Intravascular photoacoustic and optical coherence tomography imaging dual-mode system for detecting spontaneous coronary artery dissection: A feasibility study

In this work,we present an intravascular dual-mode endoscopic system capable of both intravascular photoacoustic imaging(IVPAI)and intravascular optical coherence tomography(IVOCT)for recognizing spontaneous coronary artery dissection(SCAD)phantoms.IVPAI provides high-resolution and high-penetration images of intramural hematoma(IMH)at different depths,so it is especially useful for imaging deep blood clots associated with imaging phantoms.IVOCT can readily visualize the double-lumen morphology of blood vessel walls to identify intimal tears.We also demonstrate the capability of this dual-mode endoscopic system using mimicking phantoms and biological samples of blood clots in ex vivo porcine arteries.The results of the experiments indicate that the combined IVPAI and IVOCT technique has the potential to provide a more accurate SCAD assessment method for clinical applications.

Photoacoustic/ultrasound dual-modal imaging of human nails: A pilot study

Traditional diagnostic techniques including visual examination,ultrasound(US),and magnetic resonance imaging(MRI)have limitations of in-depth information for the detection of nail disorders,resolution,and practicality.This pilot study,for thefirst time,evaluates a dualmodality imaging system that combines photoacoustic tomography(PAT)with the US for the multiparametric quantitative assessment of human nail.The study involved a small cohort offive healthy volunteers who underwent PAT/US imaging for acquiring the nail unit data.The PAT/US dual-modality imaging successfully revealed thefine anatomical structures and microvascular distribution within the nail and nail bed.Moreover,this system utilized multispectral PAT to analyze functional tissue parameters,including oxygenated hemoglobin,deoxyhemoglobin,oxygen saturation,and collagen under tourniquet and cold stimulus tests to evaluate changes in the microcirculation of the nail bed.The quantitative analysis of multispectral PAT reconstructed images demonstrated heightened sensitivity in detecting alterations in blood oxygenation levels and collagen content within the nail bed,under simulated different physiological conditions.This pilot study highlights the potential of PAT/US dual-modality imaging as a real-time,noninvasive diagnostic modality for evaluating human nail health and for early detection of nail bed pathologies.

A promising approach for quantifying focal stroke modeling and assessing stroke progression:optical resolution photoacoustic microscopy photothrombosis

To investigate the mechanisms underlying the onset and progression of ischemic stroke,some methods have been proposed that can simultaneously monitor and create embolisms in the animal cerebral cortex.However,these methods often require complex systems and the effect of age on cerebral embolism has not been adequately studied,although ischemic stroke is strongly age-related.In this study,we propose an optical-resolution photoacoustic microscopy-based visualized photothrombosis methodology to create and monitor ischemic stroke in mice simultaneously using a 532 nm pulsed laser.We observed the molding process in mice of different ages and presented age-dependent vascular embolism differentiation.Moreover,we integrated optical coherence tomography angiography to investigate age-associated trends in cerebrovascular variability following a stroke.Our imaging data and quantitative analyses underscore the differential cerebrovascular responses to stroke in mice of different ages,thereby highlighting the technique's potential for evaluating cerebrovascular health and unraveling age-related mechanisms involved in ischemic strokes.

Triple-path feature transform network for ring-array photoacoustic tomography image reconstruction

Photoacoustic imaging(PAI)is a noninvasive emerging imaging method based on the photoacoustic effect,which provides necessary assistance for medical diagnosis.It has the characteristics of large imaging depth and high contrast.However,limited by the equipment cost and reconstruction time requirements,the existing PAI systems distributed with annular array transducers are difficult to take into account both the image quality and the imaging speed.In this paper,a triple-path feature transform network(TFT-Net)for ring-array photoacoustic tomography is proposed to enhance the imaging quality from limited-view and sparse measurement data.Specifically,the network combines the raw photoacoustic pressure signals and conventional linear reconstruction images as input data,and takes the photoacoustic physical model as a prior information to guide the reconstruction process.In addition,to enhance the ability of extracting signal features,the residual block and squeeze and excitation block are introduced into the TFT-Net.For further efficient reconstruction,the final output of photoacoustic signals uses‘filter-then-upsample’operation with a pixel-shuffle multiplexer and a max out module.Experiment results on simulated and in-vivo data demonstrate that the constructed TFT-Net can restore the target boundary clearly,reduce background noise,and realize fast and high-quality photoacoustic image reconstruction of limited view with sparse sampling.

Isoindigo nanoparticles for photoacoustic imaging-guided tumor photothermal therapy

The key factor in photothermal therapy lies in the selection of photothermal agents.Traditional photothermal agents generally have problems such as poor photothermal stability and low photothermal conversion efficiency.Herein,we have designed and synthesized an isoindigo(IID)dye.We used isoindigo as the molecular center and introduced common triphenylamine and methoxy groups as rotors.In order to improve the photothermal stability and tumor targeting ability,we encapsulated IID into nanoparticles.As a result,the nanoparticles exhibited high photothermal stability and photothermal conversion efficiency(67%)upon 635 nm laser irradiation.Thus,the nanoparticles demonstrated a significant inhibitory effect on live tumors in photothermal therapy guided by photoacoustic imaging and provided a viable strategy to overcome the treatment challenges.

Characterization of cerebrovascular changes in Alzheimer's disease mice by photoacoustic imaging

The cerebral vasculature plays a significant role in the development of Alzheimer's disease(AD),however,the specific association between them remains unclear.In this paper,based on the benefits of photoacoustic imaging(PAI),including label-free,high-resolution,in vivo imaging of vessels,we investigated the structural changes of cerebral vascular in wild-type(WT)mice and AD mice at different ages,analyzed the characteristics of the vascular in different brain regions,and correlated vascular characteristics with cognitive behaviors.The results showed that vascular density and vascular branching index in the cortical and frontal regions of both WT and AD mice decreased with age.Meanwhile,vascular lacunarity increased with age,and the changes in vascular structure were more pronounced in AD mice.The trend of vascular dysfunction aligns with the worsening cognitive dysfunction as the disease progresses.Here,we utilized in vivo PAI to analyze the changes in vascular structure during the progression of AD,elucidating the spatial and temporal correlation with cognitive impairment,which will provide more intuitive data for the study of the correlation between cerebrovascular and the development of AD.

Photoacoustic elastography based on laser-excited shear wave

Elastography can be used as a diagnostic method for quantitative characterization of tissue hardness information and thus,differential changes in pathophysiological states of tissues.In this study,we propose a new method for shear wave elastography(SWE)based on laser-excited shear wave,called photoacoustic shear wave elastography(PASWE),which combines photoacoustic(PA)technology with ultrafast ultrasound imaging.By using a focused laser to excite shear waves and ultrafast ultrasonic imaging for detection,high-frequency excitation of shear waves and noncontact elastic imaging can be realized.The laser can stimulate the tissue with the light absorption characteristic to produce the thermal expansion,thus producing the shear wave.The frequency of shear wave induced by laser is higher and the frequency band is wider.By tracking the propagation of shear wave,Young’s modulus of tissue is reconstructed in the whole shear wave propagation region to further evaluate the elastic information of tissue.The feasibility of the method is verified by experiments.Compared with the experimental results of supersonic shear imaging(SSI),it is proved that the method can be used for quantitative elastic imaging of the phantoms.In addition,compared with the SSI method,this method can realize the noncontact excitation of the shear wave,and the frequency of the shear wave excited by the laser is higher than that of the acoustic radiation force(ARF),so the spatial resolution is higher.Compared to the traditional PA elastic imaging method,this method can obtain a larger imaging depth under the premise of ensuring the imaging resolution,and it has potential application value in the clinical diagnosis of diseases requiring noncontact quantitative elasticity.

High Efficiency and Anomalous Photoacoustic Behavior in Vertical CNTs Array

Miniaturized sound generators are attractive to realize intriguing functions.Thermoacoustic device’s application is seriously limited due to the frequency-doubling phenomenon.To address this issue,photoacoustic sound generator is considered as a promising alternative.Here,based on vertical single-wall carbon nanotubes(CNTs)array,we introduce a photoacoustic sound generator with internal nano-Helmholtz cavity.Different from traditional device that generates sound by periodically heating up the open space air around material,this sound generator produces an audio signal by forming a forced vibration of the air inside the CNTs.Interestingly,anomalous photoacoustic behavior is observed that the sound pressure level(SPL)curve has a resonance peak,the corresponding frequency of which is inversely proportional to the CNTs array’s height.Furthermore,the energy conversion efficiency of this photoacoustic device is 1.64 times as large as that of a graphene sponge-based photoacoustic device.Most importantly,this device can be employed for music playing,bringing a new clew for the development of musical instruments in the future.

Photoacoustic microscopy based on transparent piezoelectric ultrasound transducers

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.

Flexible fiber-laser ultrasound sensor for multiscale photoacoustic imaging

Photoacoustic imag ing(PAI)is a nonin vasive biomedical imag ing tech no logy capable of multiscale imag ing of biological samples from orga ns dow n to cells.Multiscale PAI requires differe nt ultraso und tra nsducers that are flat or focused because the current widely-used piezoelectric transducers are rigid and lack the flexibility to tune their spatial ultrasound responses.Inspired by the rapidly-developing flexible photonics,we exploited the inherent flexibility and low-loss features of optical fibers to develop a flexible fiber-laser ultrasound sensor(FUS)for multiscale PAI.By simply bending the fiber laser from straight to curved geometry,the spatial ultraso und resp onse of the FUS can be tuned for both wide-view optical-resolution photoacoustic microscopy at optical diffraction-limited depth(~1 mm)and photoacoustic computed tomography at optical dissipation-limited depth of several centimeters.A radio-frequency demodulation was employed to get the readout of the beat frequency variation of two orthogonal polarization modes in the FUS output,which ensures low-noise and stable ultrasound detection.Compared to traditional piezoelectrical transducers with fixed ultrasound responses once manufactured,the flexible FUS provides the freedom to design multiscale PAI modalities including wearable microscope,intravascular endoscopy,and portable tomography system,which is attractive to fundamental biologic-al/medical studies and clinical applications.

Low-cost photoacoustic imaging systems based on laser diode and light-emitting diode excitation

Photoacoustic imaging,an emerging biomedical imaging modality,holds great promise for preclinical and clinical researches.It combines the high optical contrast and high ultrasound resolution by converting laser excitation into ultrasonic emission.In order to generate photoacoustic signal e±-ciently,bulky Q-switched solid-state laser systems are most commonly used as excitation sources and hence limit its commercialization.As an alternative,the miniaturized semiconductor laser system has the advantages of being inexpensive,compact,and robust,which makes a signi¯cant e®ect on production-forming design.It is also desirable to obtain a wavelength in a wide range from visible to nearinfrared spectrum for multispectral applications.Focussing on practical aspect,this paper reviews the state-of-the-art developments of low-cost photoacoustic system with laser diode and light-emitting diode excitation source and highlights a few representative installations in the past decade.

Recent developments in photoacoustic imaging and sensing for nondestructive testing and evaluation

Photoacoustic(PA)imaging has been widely used in biomedical research and preclinical studies during the past two decades.It has also been explored for nondestructive testing and evaluation(NDT/E)and for industrial applications.This paper describes the basic principles of PA technology for NDT/E and its applications in recent years.PA technology for NDT/E includes the use of a modulated continuous-wave laser and a pulsed laser for PA wave excitation,PA-generated ultrasonic waves,and all-optical PA wave excitation and detection.PA technology for NDT/E has demonstrated broad applications,including the imaging of railway cracks and defects,the imaging of Li metal batteries,the measurements of the porosity and Young’s modulus,the detection of defects and damage in silicon wafers,and a visualization of underdrawings in paintings.

Application of Micro Electro Mechanical System(MEMS)Technology in Photoacoustic Imaging

Photoacoustic imaging(PAI)is a new biomedical imaging technology that provides a mixed contrast mechanism and excellent spatial resolution in biological tissues.It is a non-invasive technology that can provide in vivo anatomical and functional information.This technology has great application potential in microscopic imaging and endoscope system.In recent years,the devel-opment of micro electro mechanical system(MEMS)technology has promoted the improvement and miniaturization of the photoacoustic imaging system,as well as its preclinical and clinical appli-cations.This paper introduces the research progress of MEMS technology in photoacoustic micro-scope systems and the miniaturization of photoacoustic endoscope ultrasonic transducers,and points out the shortcomings of existing technology and the direction of future development.

Indocyanine green loaded graphene oxide for high-e±cient photoacoustic tumor therapy

Photoacoustic therapy,using the photoacoustic efect of agents for selectively kling tumor cells,has shown pronising for treat ing tumor.Utilization of high optical absorption probes can help to effectively improve the photoacoustic ther apy efficiency.Herein,we report a novel high-absorpt:ion photoacoustic probe that is composed of indocyanine green(ICG)and gr aphene oxide(GO),entitled GO-ICG,for photoacoustic ther apy.The attached ICG with narrow absorption spectral profile has strong optical absorption in the infrared region.The absorption spectrum of the GO-ICG solution reveals that the GO-ICG particles exhibited a 10-fold higher absorbance at 780 nm(its peak absorbance)as compared with GO.Importantly,ICG's fluorescence is quenched by GO via fuorescence resonance energy transfer.As a result,GO-ICG can high efficiently convert the absorbed light energy to acoustic wave under pulsed laser irradiation.We further demonstrate that GO-ICG can produce stronger photoacoustic wave than the GO and ICG alone.Moreover,we conjugate this contrast agent with integrin 0。As mono dlonal antibody to molecularly target the U87-MG human glioblastoma cells for selective tumor cell killing.Finally,our results testify that the photoacoustic therapy eficiency of GO-ICG is higher than the existing photoacoustic therapy agent.Our work demonstrates that GO-ICG is a high efficiency photo-acoustic therapy agent.This novel photoacoustic probe is likely to be an available candidate for tumor therapy.

Photoacoustic mesoscopy:pushing toward the depth limit in the high-resolution optical imaging for biomedical applications and clinical potentials

Photoacoustic mesoscopy(PAMe) offers high-sensitivity in vivo imaging based on the rich optical contrast in biological tissues,with sub-100-micron resolutions at a few millimeters depth. By benefiting from low ultrasonic scattering,this emerging technology has pushed the penetration depth beyond the optical diffuse limit unprecedented for high-resolution optical methods.Here,we review ed the state-of-art implementations of PAMe and their achievements in biological and primary clinical applications. With the high-frequency focused ultrasonic detector,the high-resolution optical visualization can be achieved by utilizing various PAMe systems. These capabilities of PAMe have made it well applicable for understanding the biological mechanisms,exploring the pathological features and analyzing the characteristics of human skin. Future improvements and prospects of PAMe are also mentioned,suggesting its great potential tow ards the corresponding emerging biomedical and clinical applications.

Chronic cranial window for photoacoustic imaging: a mini review

Photoacoustic(PA)microscopy is being increasingly used to visualize the microcirculation of the brain cortex at the micron level in living rodents.By combining it with long-term cranial window techniques,vasculature can be monitored over a period of days extending to months through a field of view.To fulfill the requirements of long-term in vivo PA imaging,the cranial window must involve a simple and rapid surgical procedure,biological compatibility,and sufficient optical-acoustic transparency,which are major challenges.Recently,several cranial window techniques have been reported for longitudinal PA imaging.Here,the development of chronic cranial windows for PA imaging is reviewed and its technical details are discussed,including window installation,imaging quality,and longitudinal stability.

Gastroscopy-conjugated photoacoustic and ultrasonic dual-mode imaging for detection of submucosal gastric cancer:in vitro study

This paper presents photoacoustic and ultrasonic dual-mode imaging for real-time detection of submucosal gastric cancer with a combination of gastroscopy.The diagnostic capacity was directly addressed via several phantoms and ex vivo experiments.Results demonstrated that superficial and submucosal gastric cancer can be diagnosed with a perceptible depth of 6.33 mm,a lateral accuracy of 2.23 mm,and a longitudinal accuracy of 0.17 mm though capturing the morphology of angiogenesis,which is a main character of the therioma-related change.The capability of gastroscopy-conjugated photoacoustic and ultrasonic dual-mode imaging system will own great potential in improving the clinical diagnostic rate of submucosal gastric cancer.

Fiber laser technologies for photoacoustic microscopy

Fiber laser technology has experienced a rapid growth over the past decade owing to increased applications in precision measurement and optical testing,medical care,and industrial applications,including laser welding,cleaning,and manufacturing.A fiber laser can output laser pulses with high energy,a high repetition rate,a controllable wavelength,low noise,and good beam quality,making it applicable in photoacoustic imaging.Herein,recent developments in fiber-laser-based photoacoustic microscopy(PAM)are reviewed.Multispectral PAM can be used to image oxygen saturation or lipid-rich biological tissues by applying a Q-switched fiber laser,a stimulated Raman scattering-based laser source,or a fiber-based supercontinuum source for photoacoustic excitation.PAM can also incorporate a single-mode fiber laser cavity as a high-sensitivity ultrasound sensor by measuring the acoustically induced lasing-frequency shift.Because of their small size and high flexibility,compact head-mounted,wearable,or hand-held imaging modalities and better photoacoustic endoscopes can be enabled using fiber-laser-based PAM.

Recent advances in applications of multimodal ultrasound-guided photoacoustic imaging technology

Photoacoustic imaging(PAI)is often performed simultaneously with ultrasound imaging and can provide functional and cellular information regarding the tissues in the anatomical markers of the imaging.This paper describes in detail the basic principles of photoacoustic/ultrasound(PA/US)imaging and its application in recent years.It includes near-infrared-region PA,photothermal,photodynamic,and multimode imaging techniques.Particular attention is given to the relationship between PAI and ultrasonic imaging;the latest high-frequency PA/US imaging of small animals,which involves not only B-mode,but also color Doppler mode,power Doppler mode,and nonlinear imaging mode;the ultrasonic model combined with PAI,including the formation of multimodal imaging;the preclinical imaging methods;and the most effective detection methods for clinical research for the future.

Effects of Light Stress on Oxygen Evolution and Photochemical Energy Stor age of Hybrid Poplar Clones Determined by Photoacoustic Technique

The oxygen evolution, thermal dissipation, and photochemical energy storage of three hybrid poplar clones, namely the triploid clone B342, the diploid clone B11 [(Populus alba×P. glandulosa)×(P.tomentosa×P.bolleana)], and the triploid clone B346 [(P.tomentosa×P. bolleana)×(P. alba×P.glandulosa)], under light stress were studied using photoacoustics. The oxygen evolution signal and photochemical energy storage varied negatively with the pretreatment_PFD (photon flux density), whereas the thermal signal varied positively with the pretreatment_PFD. Photochemical energy storage was reallocated to PSⅡ more than to PSⅠ, while the photochemical energy storage in PSⅠ was more stable than that in PSⅡ when subjected to light stress. The inhibitors streptomycin (SM), dithiothreitol (DTT) and sodium fluoride (NaF) could all affect the oxygen evolution signal. Clones B11 and B342 were more resistant to light stress than clone B346.