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Purpose: Photoacoustic imaging (PAI) used for noninvasive imaging of biological tissue has been reported in many literature. However, there are still some disadvantages in the novel technique, such as the poor efficiency of imaging. In the current PAI, multiple excitation of laser and multiple acquisition of signal are necessary for image reconstruction. In this case, laser pulses may injure biological tissue due to energy accumulation. To popularize PAI in clinical applications, it is necessary to develop a new imaging approach to increase the efficiency of PAI. Methods: A spatial phase-controlled algorithm is presented for full-field three-dimensional (3D) image reconstruction. By using the algorithm, photoabsorption sources at different depths can be reconstructed using just one set of data acquired in single laser shot. Unfocused plane transducer array and parallel data-acquisition (PDA) equipment are used for real-time photoacoustic (PA) signal detection and acquisition. Results: The spatial resolution of the 3D PAI system was analyzed. Two graphite rods at various positions in a simulation model and two bifurcate vessels in the ear of rabbit were imaged. In addition, the motion trace of one particle flowing at constant velocity was captured dynamically. Experimental results showed that spatial phase-controlled algorithm based on plane transducer array and PDA system was capable of static and dynamic 3D PAI. Conclusions: Spatial phase-controlled algorithm is introduced for 3D image reconstruction. The PA signals are collected by plane transducer array and PDA system in single pulse excitation. The acquired volumetric data are sufficient for 3D image reconstruction. Therefore, tissue can avoid the long-term exposure to light source and it is safer than the current PAI for in vivo imaging. With an increase in the repetition rate of laser pulse and speed of image display, the imaging method will realize real-time 3D imaging, which will be significant in clinical detection and medical diagnosis. [ABSTRACT FROM AUTHOR]

The transparent [Li 0.04 (K 0.5 Na 0.5) 0.96 ]NbO 3 +0.5mol% Er 2 O 3 (KNNLN-Er) lead-free piezoelectric ceramics were prepared by stereolithography technique. The influence of different sintering holding time (4h∼8h) on the micromorphology, relative density, shrinkage, electric properties, and photoluminescence properties were systematically investigated. The KNNLN-Er ceramics show the coexistence of orthorhombic and tetragonal structures. The grain size increases obviously and then decreases slightly with the holding time increasing. The KNNLN-Er ceramics exhibit good piezoelectric performance (piezoelectric constant d 33 ∼97 pC/N, electromechanical couple coefficient k t ∼0.36) and the moderate transparency of 34% when the holding time is 6h during sintering at 1120°C. Besides, the intensity of the photoluminescence emission spectra increases with the holding time increasing. Furthermore, in order to estimate the properties of the KNNLN-Er transparent ceramics, an ultrasonic transducer with a center frequency of 10.5 MHz was fabricated, which can be used for photoacoustic and fluorescence imaging. The results indicate that the KNNLN-Er ceramics have potential for multimode imaging applications. [ABSTRACT FROM AUTHOR]

Non-contact laser ultrasonic technique has been increasingly implemented for non-destructive inspections in harsh environments, high-temperature fields, and components having complex geometries. However, the poor signal-to-noise ratio and low amplitude of laser generated ultrasonic signals under a thermoelastic regime severely restrict its applications. Here, a sensitivity-enhanced all-optical probe was proposed for laser ultrasonic non-destructive testing. It consists of an optical sensor and an ellipsoidal acoustic cavity, where an optical sensor is placed at one focus of the cavity, and the detection point is set at another focus. The ultrasound signals are focused through the cavity and detected by the optical sensor. Side-by-side comparison experiments were carried out, and the results show that the probe can improve the signal amplitude by about 7.8 times compared to using a traditional optical sensor alone. The probe can make laser ultrasound detect defects with lower laser energy, which is of great significance to improve the efficiency of non-contact defect detection. [ABSTRACT FROM AUTHOR]

Photoacoustic microscopy (PAM), due to its deep penetration depth and high contrast, is playing an increasingly important role in biomedical imaging. PAM imaging systems equipped with conventional ultrasound transducers have demonstrated excellent imaging performance. However, these opaque ultrasonic transducers bring some constraints to the further development and application of PAM, such as complex optical path, bulky size, and difficult to integrate with other modalities. To overcome these problems, ultrasonic transducers with high optical transparency have appeared. At present, transparent ultrasonic transducers are divided into optical-based and acoustic-based sensors. In this paper, we mainly describe the acoustic-based piezoelectric transparent transducers in detail, of which the research advances in PAM applications are reviewed. In addition, the potential challenges and developments of transparent transducers in PAM are also demonstrated. [ABSTRACT FROM AUTHOR]

• Feedforward comb filtering effect is proposed to extract the phase information of overlapped signals from immersed ultrasonic testing of coatings. • A quantitative relation between the notch frequency and interfacial stiffness is obtained from the numerical simulation. • Decimal part of the ratio of notch frequencies to interval frequencies is proposed as a novel index to evaluate the bonding strength of coatings. • A comparative study on bonding strength assessment is conducted based on ultrasonic nondestructive test and destructive cross-cut test. • A baseline-free ultrasonic nondestructive method is proposed for quantitative evaluation of bonding strength of coatings. Because of the ability to protect and decorate materials, polyurethane coatings (PU) are being applied more and more extensively in the transportation, furniture, automotive, and electronic industries. However, it is difficult to effectively evaluate the bonding quality of coatings by conventional destructive methods for high-volume products in industrial applications. In this work, an ultrasonic nondestructive method based on the feedforward comb filtering effect was proposed to assess the bonding strength of the PU coatings. The coating and substrate interface can be modeled as a distributed spring system. The phase of the reflected ultrasonic wave is highly related to the interfacial stiffness. The superimposed signals can be well analyzed based on the comb filtering effect, and an index called the ratio of notch frequencies to interval frequencies (NIR) was constructed to represent the phase difference. Finite element simulations were conducted to show the index's construction method and variation with different interfacial stiffnesses. Immersed ultrasonic testing experiments with a transducer of 39.43 MHz were then conducted on PU coatings on two kinds of substrates made of aluminum and magnesium alloys. Each specimen was scanned as a grid to mimic the procedure of the well-known cross-cut test. The notch frequencies of the scanned received signals were applied to obtain the NIR index. To avoid the interference of the thickness of coatings, the decimal part of NIR was further proposed to link with the bonding strength obtained by the cross-cut test. This index changes accordingly with aluminum- and magnesium-based coatings' bonding strength. The results prove that the proposed ultrasonic method based on the feedforward comb filter effect is high potential to assess the bonding strength of coatings nondestructively. [ABSTRACT FROM AUTHOR]

Transcranial focused ultrasound (tFUS) is increasingly used in experimental neuroscience due to its neuromodulatory effectiveness in animal studies. However, achieving multitarget tFUS in small animals is typically limited by transducer size, energy transfer efficiency, and brain volume. The objective of this work was to construct an ultrasound system for multitarget neuromodulation in small animals. First, a miniaturized high-powered 2-D array transducer was developed. The phase delay of each array element was calculated based on the multifocal time-reversal method, generating multiple foci simultaneously in a 3-D field. The effects of the axial focal length, interfocus spacing (lateral distance between the two focal centers), and the number of foci on the focal properties of the pressure field were examined through numerical simulations. In-vitro ultrasonic measurements and transcranial simulations on a rat skull were conducted. The minimum interfocus spacing separating two −6-dB foci and the peak full-width at half-maximum were positively correlated with axial focal length; the relative relationship between the interfocus spacing and pressure field properties was similar for each axial focal length. The maximum acoustic pressure and spatial average intensity at focus in deionized water were 2.21 MPa and 133 W/cm2, respectively. The simulated and experimental results were compared, demonstrating agreement in both peak position and focus shape. The ultrasound system can provide a neuroscientific platform for evaluating the feasibility of multitarget ultrasound stimulation treatment protocols, thus improving the understanding of functional neuroanatomy. [ABSTRACT FROM AUTHOR]

Transcranial ultrasound therapy has become a noninvasive method for treating neurological and psychiatric disorders, and studies have further demonstrated that multitarget transcranial ultrasound therapy is a better solution. At present, multitarget transcranial ultrasound therapy in small animals can only be achieved by the multitransducer or phased array. However, multiple transducers may cause spatial interference, and the phased array system is complicated, expensive, and especially unsuitable for small animals. This study is the first to design and fabricate a miniature acoustic holography lens for multitarget transcranial ultrasound therapy in rats. The acoustic holographic lens, working at a frequency of 1.0 MHz, with a size of 10.08 mm $\times10.08$ mm and a pixel resolution of 0.72 mm, was designed, optimized, and fabricated. The dual-focus transcranial ultrasound generated based on the lens was measured; the full-width at half-maximum (FWHM) of the focal spots in the ${y}$ -direction was 2.15 and 2.27 mm and in the ${z}$ -direction was 2.3 and 2.36 mm. The focal length was 5.4 mm, and the distance between the two focuses was 5.6 mm, close to the desired values of 5.4 and 6.0 mm. Finally, the multiple-target blood–brain barrier opening in rats’ bilateral secondary visual cortex (mediolateral area, V2ML) was demonstrated using the transcranial ultrasound therapy system based on the lens. These results demonstrate the good performance of the multitarget transcranial ultrasound therapy system for small animals, including high spatial resolution, small size, and low cost. [ABSTRACT FROM AUTHOR]

Background: Histologic studies have demonstrated that lipid content and its spatial distribution is related to plaque vulnerability. However, in vivo imaging is still limited. Photoacoustic imaging may provide novel in vivo insights into these lipid-rich plaques. Objectives: This study sought to examine whether intravascular photoacoustic tomography (IVPAT) allows localization and quantification of lipid content in atherosclerotic plaques. Methods: Rabbits fed with a high-fat/high-cholesterol diet served as the atherosclerotic model. Catheter-based IVPAT was used to evaluate pixel-based lipid relative concentration (LRC) of the vessel wall. The aorta of 4 groups of rabbits (n = 12) were examined ex vivo with IVPAT after 0, 5, 10, and 15 weeks of a high-fat diet, respectively. Six rabbits underwent 3-dimensional (3D) IVPAT after 20 weeks of the high-fat diet. Three rabbits were examined in vivo using IVPAT without interruption of blood flow. Concentration-based lipid map and quantitative index were calculated. For subsequent histologic correlation, all specimens were evaluated with Oil Red O staining. Results: Cross-sectional LRC maps allowed visualization of concentration and depth information of lipid content in the atherosclerotic plaques. Lipid accumulation within plaque, assessed by the maximum LRC, mean LRC, and high lipid content area correlated to duration of a high-fat diet. Three-dimensional LRC maps enabled overall evaluation of focal plaques in an intact explanted aorta including spatial and structural features. In vivo-obtained LRC maps accurately showed the structure of lipid core with high contrast. Ex vivo and in vivo IVPAT results were highly consistent with histological results. Conclusions: In an animal model, IVPAT allowed characterization of spatial and quantitative features of lipid-rich plaques. [ABSTRACT FROM AUTHOR]

In vivo wide-field brain microscopy has remained a non-trivial challenge in life science research, which would provide indispensable preclinical insight into the whole-brain metabolism and hemodynamic. Here, we developed an ultra-compact micro-photoacoustic tomography (μPAT) system for fast brain imaging equipped with a 10 MHz 256-element full-ring ultrasound transducer array and 100 MS/s/ch multi-channel parallel data acquisition. The system design and calibration are presented in detail, along with the 62 μm in-plane resolution comparable to the level of acoustic-resolution photoacoustic microscopy. The μPAT system provided the ability to noninvasively use high-resolution mapping of the microvascular network of the full-view brain at different depths, cerebral ischemia, and intracerebral foreign-body. Ultra-compact μPAT holds great potential to take the technology out of the lab for preclinical imaging and clinical translation. [ABSTRACT FROM AUTHOR]

X-ray-induced acoustic computed tomography (XACT) is a unique hybrid imaging modality that combines high X-ray absorption contrast with high ultrasonic resolution. X-ray radiography and computerized tomography (CT) are currently the gold standards for 2-D and 3-D imaging of skeletal tissues though there are important properties of bone, such as elasticity and speed of sound (SOS), that these techniques cannot measure. Ultrasound is capable of measuring such properties though current clinical ultrasound scanners cannot be used to image the interior morphology of bones because they fail to address the complicated physics involved for exact image reconstruction; bone is heterogeneous and composed of layers of both cortical and trabecular bone, which violates assumptions in conventional ultrasound imaging of uniform SOS. XACT, in conjunction with the time-reversal algorithm, is capable of generating precise reconstructions, and by combining elements of both X-ray and ultrasound imaging, XACT is potentially capable of obtaining more information than any single of these techniques at low radiation dose. This article highlights X-ray-induced acoustic detection through linear scanning of an ultrasound transducer and the time-reversal algorithm to produce the first-ever XACT image of a bone sample. The results of this study should prove to enhance the potential of XACT imaging in the evaluation of bone diseases for future clinical use. [ABSTRACT FROM AUTHOR]

• A head-mounted transcranial ultrasound stimulation system for mice was built. • Ultrasound stimulation of DRN safely increased c-fos gene expression in the DRN. • Ultrasound stimulation of DRN increased 5-hydroxytryptamine levels in DRN. • Ultrasound stimulation of DRN promoted recovery from anesthesia and improved cognition in mice. • Antagonizing the 5-HT 2A receptor inhibited anesthesia recovery and cognition in mice after ultrasound stimulation of DRN. Delayed arousal and cognitive dysfunction are common, especially in older patients after general anesthesia (GA). Elevating central nervous system serotonin (5-HT) levels can promote recovery from GA and increase synaptic plasticity to improve cognition. Ultrasound neuromodulation has become a noninvasive physical intervention therapy with high spatial resolution and penetration depth, which can modulate neuronal excitability to treat psychiatric and neurodegenerative diseases. This study aims to use ultrasound to noninvasively modulate the brain 5-HT levels of mice to promote recovery from GA and improve cognition in mice. The dorsal raphe nucleus (DRN) of mice during GA was stimulated by the 1.1 MHz ultrasound with a negative pressure of 356 kPa, and the liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) method was used to measure the DRN 5-HT concentrations. The mice's recovery time from GA was assessed, and the cognition was evaluated through spontaneous alternation Y-maze and novel object recognition (NOR) tests. After ultrasound stimulation, the mice's DRN 5-HT levels were significantly increased (control: 554.0 ± 103.2 ng/g, anesthesia + US: 664.2 ± 84.1 ng/g, *p = 0.0389); the GA recovery time (return of the righting reflex (RORR) emergence latency time) of mice was significantly reduced (anesthesia: 331.6 ± 70 s, anesthesia + US: 223.2 ± 67.7 s, *p = 0.0215); the spontaneous rotation behavior score of mice was significantly increased (anesthesia: 59.46 ± 5.26 %, anesthesia + US: 68.55 ± 5.24 %; *p = 0.0126); the recognition index was significantly increased (anesthesia: 55.02 ± 6.23 %, anesthesia + US: 78.52 ± 12.21 %; ***p = 0.0009). This study indicates that ultrasound stimulation of DRN increases serotonin levels, accelerates recovery from anesthesia, and improves cognition, which could be an important strategy for treating delayed arousal, postoperative delirium, or even lasting cognitive dysfunction after GA. [ABSTRACT FROM AUTHOR]

Residual stress and its distribution are the key indicators to ensure structural integrity. However, current ultrasonic methods are not appropriate for complex stress measurement. Considering the proximity of zero-group-velocity (ZGV) mode with the cut-off frequency and its sensitivity to local material property, this paper proposed a local stress measurement method based on S1-ZGV mode. The stress field reconstruction was demonstrated numerically with a nonuniform plate. Then, a FE model was built to investigate the excitation of S1-ZGV mode by oblique incidence approach, proving that S1-ZGV mode can be effectively excited and received with a small distance. Thus, a contact ultrasonic system along with a tailor-made compact wedged transducer was built for experimental validation. Parametric studies were performed to obtain the optimal excitation conditions for S1-ZGV mode. At last, experimental validation was carried out by standard tensile testing. The stress coefficient between the frequency shift and the applied stress was obtained with a uniform plate. The stresses of the nonuniform plate at three different positions were measured, proving that S1-ZGV method is effective for local stress measurement in thin plates. [ABSTRACT FROM AUTHOR]

In this study, we propose an integrated approach which combines 3D printing and liquid precursor infiltration together to prepare alumina-toughened zirconia (ATZ) composite. Controllable manipulation of the microstructure of the composite could be realized through different infiltration times and sintering temperature. The 3D-printed ATZ with infiltration and post-CIP sintered at 1550 °C possesses the highest relative density (98.11%), hardness (12.65 ± 0.24 GPa) and fracture toughness (6.42 ± 0.33 MPa m1/2). The rates of increase in the performance compared with the undoped zirconia sintered at 1550 °C are 1.8%, 8.4% and 34.6%, respectively. The dominated toughening mechanism of ATZ could be attributed to the effect of Al2O3 inclusion on crack deflection and energy absorption. The 3D-printed ATZ sample with infiltration followed by CIP sintered at 1550 °C shows the lowest aging rate and the lowest phase transformation depth compared with 3Y-TZP (Tetragonal Zirconia Polycrystal). Our integrated approach could not only realize the complex and ultrafine shape free of molds, but also suppress the low temperature aging behavior of dental implants, which has baffled dentists for a long time. [ABSTRACT FROM AUTHOR]

In vivo identification of viable and thermally coagulated blood in a burn wound can be used to profile the type, extent, and site of the burn, thus assisting the removal of necrotic tissue in preparation for skin grafts. Recently, intensive research on photoacoustic imaging (PAI) has been conducted to evaluate burn injury. However, most PAI systems usually take the approach of direct physical contact of an acoustic detector or an impedance matching medium with the vulnerable burned skin, which exposes significant limitations on the diagnosis of burn injuries. Here, we present a noncontact PAI system, based on a custom designed air-coupled ultrasonic transducer, enabling in vivo noncontact vasculature to be imaged without contrast agents. Using the natural difference in light absorption between coagulated and non-coagulated blood at the wavelength of 532 nm, this PAI system possesses an immanent advantage to discriminate viable and thermally coagulated blood in burned tissues. Phantom experiments and burned rabbit's skin imaging have been implemented to demonstrate that the noncontact PAI technique could be valuable in the adjuvant diagnosis and observation of burns. [ABSTRACT FROM AUTHOR]

Abstract The PZT ceramics with different weight content from 78% to 89% were printed using the stereolithography method. The piezoelectric properties as well as the microstructure of the ceramics were investigated in detail. X-ray patterns and Raman spectra demonstrate that the steady PZT tetragonal phase has already formed in these sintered ceramics. Besides, the piezoelectric constant and dielectric constant were 212–345 pC/N and 760–1390, which were sligthly lower than that of the dry pressing disk. Furthermore, a two-dimensional ultrasound transducer array (8 × 8) was designed and developed to evaluate the properties of the 3D-printed PZT ceramics. [ABSTRACT FROM AUTHOR]

In this research, we creatively integrate the traditional methods of liquid precursor infiltration plus in-situ precipitation with stereolithography-based 3D printing for the fabrication of Al 2 O 3 -ZrO 2 ceramics to ensure the homogeneous distribution of ZrO 2 particle in the alumina matrix. Our characterization results shows that this combination leads to the materials with significantly better performance. The Al 2 O 3 specimen is soaked in a Zr 4+ ion solution to induce infiltration, in-situ precipitation and then sintered. X-ray diffraction analysis of the thus-treated sample indicated that Al 2 O 3 was the primary phase and t-ZrO 2 was the secondary phase. Microstructural and EDS analysis showed that the ZrO 2 particles were homogeneously distributed in the Al 2 O 3 matrix, leading to inhibited grain growth. The samples soaked in solutions for different Zr 4+ concentrations and sintered both at 1450 °C and 1550 °C showed improved mechanical properties as compared to those of pure alumina. Futhermore, the sample infiltrated using the solution with a concentration of 1.5 mol/L and sintered at 1450 °C showed similar fracture toughness (4.97 MPa m 1/2 ) with the sample sintered at 1550 °C (5.06 MPa m 1/2 ) but much better hardness (20.95 Gpa) than the sample sintered at 1550 °C (19.71 GPa). Therefore, this method could not only enhance the mechanical properties via introducing the second phase, but also lowers the sintering temperature by at least 100 °C, which would be beneficial for energy conservation and leads to significant advances in the 3D printing of ceramic components. [ABSTRACT FROM AUTHOR]

In this paper, a ceramic suspension with appropriate viscosity was prepared by optimizing the powder solid content and the dispersant content. An Al 2 O 3 -ZrO 2 ceramic green body was fabricated using the SLA technique, followed by the application of a liquid drying and two-step debinding process to prepare the defect-free Al 2 O 3 -ZrO 2 ceramic green body. The relative density, phase composition, microstructure, grain size, and mechanical properties of Al 2 O 3 -ZrO 2 samples sintered at different temperatures were compared. The main results indicated that the sample density increased with the sintering temperature until reaching a maximum density of 4.28 g/cm 3 at 1600 °C. When the temperature further increased to 1650 °C, the density dropped instead. With increasing sintering temperature, both the number of grain boundaries and the number of pores located at the grain boundaries reduced greatly. The Vickers hardness of the samples first increased and reached its maximum at 1550 °C with a value of 17.6 GPa, and then decreased with further increases in sintering temperature. The fracture toughness increased with the sintering temperature and reached a maximum value of 5.2 MPa·m 1/2  at 1650 °C. A sintering kinetics window which could offer the relationship between the sintering temperature and the relative density & grain size was set and also the microstructure evolution of the sintered body was conducted to get a deeper understanding of the 3D printing Al 2 O 3 -ZrO 2 composites. [ABSTRACT FROM AUTHOR]

In this work, a stereolithography-based method of 3D printing was successfully used to fabricate a complex-shaped triangular zirconia cutting tool with a tool withdrawal groove and a honeycomb ceramic component. The sintered bodies displayed significant shrinkage after sintering, with the maximum shrinkage being 35.26%. The XRD pattern indicated that the crystalline phase of the parts was the t-ZrO 2 phase, while SEM characterization revealed that the sintered bodies were composed of densely packed submicron-grade grains, without any discernible pores. The density of the parts was measured as 97.14% via Archimedes’ water displacement method, which is consistent with the results of SEM characterization. Additionally, the measured Vickers hardness and fracture toughness of the fabricated parts were 13.0597 GPa and 6.0380 MPa m 1/2 , respectively. These values are close to the structural properties of common zirconia ceramics prepared by conventional approaches. Hence, a novel DLP-stereolithography-based 3D printing process for the fabrication of complex and dense zirconia ceramic parts has been proposed in this work. [ABSTRACT FROM AUTHOR]

Optical-resolution photoacoustic microscopy (OR-PAM) has been significantly improved in terms of spatial resolution, detection sensitivity, imaging speed, and penetration depth. However, the popular producibility of OR-PAM system is still limited by the size and cost of solid-state laser excitation. Here, we developed a portable laser-diode-based OR-PAM (LD-OR-PAM) system using a pulsed semiconductor laser source, which was operated at 905 ± 15 nm with a pulse energy as low as 4.9 μJ. The measured lateral resolution has been improved to ∼1.5 μm from hundreds of microns. The compact and inexpensive natures of LD-OR-PAM would promote the potential clinical applications such as in dermatology. [ABSTRACT FROM AUTHOR]

Ultrasonic is one of the well-known methods for surface roughness measurement, but small roughness will only lead to a subtle variation of transmission or reflection. To explore sensitive techniques for surfaces with small roughness, nonlinear ultrasonic measurement in through-transmission and pulse-echo modes was proposed and studied based on an effective unit-cell finite element (FE) model. Higher harmonic generation in solids was realized by applying the Murnaghan hyperelastic material model. This FE model was verified by comparing the absolute value of the nonlinearity parameter with the analytical solution. Then, random surfaces with different roughness values ranging from 0 μm to 200 μm were repeatedly generated and studied in the two modes. The through-transmission mode is very suitable to measure the surfaces with roughness as small as 3% of the wavelength. The pulse-echo mode is sensitive and effective to measure the surface roughness ranging from 0.78% to 5.47% of the wavelength. This study offers a potential nondestructive testing and monitoring method for the interfaces or inner surfaces of the in-service structures. [ABSTRACT FROM AUTHOR]