Photoacoustic effect invokes auditory response in infrared neuron stimulation

Infrared neuron stimulation is regarded as an innovative approach for stimulating cochleae in animals while the exact mechanism still remains unknown.In this paper,we studied compound action potentials of guinea pig cochleae with chronic or acute deafness.We recorded optical compound action potentials and analyzed stretched cochlear preparations by fiuorescence microscopy.Photoacoustic signals were measured by hydrophone and microphone,respectively.In our experiment,we observed a switch response effect in vitro and in vivo experiments.Therefore,we proposed photoacoustic effect could invoke auditory response in infrared neuron stimulation.

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.

Detecting Photoacoustic Signals of Sulfur Hexafluoride at Varying Microphone Positions

Photoacoustic spectroscopy was used to test the photoacoustic properties of sulfur hexafluoride, an optically thick and potent greenhouse gas. While exploring the photoacoustic effect of sulfur hexafluoride, the effects of the position of the microphone within a gas cell were determined. Using a 35 cm gas cell, microphones were positioned at 17.5 cm, the middle of the gas cell, 12.5 cm, 7.5 cm, and 2.5 cm from the window of the cell. From the photoacoustic signal produced for each resonance frequency at each microphone position, the effects of acoustic pressure produced at each position on the signal recorded were observed. This is the first study done by experimentation with the photoacoustic effect to show that standing waves have different amplitudes at different microphone positions.

Comparison of the effects of water temperature on the photoacoustic signals

Acoustic impulses produced through the mechanism of the laser-induced breakdown in water have been investigated in the range from 0℃ to room temperature. Differently from the acoustic impulses produced via thermal expansion, the polarity and the amplitude of acoustic impulse produced via liquid breakdown mechanism do not change with water temperature. This indirectly proves that the production of acoustic impulse is due to the expansion of the cavity itself which includes plasma. A semiempirical description of this phenomenon is given in this paper.

Photoacoustic spectroscopy for fast and sensitive ammonia detection

A photoacoustic （PA） spectrometer with H-type first longitudinal resonant cells for ammonia detection is developed. A new PA cell structure is designed to accelerate the drift velocity of the sample gas near the cell surface, so that the short response time at the flow rate of 100 seem （standard cubic centimeter per minute） is achieved. The response time of 5 min and detection limit of 0.86 ppbv is reached for ammonia concentration measurement with a Teflon polytetrafluoroethylene （PTFE） cell. Further improvement could be expected when using a brass cell with a high quality Teflon fluorinated ethylene propylene （FEP） coating.

High-resolution photoacoustic microscope for rat brain imaging in vivo

A reflection-mode photoacoustic microscope（PAM） for rat brain imaging in vivo is constructed.A pulsed laser is used as an excitation source,and a focused ultrasound transducer is adopted to collect the photoacoustic signal.Raster scanning is applied to acquire three-dimensional（3D） data.The obtained measurements of the lateral and axial resolutions of the microscope are 45 and 15μm,respectively.The imaging depth in the chicken breast tissue is 3.1 mm at a signal-to-noise ratio（SNR） of 20 dB without any signal averaging.The imaging speed is 30 A-line/s.Experimental results in vivo demonstrate the capability of 3D imaging of the brain vessels of the rat after removing the skull.

Feasibility of photoacoustic tomography for ophthalmology

For the eyeball composed of membrane and liquid, the contrast of ultrasound imaging is not high due to its small variance in acoustic impedance. As a new imaging modality, photoacoustic tomography combines the advantages of pure optical and ultrasonic imaging together and can provide high resolution, high contrast images. In this paper, the feasibility of photoacoustic tomography for ophthalmology is studied experimentally. A Q-switched Nd：YAG pulsed laser with 7-ns pulse width is used to generate photoacoustic signal of a porcine eyeball in vitro. The two-dimensional （2D） optical absorption image of the entire eyeball is reconstructed by time-domain spherical back projection algorithm. The imaging results agree well with the histological structure of the eyeball and show a high imaging contrast.

Noninvasive photoacoustic measurement of absorption coefficient using internal light irradiation of cylindrical diffusing fiber

Absorption coefficient of biological tissue is an important parameter in biomedicine, but its determination remains a challenge. In this paper, we propose a method using focusing photoacoustic imaging technique and internal light irradiation of cylindrical diffusing fiber(CDF) to quantify the target optical absorption coefficient. Absorption coefficients for ink absorbers are firstly determined through photoacoustic and spectrophotometric measurements at the same excitation, which demonstrates the feasibility of this method. Also, the optical absorption coefficients of ink absorbers with several concentrations are measured. Finally, the two-dimensional scanning photoacoustic image is obtained. Optical absorption coefficient measurement and simultaneous photoacoustic imaging of absorber non-invasively are the typical characteristics of the method. This method can play a significant role for non-invasive determination of blood oxygen saturation, the absorption-based imaging and therapy.

Photoacoustic image reconstruction based on Bayesian compressive sensing algorithm

The photoacoustic tomography （PAT） method, based on compressive sensing （CS） theory, requires that, for the CS reconstruction, the desired image should have a sparse representation in a known transform domain. However, the sparsity of photoacoustic signals is destroyed because noises always exist. Therefore, the original sparse signal cannot be effectively recovered using the general reconstruction algorithm. In this study, Bayesian compressive sensing （BCS） is employed to obtain highly sparse representations of photoacoustic images based on a set of noisy CS measurements. Results of simulation demonstrate that the BCS-reconstructed image can achieve superior performance than other state-of-the-art CS-reconstruction algorithms.

Simulation of light delivery for photoacoustic breast imaging using the handheld probe

The photoacoustic tomography by using the handheld probe has a great potential in clinical breast imag- ing. However, tile shape of the probe limits the choice of light delivery in this setup. In this letter, we study two commonly used illumination types for handheld probe： bright-field illumination and dark-field illumination. Our results demonstrate several parameters have important impact on the photon fluence in deep breast tissue. The results will help to optimize the design of the photoaeoustie breast imaging system with a handheld probe.

Adaptive multi-sample-based photoacoustic tomography with imaging quality optimization

The energy of light exposed on human skin is compulsively limited for safety reasons which affects the power of photoacoustic （PA） signal and its signal-to-noise ratio （SNR） level. Thus, the final reconstructed PA image quality is degraded. This Letter proposes an adaptive multi-sample-based approach to enhance the SNR of PA signals and in addition, detailed information in rebuilt PA images that used to be buried in the noise can be distinguished. Both ex vivo and in vivo experiments are conducted to validate the effectiveness of our proposed method which provides its potential value in clinical trials.

Ultraefficient thermoacoustic conversion through a split ring resonator

Microwaves,which have a∼10-cm wavelength,can penetrate deeper into tissue than photons,heralding exciting deep tissue applications such as modulation or imaging via the thermoacoustic effect.Thermoacoustic conversion efficiency is however very low,even with an exogenous contrast agent.We break this low-conversion limit,using a split ring resonator to effectively collect and confine the microwaves into a submillimeter hot spot for ultrasound emission and achieve a conversion efficiency over 2000 times higher than other reported thermoacoustic contrast agents.Importantly,the frequency of emitted ultrasound can be precisely tuned and multiplexed by modulation of the microwave pulses.Such performance is inaccessible by a piezoelectric-based transducer or a photoacoustic emitter and,therefore,split ring resonators open up new opportunities to study the frequency response of cells in ultrasonic biomodulation.For applications in deep tissue localization,a split ring resonator can be used as a wireless,battery-free ultrasound beacon placed under a breast phantom.