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Introducing bond wire diagnosis for multichip IGBT modules is key to the health monitoring of modular multilevel converters (MMCs), which allows for improved field robustness, reliability, and reduced maintenance cost. This paper leverages the crosstalk phenomenon during switching transitions to detect the chip open-circuit faults caused by the bond wire lift-off using typical half-bridge IGBT modules in a multichip-parallel configuration. The cycle-controlled, non-intrusive measurement is conducted under normal operation, when the device under test is at off-state and its complementary switch is during switching transitions. Two specialized health sensitive parameters arising from the dynamic gate loop waveforms are identified and evaluated, including 1) the gate voltage VGE(t3) when the declining collector voltage reaches zero, and 2) the negative peak gate voltage VGE(t4). The sensitivity and stability of these two parameters are compared through theoretical analysis, circuit simulation and practical verification. The results show that VGE(t4) is more suitable for online monitoring, while VGE(t3) is more sensitive than VGE(t4). With managed complexity in gate drives, this proposed health awareness approach is feasible in the submodules of MMC applications, but it can also be used in other power converter topologies incorporating the half-bridge structure.

BACKGROUND: With the emergence of various new skin-lightening products, there is an urgent need to scientifically evaluate the efficacy and toxicology of these products, and provide scientific guidance for their use based on physiological differences between individuals. Visualized imaging methods and quantitative evaluation criteria play key roles in evaluating the efficacy of skin-lightening products. In order to quantify the changes in the multilayered morphology and endogenous components of human skin before and after the use of lightening products, high-resolution three-dimensional (3D) imaging of human skin is required. METHODS: In this study, photoacoustic microscopy (PAM; SSPM-532, Guangdong Photoacoustic Medical Technology Co., Ltd.) was used to capture the morphological structures of human skin and reveal skin components quantitatively. The efficacy and safety of skin-lightening products were evaluated by measuring skin melanin concentration and observing skin morphology. The melanin concentration in the epidermis was obtained by examining the linear relationship between photoacoustic (PA) signals. Further, the epidermal thickness and the melanin distribution were obtained in the cross-sectional (x-z) and lateral (x-y) images. Finally, the efficacy of skin-lightening products was evaluated according to the concentration and distribution of melanin in the epidermis, and the safety of cosmetics was assessed by observing the vascular morphology in the dermis. RESULTS: PAM noninvasively could assess the multilayered morphological structures of human skin, which allowed for quantification of epidermal thickness and melanin concentration of different skin sites. Based on this, the efficacy and safety of skin-lightening products in multilayer structures were quantitatively evaluated. CONCLUSIONS: As a quantitative imaging method, PAM, has the potential to accurately evaluate the use of skin-lightening products. The method can also be extended to assessments within the larger field of aesthetic medicine.

Background As a promising technology, photoacoustic microscopy (PAM) plays a critical role in diagnosis and assessment of dermatological conditions by providing subtle vascular networks non-invasively. However, the established PAMs are insufficient for clinical dermatology when faced with complex structures of human skin instead of animal models owing to high melanin content and superimposed vasculature for Asians, which cannot balance the spatial resolution and the imaging depth. Objectives To evaluate the ability of bifocal 532/1064-nm alternately illuminated photoacoustic microscopy (BF-PAM) to non-invasively reveal the morphological structure of human skin for improving the diagnosis and therapeutic efficacy of skin diseases. Methods A BF-PAM was developed to capture biopsy-like information of human skin from epidermis to hypodermis. The optical foci of the two excitation beams are staggered in the axial direction to form an extended depth-of-field, which can maintain the lateral resolution and the contrast of PA image. Results The imaging capability of the BF-PAM was demonstrated by depicting the vascular morphology of multilayered skin with imaging depth of ˜3 mm. Furtherly, vascular malformations in port-wine stains skin were quantitatively assessed without the need for any contrast agent, and the distribution, depth and diameter of the ectatic vessels can determine an optimal treatment protocol for port-wine stains lesions. Conclusions The quantitative vascular morphology in the dermis can be used to accurately assess vascular characteristics, in which case it enables clinicians to determine optimum treatment parameters in individual patients. As a non-invasive imaging technique, BF-PAM holds great potential to provide objective assessment to enhance the therapeutic efficacy. Ethical statement The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Chinese Ethics Committee of Registering Clinical Trials (ChiECRCT20200184) and registered with Chinese Clinical Trial Registry (ChiCTR2000034400). Before skin imaging, written informed consent was taken from all individual participants.

Photoacoustic dermoscopy (PAD) has been proven to visualize the microvascular network within the dermis noninvasively, and has great application potential and advantages. In practice, some subjects are children or unwell and may have difficulty in controlling their breathing or trembling. The artifacts caused by the uncontrollable trembling will degrade the image quality, resulting in deviation of the pathophysiological features. This work introduces a subpixel and on-line motion correction method for clinical application of PAD. The high-accuracy motion correction was realized by the subpixel motion estimation, which was achieved by five-fold upsampling the cross-correlation matrix between A-lines or B-scan images. Since the motion correction algorithm only takes the acquired data as a priori, it can be processed immediately when a B-scan is input, so it can be embedded in the acquisition program, leading to the motion correction during the data acquisition. Moreover, the algorithm was verified by the experimental data of human skin. The results demonstrated that the images after sub-pixel motion correction are obviously improved visually, and the structural similarity index measurement (SSIM) and peak signal-to-noise ratio (PSNR) between adjacent B-scan images after correction are increased by 31.6% and 47.7% compared to the uncorrected images. To conclude, the proposed algorithm can make it robust in terms of accuracy and reliability and will help PAD fulfill its clinical promise.

Although photothermal therapy (PTT) has demonstrated its clinical value and adaptability, it still requires imaging guidance to motivate the development of precise and effective treatment. For PTT, high-resolution visualization of tumor microvasculature and accurate location of nanoparticles distribution are crucial for the therapeutic outcome. Here, a wavelength-switchable photoacoustic microscopy (PAM) was developed to noninvasively investigate the tumor microvasculature and the accumulation of nanoparticles for accurately guiding PTT and evaluating the therapeutic effect. In a tumor model, PAM was used to continuously monitor the tumor microenvironment in vivo, and the proportion of microvessels in tumor site was found increased by 10%, and the diameters of the draining veins were doubled on day 7. In addition, quantitative parameters such as tumor volume and vascular density can also be demonstrated by the PAM. Meanwhile, the concentration of Den-RGD/Cy7 at the tumor site reached its maximum at 8 h by PA mapping after intravenous injection, which was used to determine the optimal irradiation timing. After treatment, photoacoustic monitoring showed that PTT can precisely kill the tumors and minimize damage to surrounding normal tissues, which was consistent with the pathological slides. The experimental results proved that PAM can provide an auxiliary means for precision PTT.

Plate loading tests were conducted to investigate the effect of a bottom boundary condition on the pressure-settlement behavior of a footing on sand with a limited thickness involving geosynthetics. Seven boundary materials including geosynthetics were used to create different boundary conditions at the bottom of the sand. Interface direct shear tests were conducted first to determine the interface friction angles between these boundary materials and sand, followed by plate loading tests to determine their pressure-settlement curves. Test results show that the sand with a limited thickness by a rigid bottom boundary had a higher bearing capacity than that with a larger thickness. The ultimate bearing capacity of the footing on the sand with a limited thickness generally increased with the increase of the interface friction angle. Geosynthetics provided better lateral restraint than other materials. An equation was developed to describe the relationship of the bearing capacity ratio of the sand with a limited thickness to that with a large thickness versus the soil thickness and the interface interaction coefficient. The effect of the boundary material on the back-calculated modulus of the sand was also evaluated.

Geosynthetics have been widely applied in flexible pavements for decades. However, the mechanistic-empirical analytical approach for geosynthetic-stabilized flexible pavements based on the elastic solution derived from the layered elastic theory has not been established. In this study, the solution for a typical three-layer geosynthetic-stabilized flexible pavement was derived according to the layered elastic theory. In the derivation, lateral restraint and tensioned membrane effect of geosynthetics quantified in terms of layer permanent deformations were considered at the interface as a continuity condition. The derived solution was then incorporated into the mechanistic-empirical approach for the calculation of pavement rutting and fatigue cracking. The result indicates that the solution derived in this study is capable of analyzing the geosynthetic-stabilized three-layer flexible pavement. The pavement elastic responses calculated using the solution obtained in this study are in line with those by the previously established solutions in the literature. The rut depths estimated using the proposed solution reasonably match those measured in the previous study. For rut reduction, the geosynthetic placed underneath the base layer is more effective. For the tensile strain relief at the bottom of the asphalt layer, the geosynthetic placed at the bottom of the asphalt shows more benefit.

β-Elemene is a volatile oil used for the treatment of cancer, but poor solubility, low bioavailability, and various adverse reactions limit its application. For ameliorating risks of the venous toxicity of β-elemene, intravenously injectable micelle of β-elemene was prepared using the thin-film hydration method. The results pointed out the micelles were uniformly spherical with about 20.96 ± 0.1966 nm in average diameter and exhibited high entrapment efficiency (99.02% ± 0.88%). As revealed by drug release studies in vitro, β-elemene micelles had sustained drug release. Compared with free β-elemene, the micelles increased the drug cellular uptake and enhanced the anti-tumor effect in vitro through retarding cell cycle and inducing apoptosis. Meanwhile, the elevated serum stability of β-elemene micelles implied less drug leakage and reduced toxicity. The wound healing and tube formation assay in vitro demonstrated the anti-metastasis and anti-angiogenesis effects of β-elemene micelles. Moreover, the pharmacokinetics study showed the AUC and T1/2 of β-elemene in micelle group were 1.79 and 1.62 times of that in free β-elemene group, suggesting the circulation time of β-elemene in the blood had been prolonged. In addition, β-elemene micelles showed a favorable antitumor response compared with the β-elemene solution on C26 colon cancer-bearing mice model. Local irritation study investigated in rabbits indicated that the β-elemene micelles strikingly mitigated the irritation to the injection sites compared with free β-elemene. These results proved that the micelle could be a good candidate as an auspicious drug delivery system of β-elemene for the prospective clinical treatment of carcinoma.

A theoretical approach is proposed to investigate blast-induced ground vibration by considering the body force. On the basis of the principle of momentum conservation at the wavefronts, we derived the reflected body waves along the ground surface and the interaction of the body wavefront and ground surface inducing the secondary surface wave that transfers outward onto the ground. Subsequently, the particle velocity on the ground surface was derived, and a parametric investigation was conducted with regard to the effects of horizontal distance from the blast source, embedded depth of the blast source, and material damping onto the ground vibration. Finally, the effect of gravity on the ground vibration was also investigated.

High-resolution photoacoustic angiography images are reconstructed from undersampled images with the help of a super-resolution deep neural network, enhancing the ability of the photoacoustic angiography systems to image dynamic processes in living tissues. However, image degradations are difficult to estimate due to a lack of knowledge of the point spread function and noise sources, resulting in poor generalization capability of the trained super-resolution model. In this work, a high-order residual cascade neural network was developed to reconstruct high-resolution vascular images, which is a neural approximating approach used to remove image degradations of photoacoustic angiography. To handle overfitting in training super-resolution model with a limited dataset, we proposed a BicycleGAN based image synthesis method in data preparation, achieving a strong regularization by forging realistic photoacoustic vascular images that act to essentially increase the training dataset. The quantitative analysis of the reconstructed results shows that the high-order residual cascade neural network surpassed the other residual super-resolution neural networks. Most importantly, we demonstrated that the generalized model could be achieved despite the limited training dataset, promising to be a methodology for few-shot super-resolution photoacoustic angiography.

Currently, most biometric methods mainly use single features, making them easily forged and cracked. In this study, a novel triple-layers biometric recognition method, based on photoacoustic microscopy, is proposed to improve the security of biometric identity recognition. Using the photoacoustic (PA) dermoscope, three-dimensional absorption-structure information of the fingers was obtained. Then, by combining U-Net, Gabor filtering, wavelet analysis and morphological transform, a lightweight algorithm called photoacoustic depth feature recognition algorithm (PADFR) was developed to automatically realize stratification (the fingerprint, blood vessel fingerprint and venous vascular), extracting feature points and identity recognition. The experimental results show that PADFR can automatically recognize the PA hierarchical features with an average accuracy equal to 92.99%. The proposed method is expected to be widely used in biometric identification system due to its high security. This article is protected by copyright. All rights reserved.

Objective: Limited by spherical focused ultrasound transducer (SUT) with a high acoustic numerical aperture, photoacoustic microscopy (PAM) suffers a rapidly degrading sensitivity and lateral resolution as increased depth. In this study, an ellipsoidal focused ultrasound transducer (EUT) was developed to address the above restriction via providing high sensitivity and lateral resolution over a large depth of field (DOF). Methods: To fabricate the EUT, the piezoelectric element was laminated onto a curved steel surface for self-focusing (the ellipsoidal continuous-focus geometry was employed instead of the spherical single-focus one). Additionally, phantoms and in vivo animal experiments were performed by an extend-focus PAM equipped with EUT to characterize its performance. Results: The EUT involved over 30 MHz center frequency and -6 dB bandwidth of 124% with a resolution-invariant focal depth of 1.39 mm, more than 3 times the DOF of the SUT. Conclusion: The in vivo imaging results demonstrated that the EUT was capable of extending the focal depth to get rid of the restriction of the visual field, while the DOF of the SUT was limited by the nature of spherical geometry. Significance: The EUT markedly enhances the image quality at different imaging depths, which has great potential for promoting the biomedical development of in vivo rapid-noninvasive PAM.

A micro-electromechanical system (MEMS) scanning mirror accelerates the raster scanning of optical-resolution photoacoustic microscopy (OR-PAM). However, the nonlinear tilt angular-voltage characteristic of a MEMS mirror introduces distortion into the maximum back-projection image. Moreover, the size of the airy disk, ultrasonic sensor properties, and thermal effects decrease the resolution. Thus, in this study, we proposed a spatial weight matrix (SWM) with a dimensionality reduction for image reconstruction. The three-layer SWM contains the invariable information of the system, which includes a spatial dependent distortion correction and 3D deconvolution. We employed an ordinal-valued Markov random field and the Harris Stephen algorithm, as well as a modified delay-and-sum method during a time reversal. The results from the experiments and a quantitative analysis demonstrate that images can be effectively reconstructed using an SWM; this is also true for severely distorted images. The index of the mutual information between the reference images and registered images was 70.33 times higher than the initial index, on average. Moreover, the peak signal-to-noise ratio was increased by 17.08% after 3D deconvolution. This accomplishment offers a practical approach to image reconstruction and a promising method to achieve a real-time distortion correction for MEMS-based OR-PAM.

Today, photoacoustic imaging (PAI) is widely used to study diseases in the skin, brain, cardiovascular, and other parts. However, these studies are often carried out using physiological slices or model animals, which indicate that many PAI techniques can only be used in the laboratory. In order to promote the transformation of PAI into clinical applications or, more specifically, to extend the application of photoacoustic (PA) microscopy to areas such as the oral cavity, throat, cervix, and abdominal viscera which are difficult to detect with conventional PA microscopy systems, a PAI pen was developed. The PAI pen can be handheld and can perform forward detection and lateral detection. The imaging area is a 2.4 mm diameter circular area. In addition, it can provide a high-speed imaging mode of four frames per second and a high-resolution imaging mode of 0.25 frames per second to meet the different needs of clinical users. In this Letter, the performance of the PAI pen was tested by imaging the phantom and the human oral cavity. The experimental results prove that the PAI pen can clearly image the microvessels of the oral cavity, which indicates that it has the same imaging capability for other similar areas and has a good prospect for assisting the diagnosis of related diseases.

Photoacoustic microscopy (PAM) provides a new method for the imaging of small-animals with high-contrast and deep-penetration. However, the established PAM systems have suffered from a limited field-of-view or imaging speed, which are difficult to both monitor wide-field activity of organ and record real-time change of local tissue. Here, we reported a dual-raster-scanned photoacoustic microscope (DRS-PAM) that integrates a two-dimensional motorized translation stage for large field-of-view imaging and a two-axis fast galvanometer scanner for real-time imaging. The DRS-PAM provides a flexible transition from wide-field monitoring the vasculature of organs to real-time imaging of local dynamics. To test the performance of DRS-PAM, clear characterization of angiogenesis and functional detail was illustrated, hemodynamic activities of vasculature in cerebral cortex of a mouse were investigated. Furthermore, response of tumor to treatment were successfully monitored during treatment. The experimental results demonstrate the DRS-PAM holds the great potential for biomedical research of basic biology.

In damage mechanics, the deep excavation of soil is a process of damage development, and soil failure can be considered a process of continuously transforming undisturbed soil to damaged soil. Therefore, this study considered the occurrence of soil damage during the pit excavation, established a soil damage model, damage evolution equation, and soil damage constitutive relationship, and then deduced a calculate model of the pile displacement under the consideration of soil damage. Based on the principle of the stratum loss method, the surface settlement around a deep excavated pit was assumed as a skewed distribution curve, and the surface settlement of the pile-anchor supporting pit was solved. Based on this established method, finite element analysis software was used to calculate the surface subsidence for a field case, and the numerical results were compared with monitoring data in the field. The results revealed that, to a certain extent, soil damage affected the distribution of surface settlement in excavated pits. With the development of soil damage, the mechanical properties of soil gradually decreased, which led to increased surface settlement and changes in the direction of the excavation pit. Because soil damage is an important factor causing surface settlement, it is meaningful to consider soil damage when calculating the surface settlement in the deep excavation of pits.

To improve the understanding of the influence of induced anisotropy on the strength and deformation characteristics of loess, a series of directional HCA tests under consolidated-drained condition were conducted. The test results indicated that the remolded loess showed a pronounced anisotropy in stress–strain relationship, strength, and deformation. The maximum difference in shear strength due to directional effect was 25% in the range of major principal stress orientation. Induced anisotropy has a great influence on the stress–strain relationship of soil, which is the essence of soil properties. In some engineering practices, the results of stress–strain analysis of soil have great influences. Approximately, isotropic remolded loess substantially eliminates its inherent anisotropy. The soil studied in this experiment is from the permafrost region of Qinghai. With the increase of engineering constructions, the geotechnical engineering problems here are becoming more and more significant. Therefore, this experiment will provide a good reference for the further study of soil anisotropy under complicated stress paths such as principal stress axis rotation.

The homogeneous, nonaqueous catalytic activity of the rhenium-thiolate complex ReL3 (L = diphenylphosphinobenzenethiolate) for the hydrogen evolution reaction (HER) has been transferred from nonaqueous homogeneous to aqueous heterogeneous conditions by immobilization on a glassy carbon electrode surface. A series of modified electrodes based on ReL3 and its oxidized precursor [ReL3][PF6] were fabricated by drop-cast methods, yielding catalytically active species with HER overpotentials for a current density of 10 mA/cm2, ranging from 357 to 919 mV. The overpotential correlates with film resistance as measured by electrochemical impedance spectroscopy and film morphology as determined by scanning and transmission electron microscopy. The lowest overpotential was for films based on the ionic [ReL3][PF6] precursor with the inclusion of carbon black. Stability measurements indicate a 2 to 3 h conditioning period in which the overpotential increases, after which no change in activity is observed within 24 h or...

Loess is a problematic soil, which is often characterized with loose structure and high potential for collapse by water or external loads. In cold regions, the challenge of loess is further...

Based on the Biot’s model for saturated porous media and functionally graded materials (FGMs), the isolation effect of saturated porous FG wave impeding block (WIB) on reducing vibration induced by a moving load in a saturated foundation is studied. The dynamic governing equations for saturated foundations under a moving load are obtained by using the coordinate transformation, and the expression of displacement and stress is derived based on the Fourier transform and the reverberation-ray matrix method. Via numerical examples, the isolation effect of saturated porous FG WIB under a moving load is analyzed. The results show that the saturated porous FG WIB can effectively reduce the vibration amplitude and has more advantages and effective under a moving load.

Although it has been demonstrated that one-dimensional, two-dimensional, and three-dimensional carbon nanomaterials can improve the CH 4 production of anaerobic digestion (AD), the effect of zero-dimensional carbon nanomaterials on AD have not been reported. To expand the application of carbon nanomaterials in AD, the effect of zero-dimensional carbon nanomaterials-carbon quantum dots (CDs) on various feedstocks (c.a. cellulose, glucose, ethanol, and vinegar residue) were investigated in this study. Results have shown that CH 4 yield from ethanol was increased by 24.59% (p = 0.396) after adding 5 g/L zinc doped carbon quantum dots (Zn-doped CDs) while that from vinegar residue was dramatically increased by 230% (p = 0.000) using 5 g/L nitrogen doped carbon quantum dots (N-doped CDs). In addition, photoluminescence demonstrated that CDs acted as a capacitor for transmitting and receiving electrons. Furthermore, co-occurrence network analysis revealed that Clostridiales might be used as a signal source to communicate with other species. This study firstly shifted the application of CDs from fluorescence to AD and manifested its positive impact on AD. In short, these findings provided a better understanding on the effects of CDs on different feedstocks of methanogenesis and revealed new evidence of stimulating methanogenesis via CDs.

Currently, the reported endoscopic system cannot meet the necessary conditions for real-time and optical-resolution clinical application simultaneously. In this study, by utilizing a high-repetition-rate laser and optimizing the overall structure of the probe, a real-time optical-resolution photoacoustic endoscope was developed, which could image targets in real time while maintaining a relatively constant lateral resolution. The endoscopic system has a best-resolution of 19 μm and a real-time imaging speed of 25 Hz. Experimental results demonstrate that this approach will push the promotion and commercialization of photoacoustic endoscopic imaging in a variety of preclinical and clinical applications.

In order to find a green, low-cost and high-performance modified raw soil method, samples were made from highland barley straw and gravel, which are unique in Qinghai-Tibet Plateau. The failure phenomenon, compressive strength, deformation capacity and load-displacement curve of different samples were studied, and the action mechanism and influence law of compressive strength of modified soil with different admixtures were analyzed and discussed. The test results show that when 0.25% highland barley straw and 20% gravel are mixed, the specimen has a smooth surface without dry shrinkage cracks, and its compressive strength and deformability are increased by 2.1 times and 30% respectively compared with that of plain soil. This content can be used as the best mixture ratio of this modified raw soil method.

The reversible methanolysis of an azomethine C[double bond, length as m-dash]N in a series of copper(ii) Schiff base complexes has been investigated through combined spectroscopic, structural, and kinetic studies. Pentadentate copper(ii) complexes [L1-Cu(X)]Y (L1 = 1,2-bis[(1-methyl-2-imidazolyl)methyleneamino]ethane; X = Y = ClO4- (1); X = Y = TfO- (2); X = Y = BF4- (3); X = H2O, Y = (ClO4-)2 (4) spontaneously add methanol in a ligand centered reaction to yield stable, isolable hemiaminal ether product complexes 5-8. In methanol free solution, 5-8 spontaneously release alcohol to regenerate 1-4. The methanol addition reaction is first-order in methanol and first-order in complex with second-order rate constants varying from 1.1 × 10-4 to 187 × 10-4 M-1 s-1 dependent on the donor ability of the axial ligand. Rate constants for methanol elimination vary from 0.67 to 3.7 × 10-4 s-1 with dependence on the counterion and water content of the solvent. Equilibrium constants for methanolysis range from 1.5 to 51 M-1. Structural comparisons of the Schiff base complexes 1-4 and the hemiaminal ether complexes 5-8 suggest methanol addition is favored by the release of ligand strain associated with three planar five-membered chelates in 1-4.

The geosynthetic-stabilized base course over a subgrade becomes a transversely isotropic layered system due to the degradation of the base modulus under cyclic loading. However, no elastic solution is available to quantify the stresses and strains of the geosynthetic-stabilized section considering base deterioration. In this study, the vertical shear modulus of the base course was modeled to decrease with the accumulation of the permanent deformation. The solution for the transversely isotropic layered elastic system was derived according to the layered elastic theory. A mechanistic-empirical procedure for the analysis of geosynthetic-stabilized roadways was then proposed by incorporating the elastic solution, the base modulus degradation model, and the soil damage model. This solution was then verified through a numerical analysis, parametric study, and stress analysis based on experimental results. The elastic solution derived in this study is valid and can be used for the analysis of geosynthetic-stabilized roadways. The base modulus degradation model reasonably captured the trend of the deterioration of the base course. The reduction in the vertical stress due to the inclusion of a geosynthetic was attributed not only to the lateral restraint and vertical support of the geosynthetic but also to the reduction in the base deterioration rate.

Micro-electro-mechanical systems (MEMS) scanner has significant advantages of miniature size, fast response and high stability, which is particularly applicable to photoacoustic laparoscopy (PAL). However, tilt angle-voltage curve of electrothermal MEMS shows a nonlinear character, which leads to inevitable nonlinear distortion in photoacoustic imaging. To overcome this problem, a nonlinear distortion correction was developed for the high-resolution forward-scanning electrothermal-MEMS-based PAL. The adaptive resampling method (ARM) was introduced to adaptively calibrate the projection of non-uniform scanning region to match the uniform scanning region. The correction performed low time complexity and high portability owing to the adaptive capacity of distortion decomposition in the reconstruction of physical models. Compared with the sample structure, phantom experiments demonstrated that the distortion was calibrated in all directions and the corrected image provided up to 96.82% high structural similarity in local subset. Furthermore, ARM was applied to imaging the abdominal cavity of rat and the vascular morphology was corrected in real-time display within a delay less than 2 seconds. All these results demonstrated that the nonlinear distortion correction possessed timely and effective correction in PAL, which suggested that it had the potential to employ to any other electrothermal-MEMS-based photoacoustic imaging systems for accurate and quantitative functional imaging.

As a promising branch of optical absorption-based photoacoustic microscopy, photoacoustic dermoscopy (PAD) can provide manifold morphologic and functional information in clinical diagnosis and the assessment of dermatological conditions. However, most PAD setups are insufficient for clinical dermatology, given their single optical resolution (OR) or acoustic resolution (AR) mode, which results in poor spatiotemporal resolution or imaging depth for visualizing the internal texture of skin. Here, a switchable optical and acoustic resolution photoacoustic dermoscope (S-OR-ARPAD) system is developed, which provides a smooth transition from OR mode in microscopic imaging of superficial skin layers to AR mode when imaging at greater depths within intensely scattering deep skin layers. The lateral resolution can be seamlessly switched between 4.4 and 47 μm as the maximum imaging depth is switched between 1.2 and 1.8 mm for skin imaging. Using the S-OR-ARPAD, we identified the two distinct resolution modes responsible for resolving features of different skin layers and demonstrated the fine structures with strong contrast in the stratum corneum, dermal papillae, and microvascular structures in the horizontal plexus by imaging the healthy human skin at different locations.