Photoacoustic Imaging
Courtesy of PhotoSound Technologies, Inc.

Photoacoustic imaging is a valuable high-contrast in vivo imaging technique for pre-clinical and clinical applications. This technique uses laser-induced ultrasound.

Ultrasound signal is generated in tissue, when it absorbs tunable wavelength laser light and expands thermo-elastically,  and their waves are detected by ultrasonic transducers. 2D or 3D images are then reconstructed from the accumulated data.

Laser sources for photoacoustic imaging include lamp-pumped tunable wavelength and diode-pumped solid-state (DPSS) tunable wavelength  OPO systems.


Found total :
40 articles, 40 selected
Product selected :
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Tunable Wavelength Devices – standalone and integrated OPO sytems
NT350 series – high energy NIR range tunable lasers
PhotoSonus M – mobile high energy tunable wavelength laser system for photoacoustic imaging
PhotoSonus T – high energy table-top tunable wavelength lasers for photoacoustic imaging
PhotoSonus X – high output power DPSS tunable laser for photoacoustic imaging
NT242 series – broadly tunable kHz pulsed DPSS lasers
NT270 series – tunable wavelength NIR-IR range DPSS lasers
NT342 series – high energy broadly tunable lasers
NT230 series – high energy broadly tunable DPSS lasers
Nanosecond Lasers
NL230 series – high energy Q-switched DPSS Nd:YAG lasers
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Photoacoustic tomography with a model-based approach involving realistic detector properties

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Authors:  P. Warbal, and R. K. Saha

A computational and experimental study is conducted to examine how directivity associated with a finite aperture sensor affects photoacoustic tomography (PAT) image reconstruction. Acoustic signals for the simulation work were computed using a discrete particle approach from three numerical phantoms including a vasculature. The theoretical framework and a Monte Carlo approach for construction of a tissue configuration are discussed in detail. While simulating forward data, the directivity of the sensor was taken into account. The image reconstruction was accomplished using system matrix based methods like l2 norm Tikhonov regularization, l1 norm regularization and total variation (TV) minimization. Accordingly, two different system matrices were constructed- (i) assuming transducer as a point detector (PD) and (ii) retaining properties of a finite detector with directivity (FDWD). Image reconstruction was also performed utilizing experimentally measured PA signals. Both the computational and experimental results demonstrate that blur-free PAT imaging can be achieved with the FDWD method. Additionally, TV minimization provides marginally better image reconstruction compared to the other schemes.

Published: 2023.   Source: Results in Optics 13, 100528 (2023)

LED-based Schlieren system for full-field photoacoustic wave acquisition and image reconstruction

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Authors:  Y. Ojeda‑Morales, D. Hernandez‑Lopez, and G. Martínez‑Ponce

In this work, full-field detection of laser-induced ultrasound waves was performed with an off-axis LED-based Schlieren system. Sensing strobe light, pulsed laser dual light-sheet excitation, and CMOS sensor device were all synchronized to capture the pressure wave as it propagated through an elastic liquid surrounding the test sample. In addition, a reconstruction algorithm based on the Radon transform was applied to the digitally recorded field in order to obtain an image of the photoacoustic source. The proposed system is capable of retrieving the profile of cylindrical and hexagonal targets.

Published: 2023.   Source: Opt. Continuum 9 (2), 2007-2016 (2023)

Fully three-dimensional sound speed-corrected multi-wavelength photoacoustic breast tomography

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Authors:  M. Dantuma, F. Lucka, S. C. Kruitwagen, A. Javaherian, L. Alink, R. P. P. van Meerdervoort, M. Nanninga, T. J. P. M. Op't Root, B. D. Santi, J. Budisky et al.

Photoacoustic tomography is a contrast agent-free imaging technique capable of visualizing blood vessels and tumor-associated vascularization in breast tissue. While sophisticated breast imaging systems have been recently developed, there is yet much to be gained in imaging depth, image quality and tissue characterization capability before clinical translation is possible. In response, we have developed a hybrid photoacoustic and ultrasound-transmission tomographic system PAM3. The photoacoustic component has for the first time three-dimensional multi-wavelength imaging capability, and implements substantial technical advancements in critical hardware and software sub-systems. The ultrasound component enables for the first time, a three-dimensional sound speed map of the breast to be incorporated in photoacoustic reconstruction to correct for inhomogeneities, enabling accurate target recovery. The results demonstrate the deepest photoacoustic breast imaging to date namely 48 mm, with a more uniform field of view than hitherto, and an isotropic spatial resolution that rivals that of Magnetic Resonance Imaging. The in vivo performance achieved, and the diagnostic value of interrogating angiogenesis-driven optical contrast as well as tumor mass sound speed contrast, gives confidence in the system's clinical potential.

Published: 2023.   Source:

Microfluidic Fabrication of Highly Efficient Hydrogel Optical Fibers for In Vivo Fiber-Optic Applications

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Authors:  G. Fitria, M. Kwon, H. Lee, A. Singh, K. Yoo, Y. Go, J. Kim, K. S. Kim, and J. Yoon

Abstract Although efficient light delivery is required for various biomedical applications, the high stiffness of traditional silica-based optical fibers limits their in vivo usage. In this study, highly deformable and stretchable soft optical fibers are prepared based on the mechanically tough hydrogels of a double network (DN) structure comprising covalently crosslinked acrylamide and ionically crosslinked alginate using a microfluidic device. Owing to the optimized chemical composition, the core/cladding structure, and the mechanical robustness of the prepared hydrogel optical fibers, highly efficient optical delivery is achieved even at highly deformed and elongated states. Furthermore, the microfluidic device further allowed the formation of dual-core, novel architectures for hydrogel optical fibers. With the aid of the dopamine moiety included in the cladding, the hydrogel optical fibers attached strongly to all surfaces tested. Light delivery is further confirmed by implantation in the biological tissues. The high light-guiding performance of the developed hydrogel optical fibers enables them to replace the conventional silica optical fibers used in UV/Vis, fluorescence, and photoacoustic spectroscopies. To demonstrate their in vivo fiber-optic application potential, they are placed inside mice, and the excitation and emission of the generated fluorescence signals are detected.

Published: 2023.   Source: Advanced Optical Materials 18 (11), 2300453 (2023)

Fast photoacoustic imaging technology for deep structure information of finger

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Authors:  T. Meng, H. Li, and Y. Liu

In this paper, we exploited the fast-imaging technology for the deep structure of finger based on photoacoustic imaging, which adopted the self-designed 128-ring-array fast photoacoustic imaging system to acquire the latent inside information of finger. The home-made photoacoustic imaging system has the merits of fast imaging, high resolution and deep imaging depth. Specifically, our system could obtain a cross section scan of finger within 0.05 or 0.1s, achieve the resolution of approach 180 μm and image the latent inside information of finger as well as extend the imaging depth over 5 cm in chicken breast tissue at the laser density of 20 mJ/cm2 (≤ANSI safety limit). In this work, we obtained the finger anatomical information of skin tissue, blood vessel tissue, and the information of tendon tissue and phalanx tissue which is relatively difficult to obtain by means of photoacoustic imaging. So, we will be able to restore an overall internal structure of a finger including its external shape its internal tendon structure and its internal phalanx structure or containing its blood vessel structure. And that more information from different angles can make its identification more accurate. It is prospective that the deep structure of finger we get by our fast photoacoustic imaging technology will help to provide more possibilities for finger identification and lead to more credible technology for human about relevant information collection and resolution.

Published: 2023.   Source: in Ninth Symposium on Novel Photoelectronic Detection Technology and Applications, J. Chu, W. Liu, and H. Xu, eds. (SPIE, 2023), pp. 126176E.

Characterizing a photoacoustic and fluorescence imaging platform for preclinical murine longitudinal studies

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Authors:  W. R. Thompson, H. F. Brecht, V. Ivanov, A. M. Yu, D. S. Dumani, D. J. Lawrence, S. Y. Emelianov, and S. A. Ermilov

Significance. To effectively study preclinical animal models, medical imaging technology must be developed with a high enough resolution and sensitivity to perform anatomical, functional, and molecular assessments. Photoacoustic (PA) tomography provides high resolution and specificity, and fluorescence (FL) molecular tomography provides high sensitivity; the combination of these imaging modes will enable a wide range of research applications to be studied in small animals.

Aim. We introduce and characterize a dual-modality PA and FL imaging platform using in vivo and phantom experiments.

Approach. The imaging platform’s detection limits were characterized through phantom studies that determined the PA spatial resolution, PA sensitivity, optical spatial resolution, and FL sensitivity.

Results. The system characterization yielded a PA spatial resolution of 173 ± 17 μm in the transverse plane and 640 ± 120 μm in the longitudinal axis, a PA sensitivity detection limit not less than that of a sample with absorption coefficient μa = 0.258 cm − 1, an optical spatial resolution of 70 μm in the vertical axis and 112 μm in the horizontal axis, and a FL sensitivity detection limit not <0.9 μM concentration of IR-800. The scanned animals displayed in three-dimensional renders showed high-resolution anatomical detail of organs.

Conclusions. The combined PA and FL imaging system has been characterized and has demonstrated its ability to image mice in vivo, proving its suitability for biomedical imaging research applications.

Published: 2023.   Source: Journal of Biomedical Optics 3 (28), 036001 (2023)

Bimetallic Hyaluronate-Modified Au@Pt Nanoparticles for Noninvasive Photoacoustic Imaging and Photothermal Therapy of Skin Cancer

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Authors:  H. H. Han, S. Kim, J. Kim, W. Park, C. Kim, H. Kim, and S. K. Hahn

Although spherical gold (Au) nanoparticles have remarkable photothermal conversion efficiency and photostability, their weak absorption in the near-infrared (NIR) region and poor penetration into deep tissues have limited further applications to NIR light-mediated photoacoustic (PA) imaging and noninvasive photothermal cancer therapy. Here, we developed bimetallic hyaluronate-modified Au–platinum (HA-Au@Pt) nanoparticles for noninvasive cancer theranostics by NIR light-mediated PA imaging and photothermal therapy (PTT). The growth of Pt nanodots on the surface of spherical Au nanoparticles enhanced the absorbance in the NIR region and broadened the absorption bandwidth of HA-Au@Pt nanoparticles by the surface plasmon resonance (SPR) coupling effect. In addition, HA facilitated the transdermal delivery of HA-Au@Pt nanoparticles through the skin barrier and enabled clear tumor-targeted PA imaging. Compared to conventional PTT via injection, HA-Au@Pt nanoparticles were noninvasively delivered into deep tumor tissues and completely ablated the targeted tumor tissues by NIR light irradiation. Taken together, we could confirm the feasibility of HA-Au@Pt nanoparticles as a NIR light-mediated biophotonic agent for noninvasive skin cancer theranostics.

Published: 2023.   Source: ACS Applied Materials & Interfaces 9 (15), 11609-11620 (2023)

Theoretical and experimental comparison of the performance of gold, titanium, and platinum nanodiscs as contrast agents for photoacoustic imaging

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Authors:  J. Wi, J. Kim, M. Y. Kim, S. Choi, H. J. Jung, C. Kim, and H. Na

Exogenous contrast agents in photoacoustic imaging help improve spatial resolution and penetration depth and enable targeted molecular imaging. To screen efficient photoacoustic signaling materials as contrast agents, we propose a light absorption-weighted figure of merit (FOM) that can be calculated using material data from the literature and numerically simulated light absorption cross-sections. The calculated light absorption-weighted FOM shows that a Ti nanodisc has a photoacoustic conversion performance similar to that of an Au nanodisc and better than that of a Pt nanodisc. The photoacoustic imaging results of Ti, Au, and Pt nanodiscs, which are physically synthesized with identical shapes and dimensions, experimentally demonstrated that the Ti nanodisc could be a highly efficient contrast agent.

Published: 2023.   Source: RSC Adv. 13, 9441-9447

Wide-field three-dimensional photoacoustic/ultrasound scanner using a two-dimensional matrix transducer array

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Authors:  W. Kim, W. Choi, J. Ahn, C. Lee, and C. Kim

Two-dimensional matrix transducer arrays are the most appropriate imaging probes for acquiring dual-modal 3D photoacoustic (PA)/ultrasound (US) images. However, they have small footprints which limit the field-of-view (FOV) to less than 10 mm × 10 mm and degrade the spatial resolution. In this study, we demonstrate a dual-modal PA and US imaging system (using a 2D matrix transducer array and a motorized 2D scanning system) to enlarge the FOV of volumetric images. Multiple PA volumes were merged to form a wide-field image of approximately 45 mm × 45 mm. In vivo imaging was demonstrated using rat sentinel lymph nodes (SLNs) and bladders stained with methylene blue. We believe that this volumetric PA/US imaging technique with a 2D matrix transducer array can be a useful tool for narrow-field real-time monitoring and wide-field imaging of various preclinical and clinical studies.

Published: 2023.   Source: Opt. Lett. 48, 343-346 (2023)

An Investigation of Signal Preprocessing for Photoacoustic Tomography

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Authors:  I. Huen, R. Zhang, R. Bi, X. Li, M. Moothanchery and M. Olivo

Photoacoustic tomography (PAT) is increasingly being used for high-resolution biological imaging at depth. Signal-to-noise ratios and resolution are the main factors that determine image quality. Various reconstruction algorithms have been proposed and applied to reduce noise and enhance resolution, but the efficacy of signal preprocessing methods which also affect image quality, are seldom discussed. We, therefore, compared common preprocessing techniques, namely bandpass filters, wavelet denoising, empirical mode decomposition, and singular value decomposition. Each was compared with and without accounting for sensor directivity. The denoising performance was evaluated with the contrast-to-noise ratio (CNR), and the resolution was calculated as the full width at half maximum (FWHM) in both the lateral and axial directions. In the phantom experiment, counting in directivity was found to significantly reduce noise, outperforming other methods. Irrespective of directivity, the best performing methods for denoising were bandpass, unfiltered, SVD, wavelet, and EMD, in that order. Only bandpass filtering consistently yielded improvements. Significant improvements in the lateral resolution were observed using directivity in two out of three acquisitions. This study investigated the advantages and disadvantages of different preprocessing methods and may help to determine better practices in PAT reconstruction.

Published: 2023.   Source: Sensors 2023, 23, 510

Size-tunable ICG-based contrast agent platform for targeted near-infrared photoacoustic imaging

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Authors:  S. Singh, G. Giammanco, C.. Hu, J. Bush, L.S. Cordova, D.J. Lawrence, J.L. Moran, P.V. Chitnis, R. Veneziano

Near-infrared photoacoustic imaging (NIR-PAI) combines the advantages of optical and ultrasound imaging to provide anatomical and functional information of tissues with high resolution. Although NIR-PAI is promising, its widespread use is hindered by the limited availability of NIR contrast agents. J-aggregates (JA) made of indocyanine green dye (ICG) represents an attractive class of biocompatible contrast agents for PAI. Here, we present a facile synthesis method that combines ICG and ICG-azide dyes for producing contrast agents with tunable size down to 230 nm and direct functionalization with targeting moieties. The ICG-JA platform has a detectable PA signal in vitro that is two times stronger than whole blood and high photostability. The targeting ability of ICG-JA was measured in vitro using HeLa cells. The ICG-JA platform was then injected into mice and in vivo NIR-PAI showed enhanced visualization of liver and spleen for 90 min post-injection with a contrast-to-noise ratio of 2.42.

Published: 2022.   Source: Photoacoustics, Volume 29, 2023, 100437, ISSN 2213-5979

Utilising nanosecond sources in diffuse optical tomography

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Authors:  M. Mozumder, J. Leskinen, and T. Tarvainen

Diffuse optical tomography (DOT) use near-infrared light for imaging optical properties of biological tissues. Time-domain (TD) DOT systems use pulsed lasers and measure time-varying temporal point spread function (TPSF), carrying information from both superficial and deep layers of imaged target. In this work, feasibility of nanosecond scale light pulses as sources for TD-DOT is studied. Nanosecond sources enable using relatively robust measurement setups with standard analogue-to-digital converter waveform digitizers, such as digital oscilloscopes. However, this type of systems have some properties, such as variations in source pulses and limited temporal sampling, that could limit their usage. In this work, these different aspects and possible limitations were studied with simulations and experiments. Simulations showed that information carried by TD data of diffuse medium is on low frequencies. This enables usage of relatively slow response time measurement electronics, and image processing using Fourier-transformed TD data. Furthermore, the temporal sampling in measurements needs to be high enough to capture the TPSF, but this rate can be achieved with standard digital oscilloscopes. It was shown that, although variations in light pulses of nanosecond lasers are larger than those of picosecond sources, these variations do not affect significantly on image quality. Overall, the simulations demonstrated the capability of nanosecond sources to be utilised in TD-DOT in diffuse medium. In this work, a prototype TD-DOT experimental system utilising a high-energy nanosecond laser was constructed. The system is relatively robust consisting of a nanosecond Nd:YAG laser combined with optical parametric oscillator for light input and optical fibres for guiding the light, and avalanche photodetector and high-bandwidth oscilloscope for TPSF measurements. The system was used in both absolute and difference imaging of two phantoms. The experiments verified that both absorbing and scattering objects can be reconstructed with good accuracy with TD-DOT using a nanosecond laser.

Published: 2022.   Source: Measurement Science and Technology 2 (34), 025901 (2022)

Deep Learning Enhances Multiparametric Dynamic Volumetric Photoacoustic Computed Tomography In Vivo (DL-PACT)

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Authors:  S. Choi, J. Yang, S.Y. Lee, J. Kim, J. Lee, W.J. Kim, S. Lee and C. Kim

Photoacoustic computed tomography (PACT) has become a premier preclinical and clinical imaging modality. Although PACT's image quality can be dramatically improved with a large number of ultrasound (US) transducer elements and associated multiplexed data acquisition systems, the associated high system cost and/or slow temporal resolution are significant problems. Here, a deep learning-based approach is demonstrated that qualitatively and quantitively diminishes the limited-view artifacts that reduce image quality and improves the slow temporal resolution. This deep learning-enhanced multiparametric dynamic volumetric PACT approach, called DL-PACT, requires only a clustered subset of many US transducer elements on the conventional multiparametric PACT. Using DL-PACT, high-quality static structural and dynamic contrast-enhanced whole-body images as well as dynamic functional brain images of live animals and humans are successfully acquired, all in a relatively fast and cost-effective manner. It is believed that the strategy can significantly advance the use of PACT technology for preclinical and clinical applications such as neurology, cardiology, pharmacology, endocrinology, and oncology.

Published: 2022.   Source: Adv. Sci. 2022, 10, 2202089

Carbon Nanotube Microscale Fiber Grid as an Advanced Calibration System for Multispectral Optoacoustic Imaging

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Authors:  M. R. Chetyrkina, J. Cvjetinovic, F. S. Fedorov, S. V. Perevoschikov, E. S. Prikhozhdenko, B. F. Mikladal, Y. G. Gladush, A. G. Nasibulin, and D. A. Gorin

Optoacoustic (photoacoustic) imaging has gained tremendous attention in research and in clinical practice as a point-of-care system for noninvasive, fast, and safe tests. The first optoacoustic (OA) tomograph has recently passed the Food and Drug Administration (FDA) approval stage for clinical applications aimed at early breast cancer diagnostics. Furthermore, a broad application of OA imaging for Biomedical and Materials Science fields requires a proper tool to test the equipment and verify the quality of the measurements on a daily basis. In the present work, we propose fibers based on single-walled carbon nanotubes (SWCNTs) as a material for designing a stable and reliable calibration grid. The main advantage of the developed test system is the broad optical absorption of SWCNT-based fibers, ranging from visible to mid-infrared regions. Inspired by stringed instruments, we elaborate a grid to calibrate and verify spatial resolution in three projections and sensitivity of OA imaging systems. Thus, the real calibration grid parameters, such as fiber length and diameter, could be translated to the OA signal measurements. This proof-of-the-concept study evaluates the geometry of fibers, that is, the length/diameter and design of fibers, such as free-standing/twisted, and shows the fabrication procedure of the calibration grid prototype toward the successful validation of the OA imaging system, including raster-scanning optoacoustic mesoscopy (RSOM) at one wavelength and tomography at several wavelengths, which have grand prospects in preclinical and clinical practices. Besides, the more advanced geometry based on double-twisted fibers, or twistrons, applied here provided us with a chance to reach the lower resolution limit for RSOM because of the difference in diameter between the thin and thick parts in the morphology is verified by scanning electron microscopy.

Published: 2022.   Source: ACS Photonics 10 (9), 3429-3439 (2022).

Tissue photothermal effect based on photoacoustic temperature feedback control

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Authors:  Y. Zhang, X. Chu, W. Cao, S. Wu, H. Lin, and Z. Li

Hotothermal therapy (PTT) is an alternative to surgery, which is commonly used to treat tumors in intracavitary organs. PTT involves heating the diseased tissue with radiation energy, resulting in tumor necrosis. In order to improve the safety and effectiveness of PT, it is necessary to monitor the tissue temperature in real time and regulate the laser power during PTT. Photoacoustic imaging (PAI) is a non-invasive and non-ionizing imaging method with high resolution and high accuracy. Due to the dependence of the thermal expansion coefficient on temperature, the Grüneisen parameter is linearly proportional to temperature, and the variation of the amplitude of the photoacoustic signal is related to the variation of the Grüneisen parameter. In this study, we propose a system for laser dose regulation with photoacoustic signal temperature feedback based on PID algorithm. The pulsed laser is irradiated on the sample surface, the ultrasonic probe receives the photoacoustic signal generated by the sample, and the photoacoustic signal is collected by the oscilloscope and transmitted to the computer, which generates the corresponding command to the heating laser according to the signal and changes the output power of the heating laser. The experimental results show that this method can effectively control the photothermal damage range.

Published: 2022.   Source: in 5th Optics Young Scientist Summit (OYSS 2022), C. Lu, Y. Cai, F. Chen et al., eds. (SPIE, 2022), pp. 124480U.

Opposing effects of energy migration and cross-relaxation on surface sensitivity of lanthanide-doped nanocrystals

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Authors:  J. Fan, L. Liang, Y. Gu, and X. Liu

Surface sensitivity of lanthanide-doped nanocrystals has a great utility in controlling their optical properties. Surface sensitivity can be principally promoted by energy migration. Herein, we demonstrate that cross-relaxation between lanthanides makes nanocrystals less sensitive to environmental changes. We show that by codoping ytterbium ions (Yb3+) and neodymium ions (Nd3+) in hexagonal-phase sodium yttrium fluorides, surface sensitivity can be manipulated by energy transfer from Yb3+ to Nd3+. These findings enhance our understanding of surface quenching of nanocrystals and offer new opportunities in developing highly luminous nanoprobes for molecular sensing and biomedical applications.

Published: 2021.   Source: Optical Materials: X 12, 100104 (2021)

Computationally Efficient Forward Operator for Photoacoustic Tomography Based on Coordinate Transformations

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Authors:  T. Sahlström, A. Pulkkinen, J. Leskinen, and T. Tarvainen

Photoacoustic tomography (PAT) is an imaging modality that utilizes the photoacoustic effect. In PAT, a photoacoustic image is computed from measured data by modeling ultrasound propagation in the imaged domain and solving an inverse problem utilizing a discrete forward operator. However, in realistic measurement geometries with several ultrasound transducers and relatively large imaging volume, an explicit formation and use of the forward operator can be computationally prohibitively expensive. In this work, we propose a transformation-based approach for efficient modeling of photoacoustic signals and reconstruction of photoacoustic images. In the approach, the forward operator is constructed for a reference ultrasound transducer and expanded into a general measurement geometry using transformations that map the formulated forward operator in local coordinates to the global coordinates of the measurement geometry. The inverse problem is solved using a Bayesian framework. The approach is evaluated with numerical simulations and experimental data. The results show that the proposed approach produces accurate 3-D photoacoustic images with a significantly reduced computational cost both in memory requirements and time. In the studied cases, depending on the computational factors, such as discretization, over the 30-fold reduction in memory consumption was achieved without a reduction in image quality compared to a conventional approach.

Published: 2021.   Source: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 6 (68), 2172-2182 (2021)

Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright

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Authors:  S. Han, R. Deng, Q. Gu, L. Ni, U. Huynh, J. Zhang, Z. Yi, B. Zhao, H. Tamura, A. Pershin et al.

The generation, control and transfer of triplet excitons in molecular and hybrid systems is of great interest owing to their long lifetime and diffusion length in both solid-state and solution phase systems, and to their applications in light emission1, optoelectronics, photon frequency conversion and photocatalysis. Molecular triplet excitons (bound electron–hole pairs) are ‘dark states’ because of the forbidden nature of the direct optical transition between the spin-zero ground state and the spin-one triplet levels. Hence, triplet dynamics are conventionally controlled through heavy-metal-based spin–orbit coupling or tuning of the singlet–triplet energy splitting via molecular design. Both these methods place constraints on the range of properties that can be modified and the molecular structures that can be used. Here we demonstrate that it is possible to control triplet dynamics by coupling organic molecules to lanthanide-doped inorganic insulating nanoparticles. This allows the classically forbidden transitions from the ground-state singlet to excited-state triplets to gain oscillator strength, enabling triplets to be directly generated on molecules via photon absorption. Photogenerated singlet excitons can be converted to triplet excitons on sub-10-picosecond timescales with unity efficiency by intersystem crossing. Triplet exciton states of the molecules can undergo energy transfer to the lanthanide ions with unity efficiency, which allows us to achieve luminescent harvesting of the dark triplet excitons. Furthermore, we demonstrate that the triplet excitons generated in the lanthanide nanoparticle–molecule hybrid systems by near-infrared photoexcitation can undergo efficient upconversion via a lanthanide–triplet excitation fusion process: this process enables endothermic upconversion and allows efficient upconversion from near-infrared to visible frequencies in the solid state. These results provide a new way to control triplet excitons, which is essential for many fields of optoelectronic and biomedical research.

Published: 2020.   Source: Nature 587, 594–599 (2020)

Optoacoustic brain stimulation at submillimeter spatial precision

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Authors:  Y. Jiang, H.J. Lee, L. Lan, H. Tseng, Ch. Yang, H. Man, X. Han, J. Cheng

Low-intensity ultrasound is an emerging modality for neuromodulation. Yet, transcranial neuromodulation using low-frequency piezo-based transducers offers poor spatial confinement of excitation volume, often bigger than a few millimeters in diameter. In addition, the bulky size limits their implementation in a wearable setting and prevents integration with other experimental modalities. Here, we report spatially confined optoacoustic neural stimulation through a miniaturized Fiber-Optoacoustic Converter (FOC). The FOC has a diameter of 600 μm and generates omnidirectional ultrasound wave locally at the fiber tip through the optoacoustic effect. We show that the acoustic wave generated by FOC can directly activate individual cultured neurons and generate intracellular Ca2+ transients. The FOC activates neurons within a radius of 500 μm around the fiber tip, delivering superior spatial resolution over conventional piezo-based low-frequency transducers. Finally, we demonstrate direct and spatially confined neural stimulation of mouse brain and modulation of motor activity in vivo.

Published: 2020.   Source: Nature Communications volume 11, Article number: 881 (2020)

High-resolution multimodal photoacoustic microscopy and optical coherence tomography image-guided laser induced branch retinal vein occlusion in living rabbits

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Authors:  V.P. Nguyen, Y. Li, W. Zhang, X. Wang, Y. M. Paulus

Joint high-resolution multimodal photoacoustic microscopy (PAM) and optical coherence tomography (OCT) was developed to improve the efficiency for visualizing newly developed retinal neovascularization (RNV) and to monitor the dynamic changes of retinal vein occlusion (RVO) in living rabbits. The RNV and RVO models were created in New Zealand rabbits by Rose Bengal laser-induced RVO. Dual modalities imaging equipment, including color fundus photography, fluorescein angiography (FA), OCT, and PAM, was used to image and assess the changes of retinal vasculature. In vivo experimental results exhibited that not only the treatment boundaries and the position of the occluded vasculature but also the structure of individual RNV were markedly observed using PAM platform with great resolution and high image contrast. The laser light energy of 80 nJ was used to induce photoacoustic signal, which is approximately half the energy of the American National Standards Institute safety limit. A cross-sectional structure of RNV was identified with the OCT modality. Furthermore, vibrant transformations in the RNV and the retinal morphology were examined at different times after laser occlusion: days 4, 28, 35, 49, and 90. PAM revealed high contrast and high resolution vascular imaging of the retina and choroid with amplified penetration depth. Through the present custom-built imaging system, both RNV and RVO can be reconstructed and observed in two and three dimensions. A unique dual modality A unique dual modality PAM and OCT can help precisely visualize and distinguish individual microvessels, microvessel depth, and the surrounding anatomy. Thus, the proposed multimodal ocular imaging platform may offer a potential equipment to enhance classification of microvasculature in a reliable and proficient manner in larger rabbit eyes.

Published: 2019.   Source: Scientific Reports 9, 10560 (2019)

Probing intervertebral discs with PhotoAcoustics

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Authors:  K. Metwally, O. Boiron, V. Deplano, S. Prost, and A. D. Silva

Photoacoustic measurements are tested as a possible tool for non invasive quantification of Water/Collagen relative content in InterVertebral Discs (IVDs).

Published: 2019.   Source: In Opto-Acoustic Methods and Applications in Biophotonics IV, (Optica Publishing Group, 2019), pp. 11077_61

Photoacoustic/Ultrasound/Optical Coherence Tomography Evaluation of Melanoma Lesion and Healthy Skin in a Swine Model

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Authors:  K. Kratkiewicz, R. Manwar, A. Rajabi-Estarabadi, J. Fakhoury, J. Meiliute, S. Daveluy, D. Mehregan, and K. (Mohammad) Avanaki

The marked increase in the incidence of melanoma coupled with the rapid drop in the survival rate after metastasis has promoted the investigation into improved diagnostic methods for melanoma. High-frequency ultrasound (US), optical coherence tomography (OCT), and photoacoustic imaging (PAI) are three potential modalities that can assist a dermatologist by providing extra information beyond dermoscopic features. In this study, we imaged a swine model with spontaneous melanoma using these modalities and compared the images with images of nearby healthy skin. Histology images were used for validation.

Published: 2019.   Source: Sensors. 2019; 19(12):2815

High-resolution, high-contrast mid-infrared imaging of fresh biological samples with ultraviolet-localized photoacoustic microscopy

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Authors:  Junhui Shi, Terence T. W. Wong, Yun He, Lei Li, Ruiying Zhang, Christopher S. Yung, Jeeseong Hwang, Konstantin Maslov, Lihong V. Wang

Mid-infrared (MIR) microscopy provides rich chemical and structural information about biological samples, without staining. Conventionally, the long MIR wavelength severely limits the lateral resolution owing to optical diffraction; moreover, the strong MIR absorption of water ubiquitous in fresh biological samples results in high background and low contrast. To overcome these limitations, we propose a method that employs photoacoustic detection highly localized with a pulsed ultraviolet laser on the basis of the Grüneisen relaxation effect. For cultured cells, our method achieves water-background suppressed MIR imaging of lipids and proteins at ultraviolet resolution, at least an order of magnitude finer than the MIR diffraction limits. Label-free histology using this method is also demonstrated in thick brain slices. Our approach provides convenient high-resolution and high-contrast MIR imaging, which can benefit the diagnosis of fresh biological samples.

Published: 2019.   Source: Nature Photonics, vol. 13, pp. 609–615 (2019)

Photoacoustic imaging in the second near-infrared window: a review

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Authors:  P. K. Upputuri, and M. Pramanik

Photoacoustic (PA) imaging is an emerging medical imaging modality that combines optical excitation and ultrasound detection. Because ultrasound scatters much less than light in biological tissues, PA generates high-resolution images at centimeters depth. In recent years, wavelengths in the second near-infrared (NIR-II) window (1000 to 1700 nm) have been increasingly explored due to its potential for preclinical and clinical applications. In contrast to the conventional PA imaging in the visible (400 to 700 nm) and the first NIR-I (700 to 1000 nm) window, PA imaging in the NIR-II window offers numerous advantages, including high spatial resolution, deeper penetration depth, reduced optical absorption, and tissue scattering. Moreover, the second window allows a fivefold higher light excitation energy density compared to the visible window for enhancing the imaging depth significantly. We highlight the importance of the second window for PA imaging and discuss the various NIR-II PA imaging systems and contrast agents with strong absorption in the NIR-II spectral region. Numerous applications of NIR-II PA imaging, including whole-body animal imaging and human imaging, are also discussed.

Published: 2019.   Source: Journal of Biomedical Optics 4 (24), 040901 (2019)

Contrast Agent Enhanced Multimodal Photoacoustic Microscopy and Optical Coherence Tomography for Imaging of Rabbit Choroidal and Retinal Vessels in vivo

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Authors:  V.P. Nguyen, Y. Li, W. Qian, B. Liu, C. Tian, W. Zhang, Z. Huang, A. Ponduri, M. Tarnowski, X. Wang, Y.M. Paulus

Multimodal imaging with photoacoustic microscopy (PAM) and optical coherence tomography (OCT) can be an effective method to evaluate the choroidal and retinal microvasculature. To improve the efficiency for visualizing capillaries, colloidal gold nanoparticles (AuNPs) have been applied as a multimodal contrast agent for both OCT and PAM imaging by taking advantage of the strong optical scattering and the strong optical absorption of AuNPs due to their surface plasmon resonance. Ultra-pure AuNPs were fabricated by femtosecond laser ablation, capped with polyethylene glycol (PEG), and administered to 13 New Zealand white rabbits and 3 Dutch Belted pigmented rabbits. The synthesized PEG-AuNPs (20.0 ± 1.5 nm) were demonstrated to be excellent contrast agents for PAM and OCT, and do not demonstrate cytotoxicity to bovine retinal endothelial cells in cell studies. The image signal from the retinal and choroidal vessels in living rabbits was enhanced by up to 82% for PAM and up to 45% for OCT, respectively, by the administered PEG-AuNPs, which enables detection of individual blood vessels by both imaging modalities. The biodistribution study demonstrated the AuNP accumulated primarily in the liver and spleen. Histology and TUNEL staining did not indicate cell injury or death in the lung, liver, kidney, spleen, heart, or eyes up to seven days after AuNP administration. PEG-AuNPs offer an efficient and safe contrast agent for multimodal ocular imaging to achieve improved characterization of microvasculature.

Published: 2019.   Source: Scientific Reports 9, 5945 (2019)

Photoacoustic transfection of DNA encoding GFP

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Authors:  Alexandre D. Silva, Carlos Serpa, Luis G. Arnaut

Photoacoustic transfection consists in the use of photoacoustic waves, generated in the thermoelastic expansion of a confined material absorbing a short pulse of a laser, to produce temporary mechanical deformations of the cell membrane and facilitate the delivery of plasmid DNA into cells. We show that high stress gradients, produced when picosecond laser pulses with a fluence of 100 mJ/cm2 are absorbed by piezophotonic materials, enable transfection of a plasmid DNA encoding Green Fluorescent Protein (gWizGFP, 3.74 MDa) in COS-7 monkey fibroblast cells with an efficiency of 5% at 20 °C, in 10 minutes. We did not observe significant cytotoxicity under these conditions. Photoacoustic transfection is scalable, affordable, enables nuclear localization and the dosage is easily controlled by the laser parameters.

Published: 2019.   Source: Scientific Reports, vol. 9, art. 2553 (2019)

High-resolution, in vivo multimodal photoacoustic microscopy, optical coherence tomography, and fluorescence microscopy imaging of rabbit retinal neovascularization

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Authors:  Wei Zhang, Yanxiu Li, Van Phuc Nguyen, Ziyi Huang, Zhipeng Liu, Xueding Wang, Yannis M. Paulus

Photoacoustic microscopy (PAM) is an emerging imaging technology that can non-invasively visualize ocular structures in animal eyes. This report describes an integrated multimodality imaging system that combines PAM, optical coherence tomography (OCT), and fluorescence microscopy (FM) to evaluate angiogenesis in larger animal eyes. High-resolution in vivo imaging was performed in live rabbit eyes with vascular endothelial growth factor (VEGF)-induced retinal neovascularization (RNV). The results demonstrate that our multimodality imaging system can non-invasively visualize RNV in both albino and pigmented rabbits to determine retinal pathology using PAM and OCT and verify the leakage of neovascularization using FM and fluorescein dye. This work presents high-resolution visualization of angiogenesis in rabbits using a multimodality PAM, OCT, and FM system and may represent a major step toward the clinical translation of the technology.

Published: 2018.   Source: Light: Science & Applications, vol. 7, art. 103 (2018)

Hydrophones based on interferometric fiber-optic sensors with applications in photoacoustics

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Authors:  A. D. Salas-Caridad, B. Eng.

Biomedical imaging used for medical diagnosis constantly requires improvement in the characteristics for imaging devices. The sensing devices are one of the most important pieces to improve in order to get images with better quality. In this thesis, it is proposed the use of interferometric fiber-optic sensors (which offer the advantages inherent to optical fibers) as devices to detect pressure/acoustic signals generated by the photoacoustic effect. It is explored the capability of using fiber-optic interferometric hydrophones in order to determine the thickness of a material derived from the acoustic signal generated when a sample is illuminated. In addition, the analysis of photoacoustic signals generated by the excitation of nanoparticles of an anisotropic material as absorption centers. Finally, the cross-section of a metallic sample was photoacoustically imaged by acquiring the pressure signals generated.

Published: 2017.   Source: Master of Optomechatronics | Leon, Guanajuato, Mexico

Photoacoustic imaging of voltage responses beyond the optical diffusion limit

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Authors:  Bin Rao, Ruiying Zhang, Lei Li, Jin-Yu Shao, Lihong V. Wang

Non-invasive optical imaging of neuronal voltage response signals in live brains is constrained in depth by the optical diffusion limit, which is due primarily to optical scattering by brain tissues. Although photoacoustic tomography breaks this limit by exciting the targets with diffused photons and detecting the resulting acoustic responses, it has not been demonstrated as a modality for imaging voltage responses. In this communication, we report the first demonstration of photoacoustic voltage response imaging in both in vitro HEK-293 cell cultures and in vivo mouse brain surfaces. Using spectroscopic photoacoustic tomography at isosbestic wavelengths, we can separate voltage response signals and hemodynamic signals on live brain surfaces. By imaging HEK-293 cell clusters through 4.5 mm thick ex vivo rat brain tissue, we demonstrate photoacoustic tomography of cell membrane voltage responses beyond the optical diffusion limit. Although the current voltage dye does not immediately allow in vivo deep brain voltage response imaging, we believe our method opens up a feasible technical path for deep brain studies in the future.

Published: 2017.   Source: Scientific Reports, vol. 7, art. 2560 (2017)

Hybrid Photoacoustic/Ultrasound tomograph for real time finger imaging

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Authors:  M. Oeri, W. Bost, N. Sénégond, S. Tretbar, M. Fournelle

We report a target-enclosing, hybrid tomograph with a total of 768 elements based on capacitive micromachined ultrasound transducer technology and providing fast, high-resolution 2-D/3-D photoacoustic and ultrasound tomography tailored to finger imaging.A freely programmable ultrasound beamforming platform sampling data at 80 MHz was developed to realize plane wave transmission under multiple angles. A multiplexing unit enables the connection and control of a large number of elements. Fast image reconstruction is provided by GPU processing. The tomograph is composed of four independent and fully automated movable arc-shaped transducers, allowing imaging of all three finger joints. The system benefits from photoacoustics, yielding high optical contrast and enabling visualization of finger vascularization, and ultrasound provides morphologic information on joints and surrounding tissue. A diode-pumped, Q-switched Nd:YAG laser and an optical parametric oscillator are used to broaden the spectrum of emitted wavelengths to provide multispectral imaging. Custom-made optical fiber bundles enable illumination of the region of interest in the plane of acoustic detection. Precision in positioning of the probe in motion is ensured by use of a motor-driven guide slide. The current position of the probe is encoded by the stage and used to relate ultrasound and photoacoustic signals to the corresponding region of interest of the suspicious finger joint. The system is characterized in phantoms and a healthy human finger in vivo. The results obtained promise to provide new opportunities in finger diagnostics and establish photoacoustic/ultrasoundtomography in medical routine.

Published: 2017.   Source: Ultrasound in Med. & Biol., 2017

Photoacoustic signal detection using interferometric fiber-optic ultrasound transducers

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Authors:  A. D. Salas-Caridad, G. Martínez-Ponce, R. Martínez-Manuel

The cross-section of a metallic sample was photoacoustically imaged using a pulsed nanosecond laser as the excitation source and a fiber-optic hydrophone system to acquire the pressure signal. The ultrasound sensor was an extrinsic Fabry-Perot fiber-optic interferometer and the band-limited photodetected output signal was recorded in a digital oscilloscope. In order to reconstruct the image, a time set of ultrasound signals acquired in a circular scan around the sample were used to solve the time-reversal equations. It was observed that image contrast can be enhanced considering the deconvolution of the sensor frequency response from each measured pressure signal.

Published: 2017.   Source: Event: SPIE Optical Engineering + Applications, 2017, San Diego, California, United States

Detecting Rat’s Kidney Inflammation Using Real Time Photoacoustic Tomography

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Authors:  M. Y. Lee, D. H. Shin, S. H. Park, W.C. Ham, S.K. Ko, C. G. Song

Photoacoustic Tomography (PAT) is a promising medical imaging modality that combines optical imaging contrast with the spatial resolution of ultrasound imaging. It can also distinguish the changes in biological features. But, real-time PAT system should be confirmed due to photoacoustic effect for tissue. Thus, we have developed a real-time PAT system using a custom-developed data acquisition board and ultrasound linear probe. To evaluate performance of our system, phantom test was performed. As a result of those experiments, the system showed satisfactory performance and its usefulness has been confirmed. We monitored the degradation of inflammation which induced on the rat’s kidney using real-time PAT.

Published: 2017.   Source: World Academy of Science, Engineering and Technology International Journal of Biotechnology and Bioengineering Vol:11, No:8, 2017

In vivo photoacoustic lipid imaging in mice using the second near-infrared window

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Authors:  G. S. Sangha, E. H. Phillips, and C. J. Goergen

Photoacoustic imaging has emerged as a promising technique to improve preclinical and clinical imaging by providing users with label-free optical contrast of tissue. Here, we present a proof-of-concept study for noninvasive in vivo murine lipid imaging using 1210 nm light to investigate differences in periaortic fat among mice of different gender, genotypes, and maturation. Acquired lipid signals suggest that adult male apoE−/− mice have greater periaortic fat accumulation compared to adolescent males, apoE−/− females, and wild-type mice. These results demonstrate the potential of photoacoustic tomography for studying vascular pathophysiology and improving the diagnosis of lipid-based diseases.

Published: 2017.   Source: Biomed. Opt. Express 2 (8), 736-742 (2017)

Magneto-elasto-electroporation (MEEP): In-vitro visualization and numerical characteristics

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Authors:  S. Betal, B. Shrestha, M. Dutta, L.F. Cotica, E. Khachatryan, K. Nash, L. Tang, A.S. Bhalla, R. Guo

A magnetically controlled elastically driven electroporation phenomenon, or magneto-elasto-electroporation (MEEP), is discovered while studying the interactions between core-shell magnetoelectric nanoparticles (CSMEN) and biological cells in the presence of an a.c. magnetic field. In this paper we report the effect of MEEP observed via a series of in-vitro experiments using core (CoFe2O4)-shell (BaTiO3) structured magnetoelectric nanoparticles and human epithelial cells (HEP2). The cell electroporation phenomenon and its correlation with the magnetic field modulated CSMEN are described in detail. The potential application of CSMEN in electroporation is confirmed by analyzing crystallographic phases, multiferroic properties of the fabricated CSMEN, influences of d.c. and a.c. magnetic fields on the CSMEN and cytotoxicity tests. The mathematical formalism to quantitatively describe the phenomena is also reported. The reported findings provide insights into the underlying MEEP mechanism and demonstrate the utility of CSMEN as an electric pulse-generating nano-probe in electroporation experiments with a potential application toward accurate and efficient targeted cell permeation.

Published: 2016.   Source: Scientific Reports 6, 32019 (2016)

Optoacoustic effect is responsible for laser-induced cochlear responses

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Authors:  N. Kallweit, P. Baumhoff, A. Krueger, N. Tinne, A. Kral, T. Ripken, H. Maier

Optical stimulation of the cochlea with laser light has been suggested as an alternative to conventional treatment of sensorineural hearing loss with cochlear implants. The underlying mechanisms are controversially discussed: The stimulation can either be based on a direct excitation of neurons, or it is a result of an optoacoustic pressure wave acting on the basilar membrane. Animal studies comparing the intra-cochlear optical stimulation of hearing and deafened guinea pigs have indicated that the stimulation requires intact hair cells. Therefore, optoacoustic stimulation seems to be the underlying mechanism. The present study investigates optoacoustic characteristics using pulsed laser stimulation for in vivo experiments on hearing guinea pigs and pressure measurements in water. As a result, in vivo as well as pressure measurements showed corresponding signal shapes. The amplitude of the signal for both measurements depended on the absorption coefficient and on the maximum of the first time-derivative of laser pulse power (velocity of heat deposition). In conclusion, the pressure measurements directly demonstrated that laser light generates acoustic waves, with amplitudes suitable for stimulating the (partially) intact cochlea. These findings corroborate optoacoustic as the basic mechanism of optical intra-cochlear stimulation.

Published: 2016.   Source: Scientific Reports 6, 28141 (2016)

Image Enchancement Algorithm of Photoacoustic Tomography using Active Countour Filtering

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Authors:  P. Palaniappan, D. H. Shin, C. G. Song

The photoacoustic images are obtained from a custom developed linear array photoacoustic tomography system. The biological specimens are imitated by conducting phantom tests in order to retrieve a fully functional photoacoustic image. The acquired image undergoes the active region based contour filtering to remove the noise and accurately segment the object area for further processing. The universal vack projection method is used as the image reconstruction algorithm. The active contour filtering is analyzed by evaluating the signal to noise ratio and comparing it with the other filtering methods.

Published: 2016.   Source: World Academy of Science, Engineering and Technology International Journal of Computer and Information Engineering Vol:10, No:4, 2016

Bond-selective photoacoustic imaging by converting molecular vibration into acoustic waves

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Authors:  J. Hui, R. Li, E. H. Phillips, C. J. Goergen, M. Sturek, and J. Cheng

The quantized vibration of chemical bonds provides a way of detecting specific molecules in a complex tissue environment. Unlike pure optical methods, for which imaging depth is limited to a few hundred micrometers by significant optical scattering, photoacoustic detection of vibrational absorption breaks through the optical diffusion limit by taking advantage of diffused photons and weak acoustic scattering. Key features of this method include both high scalability of imaging depth from a few millimeters to a few centimeters and chemical bond selectivity as a novel contrast mechanism for photoacoustic imaging. Its biomedical applications spans detection of white matter loss and regeneration, assessment of breast tumor margins, and diagnosis of vulnerable atherosclerotic plaques. This review provides an overview of the recent advances made in vibration-based photoacoustic imaging and various biomedical applications enabled by this new technology.

Published: 2016.   Source: Photoacoustics 1 (4), 11-21 (2016)

A Custom Developed Linear Array Photoacoustic Tomography for Noninvasive Medical Imaging

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Authors:  P. Palaniappan, D. H. Shin, S. H. Park, M. Y. Lee, B. Y. Kim, S. Y. Lee, S. K. Go, C. G. Song

A real-time photoacoustic tomography which is capable of imaging the changes in biological features of living subject is presented. A custom developed data acquisition board and linear array transducer is used in this photoacoustic system. A phantom test were carried out to evaluate performance of the system. The developed system showed a satisfactory performance and its usefulness were evaluated. The universal back projection algorithm is used for image reconstruction and the sensitivity is analyzed from the obtained photoacoustic images.

Published: 2016.   Source: Event: 2016 IEEE International Conference on Consumer Electronics-Asia (ICCE-Asia)

Sensitive Water Probing through Nonlinear Photon Upconversion of Lanthanide-Doped Nanoparticles

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Authors:  S. Guo, X. Xie, L. Huang, and W. Huang

Lanthanide-doped upconversion nanoparticles have received growing attention in the development of low-background, highly sensitive and selective sensors. Here, we report a water probe based on ligand-free NaYF4:Yb/Er nanoparticles, utilizing their intrinsically nonlinear upconversion process. The water molecule sensing was realized by monitoring the upconversion emission quenching, which is mainly attributed to efficient energy transfer between upconversion nanoparticles and water molecules as well as water-absorption-induced excitation energy attenuation. The nonlinear upconversion process, together with power function relationship between upconversion emission intensity and excitation power density, offers a sensitive detection of water content down to 0.008 vol % (80 ppm) in an organic solvent. As an added benefit, we show that noncontact detection of water can be achieved just by using water attenuation effect. Moreover, these upconversion nanoparticle based recyclable probes should be particularly suitable for real-time and long-term water monitoring, due to their superior chemical and physical stability. These results could provide insights into the design of upconversion nanoparticle based sensors.

Published: 2015.   Source: ACS Applied Materials & Interfaces 1 (8), 847-853 (2016)

Enhancement of objects in photoacoustic tomography using selective filtering

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Authors:  D. Shin, Y. Yang, C. G. Song

Here we developed a real-time photoacoustic tomography (PAT) imaging acquisition device based on the linear array transducer utilized on ultrasonic devices. Also, we produced a phantom including diverse contrast media and acquired PAT imaging as the light source wavelength was changing to see if the contrast media reacted. Indocyanine green showed the highest reaction around the 800-nm band, methylene blue demonstrated the same in the 750-nm band, and gold nanoparticle showed the same in the 700-nm band. However, in the case of superparamagnetic iron oxide, we observed not reaction within the wavelength bands used herein to obtain imaging. Moreover, we applied selective filtering to the acquired PAT imaging to remove noise from around and reinforce the object’s area. Consequentially, we could see the object area in the imaging was effectively detected and the image noise was removed.

Published: 2015.   Source: Bio-Medical Materials and Engineering 26 (2015) S1223–S1230