Photoacoustic generation of focused quasi-unipolar pressure pulses

The photoacoustic effect was employed to generate short-duration quasi-unipolar acoustic pressure pulses in both planar and spherically focused geometries. In the focal region, the temporal profile of a pressure pulse can be approximated by the first derivative of the temporal profile near the front transducer surface, with a time-averaged value equal to zero. This approximation agreed with experimental results acquired from photoacoustic transducers with both rigid and free boundaries. For a free boundary, the acoustic pressure in the focal region is equal to the sum of a positive pressure that follows the spatial profile of the optical energy deposition in the medium and a negative pressure that follows the temporal profile of the laser pulse

Effect of mesonic off-shell correlations in the PNJL equation of state

We study the meson contribution to the equation of state of the 2-flavor PNJL model, including the full momentum dependence of the meson polarization loops. Within the Beth-Uhlenbeck approach, we demonstrate that the contribution from the quark-antiquark continuum excitations in the spacelike region $\omega^2 - q^2 < 0$, i.e. the Landau damping, leads to an increase of the pressure for temperatures $\gtrsim 0.8\,T_c^\chi$ and a significant meson momentum cut-off dependence in the mesonic pressure and the QCD trace anomaly. We investigate the dependence of the results on the choice of the Polyakov-loop potential parameter $T_0$. From the dependence of the mesonic pressure on the current quark mass, by means of the Feynman-Hellmann theorem, we evaluate the contribution of the pion quasiparticle gas and Landau damping to the chiral condensate.Comment: 13 pages, 8 figure

High-resolution photoacoustic vascular imaging in vivo using a large-aperture acoustic lens

Reflection-mode photoacoustic microscopy with dark-field laser pulse illumination and high frequency ultrasonic detection is used to non-invasively image blood vessels in the skin in vivo. Dark-field illumination minimizes the interference caused by strong photoacoustic signals from superficial structures. A high numerical-aperture acoustic lens provides high lateral resolution, 45-120 micrometers in this system while a broadband ultrasonic detection system provides high axial resolution, estimated to be ~15-20 micrometers. The optical illumination and ultrasonic detection are in a coaxial confocal configuration for optimal image quality. The system is capable of imaging optical-absorption contrast at up to 3 mm depth in biological tissue

System for automated environmental monitoring using remote sensing data of the Earth from open data sources

Environmental monitoring using remote sensing data requires an analyst to perform a large amount of routine work related to downloading, processing and analyzing data, especially in cases when the study area is covered with a large number of satellite imagery. The paper presents the results of the design and software implementation of the system that automates downloading and processing of remotely sensed data according to developed scenarios and, thus, greatly simplifies the processing of satellite imagery. It provides the description of tools for accessing data from the archive of the United States Geological Survey (USGS) and describes the data flow in the system. The paper gives an analysis of results obtained using the developed system on the example of monitoring the state of Siberian pine forests of the Tomsk region

Photoacoustic imaging of biological tissue with intensity-modulated continuous-wave laser

We build a photoacoustic imaging system using an intensity-modulated continuous-wave laser source, which is an inexpensive, compact, and durable 120-mW laser diode. The goal is to significantly reduce the costs and sizes of photoacoustic imaging systems. By using a bowl-shaped piezoelectric transducer, whose numerical aperture is 0.85 and resonance frequency is 2.45 MHz, we image biological tissues with a lateral resolution of 0.45 mm, an axial resolution of 1 mm, and an SNR as high as 43 dB

Multifocal optical-resolution photoacoustic microscopy in vivo

Although ultrasound arrays have been exploited in photoacoustic imaging to improve imaging speed, ultrasound-array-based optical-resolution photoacoustic microscopy (OR-PAM) has never been achieved previously to our knowledge. Here we present our development of multifocal OR-PAM using a microlens array for optical illumination and an ultrasound array for photoacoustic detection. Our system is capable of imaging hemoglobin concentration and oxygenation in individual microvessels in vivo at high speed. Compared with a single focus, multiple foci reduce the scanning load and increase the imaging speed significantly. The current multifocal system can acquire 1000×500×200 voxels at ∼10 μm lateral resolution within 4 min

Simultaneous imaging of a lacZ-marked tumor and microvasculature morphology in vivo by dual-wavelength photoacoustic microscopy

Photoacoustic molecular imaging, combined with the reporter-gene technique, can provide a valuable tool for cancer research. The expression of the lacZ reporter gene can be imaged using photoacoustic imaging following the injection of X-gal, a colorimetric assay for the lacZ-encoded enzyme β-galactosidase. Dual-wavelength photoacoustic microscopy was used to non-invasively image the detailed morphology of a lacZ-marked 9L gliosarcoma and its surrounding microvasculature simultaneously in vivo, with a superior resolution on the order of 10 μm. Tumor-feeding vessels were found, and the expression level of lacZ in tumor was estimated. With future development of new absorption-enhancing reporter-gene systems, we anticipate this strategy can lead to a better understanding of the role of tumor metabolism in cancer initiation, progression, and metastasis, and in its response to therapy

Photoacoustic Doppler flow measurement in optically scattering media

We recently observed the photoacoustic Doppler effect from flowing small light-absorbing particles. Here, we apply the effect to measure blood-mimicking fluid flow in an optically scattering medium. The light scattering in the medium decreases the amplitude of the photoacoustic Doppler signal but does not affect either the magnitude or the directional discrimination of the photoacoustic Doppler shift. This technology may hold promise for a new Doppler method for measuring blood flow in microcirculation with high sensitivity