Design and Evaluation of a Weighted Periodic Sparse Array for Low-Complexity 1-D Phased Array Ultrasound Imaging Systems.

A sparse array offers a significant reduction in the complexity of ultrasonic imaging systems by decreasing the number of active elements and associated electrical circuits needed to form a focused beam. Consequently, for 1-D arrays, it has been adopted in the development of miniaturized systems such as portable, handheld, or smartphone-based systems. Previously, we developed an analytic method that can design a pair of 1-D periodic sparse arrays (PSAs) satisfying three specific constraints, which are the array size, desired grating lobe level, and sparseness factor (SF).

An Analytical Approach to Designing Optimal Sparse 1-D Phased Arrays for Handheld Ultrasound Imaging.

Sparse arrays have been studied mainly to reduce the large numbers of elements in 2-D arrays. However, they can also provide an effective means of miniaturizing ultrasound 1-D array systems for point-of-care applications. Although a variety of sparse array design strategies have been proposed, designing an optimum sparse array to simultaneously satisfy the system specification requirements and performance criteria remains a challenge.

A new frequency domain passive acoustic mapping method using passive Hilbert beamforming to reduce the computational complexity of fast Fourier transform.

Passive acoustic mapping (PAM) is the current state-of-the-art imaging tool for monitoring cavitation activity during focused ultrasound therapy such as blood-brain barrier opening. However, PAM incurs huge computational complexity. To address this issue, frequency-domain PAM (FD-PAM) was proposed.

Comparison study of passive acoustic mapping and high-speed photography for monitoring in situ cavitation bubbles.

The spatiotemporal accuracy of passive acoustic mapping (PAM) for monitoring in situ cavitation bubbles has not been assessed directly via optical means. Here, the cavitation bubbles are monitored from two image sequences obtained simultaneously with PAM and high-speed photography (HSP). The temporal accuracy of PAM for detecting cavitation nucleation and the spatial resolution for cavitation localization are compared with those measured from HSP.

Non-linear Acoustic Emissions from Therapeutically Driven Contrast Agent Microbubbles.

Non-linear emissions from microbubbles introduced to the vasculature for exposure to focused ultrasound are routinely monitored for assessment of therapy and avoidance of irreversible tissue damage. Yet the bubble-based mechanistic source for these emissions, under subresonant driving at typical therapeutic pressure amplitudes, may not be well understood. In the study described here, dual-perspective high-speed imaging at 210,000 frames per second (fps), and shadowgraphically at 10 Mfps, was used to observe cavitation from microbubbles flowing through a 500-µm polycarbonate capillary exposed to focused ultrasound of 692 kHz at therapeutically relevant pressure amplitudes.

Performance characterisation of a passive cavitation detector optimised for subharmonic periodic shock waves from acoustic cavitation in MHz and sub-MHz ultrasound.

We describe the design, construction and characterisation of a broadband passive cavitation detector, with the specific aim of detecting low frequency components of periodic shock waves, with high sensitivity. A finite element model is used to guide selection of matching and backing layers for the shock wave passive cavitation detector (swPCD), and the performance is evaluated against a commercially available device. Validation of the model, and characterisation of the swPCD is achieved through experimental detection of laser-plasma bubble collapse shock waves.

High parasite burden increases the surfacing and mortality of the manila clam (Ruditapes philippinarum) in intertidal sandy mudflats on the west coast of Korea during hot summer.

Background: Over the past few decades, mass mortality events of Manila clams have been reported from several tidal flats on the west coast of Korea during hot summers. During such mortality events, once clams simultaneously surface, they fail to re-burrow, perishing within a week. The present study aimed to identify the possible causes of the mass mortality of this clam species by investigating the Perkinsus olseni parasite burden and immune parameters of surfaced clams (SC) and normal buried clams (NBCs) when sea water or sediment temperature in the study area varied from 25 °C to 34 °C from late July through mid-August 2015.

Covert cavitation: Spectral peak suppression in the acoustic emissions from spatially configured nucleations.

Dual laser-nucleation is used to precisely configure two cavitation bubbles within a focused ultrasound field of f = 692 kHz, in proximity to the tip of a needle hydrophone. With both bubbles responding in the f/2 sub-harmonic regime, confirmed via ultra-high speed shadowgraphic imaging, an emission spectrum with no sub-harmonic content is demonstrated, for an inter-bubble spacing ≈λ. A spectral model for periodic shock waves from multiple nucleations demonstrates peak suppressions at nf/2 when applied to the experiment, via a windowing effect in the frequency domain.

An analysis of the acoustic cavitation noise spectrum: The role of periodic shock waves.

Research on applications of acoustic cavitation is often reported in terms of the features within the spectrum of the emissions gathered during cavitation occurrence. There is, however, limited understanding as to the contribution of specific bubble activity to spectral features, beyond a binary interpretation of stable versus inertial cavitation. In this work, laser-nucleation is used to initiate cavitation within a few millimeters of the tip of a needle hydrophone, calibrated for magnitude and phase from 125 kHz to 20 MHz.

Deconvolution of acoustically detected bubble-collapse shock waves.

The shock wave emitted by the collapse of a laser-induced bubble is detected at propagation distances of 30, 40and50mm, using a PVdF needle hydrophone, with a non-flat end-of-cable frequency response, calibrated for magnitude and phase, from 125kHz to 20MHz. High-speed shadowgraphic imaging at 5×10 frames per second, 10nstemporal resolution and 256 frames per sequence, records the bubble deflation from maximum to minimum radius, the collapse and shock wave generation, and the subsequent rebound in unprecedented detail, for a single sequence of an individual bubble. The Gilmore equation for bubble oscillation is solved according to the resolved bubble collapse, and simulated shock wave profiles deduced from the acoustic emissions, for comparison to the hydrophone recordings.

Size-controlled synthesis of Pd nanomaterials via proton beam irradiation.

We present a facile one-pot synthetic route for the production of palladium nanoparticles via a simple proton beam irradiation process at room temperature. The synthesis of size-controlled palladium nanostructures was realized just by changing the mean current of the proton beam and by controlling the molar concentration ratios of surfactants to Pd precursors in an aqueous phase-based solution without the addition of any harsh reductants. As the beam current was increased under the same Pd ion concentration conditions, the average diameter of the prepared Pd nanoparticles tended to be decreased.

An effective pulse sequence for simultaneous HIFU insonation and monitoring.

The HIFU interference cancellation method using pulse inversion is useful for real-time treatment monitoring; however, this method suffers from residual interference when a high duty cycle is employed. In this paper, a pulse sequence is proposed to overcome the problem. It was experimentally verified that all interference could be removed using the pulse sequence.

Synthesis of multi-walled carbon nanotube-Ag-nanoparticles composite nanomaterials using proton beam irradiation.

A new synthetic route for decorating carbon nanotubes (MWCNTs) with silver nanoparticles by proton beam irradiation at room temperature is presented. Pristine- and surface-modified MWCNTs were comparatively utilized for the preparation of MWCNT-Ag-nanoparticles nanohybrid. Silver nanoparticles on the surfaces of MWCNTs were produced in situ without any additional reducing reagents, and more importantly, all the solutions were aqueous phase-based.

Vein visualization using a smart phone with multispectral Wiener estimation for point-of-care applications.

Effective vein visualization is clinically important for various point-of-care applications, such as needle insertion. It can be achieved by utilizing ultrasound imaging or by applying infrared laser excitation and monitoring its absorption. However, while these approaches can be used for vein visualization, they are not suitable for point-of-care applications because of their cost, time, and accessibility.

The origin of magnetism in transition metal-doped ZrO2 thin films: experiment and theory.

We have investigated the magnetic properties of Fe/Co/Ni-doped ZrO2 laser ablated thin films in comparison with the known results of Mn-doped ZrO2, which is thought to be a promising material for spintronics applications. It is found that doping with a transition metal can induce room temperature ferromagnetism in 'fake' diamond. Theoretical analysis based on density functional theory confirms the experimental measurements, by revealing that the magnetic moments of Mn- and Ni-doped ZrO2 thin films are much larger than that of Fe- or Co-doped ZrO2 thin films.

Real-time monitoring of HIFU treatment using pulse inversion.

Ultrasound (US) imaging is widely used for the real-time guidance of high-intensity focused ultrasound (HIFU) treatment at a relatively low cost. However, ultrasound image guided HIFU (USgHIFU) is limited in the real-time monitoring of HIFU treatment due to the large amplitude HIFU signals received by the US imaging transducer. The amplitude of the HIFU scattered signal is generally much higher than the amplitude of the pulse-echo signal received by the imaging transducer.

Formation of flower-like Ag colloids using pulsed proton beam.

A new solution phase method is presented for the synthesis of "flower-like" silver nanomaterials using a pulsed proton beam irradiation process at room temperature. It was observed that the morphology of the prepared silver crystals was easily controlled by varying the number of exposures to the pulsed proton beam. The synthesized flower-like silver nanocrystals exhibited excellent surface enhanced Raman scattering (SERS) signals, which were attributed to the rough microstructures on the surface of the synthesized Ag crystals.

Controlling the shapes and electrical conductivities of polyaniline-wrapped MWCNTs.

Nanocomposites of carbon nanotubes with polyaniline (PANI) constitute promising conducting nanomaterials, due to their ease of synthesis, electrical conductivity, and environmental stability. Variously shaped multi-walled carbon nanotube (MWCNT)-PANI nanocomposites were synthesized, and their electrical conductivities were compared. This study shows that new synthetic methods were able to control the shapes and electrical conductivities of MWCNT-PANI nanocomposites.

Effects of water temperature change on immune function in surf clams, Mactra veneriformis (Bivalvia: Mactridae).

Surf clam, Mactra veneriformis is one of the crucial fishery resources in Korea. This study was performed to examine the immune functions of the surf clam under the stress of water temperature changes at 10 degrees C, 20 degrees C or 30 degrees C for 24h. Viable bacterial counts (VBC), total haemocyte count (THC), phagocytic activity, lysozyme activity, NRR times and SOD activity were assessed in three different water temperature groups.

Harmonic Golay coded excitation based on harmonic quadrature demodulation method.

Harmonic coded excitation techniques have been used to increase SNR of harmonic imaging with limited peak voltage. Harmonic Golay coded excitation, in particular, generates each scan line using four transmit-receive cycles, unlike conventional Golay coded excitation method, thus resulting in low frame rates. In this paper we propose a method of increasing the frame rate of said method without impacting the image quality.

A two-pulse technique for extracting 3rd harmonic from ultrasound contrast agent echo signal.

Multi-pulse techniques like CPS (contrast pulse sequence) and TPS (triplet pulse sequence) are the most popular methods for separating the 3rd harmonic signals from received signal. Those two methods, however, transmit a pulse at least three times along each scanline with different phase and amplitude, which results in the frame rate reduction. In this paper, we propose a technique using two pulses whose phase difference is 90 degrees and a simple digital filter.

A fractional filter-based beamformer architecture using postfiltering approach to minimize hardware complexity.

A novel beamformer architecture using fractional delay filters is proposed and verified through experiments. By performing interchannel summation prior to filtering operation in the manner producing no error, the proposed architecture requires only three four-tap filters for the whole beamformer and four simple demultiplexers per each channel.

Size and shape-tuned overgrowth on Au nanorods regulated by polyallylamine.

Au nanorods prepared by a photochemical method were used as seeds for the overgrowth of thin shell of gold by using a mild reducing agent, ascorbic acid at ambient conditions. The overgrowth rate along different crystal facets of the starting gold nanorods was regulated by the addition of polyallylamine. The shape of the resulting gold nanorods was different from the naturally overgrown Au nanorods without any additives.

Conducting block copolymer for simple micro- to nanopatterns.

To use conducting polymers as substitutes for metals and conventional semiconductors in device fabrication, a cost-effective process for the reproducible deposition of the conducting polymers is needed. In this letter, we report a simple solution casting method for the fabrication of micro- to nanopatterns using the conducting block copolymer, poly(thiophene-block-ethyleneoxide), which shows rectifying characteristics dependent on the pattern width.

Crystal overgrowth on gold nanorods: tuning the shape, facet, aspect ratio, and composition of the nanorods.

Electrochemically prepared Au nanorods were used as seeds for the overgrowth of thin shells of gold, silver, and palladium by using a mild reducing agent, ascorbic acid, in the presence of surfactants at ambient condition. The unique crystal facets of the starting nanorods results in anisotropic crystal overgrowth. The overgrowth rates along different crystallographical directions can be further regulated by adding foreign ions or by using different metal reduction methods.