Compact Imaging Research Articles

Toward low-noise on-chip plasmonic three-dimensional biological cell imaging

Enhancing accessibility to affordable and efficient cell imaging tools has been a longstanding worldwide objective for rapid disease detection and diagnosis. We present an innovative approach to this goal, introducing a compact, portable, and user-friendly three-dimensional (3D) cell imaging platform leveraging silicon photonics and the surface plasmon coupled emission (SPCE) phenomenon. Central to our method is a specially designed slide that incorporates a fundamental SPCE structure seamlessly integrated with a silicon nitride (SiN) waveguide. We introduce a grooved array on the slide to couple light into the waveguide, interfacing with a broadband light source. This source is employed to excite fluorescently labeled cells. The excitation is achieved using edge coupling through the SiN waveguide, directing the excitation light to the specimen placed on the SPCE platform. This integrated architecture eliminates the necessity for an additional filter to extract the required light for fluorophore excitation while enabling precise excitation of labeled cells. Following the fluorophore excitation, the emitted SPCE signals are captured and subjected to analysis. We have developed an imaging algorithm based on the emitted light patterns, which we comprehensively detail through theoretical demonstration. This algorithm has the remarkable capability of achieving 3D cell imaging. This fusion of optics and computational techniques can significantly impact the domain of cell imaging by enabling the development of easily accessible and portable point-of-care (POC) imaging tools.

Three-dimensional whole-body imaging of the bioreduction and clearance of nitroxide probes in the thoracic and abdominal regions of mice using a compact and mobile electron paramagnetic resonance imager.

Redox homeostasis plays a key role in regulating the overall health and development of organisms. This study aimed to develop a compact and mobile continuous-wave (CW) electron paramagnetic resonance (EPR) imager to facilitate stable, highly sensitive fast three-dimensional (3D)whole-body imaging of nitroxide-infused mice. A multiturn loop gap resonator with a diameter of 30 mm and length of 35 mm was designed for whole-body EPR imaging. A compact and mobile CW-EPR imager operating at 750 MHz was developed using this resonator. The automatic matching and tuning control systems were also adjusted to compensate for perturbations caused by the movement of the mice. When the mice were inserted into the resonator, the resonant frequency was easily determined for all parts of the mouse, from the head to the lower abdomen. 3D EPR images of the mouse body from the thoracic region to the lower abdomen were obtained following infusion of a nitroxide, 3-carboxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl (CxP). The EPR images clearly visualized the CxP distribution in various organs at different concentrations. Time-dependent EPR images also revealed that the signal intensities of the CxP decayed over time, and the decay rates for the heart, liver, and kidneys were evaluated. A compact and mobile EPR imager that enables 3D whole-body EPR image of nitroxide in mice was developed. The EPR imager exhibited long-term stability against motion effects caused by respiratory motion and heartbeats in mice. The EPR images clearly visualized the in vivo distribution, clearance, and metabolism of the nitroxide in organs.

Compact single-shot multispectral polarization imager through joint spectral-polarization encoding.

The technique of spectral polarization imaging (SPI) is a potent detection tool in various fields due to its ability to capture multi-dimensional information. However, existing SPI systems usually face challenges associated with architectural complexity and computational requirements, rendering them unsuitable for handheld, on-board, and real-time applications. Consequently, a compact single-shot multispectral polarization imager (CSMPI) is proposed, which employs a combined spectral-polarization encoding strategy to address the aforementioned issues. It incorporates a coded aperture for encoding multiple spectral channels together with linear polarization into a single measurement, enabling the simultaneous detection of up to nine light components with just one exposure. The resulting prototype consists solely of a color polarization detector and an imaging lens inserted with the small and easily fabricable coded aperture, which features compact dimensions of Φ5.5 cm × 21.5 cm and a light weight of approximately 670 g. This is particularly advantageous for application areas that require system miniaturization and rapid multi-dimensional detection.

Accurate 3D anthropometric measurement using compact multi-view imaging

Accurate 3D anthropometric measurement using compact multi-view imaging

A compact aerosol mobility imager (AMI) for instantaneous aerosol size distribution measurements, part I: Design and model evaluation

A compact aerosol mobility imager (AMI) for instantaneous aerosol size distribution measurements, part I: Design and model evaluation

Transparent ultrasonic transducers based on relaxor ferroelectric crystals for advanced photoacoustic imaging

Photoacoustic imaging is a promising non-invasive functional imaging modality for fundamental research and clinical diagnosis. However, achieving capillary-level resolution, wide field-of-view, and high frame rates remains challenging. To address this, we propose a transparent ultrasonic transducer design using our developed transparent Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals. Our fabrication technique incorporates quartz-glass-and-epoxy matching layers with low-resistance indium-tin-oxide electrodes through a brass-ring based structure, enabling a high frequency (28.5 MHz), wide bandwidth (78%), and enhanced pulse-echo sensitivity (2.5 V under 2-μJ pulse excitation). Our Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3-based transparent ultrasonic transducer demonstrates a four-fold enhancement in photoacoustic detection sensitivity when compared to the LiNbO3-based counterpart, leading to a 13 dB improvement of signal-to-noise ratio in microvascular photoacoustic imaging. This enables dynamic monitoring of mouse cerebral cortex microvasculature during seizures at 0.8 Hz frame rates over a 1.5 × 1.5 mm2 field-of-view. Our work paves the way for high-performance and compact photoacoustic imaging systems using advanced piezoelectric materials.

Noninvasive high-resolution deep-brain photoacoustic imaging with a negatively focused fiber-laser ultrasound transducer

Noninvasive high-resolution deep-brain imaging is essential to fundamental cognitive process study and neuroprotective drugs development. Although optical microscopes can resolve fine biological structures with good contrast without exposure to ionizing radiation or a strong magnetic field, the optical scattering limits the penetration depth and hinders its capability for deep-brain imaging. Here, in vivo high-resolution imaging of the whole mouse brain is demonstrated by using a photoacoustic computed tomography system with a negatively focused fiber-laser ultrasound transducer. By leveraging the high flexibility and low bending loss of the optical fiber, a rationally designed negatively focused fiber laser cavity exhibits a low detection limit down to 5.4 Pa and a broad view angle of ∼120 deg, enabling mouse brain imaging with a penetration larger than 7 mm and a nearly isotropic spatial resolution of ∼130 μm. In addition, the negative curvature of the fiber laser reduces the working distance, which facilitates the development of a compact and portable linear scanning imaging system. In vivo imaging of a mouse model with intracerebral hemorrhage is also showcased to demonstrate its capability for potential biomedical and clinical applications. With high spatial resolution and large tissue penetration, the system may provide a noninvasive, user-friendly, and high-performance imaging solution for biomedical research and preclinical/clinical diagnosis.

Adjoint-Assisted Shape Optimization of Microlenses for CMOS Image Sensors.

Recently, there have been significant developments in the designs of CMOS image sensors to achieve high-resolution sensing capabilities. One of the fundamental factors determining the sensor's ability to capture high-resolution images is its efficiency in focusing the visible light onto the photosensitive region of the submicron scale. In most CMOS imaging technologies, this is typically achieved through microlenses. Light collection under diverse conditions can be significantly improved through the efficient design of microlenses. While the optimization of microlenses appears to be imperative, achieving efficient designs of microlenses for high-density pixels under various conditions remains a significant challenge. Therefore, a systematic optimization approach is required to accelerate the development of efficient microlenses with enhanced optical performance. In this paper, we present an approach to optimize the shape of CMOS microlenses through adjoint sensitivity analysis (ASA). A novel figure of merit (FOM) is developed and incorporated into the optimization process to enhance the light collection. The gradient of the FOM is computed iteratively using two field simulations only. The functionality and robustness of the optimization framework are thoroughly evaluated. Furthermore, the performance of the optimized CMOS microlenses is compared to that of the conventional microlenses. The adjoint-assisted optimization framework presented here can be further used to develop efficient optical devices that perform optical manipulation such as concentrating, bending, or dispersing light in compact imaging systems.

Optimized galvanometric illumination for terahertz full-field imaging and computed tomography

The pursuit of high-resolution, high-fidelity, real-time imaging is receiving significant attention in terahertz community. In this study, a versatile illumination approach based on a double-mirror galvanometer is proposed and optimized for multiple terahertz imaging approaches. We analyzed the mechanism of galvanometric illumination and elucidated two main factors affecting its homogeneity and parallelism properties. In our module, the terahertz beam is deflected rapidly by the galvanometer which is driven by triangular voltage signals, and then focused by a self-designed aspherical f-θ lens to illuminate the object at an equal lateral scanning velocity. The object beam of different transients is periodically superimposed along the Lissajous trajectory, and is recorded by an array microbolometer in a single integration of 3 s. A homogeneous illumination field is realized with a speckle contrast of 0.11, and the resultant image achieves isotropic resolution. By adopting the proposed galvanometric illumination strategy, the average intensity of the illumination field is increased by 135% compared to expanded coherent illumination, and the speckle contrast is reduced by 83.5% compared to other galvanometric illumination. By virtue of leading low speckle noise, illumination homogeneity and parallelism, a compact imaging system is built for terahertz full-field imaging and computed tomography achieving high imaging speed and fidelity. As a successful attestation of terahertz beam steering, this study is very promising to reduce the total cost, increase the performance and expand the application of terahertz imaging.

Three-channel-switchable coded aperture snapshot multispectral polarization imaging.

An ingenious and compact snapshot multispectral polarization imaging method is proposed based on a new, to the best of our knowledge, three-channel-switchable spectral polarization coded aperture. We utilize the coded aperture to simultaneously select three-channel light components and encode them with specific spectrum-polarization coefficients. It enables easy retrieval of each channel's light component from the mixed information via polarization measurements and linear decoding operations. Distinct three-channel light components can be detected simultaneously, thus achieving either three spectral images or linearly polarized ones per snapshot. The number of detectable light components is unlimited and triple that of snapshot times, showing its superior capability in measuring spectral polarization properties. The resulting prototype is miniaturized, featuring compact dimensions of Φ5.5 cm × 25 cm and a light weight of ∼800 g. This is attributed to its simplistic structure comprising a monochrome polarization detector and an imaging lens integrated with the coded aperture, making it suitable for portable and on-board applications. Furthermore, the absence of advanced or costly production technologies for manufacturing the prototype ensures an affordable price for its acquisition, facilitating widespread adoption and application of the proposed method.

Differentiable design of compact imaging systems with curved Fresnel optics

Phase elements can improve the performance and reduce the size of imaging systems, thanks to the additional degrees of freedom that are offered by the independent phase gradient on top of a refractive/reflective surface. Possible implementations include diffractive elements or metasurfaces, but these suffer from diffractive dispersion. Similar optical functionality however can be provided by thin, curved Fresnel optics, which solely rely on refraction. In this study, a differentiable raytracing framework is presented that offers precise and rapid optimization of curved Fresnel surfaces, by modeling them as a combination of a distinct geometrical and refractive surface, both differentiable with respect to the imaging merit function. The method is demonstrated by designing a compact imaging and projection lens, both with high numerical aperture. The paper analyzes the impact of Fresnelizing the optimized "theoretical" surfaces on both the imaging performance and transmission efficiency. It furthermore shows how the system performance can be enhanced through dedicated post-processing steps, emphasizing the practical relevance of compact Fresnel optics.

Metasurfaces‐Enabled Advanced Multidimensional Imaging: Principle and Applications

AbstractThe efficient acquisition of multidimensional information—spatial, polarization, frequency, and phase of optical fields, is a key research focus. Metasurfaces, which are emerging as planar arrays of artificial nanostructures, offer significant advantages in advanced imaging due to their exceptional ability to manipulate electromagnetic waves through subwavelength optical resonators. Meanwhile, the rapidly developing computational imaging algorithms have also greatly enhanced the performance of metasurfaces in multi‐dimensional imaging. In this review, we focus on the research progress in metasurface‐empowered multidimensional imaging, including advanced spatial imaging, compact polarization imaging, high‐resolution spectral imaging, single‐shot phase imaging, and edge imaging. Their basic principles and imaging results will also be presented. Furthermore, a summary of several current challenges and anticipation in various future directions within this field will also be provided.

Metasurface-enabled 3D imaging via local bright spot gray scale matching using the structured light dot array.

Three-dimensional (3D) imaging is widely utilized in various applications, such as light detection, autonomous vehicles, and machine vision. However, conventional 3D imaging systems often rely on bulky optical components. Metasurfaces, as next-generation optical devices, possess flexible wavefront modulation capabilities and excellent combination with computer vision algorithms. Here, we propose a large field-of-view (FOV) structured light dot array projection device based on a metasurface, covering a 2π-FOV, for projecting coded point clouds in Fourier space. We explore a local bright spot gray scale matching algorithm for depth extraction, enabling 3D imaging. This algorithm simplifies the data processing flow and optimizes depth extraction and feature matching processes through a customized region gray scale comparison. As a result, it effectively reduces computational complexity and enhances tolerance to image quality fluctuations. The proposed approach provides new possibilities for developing compact and high-performance planar 3D optical imaging devices, which will drive the advancement of fields such as computer vision and artificial intelligence.

Optimization study on the compact thermal neutron imaging system based on portable D-T neutron generator

The distribution of lithium in lithium-ion batteries is critical to their performance and lifespan. Studies have shown that thermal neutron imaging can effectively perform non-destructive testing of this distribution. However, most current thermal neutron imaging systems rely on expensive, bulky, and immobile nuclear reactors or spallation neutron sources, significantly limiting their application scenarios. Therefore, this study adopts a portable D-T neutron generator as the neutron source and uses Monte Carlo simulation methods to optimize the design of key components in the thermal neutron imaging system. Simulation results indicate that the optimized thermal neutron imaging system achieves a thermal neutron flux of 8.36 × 104 n·cm−2·s−1 and a thermal neutron content (TNC) of 14.4% at a collimation ratio of 50. Within an imaging range of Φ100 mm, the non-uniformity of the thermal neutron fluence is approximately 2.07%. Simulation imaging results of lithium and iron step wedges demonstrate that the compact thermal neutron imaging system designed in this study can effectively distinguish between iron and lithium of the same thickness. This finding provides an important reference for subsequent detection of lithium distribution within lithium-ion batteries.

Comprehensive validation of a compact laser speckle contrast imaging system for vascular function assessment: from the laboratory to the clinic.

Proper organ functioning relies on adequate blood circulation; thus, monitoring blood flow is crucial for early disease diagnosis. Laser speckle contrast imaging (LSCI) is a noninvasive technique that is widely used for measuring superficial blood flow. In this study, we developed a portable LSCI system using an 805-nm near-infrared laser and a monochrome CMOS camera with a 10 × macro zoom lens. The system achieved a high-resolution imaging (1280 × 1024 pixels) with a working distance of 10 to 35 cm. The relative flow velocities were visualized via a spatial speckle contrast analysis algorithm with a 5 × 5 sliding window. In vitro experiments demonstrated the system's ability to image flow velocities in a fluid model, and a linear relationship was observed between the actual flow rate and the relative flow rate obtained by the system. The correlation coefficient (R2) exceeded 0.83 for volumetric flow rates of 0 to 0.2 ml/min when channel widths were greater than 1.2 mm, and R2 > 0.94 was obtained for channel widths exceeding 1.6 mm. Comparisons with laser Doppler flowmetry (LDF) revealed a strong positive correlation between the LSCI and LDF results. In vivo experiments captured postocclusive reactive hyperemic responses in rat hind limbs and human palms and feet. The main research contribution is the development of this compact and portable LSCI device, as well as the validation of its reliability and convenience in various scenarios and environments. Future applications of this technology include evaluating blood flow changes during skin injuries, such as abrasions, burns, and diabetic foot ulcers, to aid medical institutions in treatment optimization and to reduce treatment duration.

Wide FOV metalens for near-infrared capsule endoscopy: advancing compact medical imaging.

This study presents the design, fabrication, and characterization of a wide field-of-view (FOV) metalens optimized for capsule endoscopy. The metalens achieved a 165° FOV with a high modulation transfer function (MTF) of 300 lines per millimeter (lp/mm) across the entire FOV, operating in the near-infrared (NIR) narrow-bandpass imaging at 940 nm. The performance of the metalens-based system is evaluated using two bandwidths, 12 nm and 32 nm, showing MTF values of 0.2 and 0.3 at 250 lp/mm, respectively. The metalens-based system maintains a compact form factor with a total track length of 1.4 mm and a diameter of 1.58 mm. Compared to a traditional 108° FOV endoscope, the nano-optic capsule endoscope demonstrated superior performance in terms of FOV, contrast, and resolution. This advancement represents a significant step toward enhancing diagnostic capabilities in medical imaging, offering improved performance in a more compact package compared to conventional optics.

Relationship Between the Distribution of the Pinewood Nematode (Bursaphelenchus xylophilus) and the Development of Xylem Embolism in the Stems of Japanese Black Pine (Pinus thunbergii) Seedlings Monitored by Magnetic Resonance Imaging.

The development of xylem embolism in 1-year-old stems of Japanese black pine (Pinus thunbergii) seedlings was monitored by compact magnetic resonance imaging (MRI) after inoculation with the pinewood nematode (Bursaphelenchus xylophilus). In parallel, the nematode distribution and population structure in the stems were examined by isolating the nematodes using the Baermann funnel technique. The vertical length and volume of massive embolisms in each seedling were strongly correlated with the maximum relative embolized area (REA) in stem cross-sections. Embolism development and nematode reproduction were not restricted to the inoculation site, as any portion of the stem could be the initial point of a population burst. The nematode population in the stem xylem was strongly correlated with the REA and with the circumferential proportion of cambial death in cross-sections monitored by MRI. The proportion of second-stage juveniles was also correlated with the REA in the xylem. In contrast, the nematode population in bark tissue was not correlated with either the REA or cambial death. These results suggested that nematode reproduction in the cambial zone is the key step in pine wilt disease, and second-stage juveniles were suggested to induce massive embolisms in the advanced stage of the disease.

Compact staring-type underwater spectral imaging system utilizing k-Nearest neighbor-based interpolation for spectral reconstruction

Besides the challenges posed by the complex optical properties of water, underwater spectral imaging face significant issues, including system bulkiness, optical complexity, and high spectral resolution requirement. This study introduces a compact staring-type underwater spectral imaging system designed to overcome these limitations. Featuring a 6-channel rotary spectral camera, the system is optimized for optical simplicity, and spectral efficiency. It employs a k-Nearest Neighbor (KNN)-based spectral reconstruction method to substantially enhance spectral resolution. Auto-focusing and image registration techniques, utilizing the Tenengrad function and Scale-Invariant Feature Transform (SIFT) feature points, ensure sharp and aligned multi-channel imagery. Experimental validation demonstrates the system’s capability to accurately reconstruct spectral reflectance data across the 400 nm to 700 nm band, significantly increasing spectral resolution from 6 to 31 channels. The spectral reflectance reconstruction results, achieving an average Root Mean Square Error (RMSE) of 0.0651 and Goodness of Fit Coefficient (GFC) of 0.9871, highlight the system’s efficiency in precise spectral analysis. This advancement in spectral resolution and adaptability to diverse underwater applications marks a significant leap forward in underwater observation and monitoring through spectral imaging.

Far-Field Phase-Shifting Structured Light Illumination Enabled by Polarization Multiplexing Metasurface for Super-Resolution Imaging.

The phase-shifting structured light illumination technique is widely used in imaging but often relies on mechanical translation stages or spatial light modulators, leading to system instability, low displacement accuracy, and limited integration feasibility. In response to these challenges, we propose and demonstrate an approach for generating far-field phase-shifting structured light using a polarization multiplexing metasurface. By controlling the polarization states of incident and transmitted light, the metasurface creates a three-step displacement of structured light, eliminating the need to move samples or illumination sources. As a proof of concept, we experimentally demonstrate microscopic imaging using structured light illumination generated by metasurfaces, extracting high-frequency information from objects, and surpassing the diffraction limit. The proposed metasurface platform offers a promising approach for developing compact and robust phase-shifting imaging systems, with broad prospects in quantitative detection, machine vision, and beyond.

Development of a Novel Male Reproductive Toxicity Assessment Method to Predict Male-mediated Effects on the Next Generation

Less than 10% of the candidate drug compounds are associated with male reproductive toxicity. Genetic and/or epigenetic information on sperm may be crucial for fetal development. Therefore, developmental toxicity, such as paternally transmitted birth defects, is possible if genetic abnormalities in the male germ line persist and accumulate in the sperm during spermatogenesis. First, this study provides an overview of chemical and male reproductive toxicity, which may lead to developmental toxicity from the perspective of male reproduction. Second, we demonstrate methods for evaluating male reproductive toxicity to anticipate male-mediated developmental toxicity. We developed a novel staining technique for evaluating sperm quality, as well as a noninvasive imaging analysis of male reproductive toxicity. The former is a mammalian male germ cell-specific staining method using reactive blue 2 dye (RB2), as previously confirmed in human sperm, and a method for detecting the early-stage DNA fragmentation in a single nucleus from mouse spermatozoa using single-cell pulsed-field gel electrophoresis. The latter is a new, ready-to-use, and compact magnetic resonance imaging (MRI) platform utilizing a high-field permanent magnet to evaluate male reproductive toxicity. The histopathological analysis supported the suitability of the MRI platform. The present study, for the first time, revealed a rapid, noninvasive evaluation of male reproductive toxicity in vivo using compact MRI. These novel toxicity assessments can help predict male-mediated developmental toxicity, contributing to accelerated drug discovery and drug repositioning.