Highly sensitive self-focused ultrasound transducer with a bionic back-reflector for multiscale-resolution photoacoustic microscopy.

In this study, we designed a self-focused ultrasonic transducer made of polyvinylidene fluoride (PVDF). This transducer involves a back-reflector, which is modeled after tapetum lucidum in the eyes of some nocturnal animals. The bionic structure reflects the ultrasound, which passes through the PVDF membrane, back to PVDF and provides a second chance for the PVDF to convert the ultrasound to electric signals. This design increases the amount of ultrasound absorbed by the PVDF, thereby improving the detection sensitivity. Both ultrasonic and photoacoustic (PA) experiments were conduct to characterize the performance of the transducer. The results show that the fabricated transducer has a center frequency of 13.07 MHz, and a bandwidth of 96% at -6 dB. With an acoustic numerical aperture (NA) of 0.64, the transducer provides a lateral resolution of 140µm. Importantly, the bionic design improves the detection sensitivity of the transducer about 30%. Finally, we apply the fabricated transducer to optical-resolution (OR) and acoustic-resolution photoacoustic microscopy (AR-PAM) to achieve multiscale-resolution PA imaging. Imaging of the bamboo leaf and the leaf skeleton demonstrates that the proposed transducer can provide high spatial resolution, better imaging intensity and contrast. Therefore, the proposed transducer design will be useful to enhance the performance of multiscale-resolution PAM.

Enhancing tissue imaging contrast in photoacoustic tomography using the ultrasound thermal effect.

Photoacoustic imaging is a powerful technique for obtaining high-resolution images of vascular distribution and physiological information about blood by utilizing the light absorption coefficient as an imaging contrast. However, visualizing weakly light-absorbing components without specific contrast agents or multi-wavelength techniques presents a challenge due to significant differences in light absorption between these components and blood. In this study, we propose a novel method that leverages the thermal effect of ultrasound to induce temperature differences and enhance the contrast of photoacoustic imaging. We conducted phantom experiments to verify the feasibility of our method. Our method effectively highlighted weakly light-absorbing components with strong acoustic absorption, even in the presence of highly light-absorbing components such as blood or melanin. Furthermore, it enabled the differentiation of components with similar light absorption but different acoustic absorption.

Elevation Resolution Enhancement Oriented 3D Ultrasound Imaging.

Three-dimensional (3D) ultrasound imaging can be accomplished by reconstructing a sequence of two-dimensional (2D) ultrasound images. However, 2D ultrasound images usually suffer from low resolution in the elevation direction, thereby impacting the accuracy of 3D reconstructed results. The lateral resolution of 2D ultrasound is known to significantly exceed the elevation resolution. By combining scanning sequences acquired from orthogonal directions, the effects of poor elevation resolution can be mitigated through a composite reconstructing process. Moreover, capturing ultrasound images from multiple perspectives necessitates a precise probe positioning method with a wide angle of coverage. Optical tracking is popularly used for probe positioning for its high accuracy and environment-robustness. In this paper, a novel large-angle accurate optical positioning method is used for enhancing resolution in 3D ultrasound imaging through orthogonal-view scanning and composite reconstruction. Experiments on two phantoms proved that our method could significantly improve reconstruction accuracy in the elevation direction of the probe compared with single-angle parallel scanning. The results indicate that our method holds the potential to improve current 3D ultrasound imaging techniques.

Demonstration Study of Reflector-Based Volumetric Speed-of-Sound Imaging With Linear Ultrasound Arrays.

Conventional B-mode ultrasound imaging has difficulty in delineating homogeneous soft tissues with similar acoustic impedances, as the reflectivity depends on the acoustic impedance at the interface. As a quantitative imaging biomarker sensitive to alteration of biomechanical properties, speed-of-sound (SoS) holds promising potential for tissue and disease differentiation such as delineation of different breast tissue types with similar acoustic impedance. Compared to two-dimensional (2D) SoS images, three-dimensional (3D) volumetric SoS images achieved through a full-angle ultrasound scan can reveal more intricate morphological structures of tissues; however, they generally require a ring transducer. In this study, we introduce a 3D SoS reconstruction system that utilizes hand-held linear arrays instead. This system employs a passive reflector positioned opposite the linear arrays, serving as an echogenic reference for time-of-flight (ToF) measurements, and a high-definition camera to track the location corresponding to each group of transmit-receive data. To merge these two streams of ToF measurements and location tracking, a voxel-based reconstruction algorithm is implemented. Experimental results with gelatin phantom and ex vivo tissue have demonstrated the stability of our proposed method. Moreover, the results underscore the potential of this system as a complementary diagnostic modality, particularly in the context of diseases such as breast cancer.

Volumetric B-mode ultrasound and Doppler Imaging: Automatic Tracking With One Single Camera.

Vascular diseases may occur in the upper extremities, and the lesions can span the entire length of the blood vessel. One of the most popular methods to identify vascular disorders is ultrasound Doppler imaging. However, traditional two-dimensional (2D) ultrasound Doppler imaging cannot capture the entire length of a long vessel in one image. Medical professionals often have to painstakingly reconstruct three-dimensional (3D) data using 2D ultrasound images to locate the lesions, especially for large blood vessels. 3D ultrasound Doppler imaging can display the morphological structure of blood vessels and the distribution of lesions more directly, providing a more comprehensive view compared to 2D imaging. In this work, we propose a wide-range 3D volumetric ultrasound Doppler imaging system with dual modality, in which a high-definition camera is adopted to automatically track the movement of the ultrasound transducer, simultaneously capturing a corresponding sequence of 2D ultrasound Doppler images. We conducted experiments on human arms using our proposed system and separately with X-ray computerized tomography (X-CT). The comparison results prove the potential value of our proposed system in the diagnosis of arm vascular diseases.

In vivo structural and functional imaging of human nailbed microvasculature using photoacoustic microscopy.

Monitoring microvascular structure and function is of great significance for the diagnosis of many diseases. In this study, we demonstrate the feasibility of OR-PAM to nailbed microcirculation detection as a new, to the best of our knowledge, application scenario in humans. We propose a dual-wavelength optical-resolution photoacoustic microscopy (OR-PAM) with improved local-flexible coupling to image human nailbed microvasculature. Microchip lasers with 532 nm wavelength are employed as the pump sources. The 558 nm laser is generated from the 532 nm laser through the stimulated Raman scattering effect. The flowing water, circulated by a peristaltic pump, maintains the acoustic coupling between the ultrasonic transducer and the sample. These designs improve the sensitivity, practicality, and stability of the OR-PAM system for human in vivo experiments. The imaging of the mouse ear demonstrates the ability of our system to acquire structural and functional information. Then, the system is applied to image human nailbed microvasculature. The imaging results reveal that the superficial capillaries are arranged in a straight sagittal pattern, approximately parallel to the long axis of the finger. The arterial and venular limbs are distinguished according to their oxygen saturation differences. Additionally, the images successfully discover the capillary loops with single or multiple twists, the oxygen release at the end of the capillary loop, and the changes when the nailbed is abnormal.

Diffusion-relaxation correlation spectrum imaging for predicting tumor consistency and gross total resection in patients with pituitary adenomas: a preliminary study.

OBJECTIVE: To evaluate the ability of diffusion-relaxation correlation spectrum imaging (DR-CSI) to predict the consistency and extent of resection (EOR) of pituitary adenomas (PAs). METHODS: Forty-four patients with PAs were prospectively enrolled. Tumor consistency was evaluated at surgery as either soft or hard, followed by histological assessment. In vivo DR-CSI was performed and spectra were segmented following to a peak-based strategy into four compartments, designated A (low ADC), B (mediate ADC, short T2), C (mediate ADC, long T2), and D (high ADC). The corresponding volume fractions ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]) along with the ADC and T2 values were calculated and assessed using univariable analysis for discrimination between hard and soft PAs. Predictors of EOR > 95% were analyzed using logistic regression model and receiver-operating-characteristic analysis. RESULTS: Tumor consistency was classified as soft (n = 28) or hard (n = 16). Hard PAs presented higher [Formula: see text] (p = 0.001) and lower [Formula: see text] (p = 0.013) than soft PAs, while no significant difference was found in other parameters. [Formula: see text] significantly correlated with the level of collagen content (r = 0.448, p = 0.002). Knosp grade (odds ratio [OR], 0.299; 95% confidence interval [CI], 0.124-0.716; p = 0.007) and [Formula: see text] (OR, 0.834, per 1% increase; 95% CI, 0.731-0.951; p = 0.007) were independently associated with EOR > 95%. A prediction model based on these variables yielded an AUC of 0.934 (sensitivity, 90.9%; specificity, 90.9%), outperforming the Knosp grade alone (AUC, 0.785; p < 0.05). CONCLUSION: DR-CSI may serve as a promising tool to predict the consistency and EOR of PAs. CLINICAL RELEVANCE STATEMENT: DR-CSI provides an imaging dimension for characterizing tissue microstructure of PAs and may serve as a promising tool to predict the tumor consistency and extent of resection in patients with PAs. KEY POINTS: • DR-CSI provides an imaging dimension for characterizing tissue microstructure of PAs by visualizing the volume fraction and corresponding spatial distribution of four compartments ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]). • [Formula: see text] correlated with the level of collagen content and may be the best DR-CSI parameter for discrimination between hard and soft PAs. • The combination of Knosp grade and [Formula: see text] achieved an AUC of 0.934 for predicting the total or near-total resection, outperforming the Knosp grade alone (AUC, 0.785).

Local-flexible coupling optical-resolution photoacoustic microscopy with enhanced sensitivity.

An acoustic coupling scheme largely determines the performance of optical-resolution photoacoustic microscopy (OR-PAM), including practicability, sensitivity, and stability. In this study, we propose OR-PAM based on a local-flexible acoustic coupling scheme, which includes a well-designed combiner connecting a set of circulating systems. The combiner integrates an objective lens and an ultrasonic transducer, controls the water level, restricts the flow rate, and drains bubbles. The circulating system provides sustained and steady flowing water. The flowing water constrained in the combiner and the circulating system forms a flexible and stable local contact between the sample and the transducer. Phantom experiments demonstrate that the proposed method can maintain high optical resolution but improve the detection sensitivity by approximately 1.9 times in comparison to dry coupling. In vivo imaging experiments of the mouse eyeground are conducted to examine the practicability of the proposed system in biomedicine. Moreover, in vivo experiments show that OR-PAM based on local-flexible coupling can reveal more details of eyeground microvasculatures, benefiting from its enhanced sensitivity. These merits promise that OR-PAM based on local-flexible coupling may have broad applications in biomedical fields.

Tunable acoustic metasurface based on tunable piezoelectric composite structure.

Due to the potential engineering needs, the passive tunable metasurfaces with a high performance equivalent to the active phased array is worthy of research. Here, a passive ultrathin metasurface unit composed of a piezoelectric composite structure (PCS) connected to an external capacitor, which can modulate the phase of the transmitted acoustic waves at a deep subwavelength scale only by controlling the external capacitor but without changing the structure, is proposed. Then, a tunable acoustic metasurface composed of 20 identical PCSs is introduced to realize three acoustic functions, beam steering, beam focusing, and tweezer-like beam generating, just by changing the external capacitors. The phase-control abilities of the PCS unit and three functions of the designed metasurface are proved both numerically and experimentally. This study provides the possibility to design ultrathin tunable acoustic metasurfaces with the ability of precise control and passive materials.

Multispectral photoacoustic holography of elastomers from a bright background.

Photoacoustic imaging of elastomers has important biomedical value. However, a bright background, e.g., blood vessels in living tissue, brings a challenge for photoacoustic elastography. In this study, we predicted that the spectrum of photoacoustic signals from elastomers with high elasticity could appear as narrow peaks at the eigen-frequencies of elastomers, but the signals from a bright background, e.g., blood vessel, show flat broadband spectrum for their low-quality factor. Even when the two kinds of signals are mixed together, the signals from elastomers can be identified from the spectrum since they present as convex narrow peaks on a wide base. Based on this factor, we propose a multispectral photoacoustic holography to realize selective imaging of tiny elastomers. This method recovers the image only using several frequency components in photoacoustic signals, instead of the whole-band signal. Since these narrow peaks in the spectrum correspond to the eigen-vibration of elastomers, the proposed method can highlight the elastomers with high elasticity from a bright background with low elasticity. The method was validated by experiments. This study might be helpful to localize elastic anomalous areas in the tissue, such as calcification in the vascular network, microcalcification in a tumor, and implants.

miR-484 targeting of Yap1-induced LPS-inhibited proliferation, and promoted apoptosis and inflammation in cardiomyocyte.

Apoptosis and inflammation were the main hallmarks of sepsis-induced cardiomyopathy (SIC). Yes-associated protein isoform 1 (Yap1) and miR-484 were involved in mitochondrial fission and apoptosis, especially proapoptotic roles in SIC. Here, we investigated the role of Yap1 and miR-484 in lipopolysaccharide (LPS)-treated H9c2 cells. Yap1 was downregulated, while miR-484 was elevated by LPS treatment. Cell counting kit-8, flow cytometry, western blotting, and ELISA showed that miR-484 inhibitor significantly improved cell viability, decreased apoptosis, suppressed NLRP3 inflammasome formation, and reduced secretion of inflammatory cytokines TNF-α, IL-1ß, and IL-6. Yap1, directly targeted by miR-484 shown in the luciferase assay, was more like a compensatory regulator of LPS stimulation. Knockdown of Yap1 inverted the effects of miR-484 inhibitor, including decreased cell viability, and promoted apoptosis and inflammation. These revealed miR-484 directly targeted mRNA of Yap1 to inhibit cell viability, and promote apoptosis and inflammation in LPS-treated H9c2 cells.

Trileaflet Aortic Valve Reconstruction Using Bovine Pericardium.

AIM: For several years now, trileaflet aortic valve reconstruction has been performed in patients with various aortic valve diseases. This study aimed to explore the feasibility and durability of trileaflet aortic valve reconstruction with bovine pericardium. METHOD: Trileaflet aortic valve reconstruction with bovine pericardium was performed in 519 patients with various aortic valve diseases from April 2008 to December 2019. The results for all 519 patients were reviewed retrospectively. Mean age was 48.04±19.08 years (range, 13-80 years), and 40 patients were younger than 18 years of age. Thirty-four (34) patients had aortic stenosis, 344 patients had aortic regurgitation, and 141 patients had both aortic stenosis and regurgitation. One hundred and fifty-four (154) patients had bicuspid aortic valves, and three patients had quadricuspid aortic valves. The size of the pericardial leaflets was designed to be individually proportional to the size of the aortic root. RESULTS: Mean length of follow-up was 41.97±22.68 years (range, 1-127 months). In total, 448 patients were reviewed, and the follow-up rate was 86.4%. All procedures were successful without conversion to prosthetic valve replacement during the procedure. Six (6) patients died after the procedure (in-hospital mortality, 1.2%). All-cause mortality occurred in 11 patients during the follow-up period. The 10-year cumulative survival rate was 94.7%±2.9%. Redo aortic valve surgery was performed in 11 patients after the procedure. The actuarial freedom from redo aortic valve surgery after the procedure was 88.2%±5.2%. At the end of the follow-up, the mean peak was 29.1±9.6 mmHg and mean gradient was 15.6±6.2 mmHg. CONCLUSIONS: The mid- and long-term outcomes in patients with various aortic valve diseases undergoing trileaflet aortic valve reconstruction with bovine pericardium are encouraging. The engineered pericardial leaflets should be individually proportional to the size of the aortic root.

Enhancement of photoacoustic tomography of acoustically inhomogeneous tissue by utilizing a memory effect.

One of the major challenges for photoacoustic tomography is the variance of the speed of sound (SOS) in realistic tissue, which could lead to defocusing in image reconstruction and degrade the reconstructed image. In this study, we propose a method to optimize the SOS used for image reconstruction based on a memory effect of photoacoustic signal. We reveal that the photoacoustic signals received by two adjacent transducers have a high degree of similarity in waveform, while a time delay exists between them. The time delay is related to the SOS. Based on this physical phenomenon, an iterative operation is implemented to estimate the SOS used for image reconstruction. Both simulations and experiments confirm that the method significantly enhances the reconstructed image in inhomogeneous tissue. This study may have potential value in improving the performance of photoacoustic tomography in biomedical applications.

Photoacoustic-ultrasonic dual-mode microscopy with local speed-of-sound estimation.

Synthetic aperture imaging and virtual point detection have been exploited to extend the depth of view of photoacoustic microscopy. The approach is commonly based on a constant assumed sound speed, which reduces image quality. We propose a new, to the best of our knowledge, self-adaptive technique to estimate the speed of sound when integrated with this hybrid strategy. It is accomplished through linear regression between the square of time of flight detected at individual virtual detectors and the square of their horizontal distances on the focal plane. The imaging results show our proposed method can significantly improve the lateral resolution, imaging intensity, and spatial precision for inhomogeneous tissue.

Simultaneous scattering-absorption dual-modal cell imaging in a single shot by a transmission-mode photoacoustic microscope.

A microscopy scheme is proposed to simultaneously achieve optical scattering-absorption dual-contrast imaging of a transparent or semi-transparent specimen. This scheme is based on a transmission-mode photoacoustic microscope. We find that two peaks exist in the detected photoacoustic signal. One peak is caused by the optical absorption of the specimen, and the other is related to both the optical scattering and absorption of the specimen. Therefore, both the absorption and scattering information can be simultaneously extracted by analyzing the same photoacoustic signal excited by a single-shot laser pulse. After the microscope is validated by imaging a binary mixture consisting of particles with different optical properties, it successfully acquires dual images of red blood cells with different contrasts. Quantitative analysis reveals that the optical absorption and scattering properties of the specimen can be derived from the two images. The proposed dual-modal imaging method would be useful in revealing the structural and functional properties of tissues at the cell level or the clinical assessment of pathological sections.

Circ0120816 acts as an oncogene of esophageal squamous cell carcinoma by inhibiting miR-1305 and releasing TXNRD1.

BACKGROUND: Circular RNAs (circRNAs) have been discovered to participate in the carcinogenesis of multiple cancers. However, the role of circRNAs in esophageal squamous cell carcinoma (ESCC) progression is yet to be properly understood. This research aimed to investigate and understand the mechanism used by circRNAs to regulate ESCC progression. METHODS: Bioinformatics analysis was first performed to screen dysregulated circRNAs and differentially expressed genes in ESCC. The ESCC tissue samples and adjacent normal tissue samples utilized in this study were obtained from 36 ESCC patients. All the samples were subjected to qRT-PCR analysis to identify the expression of TXNRD1, circRNAs, and miR-1305. Luciferase reporter assay, RNA immunoprecipitation assay and RNA pull-down assay were later conducted to verify the existing relationship among circ0120816, miR-1305 and TXNRD1. CCK-8, BrdU, cell adhesion, cell cycle, western blot and caspase 3 activity assays were also employed to evaluate the regulation of these three biological molecules in ESCC carcinogenesis. To evaluate the effect of circ0120816 on ESCC tumor growth and metastasis, the xenograft mice model was constructed. RESULTS: Experimental investigations revealed that circ0120816 was the highest upregulated circRNA in ESCC tissues and that this non-coding RNA acted as a miR-1305 sponge in enhancing cell viability, cell proliferation, and cell adhesion as well as repressing cell apoptosis in ESCC cell lines. Moreover, miR-1305 was observed to exert a tumor-suppressive effect in ESCC cells by directly targeting and repressing TXNRD1. It was also noticed that TXNRD1 could regulate cyclin, cell adhesion molecule, and apoptosis-related proteins. Furthermore, silencing circ0120816 was found to repress ESCC tumor growth and metastasis in vivo. CONCLUSIONS: This research confirmed that circ0120816 played an active role in promoting ESCC development by targeting miR-1305 and upregulating oncogene TXNRD1.

Study of spatiotemporal liquid dynamics in a vibrating vocal fold by using a self-oscillating poroelastic model.

The main purpose of this study is to investigate the spatiotemporal interstitial fluid dynamics in a vibrating vocal fold. A self-oscillating poroelastic model is proposed to study the liquid dynamics in the vibrating vocal folds by treating the vocal fold tissue as a transversally isotropic, fluid-saturated, porous material. Rich spatiotemporal liquid dynamics have been found. Specifically, in the vertical direction, the liquid is transported from the inferior side to the superior side due to the propagation of the mucosal wave. In the longitudinal direction, the liquid accumulates at the anterior-posterior midpoint. However, the contact between the two vocal folds forces the accumulated liquid out laterally in a very short time span. These findings could be helpful for exploring etiology of some laryngeal pathologies, optimizing laryngeal disease treatment, and understanding hemodynamics in the vocal folds.

CLRS: Continual Learning Benchmark for Remote Sensing Image Scene Classification.

Remote sensing image scene classification has a high application value in the agricultural, military, as well as other fields. A large amount of remote sensing data is obtained every day. After learning the new batch data, scene classification algorithms based on deep learning face the problem of catastrophic forgetting, that is, they cannot maintain the performance of the old batch data. Therefore, it has become more and more important to ensure that the scene classification model has the ability of continual learning, that is, to learn new batch data without forgetting the performance of the old batch data. However, the existing remote sensing image scene classification datasets all use static benchmarks and lack the standard to divide the datasets into a number of sequential learning training batches, which largely limits the development of continual learning in remote sensing image scene classification. First, this study gives the criteria for training batches that have been partitioned into three continual learning scenarios, and proposes a large-scale remote sensing image scene classification database called the Continual Learning Benchmark for Remote Sensing (CLRS). The goal of CLRS is to help develop state-of-the-art continual learning algorithms in the field of remote sensing image scene classification. In addition, in this paper, a new method of constructing a large-scale remote sensing image classification database based on the target detection pretrained model is proposed, which can effectively reduce manual annotations. Finally, several mainstream continual learning methods are tested and analyzed under three continual learning scenarios, and the results can be used as a baseline for future work.

RSI-CB: A Large-Scale Remote Sensing Image Classification Benchmark Using Crowdsourced Data.

Image classification is a fundamental task in remote sensing image processing. In recent years, deep convolutional neural networks (DCNNs) have experienced significant breakthroughs in natural image recognition. The remote sensing field, however, is still lacking a large-scale benchmark similar to ImageNet. In this paper, we propose a remote sensing image classification benchmark (RSI-CB) based on massive, scalable, and diverse crowdsourced data. Using crowdsourced data, such as Open Street Map (OSM) data, ground objects in remote sensing images can be annotated effectively using points of interest, vector data from OSM, or other crowdsourced data. These annotated images can, then, be used in remote sensing image classification tasks. Based on this method, we construct a worldwide large-scale benchmark for remote sensing image classification. This benchmark has large-scale geographical distribution and large total image number. It contains six categories with 35 sub-classes of more than 24,000 images of size 256 × 256 pixels. This classification system of ground objects is defined according to the national standard of land-use classification in China and is inspired by the hierarchy mechanism of ImageNet. Finally, we conduct numerous experiments to compare RSI-CB with the SAT-4, SAT-6, and UC-Merced data sets. The experiments show that RSI-CB is more suitable as a benchmark for remote sensing image classification tasks than other benchmarks in the big data era and has many potential applications.

Artifact-free imaging through a bone-like layer by using an ultrasonic-guided photoacoustic microscopy.

Reflection artifacts caused by a bone-like layer badly degrade the quality of photoacoustic images in many biomedical applications, e.g., in vivo brain imaging through the skull. We proposed an ultrasonic-guided photoacoustic microscopy (PAM) to remove the reflection artifacts. This system is developed from dual-mode microscopy, integrating a scanning acoustic microscopy with a conventional PAM. Based on similar propagation characteristics of a photoacoustic signal and ultrasonic echo in a bone-like layer, we employ the ultrasonic echo as a filter to remove the multiple reflected artifacts in photoacoustic signals and obtain artifact-free images. An experiment of imaging a phantom below a bone-like film is used to demonstrate the performance of this method. The results suggest that this method can achieve an artifact-free image of the phantom under the film successfully, whereas the conventional PAM fails to achieve clean images of the vessel-like absorbers. This study might improve the imaging quality of PAM in many biomedical applications.