FOV 240mm. In the higher FOV = 320 mm, we obtained SNR values of (15.2, 17.5, 37.2) for ST (5, 7, 9 mm). As a conclusion, the images quality which can be measured by SNR value is affected by types of ASL and also different parameters.

Multispectral interference filter arrays with compensation of angular dependence or extended spectral range.

Thin film Fabry-Perot filter arrays with high selectivity can be realized with a single patterning step, generating a spatial modulation of the effective refractive index in the optical cavity. In this paper, we investigate the ability of this technology to address two applications in the field of image sensors. First, the spectral tuning may be used to compensate the blue-shift of the filters in oblique incidence, provided the filter array is located in an image plane of an optical system with higher field of view than aperture angle. The technique is analyzed for various types of filters and experimental evidence is shown with copper-dielectric infrared filters. Then, we propose a design of a multispectral filter array with an extended spectral range spanning the visible and near-infrared range, using a single set of materials and realizable on a single substrate.

Increasing the spatial resolution of near infrared chemical images (NIR-CI): The super-resolution paradigm applied to pharmaceutical products

Near-infrared chemical imaging (NIR-CI) is widely used in the pharmaceutical industry not only to provide the concentration of a compound of interest but far more often to obtain the spatial distribution of different ingredients within the considered sample like a single tablet. For such sample characterization, having a high field of view is of major interest. As well as their high field of view, recent NIR-CI spectrometers have the ability to acquire thousands of spectra in a very short time due to focal plane array detector they use. Nevertheless, the spatial resolution is often limited which implies that generated chemical images are often biased. In view of this it was deemed appropriate to develop a new chemometrics methodology called “super-resolution” in order to increase the spatial resolution of spectroscopic images. The main idea is the fusion of several low-resolution images of the same sample observed from different point of view in order to generate one higher-resolution image. We offer here an objective and quantitative evaluation of the super-resolution concept with applications on pharmaceutical solid samples.

The GLAST LAT tracker construction and test

GLAST is a next generation high-energy gamma-ray observatory designed for making observations of celestial gamma-ray sources in the energy band extending from 10 KeV to more than 300 GeV. Respect to the previous instrument EGRET, GLAST will have a higher effective area (six times more), higher field of view, energy range and resolution, providing an unprecedented advance in sensitivity (a factor 30 or more). The main scientific goals are the study of all gamma-ray sources such as blazars, gamma-ray bursts, supernova remnants, pulsars, diffuse radiation, and unidentified high-energy sources. The construction and test of the Large Area Telescope (LAT) tracker, has been a great effort during the past years, involving tens of people from many Italian INFN sections and industrial partners. Environmental and performance tests of the hardware, detectors and reading electronics, have been carried on during all the steps of the LAT construction. The resulting LAT performance are better than the ones required by the original science proposal, demonstrating the quality of the italian group effort. In this article we summarize the LAT construction and test workflow, presenting its main results.

A PET scanner employing CsI films as photocathode

Medical imaging is a fundamental tool in the diagnosis, treatments, and monitoring of disease processes as cancer. Detectors of large area and high Field Of View are necessary to scan the whole body in a reasonable time. Relatively large area photodetectors are necessary even for imaging of small mice and rats with high sensitivities and spatial resolutions, generally obtained by using pinhole or multipinhole collimators . Standard PET scanners, with scintillators coupled to photomultipliers, have generally a limited detector area due to the high costs of both scintillators and photomultipliers. In this respect, the replacement of photomultipliers with gaseous photodetectors represents a possible solution of the problem and brings the additional advantage to provide devices with sensitive areas free from dead regions. In this paper we report on a PET scanner equipped with a multiwire proportional chamber with a CsI thin film as photoconverter. A similar approach has already been successfully pursued in nuclear and particle physics experiments . A prototype of such a PET detector has been designed and built, and will be tested soon. Possible solutions for increasing the photoelectron number, and thus the detector performance, are presented.