High-resolution Imaging System Research Articles

Spatial-spectral encoding and dictionary optimization in compressive single-pixel hyperspectral imaging based on mutual coherence minimization

A single-pixel detector based hyperspectral system provides an effective way to obtain the spatial-spectral information of target scenes. However, complex spectral dispersion and the substantial number of measurements not only increase the complexity of the system but also decrease the sampling efficiency and the reconstruction accuracy. In this paper, we propose a compressive sensing (CS) theory based single-pixel hyperspectral imaging system. Based on structured illumination, the spatial information is modulated by binary spatial patterns displayed on a liquid crystal on silicon (LCoS), while polarizing elements at specific angles, acting as a serious of filters, modulate the spectral dimension, effectively avoiding spectral dispersion. In terms of sampling efficiency, the application of CS significantly decreases the number of measurements required compared to the Nyquist-Shannon sampling theorem. Besides, to improve the reconstruction accuracy, mutual coherence minimization is employed to optimize the pre-trained dictionary, spatial patterns and filters. Furthermore, a two-step encoding method based on macro-pixel segmentation is proposed to address the issue of low resolution constrained by the size of the dictionary. Compared to the unoptimized system and dictionary, the proposed method achieves more accurate reconstruction results in both spectral and spatial dimensions. This work may provide opportunities for high-resolution single-pixel hyperspectral imaging systems based on CS.

Stretchable Ultrasound Metalens for Biomedical Zoom Imaging and Bone Quality Assessment with Subwavelength Resolution.

Ultrasound imaging is extensively used in biomedical science and clinical practice. Imaging resolution and tunability of imaging plane are key performance indicators, but both remain challenging to be improved due to the longer wavelength compared with light and the lack of zoom lens for ultrasound. Here, the ultrasound zoom imaging based on a stretchable planar metalens that simultaneously achieves the subwavelength imaging resolution and dynamic control of the imaging plane is reported. The proposed zoom imaging ultrasonography enables precise bone fracture diagnosis and comprehensive osteoporosis assessment. Millimeter-scale microarchitectures of the cortical bones at different depths can be selectively imaged with a 0.6-wavelength resolution. The morphological features of bone fractures, including the shape, size and position, are accurately detected. Based on the extracted ultrasound information of cancellous bones with healthy matrix, osteopenia and osteoporosis, a multi-index osteoporosis evaluation method is developed. Furthermore, it provides additional biological information in aspects of bone elasticity and attenuation to access the comprehensive osteoporosis assessment. The soft metalens also features flexibility and biocompatibility for preferable applications on wearable devices. This work provides a strategy for the development of high-resolution ultrasound biomedical zoom imaging and comprehensive bone quality diagnosis system.

Uncertainty quantification for velocity measurement with 2D2C particle image velocimetry

Abstract In this paper, a theoretical model of dimensionless instantaneous and average velocity measurement uncertainty quantification with 2D2C particle image velocimetry (PIV) is established under the framework of generally adopted international uncertainty quantification standards. The effectiveness of the model is verified using uniform flow field testing data. Combined with semi-quantitative analysis of the theoretical model, uncertainty control suggestions for PIV measurements are given. The major sources affecting the uncertainty of instantaneous velocity measurements are the reference velocity, particle instantaneous pixel displacement, and their correlation term. For average velocity measurement uncertainty quantification, the uncertainty of particle average pixel displacement is effectively controlled by taking a large number of particle images. Thus, three single-component terms — the calibration factor, particle average pixel displacement and reference velocity — and two correlation terms — the particle average pixel displacement–calibration factor and the particle average pixel displacement–reference velocity — all make an important contribution to the average velocity measurement uncertainty. To reduce the uncertainty of PIV velocity measurement, one can reduce the reference velocity measurement uncertainty, optimize the PIV algorithm and improve the calibration factor by applying a high spatial resolution imaging system in experiments. In addition, reducing the reference velocity measurement uncertainty and improving the spatial resolution are key feasible methods.

A High-Resolution Magnetic Field Imaging System Based on the Unpackaged Hall Element Array

We have designed a high-resolution magnetic field imaging system using 256 unpackaged Hall elements. These unpackaged Hall elements are arranged in a Hall linear array, and the distance between adjacent elements reaches 255 µm. The sensitivity of the unpackaged Hall element array can be adjusted using a computer to measure magnetic environments with different magnetic field strengths. High-resolution magnetic field images of 256 × 256 pixels can be generated by moving the array using the X–Y axis motorized rail. This spatial resolution can reach 99.61 pixels per inch (ppi). This rail allows for the spatial resolution of the system to be further increased to 199.22 ppi by using a special movement route. In the experiments, we employ this system to image magnetized metal scissors, and the result displays the structural features of the scissor surface. We also detected the magnetic suction wireless charging coil inside an Apple phone. The image obtained shows the shape of the coil and the gap between the magnets. The high-resolution magnetic imaging system displays the magnetic characteristics of the sample very well and easily obtains information about small-shaped structures and defects on the sample surface. This provides the system with potential in several fields such as quality inspection, security, biomedicine, and detection imaging.

Tb3+ doped silicoborate glass scintillator for high resolution synchrotron X-rays imaging application

This research aims to develop a combination of SiO2 and B2O3 glass former (called, silicoborate glass) to be used as a scintillation material for digital radiography application. The silicoborate glass doped with different concentration of Tb2O3, xTb2O3–7.5Gd2O3–40Na2O–5SiO2– (47.5-x)B2O3, where x = 0, 1, 2, and 3 mol% (xTb:7.5Gd) were prepared by melting and then rapid quenching in graphite mold. The density of the prepared glasses was high with Tb2O3 concentration, indicating that the glass became denser and could strongly interact with X-rays. The molar volume increased with Tb2O3 concentration, suggesting the increase of Non-Bridging Oxygen (NBOs) in glass matrix. The xTb:7.5Gd glasses absorbed photons in visible and near-infrared regions and was observed that the absorption bands increased with Tb2O3 concentration, which was the result of the 4f6-4f6 transitions behavior of Tb3+ ions. The photoluminescence and radioluminescence results revealed the distinct emission occurring at 544 nm (5D4→7F5). The photoluminescence quantum yield (PLQY) of glass had the maximum efficiency at 30.85%. The luminescence peak area under X-rays excitation glass was maximum at 109% of BGO crystal. CIE 1931 chromaticity of the xTb:7.5Gd glasses showed the color coordinates in yellowish-green area. The decay time of the xTb:7.5Gd glasses were in the millisecond range for different excitations. The probability of energy transfer was investigated between Gd3+ and Tb3+ ions in glass and may occur mainly between the 6P7/2 level of Gd3+ and 5H7 level of Tb3+. The X-rays imaging using the developed glass as a scintillator was performed by Synchrotron X-rays and the spatial resolution 6 lp/mm was achieved. These results demonstrate that the 3 mol% of Tb2O3 doped silicoborate glass can be used as a scintillator and can be applied for a high-resolution Synchrotron X-rays imaging system.

Lens-free reflective topography for high-resolution wafer inspection

The demand for high-resolution and large-area imaging systems for non-destructive wafer inspection has grown owing to the increasing complexity and extremely fine nature of semiconductor processes. Several studies have focused on developing high-resolution imaging systems; however, they were limited by the tradeoff between image resolution and field of view. Hence, computational imaging has arisen as an alternative method to conventional optical imaging, aimed at enhancing the aforementioned parameters. This study proposes a method for improving the resolution and field of view of an image in a lens-less reflection-type system. Our method was verified by computationally restoring the final image from diffraction images measured at various illumination positions using a visible light source. We introduced speckle illumination to expand the numerical aperture of the entire system, simultaneously improving image resolution and field of view. The image reconstruction process was accelerated by employing a convolutional neural network. Using the reconstructed phase images, we implemented high-resolution topography and demonstrated its applicability in wafer surface inspection. Furthermore, we demonstrated an ideal diffraction-limited spatial resolution of 1.7 μm over a field of view of 1.8 × 1.8 mm2 for the topographic imaging of targets with various surface roughness. The proposed approach is suitable for applications that simultaneously require high throughput and resolution, such as wafer-wide integrated metrology, owing to its compact design, cost-effectiveness, and mechanical robustness.

UV imaging for the rapid at-line content determination of different colourless APIs in their tablets with artificial neural networks

This paper presents a novel high-resolution and rapid (50 ms) UV imaging system, which was used for at-line, non-destructive API content determination of tablets. For the experiments, amlodipine and valsartan were selected as two colourless APIs with different UV induced fluorescent properties according to the measured solid fluorescent spectra. Images were captured with a LED-based UV illumination (385–395 nm) of tablets containing amlodipine or valsartan and common tableting excipients. Blue or green colour components from the RGB colour space were extracted from the images and used as an input dataset to execute API content prediction with artificial neural networks. The traditional destructive, solution-based transmission UV measurement was applied as reference method. After the optimization of the number of hidden layer neurons it was found that the relative error of the content prediction was 4.41 % and 3.98 % in the case of amlodipine and valsartan containing tablets respectively. The results open the possibility to use the proposed UV imaging-based system as a rapid, in-line tool for 100 % API content screening in order to greatly improve pharmaceutical quality control and process understanding.

New Vacuum Solar Telescope Achieves Narrowband Infrared Solar Imaging Observation at He i 10830 Å

The near-infrared imaging channel constitutes a crucial component of the multichannel high-resolution imaging system of the New Vacuum Solar Telescope (NVST). We have successfully achieved high-resolution, narrowband imaging of the chromosphere using He i 10830 Å triplet within this channel, which significantly enhances the imaging observation capabilities of NVST. This paper provides a concise overview of the optical system associated with the near-infrared imaging channel, detailing data processing procedures and presenting several observed images. Leveraging a high-resolution image reconstruction algorithm, we were able to generate a narrowband image near the diffraction limit at 10830 Å with a temporal resolution of less than 10 s.

Development of printed X-ray grating and its application to an imaging system

The short wavelength of X-rays makes them attractive for high-resolution imaging systems in fields ranging from medicine to industry. The thin-film grating required for X-ray imaging can be created using printing, which is a cost-effective method for large-area imaging. Since the grating resolution (line/space, or L/S) influences the imaging resolution, it is crucial to enhance the L/S through printing methods. In this study, thin-film gratings were fabricated from silver nanoparticles using letterpress inversion printing, achieving a maximum L/S grating resolution of 1 μm/1 μm (the highest resolution achieved through printing). Subsequently, the cross-section of a pine needle was successfully imaged.

A High-Resolution Hyperspectral Imaging System for the Retina.

In this study, we developed an imaging system that can acquire and produce high-resolution hyperspectral images of the retina. Our system combines the view from a high-resolution RGB camera and a snapshot hyperspectral camera together. The method is fast and can be constructed into a compact imaging device. We tested our system by imaging a calibrated color chart, biological tissues ex vivo, and a phantom of the human retina. By using image pansharpening methods, we were able to produce a high-resolution hyperspectral image. The images from the hyperspectral camera alone have a spatial resolution of 0.2 mm/pixel, whereas the pansharpened images have a spatial resolution of 0.1 mm/pixel, a 2x increase in spatial resolution. Our method has the potential to capture images of the retina rapidly. Our method preserves both the spatial and spectral fidelity, as shown by comparing the original hyperspectral images with the pansharpened images. The high-resolution hyperspectral imaging device can have a variety of applications in retina examinations.

A High-Resolution 3D Ultrasound Imaging System Oriented towards a Specific Application in Breast Cancer Detection Based on a 1 × 256 Ring Array.

This paper presents the design and development of a high-resolution 3D ultrasound imaging system based on a 1 × 256 piezoelectric ring array, achieving an accuracy of 0.1 mm in both ascending and descending modes. The system achieves an imaging spatial resolution of approximately 0.78 mm. A 256 × 32 cylindrical sensor array and a digital phantom of breast tissue were constructed using the k-Wave toolbox. The signal is acquired layer by layer using 3D acoustic time-domain simulation, resulting in the collection of data from each of the 32 layers. The 1 × 256 ring array moves on a vertical trajectory from the chest wall to the nipple at a constant speed. A data set was collected at intervals of 1.5 mm, resulting in a total of 32 data sets. Surface rendering and volume rendering algorithms were used to reconstruct 3D ultrasound images from the volume data obtained via simulation so that the smallest simulated reconstructed lesion had a diameter of 0.3 mm. The reconstructed three-dimensional image derived from the experimental data exhibits the contour of the breast model along with its internal mass. Reconstructable dimensions can be achieved up to approximately 0.78 mm. The feasibility of applying the system to 3D breast ultrasound imaging has been demonstrated, demonstrating its attributes of resolution, precision, and exceptional efficiency.

A high-resolution handheld millimeter-wave imaging system with phase error estimation and compensation

Despite the enormous potential of millimeter-wave (mmWave) imaging, the high cost of large-scale antenna arrays or stringent prerequisites of the synthetic aperture radar (SAR) principle impedes its widespread application. Here, we report a portable, affordable, and high-resolution 3D mmWave imaging system by overcoming the destructive motion error of handheld SAR imaging. This is achieved by revealing two important phenomenons: spatial asymmetry of motion errors in different directions, and local similarity of phase errors exhibited by different targets, based on which we formulate the challenging phase error estimation problem as a tractable point spread function optimization problem. Experiments demonstrate that our approach can recover high-fidelity 3D mmWave images from severely distorted signals and augment the aperture size by over 50 times. Since our system does not rely on costly massive antennas or bulky motion controllers, it can be applied for diverse applications including security inspection, autonomous driving, and medical monitoring.

Design of compact high resolution imaging system for cold atom experiments

In cold atom experiments, high resolution imaging systems have been used to extract <i>in-situ</i> density information when studying quantum gases, which is one of the hot topics in this field. Such a system is usually called “quantum-gas microscope”. In order to achieve a long working distance and large magnification, high resolution imaging of cold atoms through a vacuum window usually requires a long distance between the atoms and the camera. However, due to space limitation caused by a large number of nearby optical elements, it may be difficult to realize a long imaging system, which is a common case in cold atom experiments. Herein we present an imaging system that can achieve a short distance between the atoms and the image plane with diffraction-limited 1 μm resolution and 50 magnification. The telephoto lens design is adopted to reduce the back focal length and enhance the pointing stability of the imaging lens. The system is optimized at an operating wavelength of 767 nm and corrects aberrations induced by a 5-mm-thick silica vacuum window. At a working distance of 32 mm, a diffraction-limited field of view of 408 μm is obtained. The simulation result shows that by changing the air space between lenses, our design operates across a wide range of window thicknesses (0–15 mm), which makes it robust enough to be used in typical laboratories. This compact imaging system is made from commercial on-shelf <i>Φ</i>2 in (1 in = 2.54 cm) singlets and consists of two components: a microscope objective with a numerical aperture of 0.47 and a telephoto objective with a long effective focal length of 1826 mm. Both are infinitely corrected, allowing the distance between them to be adjusted to insert optical elements for irradiating atoms with laser beams of different wavelengths without affecting the imaging resolution. Taking the manufacturing and assembling tolerances into consideration, the Monte Carlo analyses show that more than 95% of the random samples are diffraction-limited within the field of view. This high success rate ensures that these two objectives can be achieved easily in the experiment. Combined with its performance with other wavelengths (470–1064 nm), this imaging system can be used for imaging different atom species, such as sodium, lithium, and cesium.

Design and experiment of high-resolution detection imaging system with ultra-thin and ultra-short object-image distance

Design and experiment of high-resolution detection imaging system with ultra-thin and ultra-short object-image distance

Pilot testing of a simple alternative tissue processing method for immunofluorescence staining

Background: The image quality of tissues obtained with high-resolution imaging systems depends on several factors including the quality of sections prepared by different tissue processing methods. Fresh frozen sections and formalin-fixed paraffinembedded (FFPE) sections are the two routinely employed methods in histopathological examination having their own merits and demerits. Aims and Objectives: We tested the feasibility of a hybrid tissue processing method that could reduce the processing time without compromising the quality of processed and stained tissues. Materials and Methods: Bovine pancreatic tissue was utilized to standardize the process. The steps included fixation of tissue in formalin, followed by embedding in optimal cutting temperature compound and then cryo-sectioning to obtain 50 μm slices for immunostaining. The prepared thick slices were immunostained with islet markers and assessed by confocal imaging. Results: The images revealed that the staining quality was comparable with FFPE sections, though the tissue processing time was significantly curtailed. The modified Leica microsystems scoring system revealed a nearly 80% overall total score for the processed tissue specimens, indicating acceptable levels of quality of the tissues. We also observed that the staining quality of these formalin-fixed cryo-slices was preserved without tissue deterioration for up to 1 month when stored in formalin, indicating its storage potential for future applications. Conclusion: The proof of concept of the hybrid tissue processing method tested in this study will encourage researchers to extrapolate its use to the human pancreas, other solid organs, and other staining techniques for evaluating its general utility.

Switchable LED-based laparoscopic multispectral system for rapid high-resolution perfusion imaging.

Multispectral imaging (MSI) is an approach for real-time, quantitative, and non-invasive tissue perfusion measurements. Current laparoscopic systems based on mosaic sensors or filter wheels lack high spatial resolution or acceptable frame rates. To develop a laparoscopic system for MSI-based color video and tissue perfusion imaging during gastrointestinal surgery without compromising spatial or temporal resolution. The system was built with 14 switchable light-emitting diodes in the visible and near-infrared spectral range, a 4K image sensor, and a 10mm laparoscope. Illumination patterns were created for tissue oxygenation and hemoglobin content monitoring. The system was calibrated to a clinically approved laparoscopic hyperspectral system using linear regression models and evaluated in an occlusion study with 36 volunteers. The root mean squared errors between the MSI and reference system were 0.073 for hemoglobin content, 0.039 for oxygenation in deeper tissue layers, and 0.093 for superficial oxygenation. The spatial resolution at a working distance of 45mm was . The effective frame rate was 20fps. High-resolution perfusion monitoring was successfully achieved. Hardware optimizations will increase the frame rate. Parameter optimizations through alternative illumination patterns, regression, or assumed tissue models are planned. Intraoperative measurements must confirm the suitability during surgery.

Neural network-assisted design of GSST-based achromatic metalens with continuously variable focal heights

Recently developed achromatic metalens show great potential to replace conventional lenses. However, current long-wavelength infrared (LWIR) achromatic metalens are limited to fixed functions, severely hampers their integration and application. In order to address this limitation, Ge2Sb2Se4Te1 (GSST) and Silicon (Si) are used as materials for continuously variable focus height broadband achromatic metalens (CVFHBAM) at LWIR. Specifically, the multipole decomposition is performed within the operating band (8–12μm) to avoid undesired resonances and ensure the high degree of linearity of the meta-atoms. A tandem neural network is utilized for parameter optimization. Numerical results show that the CVFHBAM is well-corrected for chromatic aberration within the operating wavelength. By varying the crystalline fraction of GSST, focal length can continuously varied up to five times the center wavelength while maintaining achromatic focus, and the average numerical aperture (NA) is varied from 0.345 to 0.454. In addition, by calculating the Strehl ratio values, the transverse dimensions of the corresponding focal spots almost reach sub-diffractive focusing. The average focusing efficiencies are 57.74%, 64.32%, 68.94% and 71.48% respectively, for the four selected crystalline states. The results show that CVFHBAM has a promising application in developing high-resolution LWIR imaging and spectroscopy systems.

Evaluation of Meibomian gland structure and appearance after therapeutic Meibomian gland expression

ABSTRACT Clinical Relevance Evaluating how Meibomian glands can change in appearance has the potential to advance the understanding of Meibomian gland health and may lead to enhanced diagnosis and therapy. Background This work aimed to investigate Meibomian gland appearance after therapeutic Meibomian gland expression. Methods Fifteen subjects attended three study visits over a two-week period. Meibography was performed before and after therapeutic Meibomian gland expression, the following day, and 2 weeks after expression. Six central glands were used to calculate Meibomian gland morphological parameters such as gland length ratio, gland width, gland area, gland tortuosity, and gland contrast. A custom semi-automated image analysis software was used to calculate Meibomian gland metrics. Furthermore, a high-resolution imaging system was developed to capture clear images of the Meibomian glands, free of any artefacts, which were used for precise calculations of Meibomian gland contrast. Results The expression procedure had a significant impact on Meibomian gland contrast and length ratio immediately afterwards. The least square mean difference (95% CI) from baseline for Michelson contrast was −0.006 (−0.010, −0.001) and −1.048 (−2.063, −0.033) for simple contrast. The least square mean ratio of the gland length ratio immediately after the expression to baseline was 0.758 (0.618, 0.931). Conclusions Following therapeutic expression, Meibomian glands exhibit reduced brightness and length. However, within 24 h, they appear to recover and return to their baseline state, indicating a relatively short recovery time. This sheds light on whether meibography is solely focused on capturing gland structure or if it also captures acinar activity. The hyperreflective properties of lipids suggest that the decrease in contrast observed after expression could be attributed to a reduction in the visualisation of acini activity. A decrease in Meibomian gland length ratio implies that the loss of gland structure following treatment may be indicative of a temporary structural alteration.

Comparison in Detection Rate of Clinically Significant Prostate Cancer Between Microultrasound-guided Prostate Biopsy (ExactVu) and Multiparametric Resonance Imaging-guided Prostate Biopsy (Koelis System)

ObjectivesTo compare the detection rate of clinically significant prostate cancer (csPC) and prostate cancer and to find out the diagnostic concordance between microultrasound (mUS), a high-resolution imaging system that can identify suspicious prostate lesions and biopsy them in real time, and multiparametric magnetic resonance imaging (mpMRI)-guided prostate fusion biopsies. MethodsA prospective, multicentre, single-blind, single cohort study was conducted involving 80 patients with clinically suspected prostate cancer who underwent concomitant mpMRI-guided fusion prostate biopsy (KoelisTM System) and microultrasound-guided biopsy (ExactVuTM System) Results:The detection rate of csPC was slightly higher for image-guided fusion biopsy (21.25% vs. 18.75%), but this difference was not statistically significant (p=0.453). There was also no significant difference in overall PC diagnosis (50% vs. 51.25%, p = 0.897). The degree of agreement between the two diagnostic techniques for the detection of csPC as assessed by Cohen's Kappa concordance index was satisfactory κ ̂ = 0.676. The degree of ISUP of targeted biopsies obtained from concordant lesions was also represented by satisfactory concordance with a Kappa index of κ ̂ = 0. 696. ConclusionsMicroultrasound-guided biopsy is presented as an effective diagnostic method for the diagnosis of csPC compared to image-guided fusion biopsy. No differences are found in the detection rates of csPC and PC between the two strategies and satisfactory concordance is found in terms of histopathological findings.

Super-resolution macroscopic imaging via unknown speckle illumination using sparse aperture transmitter

Optical sparse aperture imaging technology has promising applications in the next generation of high-resolution imaging systems, but the phasing errors correction of sparse aperture is an urgent problem to be addressed. In this paper, we propose a blind structured-illumination super-resolution imaging system using a sparse aperture as the transmitter to overcome phasing errors and obtain higher resolution. In our scheme, an unknown pattern is projected onto the object by a sparse aperture system. By translating the unknown pattern, a sequence of modulated raw images is obtained. Based on these low-resolution raw images, the super-resolution object and the unknown illumination pattern are jointly estimated by the Adam algorithm. Here we show, both in the simulation and experiment, the resolution of reconstructions using sparse aperture as transmitter are similar to those using monolithic lens. Furthermore, we validate that the proposed method can protect the reconstruction effect from piston error and widen the tolerance range of tip/tilt error (peak-valley values) up to 0.5λ. At the same time, our proposed system can also alleviate to some extent the problem of mid-frequency modulation transfer function (MTF) attenuation that exists in sparse aperture imaging. Our approach not only simplifies the process of constructing synthetic aperture system, but also provides a novel application for synthetic aperture systems.