Widefield functional speckle-correlation optical scattering mesoscopy toward hemodynamic imaging.

Speckle-correlation optical scattering imaging (SCOSI) has shown the potential for non-invasive biomedical diagnostic applications, which directly utilizes the scattering patterns to reconstruct the deep and non-line-of-sight objects. However, the course of the translation of this technique to preclinical biomedical imaging applications has been postponed by the following two facts: 1) the field of view of SCOSI was significantly limited by the optical memory effect, and 2) the molecular-tagged functional imaging of the biological tissues remains largely unexplored. In this work, a proof-of-concept design of the first-generation widefield functional SCOSI (WF-SCOSI) system was presented for simultaneously achieving mesoscopic mapping of fluid morphology and flow rate, which was realized by implementing the concepts of scanning synthesis and fluorescence scattering flowmetry. The ex vivo imaging results of the fluorescence-labeled large-scale blood vessel network phantom underneath the strong scatters demonstrated the effectiveness of WF-SCOSI toward non-invasive hemodynamic imaging applications.

Thermal-tagging photoacoustic remote sensing flowmetry.

Ultrasound coupling is one of the critical challenges for traditional photoacoustic (or optoacoustic) microscopy (PAM) techniques transferred to the clinical examination of chronic wounds and open tissues. A promising alternative potential solution for breaking the limitation of ultrasound coupling in PAM is photoacoustic remote sensing (PARS), which implements all-optical non-interferometric photoacoustic measurements. Functional imaging of PARS microscopy was demonstrated from the aspects of histopathology and oxygen metabolism, while its performance in hemodynamic quantification remains unexplored. In this Letter, we present an all-optical thermal-tagging flowmetry approach for PARS microscopy and demonstrate it with comprehensive mathematical modeling and ex vivo and in vivo experimental validations. Experimental results demonstrated that the detectable range of the blood flow rate was from 0 to 12 mm/s with a high accuracy (measurement error:±1.2%) at 10-kHz laser pulse repetition rate. The proposed all-optical thermal-tagging flowmetry offers an effective alternative approach for PARS microscopy realizing non-contact dye-free hemodynamic imaging.

Limited view correction in low-optical-NA photoacoustic microscopy.

Photoacoustic microscope (PAM) with a low-optical NA suffers from a limited view along the optical axis, due to the coherent cancellation of acoustic pressure waves after being excited with a smoothly focused beam. Using larger-NA (NA > 0.3) objectives can readily overcome the limited-view problem, while the consequences are the shallow working distance and time-consuming depth scanning for large-volume imaging. Instead, we report an off-axis oblique detection strategy that is compatible with a low-optical-NA PAM for turning up the optical-axis structures. Comprehensive photoacoustic modeling and ex vivo phantom and in vivo mouse brain imaging experiments are conducted to validate the efficacy of correcting the limited view. Proof-of-concept experiment results show that the visibility of optical-axis structures can be greatly enhanced by making the detection angle off the optical axis larger than 45°, strongly recommending that off-axis oblique detection is a simple and cost-effective alternative method to solve the limited-view problems in low-optical-NA PAMs.

Random motion blur for optical image encryption.

We present a compact optical encryption scheme by using a continuous-random-motion blurring model in an optical imaging system. Image encryption is performed by additive motion blur effects with continuous and random shifts of a camera. Real-time random phase modulation can be achieved without the use of random phase mask. Storage of the key is more convenient, which only requires parameters of motion. In addition, modulation characteristics are different from the traditional encryption schemes. On the premise of high security, modulation space is broadened, and flexibility of encryption is further improved. Simulations and experiments verify the validity of the motion blur-based crypto-system and demonstrate its security under several attacks. This novel method will be significant for the practical applications in the field of optical information security.

Lensfree on-chip microscopy based on single-plane phase retrieval.

We propose a novel single-plane phase retrieval method to realize high-quality sample reconstruction for lensfree on-chip microscopy. In our method, complex wavefield reconstruction is modeled as a quadratic minimization problem, where total variation and joint denoising regularization are designed to keep a balance of artifact removal and resolution enhancement. In experiment, we built a 3D-printed field-portable platform to validate the imaging performance of our method, where resolution chart, dynamic target, transparent cell, polystyrene beads, and stained tissue sections are employed for the imaging test. Compared to state-of-the-art methods, our method eliminates image degradation and obtains a higher imaging resolution. Different from multi-wavelength or multi-height phase retrieval methods, our method only utilizes a single-frame intensity data record to accomplish high-fidelity reconstruction of different samples, which contributes a simple, robust, and data-efficient solution to design a resource-limited lensfree on-chip microscope. We believe that it will become a useful tool for telemedicine and point-of-care application.

Enormous electro-optic effect in paraelectric nanodisordered KTa1-xNbxO3 crystal.

Recent experiments have revealed that the order of the electro-optic (EO) effect depends on the frequency of electric field in paraelectric nanodisordered KTa1-xNbxO3 (KTN) crystal. Through the dielectric frequency spectrum under the bias electric field, enormous linear and quadratic EO effects were discovered at the resonance frequencies, which changed the perception that only the quadratic EO effect exists. Applying just a small AC electric field of 6 V/mm, the effective linear EO coefficient reached 478 pm/V at 609 kHz, and the effective quadratic EO coefficient reached 4.39*10-13m2V-2at 302 kHz. The reason why an extremely low electric field results in an enormous EO coefficient is attributed to the resonance between the polar nanoregions (PNRs) and the electric field, induced by the field-driven reorientation of free dipoles on the boundary of the PNRs. In addition, the order of EO effect depending on the frequency of electric field was attributed to the motion modes of the PNR. This finding improves the understanding of how the EO effect is caused by field-driven PNR dynamics, but also provides a basis for the development of EO devices.

Spectrum sampling optimization for quantitative phase imaging based on Kramers-Kronig relations.

Annular-illumination quantitative phase imaging based on space-domain Kramers-Kronig relations (AIKK) is a newly developed technique that is object-independent and non-iterative reconstructed inherently. Only capturing four low-resolution images, the AIKK system gains a resolution enhancement of nearly twofold. Under matching constraints between the illumination wave vector and pupil function aperture, we set a spectrum sampling criterion and establish a spectrum effective utilization model to search for the optimal solution of spectrum distribution for the specific annular structure. In view of the square spectrum structure, a diagonal-expanded sampling based AIKK method (DES-AIKK) is presented to get rid of the pixel aliasing problem. It is worth noting that the space-bandwidth-time product (SBP-T) further increases to 439.51 megapixels (1.8× of AIKK). Our work provides the guidelines and insights for designing the most suitable AIKK platform for high-throughput microscopic applications in pathology and real-time dynamic observation.

Fast autofocusing based on pixel difference with the Tanimoto coefficient between images.

Focusing objects accurately over short time scales is an essential and nontrivial task for a variety of microscopy applications. In this Letter, an autofocusing algorithm using pixel difference with the Tanimoto coefficient (PDTC) is described to predict the focus. Our method can robustly distinguish differences in clarity among datasets. The generated auto-focusing curves have extremely high sensitivity. A dataset of a defocused stack acquired by an Olympus microscope demonstrates the feasibility of our technique. This work can be applied in full-color microscopic imaging systems and is also valid for single-color imaging.

High-performance lensless diffraction imaging from diverse holograms by three-dimensional scanning.

For lensless diffraction imaging, it is a challenging dilemma to achieve a large field of view (FOV) and high resolution with a small amount of data at the same time. Ptychography can reconstruct the high-resolution image and illumination light simultaneously. But the illumination is limited to a small size by a probe in typical ptychography. For large samples, it takes much time to collect abundant patterns and has strict requirements for the computing power of computers. Another widely applied method, multi-height measurement, can realize a wide FOV with several holograms. But, the recovered image is easily destroyed by the background noise. In this Letter, a lensless diffraction imaging method by three-dimensional scanning is proposed. All positions of the object are different in three directions instead of scanning schemes only on a plane or along the optic axis, so more diversity of diffraction information is obtained. We apply the illumination without the limit of a confined aperture, which means that the imaging FOV of a pattern is equal to the size of the utilized image sensor. In comparison with the multi-height method, our method can separate the illumination background noise from the retrieved object. Consequently, the proposed method realized high resolution and contrast, large FOV, and the removal of background noise simultaneously. Experimental validations and comparisons with other methods are presented.

Radially polarized cosine non-uniformly correlated beams and their propagation properties.

We introduce a kind of radially polarized partially coherent (RPPC) beam with a prescribed non-uniform correlation function, called a radially polarized cosine non-uniformly correlated (RPCNUC) beam. Based on the extended Huygens-Fresnel principle, we study the propagation properties in free space and in a turbulent atmosphere. Unlike RPPC beams with uniform coherence, RPCNUC beams possess the invariance of dark hollow cores and radial polarization, and exhibit self-focusing properties. In a turbulent atmosphere, the intensity distribution demonstrates self-healing properties over a certain propagation distance. We also investigate how to adjust the beam parameters to reduce the turbulence-induced degradation in detail.

Managing Emergent Surgery for Ruptured Abdominal Aortic Aneurysm during the COVID-19 Pandemic.

BACKGROUND: Coronavirus disease 2019 (COVID-19) has become a global pandemic which may compromise the management of vascular emergencies. An uncompromised treatment for ruptured abdominal aortic aneurysm (rAAA) during such a health crisis represents a challenge. This study aimed to demonstrate the treatment outcomes of rAAA and the perioperative prevention of cross-infection under the COVID-19 pandemic. METHODS: In cases of rAAA during the pandemic, a perioperative workflow was applied to expedite coronavirus testing and avoid pre-operative delay, combined with a strategy for preventing cross-infection. Data of rAAA treated in 11 vascular centers between January-March 2020 collected retrospectively were compared to the corresponding period in 2018 and 2019. RESULTS: Eight, 12, and 14 rAAA patients were treated in 11 centers in January-March 2018, 2019, and 2020, respectively. An increased portion were treated at local hospitals with a comparable outcome compared with large centers in Guangzhou. With EVAR-first strategy, 85.7% patients with rAAA in 2020 underwent endovascular repair, similar to that in 2018 and 2019. The surgical outcomes during the pandemic were not inferior to that in 2018 and 2019. The average length of ICU stay was 1.8 ± 3.4 days in 2020, tending to be shorter than that in 2018 and 2019, whereas the length of hospital stay was similar among 3 years. The in-hospital mortality of 2018, 2019, and 2020 was 37.5%, 25.0%, and 14.3%, respectively. Three patients undergoing emergent surgeries were suspected of COVID-19, though turned out to be negative after surgery. CONCLUSIONS: Our experience for emergency management of rAAA and infection prevention for healthcare providers is effective in optimizing emergent surgical outcomes during the COVID-19 pandemic.

Automatic Extraction of Power Lines from Aerial Images of Unmanned Aerial Vehicles.

Automatic power line extraction from aerial images of unmanned aerial vehicles is one of the key technologies of power line inspection. However, the faint power line targets and complex image backgrounds make the extraction of power lines a greater challenge. In this paper, a new power line extraction method is proposed, which has two innovative points. Innovation point one, based on the introduction of the Mask RCNN network algorithm, proposes a block extraction strategy to realize the preliminary extraction of power lines with the idea of "part first and then the whole". This strategy globally reduces the anchor frame size, increases the proportion of power lines in the feature map, and reduces the accuracy degradation caused by the original negative anchor frames being misclassified as positive anchor frames. Innovation point two, the proposed connected domain group fitting algorithm solves the problem of broken and mis-extracted power lines even after the initial extraction and solves the problem of incomplete extraction of power lines by background texture interference. Through experiments on 60 images covering different complex image backgrounds, the performance of the proposed method far exceeds that of commonly used methods such as LSD, Yolact++, and Mask RCNN. DSCPL, TPR, precision, and accuracy are as high as 73.95, 81.75, 69.28, and 99.15, respectively, while FDR is only 30.72. The experimental results show that the proposed algorithm has good performance and can accomplish the task of power line extraction under complex image backgrounds. The algorithm in this paper solves the main problems of power line extraction and proves the feasibility of the algorithm in other scenarios. In the future, the dataset will be expanded to improve the performance of the algorithm in different scenarios.

Severity of albuminuria as an early indicator for wound healing in type 2 diabetic foot ulcers.

This study aimed to investigate the relationship between the severity of albuminuria and wound healing in type 2 diabetic foot ulcers. A total of 121 patients with diabetic foot ulcers were recruited from January 2015 to June 2017 and divided into nonproliferation and proliferation groups according to their healing status. Univariate and multivariate logistic regression were performed to assess the risk factors of wound proliferation. Skin biopsies were also taken from normal tissue near the wound in 54 participants. The microvessel density as well as the relationships among the microvessel density, albuminuria and wound proliferation were evaluated. Results showed that in a multiple linear regression model, factors including body-mass index, microalbuminuria, and macroalbuminuria showed independently significant association with wound healing in patients. The receiver operating characteristic curve analysis indicated albuminuria as a predicator for wound healing with a cutoff value of 32 mg/g. Meanwhile, normoalbuminuric patients showed significantly higher level of skin microvessels density than microalbuminuria and macroalbuminuria patients, while microalbuminuria patients also had statistically more microvessels that macroalbuminuria patients. The microvessel density were statistically significantly higher in the proliferation group than that in the nonproliferation group. In summary, this study suggested that albuminuria can be used as an independent indicator for the healing of type 2 diabetic foot ulcers.

Ptychography imaging by 1-D scanning with a diffuser.

It is beneficial to improve the resolution by a diffuser in imaging systems, because higher frequency information could be involved into the captured patterns via scattering effect. In this paper, a lensless imaging method is designed by 1-D scanning. A diffuser is placed upstream of the object, which is translated in a one-dimensional path and corresponding positions are corrected by cross-correlation. Our method requires a diffraction pattern of the object without a diffuser to speed up convergence and improve resolution. In field reconstruction, the amplitude constraint is added into the iterative phase retrieval algorithm. The high-quality complex-valued images can be obtained with ∼15 patterns. As a ptychography, the proposed method only needs a 1-D device, which could simplify the experimental equipment for reducing costs and measurement time.

Multi-hyperbolic sine-correlated beams and their statistical properties in turbulent atmosphere.

We introduce a partially coherent beam, called a multi-hyperbolic sine-correlated (MHSC) beam, by employing a multi-hyperbolic sine function to modulate the spectral degree of coherence. Based on the extended Huygens-Fresnel principle and second-order moments of the Wigner distribution function, we derive the analytical expressions for the spectral intensity, the root-mean-square (rms) angular width and the M2 factor in turbulent atmosphere. Numerical results show that the intensity profile, which keeps the dark-hollow invariant in free space, will be gradually destroyed by the turbulence along the propagation distance. We believe that the MHSC beams have significant advantage over the hyperbolic sine-correlated beams for reducing the turbulence-induced degradation, especially for the MHSC beams with a higher beam order N. The effects of the beams parameters and the turbulent atmosphere on the beam quality are analyzed in detail.

Accurate angle estimation based on moment for multirotation computation imaging.

In a multirotation computation imaging system, the fidelity of the reconstructed result is limited by the accuracy of the estimated rotation angles. Here, an accurate angle detection method using image moment is proposed to estimate angles of diffraction images. The second moment of a digital image is adopted as the rotational inertia in order to estimate angles of diffraction images. Compared with previous versions based on Radon/Hough transform, it has higher accuracy and is simultaneously time-saving, which is verified in both simulation and experiment. The angle error of moment method is narrowed down within 0.1°, or even less, and it also can perform well in sample diversity or when slightly out of focus.

Baseline and early 3D-CUBE volume reconstruction of locally advanced rectal cancer to predict tumor response after neoadjuvant chemotherapy.

PURPOSE: To explore whether volumetric measurements of 3D-CUBE sequences based on baseline and early treatment time can predict neoadjuvent chemotherapy (NCT) efficacy of locally advanced rectal cancer (LARC). MATERIAL AND METHOD: 73 patients with LARC were enrolled from February 2014 to January 2018. All patients underwent MRIs during the baseline period before NCT (BL-NCT) and the first month of NCT (FM-NCT), and tumor volume (TV) was measured using 3D-CUBE, and tumor volume reduction (TVR) and tumor volume reduction rate (TVRR) were calculated. In addition, tumor invasion depth, tumor maximal length, range of tumor involvement in the circumference of intestinal lumen and distance from inferior part of tumor to the anal verge were measured using baseline high-spatial-resolution T2-weighted MRIs. All patients were categorized into sensitive and insensitive groups based on post-surgical pathology after completion of the full courses of NCT. The receiver operating characteristic (ROC) curve was used to analyze the value of different MRI parameters in predicting efficacy of NCT. RESULTS: Statistically significant differences in TV of BL-NCT, TVR and TVRR from BL-NCT to FM-NCT were detected between sensitive and insensitive groups (P < 0.05, respectively). The areas under the curves (AUC) of ROC of TVR and TVRR in predicting efficacy of NCT (0.890 [95% CI, 0.795∼0.951], 0.839 [95% CI, 0.735∼0.915]) were significantly better than that of TV (0.660 [95% CI, 0.540∼0.767]) (P < 0.05, respectively). CONCLUSION: Reconstruction of 3D-CUBE volume in the first month of NCT is necessary, and both TVR and TVRR can be used as early predictors of NCT efficacy.

Lensfree on-chip microscopy based on dual-plane phase retrieval.

In lensfree on-chip microscopy, the iterative phase retrieval with defocused images easily enables a high-resolution and whole field reconstruction. However, on the reconstruction of the dense sample, conventional methods suffer from the stagnation problem and noise affection under two intensity measurements, which gives rise to a remarkable loss of the image contrast and resolution. Here we propose a novel dual-plane phase retrieval algorithm to perform a stable and versatile lensless reconstruction. A weighted feedback constraint was utilized to speed up the convergence. Then, a gradient descent minimization based on total variation metric was proposed to suppress the noise affection. With these two object constraints, a smoothed but resolution-preserving result can be achieved. Numerical simulations of Gaussian and Poisson noise were given to prove the noise-robustness of our method. The experiments of USAF resolution target, H&E stained pathological slide, and label-free microglia cell demonstrated the superior performance of our approach compared to other state-of-the-art methods.

Structured illumination imaging without grating rotation based on mirror operation on 1D Fourier spectrum.

Structured illumination microscopy (SIM) is a rapidly developing a super-resolution optical microscopy technique. With SIM, the grating is needed in order to rotate several angles for illuminating the sample in different directions. Multiple rotations reduce the imaging speed and grating rotation angle errors damage the image recovery quality. We introduce mirror transformation on one-dimension (1D) Fourier spectrum to SIM for resolving the problems of low imaging speed and severe impact on image reconstruction quality by grating rotation angle errors. When mirror operation and SIM are combined, the grating is placed at an orientation for obtaining three shadow images. The three shadow images are acquired by CCD at three different phase shift for a direction of grating. Thus, the SIM imaging speed is faster and the effect on image reconstruction quality by grating rotation angle errors is greatly reduced.

Propagation properties of radially polarized multi-Gaussian Schell-model beams in oceanic turbulence.

By utilizing the extended Huygens-Fresnel principle, we derive the analytical formulas for the cross-spectral density matrix elements of a radially polarized multi-Gaussian Schell-model (RPMGSM) beam propagating in oceanic turbulence. Effects of beam parameters and oceanic turbulence parameters on the propagation properties of RPMGSM beams are investigated in detail by numerical simulation. Our results show that the RPMGSM beam with larger beam order M has an advantage over the radially polarized Gaussian Schell-model beam for reducing turbulence-induced degradation. Compared with temperature-induced turbulence fluctuation, the salinity-induced turbulence fluctuation makes a greater contribution to the influence on propagation properties of RPMGSM beams.