Publication database

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.

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.

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.

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.

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.

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 back 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.

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.

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.

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.

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.