Gain In Resolution Research Articles

Expanding the field of view - a simple approach for interactive visualisation of electron microscopy data.

The unparalleled resolving power of electron microscopy is both a blessing and a curse. At 30,000× magnification, 1 µm corresponds to 3 cm in the image and the field of view is only a few micrometres or less, resulting in an inevitable reduction in the spatial data available in an image. Consequently, the gain in resolution is at the cost of loss of the contextual 'reference space', which is crucial for understanding the embedded structures of interest. This problem is particularly pronounced in immunoelectron microscopy, where the detection of a gold particle is crucial for the localisation of specific molecules. The common solution of presenting high-magnification and overview images side by side often insufficiently represents the cellular environment. To address these limitations, we propose here an interactive visualization strategy inspired by digital maps and GPS modules which enables seamless transitions between different magnifications by dynamically linking virtual low magnification overview images with primary high-resolution data. By enabling dynamic browsing, it offers the potential for a deeper understanding of cellular landscapes leading to more comprehensive analysis of the primary ultrastructural data.

Metal Polycation Adduction to Lipids Enables Superior Ion Mobility Separations with Ultrafast Ozone-Induced Dissociation.

Specific lipid isomers are functionally critical, but their structural rigidity and usually minute geometry differences make separating them harder than other biomolecules. Such separations by ion mobility spectrometry (IMS) were recently enabled by new high-definition methods using dynamic electric fields, but major resolution gains are needed. Another problem of identifying many isomers with no unique fragments in ergodic collision-induced dissociation (CID) was partly addressed by the direct ozone-induced dissociation (OzID) that localizes the double bonds, but a low reaction efficiency has limited the sensitivity, dynamic range, throughput, and compatibility with other tools. Typically lipids are analyzed by MS as singly charged protonated, deprotonated, or ammoniated ions. Here, we explore the differential IMS (FAIMS) separations with OzID for exemplary lipids cationized by polyvalent metals. These multiply charged adducts have much greater FAIMS compensation voltages (UC) than the 1+ ions, with up to 10-fold resolution gain enabling baseline isomer separations even at a moderate resolving power of the SelexION stage. Concomitantly OzID speeds up by many orders of magnitude, producing a high yield of diagnostic fragments already in 1 ms. These capabilities can be ported to the superior high-definition FAIMS and high-pressure OzID systems to take lipidomic analyses to the next level.

Deep-ultraviolet Fourier ptychography (DUV-FP) for label-free biochemical imaging via feature-domain optimization

We present deep-ultraviolet Fourier ptychography (DUV-FP) for high-resolution chemical imaging of biological specimens in their native state without exogenous stains. This approach uses a customized 265-nm DUV LED array for angle-varied illumination, leveraging the unique DUV absorption properties of biomolecules at this wavelength region. We implemented a robust feature-domain optimization framework to overcome common challenges in Fourier ptychographic reconstruction, including vignetting, pupil aberrations, stray light problems, intensity variations, and other systematic errors. By using a 0.12 numerical aperture low-resolution objective lens, our DUV-FP prototype can resolve the 345-nm linewidth on a resolution target, demonstrating at least a four-fold resolution gain compared to the captured raw images. Testing on various biospecimens demonstrates that DUV-FP significantly enhances absorption-based chemical contrast and reveals detailed structural and molecular information. To further address the limitations of conventional FP in quantitative phase imaging, we developed a spatially coded DUV-FP system. This platform enables true quantitative phase imaging of biospecimens with DUV light, overcoming the non-uniform phase response inherent in traditional microscopy techniques. The demonstrated advancements in high-resolution, label-free chemical imaging may accelerate developments in digital pathology, potentially enabling rapid, on-site analysis of biopsy samples in clinical settings.

Using Temporally and Spatially Resolved Measurements to Improve the Sensitivity of Fluorescence-Based Immunoassays.

Detecting low concentrations of biomarkers is essential in clinical laboratories. To improve analytical sensitivity, especially in identifying fluorescently labeled molecules, typical optical detection systems, consisting of a photodetector or camera, utilize time-resolved measurements. Taking a different approach, magnetic modulation biosensing (MMB) is a novel technology that combines fluorescently labeled probes and magnetic particles to create a sandwich assay with the target molecules. By concentrating the target molecules and then using time-resolved measurements, MMB provides the rapid and highly sensitive detection of various biomarkers. Here, we propose a novel signal-processing algorithm that enhances the detection and estimation of target molecules at low concentrations. By incorporating both temporally and spatially resolved measurements using human interleukin-8 as a target molecule, we show that the new algorithm provides a 2-4-fold improvement in the limit of detection and an ~25% gain in quantitative resolution.

Spatial wavefront shaping with a multipolar-resonant metasurface for structured illumination microscopy [Invited

Structured illumination microscopy (SIM) achieves superresolution in fluorescence imaging through patterned illumination and computational image reconstruction, yet current methods require bulky, costly modulation optics and high-precision optical alignment, thus hindering the widespread implementation of SIM. To address this challenge, this work demonstrates how nano-optical metasurfaces, rationally designed to tailor the far-field optical wavefront at sub-wavelength dimensions, hold great potential as ultrathin, single-surface, all-optical wavefront modulators for SIM. We computationally demonstrate this principle with a multipolar-resonant metasurface composed of silicon nanostructures that generate versatile optical wavefronts in the far field upon variation of the polarization or angle of incident light. Algorithmic optimization is performed to identify the seven most suitable illumination patterns for SIM generated by the metasurface based on three key criteria. We quantitatively demonstrate that multipolar-resonant metasurface SIM (mrm-SIM) achieves resolution gain that is comparable to conventional methods by applying the seven optimal metasurface-generated wavefronts to simulated fluorescent objects and reconstructing the objects using proximal gradient descent. Notably, we show that mrm-SIM achieves these resolution gains with a far-field illumination pattern that circumvents complex equipment and alignment requirements of comparable methodologies. The work presented here paves the way for a metasurface-enabled experimental simplification of structured illumination microscopy.

NBS-SNI, an extension of the network-based statistic: Abnormal functional connections between important structural actors.

Elucidating the coupling between the structure and the function of the brain and its development across maturation has attracted a lot of interest in the field of network neuroscience in the last 15 years. Mounting evidence supports the hypothesis that the onset of certain brain disorders is linked with the interplay between the structural architecture of the brain and its functional processes, often accompanied with unusual connectivity features. This paper introduces a method called the network-based statistic-simultaneous node investigation (NBS-SNI) that integrates both representations into a single framework, and identifies connectivity abnormalities in case-control studies. With this method, significance is given to the properties of the nodes, as well as to their connections. This approach builds on the well-established network-based statistic (NBS) proposed in 2010. We uncover and identify the regimes in which NBS-SNI offers a gain in statistical resolution to identify a contrast of interest using synthetic data. We also apply our method on two real case-control studies, one consisting of individuals diagnosed with autism and the other consisting of individuals diagnosed with early psychosis. Using NBS-SNI and node properties such as the closeness centrality and local information dimension, we found hypo- and hyperconnected subnetworks and show that our method can offer a 9 percentage points gain in prediction power over the standard NBS.

Метод эффективных вычитаний: работа с данными Иркутского радара некогерентного рассеяния

For incoherent scatter measurements, the effective subtraction technique is to alternate the duration of amplitude-modulated signals between a pair of consequently radiated pulses. The resulting gain of spatial resolution enables us to steadily assess the electron density profile by the Faraday rotation method. The paper describes the electron density measurement technique, which involves analyzing narrow-band signals from Irkutsk Incoherent Scatter Radar, and proposes an automated method of determining the electron density for the problem in which the convolution of the radiated signal waveform with backscatter signal cannot be neglected. The inverse problem of electron density recovery is considered as a standard nonlinear optimization problem, which is solved using the algorithms for global and local optimization applied consequently. We compare the electron density profiles obtained by analyzing different pulse waveforms and from Irkutsk ionosonde data.

Effective subtraction technique: implementation for Irkutsk Incoherent Scatter Radar

For incoherent scatter measurements, the effective subtraction technique is to alternate the duration of amplitude-modulated signals between a pair of consequently radiated pulses. The resulting gain of spatial resolution enables us to steadily assess the electron density profile by the Faraday rotation method. The paper describes the electron density measurement technique, which involves analyzing narrow-band signals from Irkutsk Incoherent Scatter Radar, and proposes an automated method of determining the electron density for the problem in which the convolution of the radiated signal waveform with backscatter signal cannot be neglected. The inverse problem of electron density recovery is considered as a standard nonlinear optimization problem, which is solved using the algorithms for global and local optimization applied consequently. We compare the electron density profiles obtained by analyzing different pulse waveforms and from Irkutsk ionosonde data.

Superresolution Expansion Microscopy in Dictyostelium Amoebae.

Expansion microscopy (ExM) is a superresolution technique for fixed specimens that improves resolution of a given microscopy system approximately fourfold. The gain in resolution in ExM is not achieved by improvement of the resolution of the microscope itself but by isotropic expansion of the sample. To achieve this, the sample is cross-linked to an expandable gel matrix that swells approximately fourfold by incubation in water. We have applied the method to Dictyostelium amoebae and discuss the pros and cons of different labeling techniques in combination with pre- and post-expansion staining protocols.

Resolution recovery on list mode MLEM reconstruction for dynamic cardiac SPECT system

The Dynamic Cardiac SPECT (DC-SPECT) system is being developed at the Massachusetts General Hospital, featuring a static cardio focus asymmetrical geometry enabling simultaneous high-resolution and high-sensitivity imaging. Among 14 design iterations of the DC-SPECT with varying number of detector heads, system sensitivity and resolution, the current version under development features 10 mm FWHM geometrical resolution (without resolution recovery) and 0.07% sensitivity at the center of the FOV, this is 1.5× resolution gain and 7× sensitivity gain compared to a conventional dual head gamma camera (0.01% sensitivity and 15-mm resolution). This work presents improvement in imaging resolution by implementing a spatially variant point spread function (SV-PSF) with list mode MLEM reconstruction. A resolution recovery method by PSF deconvolution is validated on list mode MLEM reconstruction for the DC-SPECT. A spatial invariant PSF is included as an additional test to show the influence of the PSF modelling accuracy on reconstructed image quality. We compare the MLEM reconstruction with and without PSF deconvolution; an analytic model is used for the calculation of system response, and the results are compared to the reconstruction with system modelling using Monte Carlo (MC) based methods. Results show that with PSF modelling applied, the quality of the reconstructed image is improved, and the DC-SPECT system can achieve a 4.5 mm central spatial resolution with average 795 counts/Mbq. Both the SV-PSF and the spatial-invariant PSF improve the image quality, and the reconstruction with SV-PSF generates line profiles closer to the ground truth. The results show substantial improvement over the GE Discovery 570c performance (7 mm spatial resolution with an average 460 counts/MBq, 5.8 mm resolution at the FOV center). The impact of PSF deconvolution is significant, improvement of the reconstructed image quality is evident in comparison to MC simulated system matrix with the same sampling size in the simulation.

Label-free image scanning microscopy for kHz super-resolution imaging and single particle tracking.

We report the modification of a label-free image scanning microscope (ISM) to perform asynchronous 2D imaging at up to 24kHz while keeping the lateral resolution gain and background rejection of a regular label-free ISM setup. Our method uses a resonant mirror oscillating at 12kHz for one-direction scanning and a chromatic line for instantaneous scanning in the other direction. We adapt optical photon reassignment in this scanning regime to perform fully optical super-resolution imaging. We exploit the kHz imaging capabilities of this confocal imaging system for single nanoparticle tracking down to 20 nm for gold and 50 nm for silica particles as well as imaging freely moving Lactobacillus with improved resolution.

Structured modulation multi-height microscopy for high-resolution imaging.

Conventional multi-height microscopy techniques introduce different object-to-detector distances to obtain multiple measurements for phase retrieval. However, surpassing the diffraction limit imposed by the numerical aperture (NA) of the objective lens remains a challenging task. Here, we report a novel structured modulation multi-height microscopy technique for quantitative high-resolution imaging. In our platform, a thin diffuser is placed in between the sample and the objective lens. By translating the diffuser to different axial positions, a sequence of modulated intensity images is captured for reconstruction. The otherwise inaccessible high-resolution object information can thus be encoded into the optical system for detection. In the construction process, we report a ptychographic phase retrieval algorithm to recover the existing wavefront of the complex object. We validate our approach using a resolution target, a phase target, and various biological samples. We demonstrate a ∼4-fold resolution gain over the diffraction limit. We also demonstrate our approach to achieve a 6.5 mm by 4.3 mm field of view and a half-pitch resolution of 1.2 µm. The reported methodology provides a portable, turnkey solution for quantitative high-resolution imaging with potential applications in disease diagnosis, sample screening, and other fields.

Resolution-enhanced x-ray ghost imaging with polycapillary optics

Ghost imaging (GI) enables compressive and lens-free image formation using a single-pixel detector and structured illumination, thus providing a promising and cost-effective approach to dose-reduced x-ray imaging. At this stage, a major bottleneck in almost all x-ray GI schemes is that the minimum resolution is strictly subject to the unit size of structured illumination. To overcome this widespread and inflexible resolution limitation, we introduced polycapillary optics into x-ray GI, in which polycapillary x-ray optics scaled down the input x-ray shadow pattern intactly and experimentally enabled a ∼3× resolution improvement. In general, polycapillary x-ray optics could be flexibly integrated in various x-ray GI applications with a demand of resolution larger than the diameter of the individual capillary composing of polycapillary optics, to achieve free resolution gain.

Three-dimensional ultrasound image reconstruction based on 3D-ResNet in the musculoskeletal system using a 1D probe: ex vivo and in vivo feasibility studies

Objective. Three-dimensional (3D) ultrasound (US) is needed to provide sonographers with a more intuitive panoramic view of the complex anatomical structure, especially the musculoskeletal system. In actual scanning, sonographers may perform fast scanning using a one-dimensional (1D) array probe .at random angles to gain rapid feedback, which leads to a large US image interval and missing regions in the reconstructed volume. Approach. In this study, a 3D residual network (3D-ResNet) modified by a 3D global residual branch (3D-GRB) and two 3D local residual branches (3D-LRBs) was proposed to retain detail and reconstruct high-quality 3D US volumes with high efficiency using only sparse two-dimensional (2D) US images. The feasibility and performance of the proposed algorithm were evaluated on ex vivo and in vivo sets. Main r esults. High-quality 3D US volumes in the fingers, radial and ulnar bones, and metacarpophalangeal joints were obtained by the 3D-ResNet, respectively. Their axial, coronal, and sagittal slices exhibited rich texture and speckle details. Compared with kernel regression, voxel nearest-neighborhood, squared distance weighted methods, and a 3D convolution neural network in the ablation study, the mean peak-signal-to-noise ratio and mean structure similarity of the 3D-ResNet were up to 28.53 ± 1.29 dB and 0.98 ± 0.01, respectively, and the corresponding mean absolute error dropped to 0.023 ± 0.003 with a better resolution gain of 1.22 ± 0.19 and shorter reconstruction time. Significance. These results illustrate that the proposed algorithm can rapidly reconstruct high-quality 3D US volumes in the musculoskeletal system in cases of a large amount of data loss. This suggests that the proposed algorithm has the potential to provide rapid feedback and precise analysis of stereoscopic details in complex and meticulous musculoskeletal system scanning with a less limited scanning speed and pose variations for the 1D array probe.

Defect angle as prognostic indicator in the reconstructive therapy of peri-implantitis.

To analyze the influence of the characteristics of bone defects caused by peri-implantitis on the clinical resolution and radiographic bone gain following reconstructive surgery. This is a secondary analysis of a randomized clinical trial. Periapical x-rays of bone defects, caused by peri-implantitis exhibiting intrabony component, were analyzed at baseline and 12-month follow-up after reconstructive surgery. Therapy consisted of anti-infective therapy along with a mixture of allografts with or without a collagen barrier membrane. The association of defect configuration, defect angle (DA), defect width (DW), and baseline marginal bone level (MBL) with clinical resolution (based on a prior defined composite criteria) and radiographic bone gain was correlated by means of generalized estimating equations. Overall, 33 patients with a total of 48 implants exhibiting peri-implantitis were included. None of the evaluated variables yielded statistical significance with disease resolution. Defect configuration demonstrated statistical significance when compared to class 1B and 3B, favoring radiographic bone gain for the former (p = 0.005). DW and MBL did not demonstrate statistical significance with radiographic bone gain. On the contrary, DA exhibited strong statistical significance with bone gain (p < 0.001) in the simple and multiple logistic regression analyses. Mean DA reported in this study was 40°, and this resulted in 1.85 mm radiographic bone gain. To achieve ≥1 mm of bone gain, DA must be <57°, while to attain ≥2 mm of bone gain, DA must be <30°. Baseline DA of peri-implantitis intrabony components predicts radiographic bone gain in reconstructive therapy (NCT05282667-this clinical trial was not registered prior to participant recruitment and randomization).

Passive Tone Detection for Moving Targets Based on Long-Time Coherent Integration

The detection of sinusoidal signals embedded in noise is an important topic in passive sonar signal processing. The performance of existing tone detection techniques is limited by the Doppler frequency shift, which is caused by the relative motion between moving targets and the receiver. In this study, an algorithm based on long-time coherent integration is proposed to achieve robust tonal signal detection under the influence of a Doppler frequency shift. First, the received narrowband signals radiated by moving targets are split into multiple segments through a window-length constraint. The results obtained by applying a discrete Fourier transform (DFT) to the data segments are modeled as a polynomial phase signal in the frequency domain. Then, the polynomial Radon-polynomial Fourier transform (PRPFT) is applied to simultaneously compensate the time-variant frequency drift and phase difference. To avoid the gain loss due to the discretization of the phase difference compensation in PRPFT, a phase compensation factor searching algorithm is proposed. The simulation results show that the proposed algorithm can provide higher frequency resolution and higher coherent integration gain even in the case of a severe Doppler shift. Furthermore, the results of sea trials demonstrate that the proposed method can perfectly achieve coherent integration for signals with a duration of several hundred seconds under different experimental conditions.

The Effect of Pilot Reuse Factor on Massive MIMO Spectral Efficiency

Due to their much increased spatial resolution and array gain, large-scale antenna arrays have the potential to significantly enhance the spectral efficiency of wireless systems. Recent research in the area of massive Multiple-Input Multiple-Output (MIMO) antennas shows that user channels are enhanced as the number of antennas at the Base Stations (BSs) rises, allowing achieving high signal improvement with minimum inter-user interference. The combined effects of the pilot reuse factor and the BS number of antennas on average overall spectral efficiency in huge MIMO antennas will be investigated. To examine the SE of these receivers, several channel estimators will be utilized, including LMMSE, ZF, and MR methods. Theoretically, BS could offer a substantially higher average total SE if it had more antennas.

Imaging dendritic spines in the hippocampus of a living mouse by 3D-stimulated emission depletion microscopy.

Stimulated emission depletion (STED) microscopy has been used to address a wide range of neurobiological questions in optically well-accessible samples, such as cell culture or brain slices. However, the application of STED to deeply embedded structures in the brain of living animals remains technically challenging. In previous work, we established chronic STED imaging in the hippocampus in vivo but the gain in spatial resolution was restricted to the lateral plane. In our study, we report on extending the gain in STED resolution into the optical axis to visualize dendritic spines in the hippocampus in vivo. Our approach is based on a spatial light modulator to shape the focal STED light intensity in all three dimensions and a conically shaped window that is compatible with an objective that has a long working distance and a high numerical aperture. We corrected distortions of the laser wavefront to optimize the shape of the bottle beam of the STED laser. We show how the new window design improves the STED point spread function and the spatial resolution using nanobeads. We then demonstrate the beneficial effects for 3D-STED microscopy of dendritic spines, visualized with an unprecedented level of detail in the hippocampus of a living mouse. We present a methodology to improve the axial resolution for STED microscopy in the deeply embedded hippocampus in vivo, facilitating longitudinal studies of neuroanatomical plasticity at the nanoscale in a wide range of (patho-)physiological contexts.

Spatial Resolution Optimization Technology of Raman OTDR Using Variable Sampling Rate

The technology to improve the spatial resolution of distributed sensing has always been a research hotspot. In this paper, a ROTDR (Raman-OTDR) system with a variable sampling rate and a spatial resolution optimization algorithm are designed, as shown in the figure, which makes the distribution of sampling points dense and improves spatial resolution. A point selection matrix based on the reconstruction algorithm is generated to reconstruct a one-dimensional high-precision signal. Furthermore, an optimization algorithm based on the reconstruction algorithm is designed, which can select the sampling rate and flexibly set the desired spatial resolution. Sampling rate combination and offset distance are set as the output of this algorithm to improve the response time and eliminate the blind area in the reconstruction process. The simulation results show that the reconstruction algorithm can improve the spatial resolution of the distributed temperature measurement system to 0.25 m at the cost of sampling ten times at different sampling rates (91 MHZ - 100 MHZ), representing a resolution gain of four times compared with the spatial resolution limited to 1 m by the acquisition card. This paper also compares the sampling results at a single sampling rate, random sampling rate combination, and optimized sampling rate combination to certify the effectiveness of this technology. The sampling result at an optimized sampling rate combination has the highest measurement accuracy.

High-quality manipulable fiber-microsphere for super-resolution microscopy.

Despite the gain in resolution brought by microsphere (MS)-assisted microscopy, it has always faced several limitations, such as a limited field of view, surface defects, low contrast, and lack of manipulability. This Letter presents a new type of MS created at the tip of an optical fiber, which we call a fiber microsphere (fMS). The fMS is made from a single-mode or coreless fiber, molten and stretched, ensuring high homogeneity and a sphere diameter smaller than the fiber itself. In addition, the connection between the fMS and the fiber makes scanning the sample a simple task, offering a solution to the difficulties of handling. The fabrication procedure of the fMS and the optical system used in the study are detailed. Our measurements show a clear superiority of the fMS over the soda-lime MS in resolving power and imaging performance.