Piezoelectric-Layered Structures Based on Synthetic Diamond

Results of theoretical, modeling, and experimental investigation of microwave acoustic properties of piezoelectric layered structure “Me1/AlN/Me2/(100) diamond” have been presented within a wide frequency band 0.5–10 GHz. The highest among known material quality parameter Q × f ~ 1014 Hz for the IIa type synthetic diamond at operational frequency ~10 GHz has been found. Conditions of UHF excitation and propagation of the bulk, surface, and Lamb plate acoustic waves have been established and studied experimentally. Frequency dependencies of the impedance and quality factor have been studied to obtain a number of piezoelectric layered structure parameters as electromechanical coupling coefficient, equivalent circuit parameters, etc. Results of 2D finite element modeling of a given piezoelectric layered structure have been compared with the experimental ones obtained for the real high-overtone bulk acoustic resonator. An origin of high-overtone bulk acoustic resonator’s spurious resonant peaks has been studied. Results on UHF acoustic attenuation of IIa-type synthetic single crystalline diamond have been presented and discussed in terms of Akhiezer and Landau–Rumer mechanisms of phonon–phonon interaction. Identification and classification of Lamb waves belonging to several branches as well as dispersive curves of phase velocities have been executed. Necessity of introducing a more correct Lamb-mode classification has been recognized

Axially-segmented cylindrical array for intravascular shear wave imaging

We have fabricated a cylindrical intravascular ultrasound (IVUS) transducer array prototype capable of generating an acoustic radiation force impulse (ARFI) for shear wave elasticity imaging (SWEI). The prototype array was a 4-mm long, 2.5-mm diameter, 4 MHz PZT-8 tube, axially segmented into 12 elements on a 334 μm pitch. This transducer array was used in custom vessel phantoms and in ex vivo porcine artery experiments to investigate the potential for IVUS SWEI to distinguish soft lipid cores from stiffer surrounding tissues. By using this array transducer to generate a radially-directed ARFI push , and a Verasonics linear array probe to track displacements in planes parallel to the push , SWEI images of a vessel phantom with hard vessel walls and a soft inclusion were obtained. In tissue-mimicking phantoms, focusing the transducer array to a range of 5 mm generated ARFI displacements up to 1.36 and 1.76 times greater than unfocused excitations in the soft and stiff regions, respectively. The measured shear wave speed in the soft inclusion and stiff vessel wall was 0.97±0.59 m/s and 1.66±0.91 m/s, respectively, and was close to the calibrated measurements of 1.21±0.05 m/s and 1.56±0.05 m/s, respectively. A SWEI image of an ex vivo porcine renal artery was obtained using the prototype transducer and external tracking array, and showed an average shear wave speed of 3.97±1.12 m/s. These results demonstrate the potential of this IVUS array to enable SWEI, to quantifiably assess vulnerable vascular plaques

Cylindrical Transducer for Intravascular ARFI Imaging: Design and Feasibility

Intravascular acoustic radiation force impulse (IV-ARFI) imaging has the potential to identify vulnerable atherosclerotic plaques and improve clinical treatment decisions and outcomes for patients with coronary heart disease. Our long-term goal is to develop a thin, flexible catheter probe that does not require mechanical rotation to achieve high-resolution IV-ARFI imaging. In this work, we propose a novel cylindrical transducer array design for IV-ARFI imaging and investigate the feasibility of this approach. We present the construction of a 2.2-mm-long, 4.6-Fr cylindrical prototype transducer to demonstrate generating large ARFI displacements from a small toroidal beam, and we also present simulations of the proposed IV-ARFI cylindrical array design using Field II and a cylindrical finite-element model of vascular tissues and soft plaques. The prototype transducer was found to generate peak radial displacements of over 10~\mu \text{m} in soft gelatin phantoms, and simulations demonstrate the ability of the array design to obtain ARFI images and distinguish soft plaque targets from surrounding, stiffer vessel wall tissue. These results suggest that high-resolution IV-ARFI imaging is possible using a cylindrical transducer array

Cylindrical Transducer Array for Intravascular Shear Wave Elasticity Imaging: Preliminary Development

We present an intravascular ultrasound (IVUS) transducer array designed to enable shear wave elasticity imaging (SWEI) of arteries for the detection and characterization of atherosclerotic soft plaques. Using a custom dicing fixture, we have fabricated single-element and axially-segmented array transducer prototypes from 4.6-Fr to 7.6-Fr piezoceramic tubes, respectively. Focused excitation of the array prototype at 4 MHz yielded a focal gain of 5× in intensity, for an estimated 60 mW/cm2 I sppa and 1.6-MPa negative peak pressure at 4.5-mm range in water. The single-element transducer generated a peak radial displacement of 10.3 μ m in a uniform elasticity phantom, with axial shear waves detectable by an external linear array probe up to 5 mm away from the excitation plane. In a vessel phantom with a soft inclusion, the array prototype generated peak displacements of 2.2 and 0.5~ μ m in the soft inclusion and vessel wall regions, respectively. A SWEI image of the vessel phantom was reconstructed, with measured shear wave speed (SWS) of 1.66 ± 0.91 m/s and 0.97 ± 0.59 m/s for the soft inclusion and vessel wall regions, respectively. The array prototype was also used to obtain a SWEI image of an ex vivo porcine artery, with a mean SWS of 3.97 ± 1.12 m/s. These results suggest that a cylindrical intravascular ultrasound (IVUS) transducer array could be made capable of SWEI for atherosclerotic plaque detection in coronary arteries

Passive Cavitation Mapping by Cavitation Source Localization from Aperture-Domain Signals - Part II: Phantom and in Vivo Experiments

Passive cavitation mapping (PCM) techniques typically utilize a time-exposure acoustic (TEA) approach, where the received radio frequency data are beamformed, squared, and integrated over time. Such PCM-TEA cavitation maps typically suffer from long-tail artifacts and poor axial resolution with pulse-echo diagnostic arrays. Here, we utilize a recently developed PCM technique based on cavitation source localization (CSL), which fits a hyperbolic function to the received cavitation wavefront. A filtering method based on the root-mean-square error (rmse) of the hyperbolic fit is utilized to filter out spurious signals. We apply a wavefront correction technique to the signals with poor fit quality to recover additional cavitation signals and improve cavitation localization. Validation of the PCM-CSL technique with rmse filtering and wavefront correction was conducted in experiments with a tissue-mimicking flow phantom and an in vivo mouse model of cancer. It is shown that the quality of the hyperbolic fit, necessary for the PCM-CSL, requires an rmse \u3c 0.05 mm2 in order to accurately localize the cavitation sources. A detailed study of the wavefront correction technique was carried out, and it was shown that, when applied to experiments with high noise and interference from multiple cavitating microbubbles, it was capable of effectively correcting noisy wavefronts without introducing spurious cavitation sources, thereby improving the quality of the PCM-CSL images. In phantom experiments, the PCM-CSL was capable of precisely localizing sources on the therapy beam axis and off-axis sources. In vivo cavitation experiments showed that PMC-CSL showed a significant improvement over PCM-TEA and yielded acceptable localization of cavitation signals in mice

Elastic Waves in Piezoelectric Layeres Structures

Получены уравнения, применяемые для расчета параметров акустических волн в слоистых пье- зоэлектрических структурах, включая влияние внешнего однородного электрического поля. Про- ведены компьютерные расчеты распространения акустических волн в слоистых структурах "AlN/алмаз", "BGO/плавленый кварц", "LGS/плавленый кварц" для основных кристаллических срезов. Рассчитаны дисперсионные зависимости фазовых скоростей, КЭМС, потока энергии как функции произведения hf, а также анизотропия параметров волн. Выполнена идентификация акустических мод. Сделаны оценки гибридизации акустических мод. Указаны срезы и направ- ления с оптимальным сочетанием акустических свойств (высокие фазовая скорость и КЭМС, минимальное отклонение потока энергии и т.п.).Relations used for calculation of the layered piezoelectric structures parameters, including the influence of the uniform dc electric field have been obtained. Computer simulations of acoustic wave propagation in the AlN/diamond, BGO/fused quartz, LGS/fused quartz layered structures have been fulfilled for the main crystalline cuts. Dispersion dependences of the phase velocities, electromachanical coupling coefficients, the power flow angles as a function of the h f product and the anisotropy of the wave propagation parameters have been presented. Identification of acoustic modes has been completed. Es- timations of the acoustic modes hybridization have been obtained. Crystalline cuts and directions with optimal combination of acoustic properties such as high phase velocity and EMCC, the minimal PFA etc. have been specified

Elastic Waves in Piezoelectric Layeres Structures

Получены уравнения, применяемые для расчета параметров акустических волн в слоистых пье- зоэлектрических структурах, включая влияние внешнего однородного электрического поля. Про- ведены компьютерные расчеты распространения акустических волн в слоистых структурах "AlN/алмаз", "BGO/плавленый кварц", "LGS/плавленый кварц" для основных кристаллических срезов. Рассчитаны дисперсионные зависимости фазовых скоростей, КЭМС, потока энергии как функции произведения hf, а также анизотропия параметров волн. Выполнена идентификация акустических мод. Сделаны оценки гибридизации акустических мод. Указаны срезы и направ- ления с оптимальным сочетанием акустических свойств (высокие фазовая скорость и КЭМС, минимальное отклонение потока энергии и т.п.).Relations used for calculation of the layered piezoelectric structures parameters, including the influence of the uniform dc electric field have been obtained. Computer simulations of acoustic wave propagation in the AlN/diamond, BGO/fused quartz, LGS/fused quartz layered structures have been fulfilled for the main crystalline cuts. Dispersion dependences of the phase velocities, electromachanical coupling coefficients, the power flow angles as a function of the h f product and the anisotropy of the wave propagation parameters have been presented. Identification of acoustic modes has been completed. Es- timations of the acoustic modes hybridization have been obtained. Crystalline cuts and directions with optimal combination of acoustic properties such as high phase velocity and EMCC, the minimal PFA etc. have been specified

Acoustically Driven Microbubbles Enable Targeted Delivery of microRNA‐Loaded Nanoparticles to Spontaneous Hepatocellular Neoplasia in Canines

Spatially localized microbubble cavitation by ultrasound offers an effective means of altering permeability of natural barriers (i.e. blood vessel and cell membrane) in favor of nanomaterials accumulation in the target site. In this study, a clinically relevant, minimally invasive ultrasound guided therapeutic approach is investigated for targeted delivery of anticancer microRNA loaded PLGA-b-PEG nanoparticles to spontaneous hepatocellular neoplasia in a canine model. Quantitative assessment of the delivered microRNAs revealed prominent and consistent increase in miRNAs levels (1.5-to 2.3-fold increase (p<0.001)) in ultrasound treated tumor regions compared to untreated control regions. Immunohistology of ultrasound treated tumor tissue presented a clear evidence for higher amount of nanoparticles extravasation from the blood vessels. A distinct pattern of cytokine expression supporting CD8+ T cells mediated "cold-to-hot" tumor transition was evident in all patients. On the outset, proposed platform can enhance delivery of miRNA-loaded nanoparticles to deep seated tumors in large animals to enhance chemotherapy