Search

Background Acoustic cavitation plays an important role in the medical treatment using high-intensity focused ultrasound (HIFU), but unnecessarily strong cavitation also could deform the morphology and enlarge the size of lesions. It is known that the increase of ambient hydrostatic pressure (Pstat) can control the acoustic cavitation. But the question of how the decrease of Pstat and dissolved oxygen concentration (DOC) influence the strength of cavitation has not been thoroughly answered. In this study, we aimed to investigate the relationship among the Pstat, DOC and the strength of cavitation. Methods Ex vivo bovine liver tissues were immersed in degassed water with different DOC of 1.0 mg/L, 1.5 mg/L and 2.0 mg/L. Ultrasound (US) of 1 MHz and the spatial and temporal average intensity (Isata) of 6500 W/cm2 was used to expose two groups of in vitro bovine livers for 2 s; one group was under atmospheric pressure (Pstat = 1 bar) and the other was under sub-atmospheric pressure (Pstat = 0.1 bar). Acoustic cavitation was detected by a passive cavitation detector (PCD) during the exposure process. Echo signals at the focal zone of HIFU were monitored by B-mode ultrasound imaging before and after exposure. The difference between two pressure groups was tested using paired sample t-test. The difference among different DOC groups was evaluated by one-way analysis of variance (ANOVA). Results The results demonstrated a significant difference of broadband acoustic emissions from the cavitation bubbles, echo signals on B-mode image, morphology of lesions under various conditions of ambient pressure and DOC. The lesion volume in tissue was increased with the increase of ambient pressure and DOC. Conclusion Cavitation could be suppressed through sub-atmospheric pressure and low DOC level in liver tissue, which could provide a method of controlling cavitation in HIFU treatment to avoid unpredictable lesions.

For 1–3 piezoelectric composite high-power transducers applied to FUS surgery, avoiding the electro-acoustic output performance fluctuating with the temperature is an important task. In this work, 1–3 type piezocomposites were fabricated with dice and fill method. The PZT4 piezoceramic was used as active phase, and mica powder modified epoxy resin E51 was used as passive phase: the mass ratio of the epoxy and mica powder was 10:x. Those composites were evaluated for power transducer applications with air backing and without front layer. The effect of mica powder modified polymer filler on the electro-acoustic output behavior and thermal stability of the transducer were detailed investigated. The results show that mica power could increase the storage modulus and the toughness of the polymer. As a result, an elevated kt of 0.7 was observed when the adding amount was 50 wt%. The electro-acoustic conversion efficiency (ηea) of the transducer substantial increased to 81–83% and with good thermal stability when x = 1–5. The research results show that adding mica powder in the filler materials was one of the potential methods to prepare high-power piezocomposite transducer.

Nanodiamonds (NDs) as drug delivery vehicles are of great significance in anticancer therapy through enhancing drug retention. However, the major barrier to clinical application of NDs is insufficient tumor penetration owing to their strong aggregation and low passive penetration efficiency. Herein, the core-crosslinked pullulan carrier, assembled using the visible light-induced diselenide (Se–Se) bond crosslinking method for encapsulating nanodiamonds-doxorubicin (NDX), is proposed to improve monodispersity. Furthermore, the core-crosslinked diselenide bond provides the nanosystem with redox-responsive capability and improved structural stability in a physiological environment, which prevents premature drug leakage and achieves tumor site-specific controlled release. What's more, ultrasound (US) is utilized to promote nanosystem intratumoral penetration via enlarged tumor vascular endothelium cell gaps. As expected, the nanosystem combined with ultrasound can enhance anti-tumor efficacy with deep penetration and excellent retention performance in a HepG2 xenograft mouse model. This study highlights the ability of the integrated therapeutic paradigm to overcome the limitation of nanodiamonds and the potential for further application in cancer therapy.

Stimulus-responsive drug delivery nanosystems (DDSs) are of great significance in improving cancer therapy for intelligent control over drug release. However, among them, many DDSs are unable to realize rapid and sufficient drug release because most internal stimulants might be consumed during the release process. To address the plight, an abundant supply of stimulants is highly desirable. Herein, a core crosslinked pullulan-di-(4,1-hydroxybenzylene)diselenide nanosystem, which could generate abundant exogenous-stimulant reactive oxygen species (ROS) via tumor-specific NAD(P)H:quinone oxidoreductase-1 (NQO1) catalysis, was constructed by the encapsulation of β-lapachone. The enzyme-catalytic-generated ROS induced self-triggered cascade amplification release of loaded doxorubicin (DOX) in the tumor cells, thus achieving efficient delivery of DOX to the nuclei of tumor cells by breaking the diselenide bond of the nanosystem. As a result, the antitumor effect of this nanosystem was significantly improved in the HepG2 xenograft model. In general, this study offers a new paradigm for utilizing the interaction between the loaded agent and carrier in the tumor cells to obtain self-triggered drug release in the design of DDSs for enhanced cancer therapy.

Based on the acousto-optic interaction, we propose a laser deflection method for rapidly, non-invasively and quantitatively measuring the peak positive pressure of HIFU fields. In the characterization of HIFU fields, the effect of nonlinear propagation is considered. The relation between the laser deflection length and the peak positive pressure is derived. Then the laser deflection method is assessed by comparing it with the hydrophone method. The experimental results show that the peak positive pressure measured by laser deflection method is little higher than that obtained by the hydrophone, confirming that they are in reasonable agreement. Considering that the peak pressure measured by hydrophones is always underestimated, the laser deflection method is assumed to be more accurate than the hydrophone method due to the absence of the errors in hydrophone spatial-averaging measurement and the influence of waveform distortion on hydrophone corrections. Moreover, noting that the Lorentz formula still remains applicable to high-pressure environments, the laser deflection method exhibits a great potential for measuring HIFU field under high-pressure amplitude. Additionally, the laser deflection method provides a rapid way for measuring the peak positive pressure, without the scan time, which is required by the hydrophones.

Nanodiamond as a drug carrier is of great significance in improving cancer therapy by overcoming chemoresistance. However, its clinical application is severely limited because of insufficient tumor vascular penetration. To address this limitation, pullulan-all-trans-retinal (pullulan-ATR) self-assembled nanoparticles were prepared as nanocarriers, which encapsulated doxorubicin-loaded nanodiamonds, to construct a core-shell structured coloading nanosystem. The obtained composite nanoparticles show a homogeneous size distribution with good dispersity and pH sensitivity. Furthermore, ultrasound was utilized to promote the intratumoral penetration of these nanoparticles. As a result, the intracellular retention of DOX was efficiently enhanced, and DOX in the tumor tissue reached 17.3% of the injected dosage. The antitumor effect of this combined strategy was remarkably improved in both the DOX-sensitive HepG2 and DOX-resistant HepG2/ADR tumor models in vivo. This new strategy might serve as a powerful method to address the limitation of nanodiamonds and provide innovative ideas for the application of nanoparticles in clinical cancer therapy.

The spontaneous self-assembly of chiral nanoparticles (NPs) into stationary fabrication has garnered great interest in technique investigation and science advancement due to its expected apparent properties via orderly collective behaviors. However, this kind of characterization of assembled nanoparticles superstructure (NPS) is rarely reported and is distinguished with monodispersed chiral NPs. In this work, we used l-cysteine (Cys) as the chiral molecule in the form of functional surfactant, which had capped CdS/CdTe NPs and was treated as a linkage bridge for constructing orderly assembled NPS. Among the circular dichrosim (CD) phenomenon, Cys ligands exhibit related changes in CD absorption, while whole-molecule solution was used for treatment in different pH-controlling procedures. Synthesized chiral NPs are organized into ordered rod-shaped NPS during the spontaneous self-assembly process, and the CD response of NPS is monitored in different cultivating times; it showed a persuasive response appears in sum frequency generation (SFG) spectroscopy. Both experimental works and theory calculation convey that the ordered stacking of chiral stabilizer and the chirality of NPS, which are identified from chiral molecular status and their collective optical activity, originated from ligand asymmetry.

Conventional hydrophones are usually used below their resonance frequency over a wide frequency band. Resent study showed that the hydrophones operated around the resonance frequency had potential applications in weak signal diagnosis for improving the sensitivity or resolution. However, the conventional hydrostatic model based on off-resonance hydrophone design is incapable of analyzing the hydrophones operated around the resonance frequencies, where the electromechanical response is changed sharply with frequencies. To expand the operating limits of the hydrostatic model, a dynamic model of fluid–structure interaction for analyzing the 1–3 piezoelectric composite hydrophones is presented. An analytical solution for output voltage of the hydrophone operated in thickness-stretch vibration is derived. This dynamic model is sufficient to analyze the 1–3 piezoelectric composite hydrophones over the entire frequency range, especially around the resonance. In addition, the output voltage obtained by dynamic model in the off-resonance range agrees well with those obtained by hydrostatic model. To verify the theoretical analysis, we fabricated a 1–3 piezoelectric composite hydrophone and experimentally measured the output voltage. Experimental results around the resonance show good agreement with the dynamic theory. The output voltage which peaks at the anti-resonance frequency as expected is of three orders of magnitude higher than that of conventional off-resonance hydrophones.

Nanoemulsions as synergists of high intensity focused ultrasound (HIFU) have been widely investigated, since they possess huge potential for improving the efficiency to ablate tumor. However, their clinical applications are limited due to the unsatisfactory phase-transition effect of nanoemulsions during the process of generating nanobubbles. Herein, a novel synergist for HIFU therapy was designed by encapsulating 1,1,2-trichlorotrifluoroethane (CFC) into pH-sensitive pullulan-doxorubicin (Pu-DOX/CFC) nanoparticles. These Pu-DOX/CFC nanoemulsions, with moderate vaporization temperature threshold of 47 °C, could provide favorable phase-transition effect, thus facilitating HIFU energy deposition. Meanwhile, Pu-DOX/CFC nanoemulsions could effectively deliver DOX/CFC to the tumor site and carry out combined therapy. The in vitro and in vivo results confirmed that Pu-DOX/CFC nanoemulsions notably enhanced both ablation and therapeutic efficiency comparing with other synergists. In conclusion, Pu-DOX/CFC nanoemulsions might serve as a novel synergist for HIFU therapy, and possess great potential in clinical implication.

Aim: To build up a combined therapy strategy to address limitations of the enhanced permeability and retention (EPR) effect and improve the efficiency of tumor therapy. Materials & methods: A pH-sensitive nanocomplex for co-delivery of doxorubicin (DOX) and all-trans retinoic acid (ATRA) was developed based on nanodiamonds (DOX/ATRA-NDs) to enhance intracellular retention of drugs. Meanwhile, ultrasound was employed to enhance tumor vascular penetration of DOX-ATRA-NDs. Results: The distribution of DOX/ATRA-NDs in the tumor tissues increased threefold when ultrasound was applied at 1 MHz and 0.6 W/cm2. Comparing with unmodified chemotherapeutics, the combined therapy induced more tumor cells apoptosis and greater tumor growth inhibition in both liver and breast tumor models. Conclusion: DOX-ATRA-NDs demonstrate great potential in clinical applications.

For bulk piezoelectric ceramics plates, the fundamental thickness-stretch (TSt) waves are always coupled to the in-plane extension waves and the symmetric thickness-shear waves. The occurrence of these spurious modes in bulk piezoelectric ceramics plates is undesirable as it may interfere with the operation of transducers. 1–3 piezoelectric composites are promising candidates to suppress the spurious modes mentioned above. However, theoretical modelling of multiphase ceramic composite objects is very complex. In this study, a simple analytical TSt vibration model is constructed from three-dimensional equations of linear piezoelectricity. The mechanical damping is considered in the model by introducing a complex elastic constant. The performance of 1–3 piezoelectric composites is analysed and the electrical impedance results from theoretical and experimental analysis are compared. The results show that there is excellent agreement between the experimental electrical impedance and that obtained by the theor...

The conventional hydrostatic model based on static analysis is frequency-independent and inadequate to fully evaluate the present hydrophone's full range of receiving sensitivity. To expand the operating limits of the hydrostatic model, a dynamic fluid-structure interaction model for analyzing the sensitivity of piezoelectric hydrophones is presented. An analytical solution that governs the receiving sensitivity of the piezoelectric hydrophones over a wide frequency range, in both the non-resonance frequency and the resonance frequency regions, is derived. The theoretical result shows that the derived receiving sensitivity agrees well with the hydrostatic model. Additionally, the experimental results verify the theory presented in resonance frequency range.

A novel multifunctional nanotheranostic agent with targeting, redox-responsive ultrasound imaging and ultrasound imaging-guided high-intensity focused ultrasound (HIFU) therapy (MSNC-PEG-HA(SS)-PFH, abbreviated as MPH(SS)-PFH) capabilities is developed. The redox-responsive guest molecule release and ultrasound imaging functions can be both integrated in such a "smart" theranostic agent, which is accomplished by the redox-triggered transition from the crosslinking state to retrocrosslinking state of the grafted polyethylene glycol-disulfide hyaluronic acid molecules on the particle surface when reaching a reducing environment in vitro. More importantly, under the tailored ultrasound imaging guiding, in vivo Hela tumor-bearing nude mice can be thoroughly and spatial-accurately ablated during HIFU therapy, due to the targeted accumulation, responsive ultrasound imaging guidance and the synergistic ablation functions of nanotheranostic agent MPH(SS)-PFH in the tumors. This novel multifunctional nano-platform can serve as a promising candidate for further studies on oncology therapy, due to its high stability, responsive and indicative ultrasound imaging of tumors, and enhanced HIFU therapeutic efficiency and spatial accuracy under ultrasound-guidance.

An inorganic enhancement agent (EA) for high-intensity focused ultrasound (HIFU) imaging based on mesoporous silica nanocapsules is presented. The pronounced coagulative necrosis effects demonstrate, both in vitro and in vivo, that the EA can be developed as a highly promising theranostic agent for effective HIFU imaging and therapy owing to its high stability, efficient perfluorohexane loading and release, enhanced tumor ablation capability, and easy uptake by target tissues. Copyright

The radiation effect of the electrical fast transient (EFT) is usually more serious than that of the conduction and more difficult to be suppressed in electromagnetic compatibility (EMC) test. The energy of EFT concentrate at the range below 100MHz, which means the disturbance in circuits is mostly caused by the radiated energy of EFT through cable coupling. This paper established a calculation model about double parallel cables and did a lot of numerical calculations about EFT coupling between the cables using the theory of transmission line. The characteristics of cable coupling of EFT under different exciting voltage, cable spacing, cable height and load impedance were researched systematically. An experimental device of cable coupling of EFT was designed for verifying the calculation results, which provided an important guidance for EFT suppression and system wiring.

There's more and more requirement for fast rise time pulse generator especially with high repetition frequency and high voltage. A cost effective and portable high-repetition high voltage nanosecond rectangular pulse generator is developed in this paper using serial avalanche transistors. By carefully designing the serial transistor circuit and PCB, the stray inductance and voltage reflection are reduced effectively, which make the output rectangular pulse obtain 2.5 ns rise time. The amplitude output pulse can reach up to 2.5 kV with 12.5 ns width. The pulse time jitter is less than 100 ps even in10 kHz high repetition frequency output mode.

We proposed a research of a heart sound envelope extraction system in this paper. The system was implemented on LabVIEW based on the Hilbert-Huang transform (HHT). We firstly used the sound card to collect the heart sound, and then implemented the complete system program of signal acquisition, pretreatment and envelope extraction on LabVIEW based on the theory of HHT. Finally, we used a case to prove that the system could collect heart sound, preprocess and extract the envelope easily. The system was better to retain and show the characteristics of heart sound envelope, and its program and methods were important to other researches, such as those on the vibration and voice, etc.

This paper reports the study and design of a visualization system of the ultrasonic rhinitis therapeutic apparatus with the function of endoscopic sinus. On Linux operating platform, we captured the video data of a video capture card that connected the endoscopic sinus using Video4Linux (V4L2) that was provided by the operating system. The video images were displayed by Qt. The visualization system solved the problem that the current ultrasonic rhinitis therapeutic apparatus had to rely on the large and expensive endoscopy equipment. And this simplified the doctors' operation, met the need of monitoring nasal cavity in the process of operating, greatly reduced the costs of treatment and would contribute to the promotion of the instrument. As a result, it has been tested that the nasal endoscopic image achieved by the system is clear and smooth, and fully meet the clinical needs of ultrasonic treatment of rhinitis.

Implantable devices used to replace or assist the operation of certain organs in the human body have been widely used. The traditional power supply method for implantable devices, such as disposable batteries or energy transmission by a puncture through the skin tissue, could carry the risk of the skin infection. Once running out of power, replacement of a new one requires re-operation. To overcome these problems above, a new energy supply method using ultrasound for the implantable devices operating in the body was proposed. In this paper, we presented our recent modeling results on power transmission through an elastic wall by piezoelectric transducers and ultrasound. This included the case of finite piezoelectric transducers on plates, power transmission through circular cylindrical shells. Then, a wireless and non-invasive energy supply method using ultrasound for the implantable devices operating in the body was proposed, in which a piezoelectric transducer was set on a recharging batteries that power implantable devices to receive the ultrasonic energy. The results demonstrated the operating principles of using ultrasound for implantable devices.

In the practical application of passive network impedance matching, variations in component tolerance, process, and load impedance may make the performance of impedance-matching network deviate from the designed or simulated result. The current work investigates the effect of these parameter variations on performance of T network impedance matching. The sensitivities of the resulting reflection coefficient to the parameter variations are theoretically studied. The formulas for calculating the resulting reflection coefficient caused by parameter variations are derived from quality factor-based design method. The analysis results can provide reference for design process and an opportunity for a better understanding of the dynamic behavior of the narrowband impedance-matching networks.

Au nanoparticles-coated, perfluorohexane-encapsulated and PEGylated mesoporous silica nanocapsule-based enhancement agents (MSNC@Au-PFH-PEG, abb. as MAPP) have been synthesized, for the ultrasound-induced cytoclasis, contrast-intensified ultrasound (US) imaging and US-guided high intensity focused ultrasound (HIFU) surgical therapy. Both the US-induced thermal effect and US triggered release of loaded model drug with MAPP under US exposure indicated the excellent US sensitivity of MAPP and its applicability for the combined chemo-/thermal therapy and future potential for HIFU ablation; US imaging under different modes verify the attractive US contrast intensification by using MAPP; US-guided HIFU therapy ex vivo and in vivo with MAPP is found to be highly efficient on rabbit VX2 xenograft tumor ablation due to the high thermal energy accumulation and increased mechanical/thermal effects from US-induced PFH bubble cavitations. MAPP can be promisingly used as an inorganic theranostic platform for contrast-intensified US imaging, combined chemotherapy and efficient HIFU tumor ablation under the guidance by the intensified US.

Bloodless surgical knife: Nano-biotechnology has been introduced into imaging-guided high-intensity focused ultrasound (HIFU) cancer surgery by adopting engineered multifunctional manganese-based mesoporous composite nanocapsules as the contrast agents for T(1)-weighted magnetic resonance imaging (MRI) and simultaneously as synergistic agents for MRI-guided HIFU cancer surgery.

A potential platform for simultaneous anticancer drug delivery and MRI cell imaging has been demonstrated by uniform hollow inorganic core/shell structured multifunctional mesoporous nanocapsules, which are composed of functional inorganic (Fe(3)O(4), Au, etc.) nanocrystals as cores, a thin mesoporous silica shell, and a huge cavity in between. The synthetic strategy for the creation of huge cavities between functional core and mesoporous silica shell is based on a structural difference based selective etching method, by which solid silica middle layer of Fe(2)O(3)@SiO(2)@mSiO(2) (or Au@SiO(2)@mSiO(2)) composite nanostructures was selectively etched away while the mesoporous silica shell could be kept relatively intact. The excellent biocompatibility of obtained multifunctional nanocapsules (Fe(3)O(4)@mSiO(2)) was demonstrated by very low cytotoxicity against various cell lines, low hemolyticity against human blood red cells and no significant coagulation effect against blood plasma. The cancer cell uptake and intracellular location of the nanocapsules were observed by confocal laser scanning microscopy and bio-TEM. Importantly, the prepared multifunctional inorganic mesoporous nanocapsules show both high loading capacity (20%) and efficiency (up to 100%) for doxorubicin simultaneously because of the formation of the cavity, enhanced surface area/pore volume and the electrostatic interaction between DOX molecules and mesoporous silica surface. Besides, the capability of Fe(3)O(4)@mSiO(2) nanocapsules as contrast agents of MRI was demonstrated both in vitro and in vivo, indicating the simultaneous imaging and therapeutic multifunctionalities of the composite nanocapsules. Moreover, the concept of multifunctional inorganic nanocapsules was extended to design and prepare Gd-Si-DTPA grafted Au@mSiO(2) nanocapsules for nanomedical applications, further demonstrating the generality of this strategy for the preparation of various multifunctional mesoporous nanocapsules.

To investigate high-power High-Intensity Focused Ultrasound (HIFU) generated acoustic field and the characteristic and significance of the method of acoustic field measurement. In this paper, thermocouple measurements of HIFU using power of 40W, 70W, 100W, 150W and 200W. The irradiation time at the phantom focal region was 1 second for temperature field distribution. The relationship between instantaneous temperature rise and the acoustic intensity was used to determine HIFU acoustic field distribution. The results showed that, as the acoustic power increases, the radius of the focal region gradually grows toward the width of -6dB; the focal region is widest when the acoustic power is 100W. The focal plane area and acoustic surface area increases with the increase in power. The use of thermocouples to measure the instantaneous temperature rise in the phantom focal region to describe the high-intensity acoustic field distribution of HIFU is a feasible method.

Bulk piezoelectric ceramics operating in thickness-stretch (TSt) modes have been widely used in acoustic-related devices. However, the fundamental TSt waves are always coupled with other modes, and the occurrence of these spurious modes in bulk piezoelectric ceramics affects its performance. To suppress the spurious modes, 1-3 piezoelectric composites are promising candidates. However, theoretical modeling of multiphase ceramic composite objects is very complex. In this study, a 1-3 piezoelectric composite sample and a bulk piezoelectric sample are fabricated. The electrical impedance of these two samples are compared. A simple analytical TSt vibration mode from the three dimensional equations of linear piezoelectricity is used to model the performance of 1-3 piezoelectric composites. The theoretical results agree well with the experimental results.

Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the spherical cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results.

Harvesting longitudinal ultrasonic energy from the surroundings has been highlighted as an alternative to conventional batteries. The energy can be used to power portable electronics and wireless sensors operating at remote locations. In this paper, an ultrasonic energy harvester made of a 1–3 piezoelectric composite is proposed. This harvester could convert longitudinal-mode ultrasonic vibrations into electrical energy. A theoretical analysis of a 1–3 piezoelectric composite harvester operating with thickness-stretch modes is performed. The results show that maximum output power dissipated in the load can be achieved when the load resistor is equal to the impedance of the harvester. Under such conditions, two peaks of maximum output power occur at the antiresonance frequency and resonance frequency. An experimental study following the theoretical model confirms the feasibility of extracting certain amounts of ultrasonic vibration energy using a 1–3 piezoelectric composite harvester. Both the experimental and theoretical studies show that the output voltages for different pure resistive loads peak at different operating frequencies. As the pure resistive load increases, the operating frequency varies from the resonance frequency to the antiresonance frequency.

This Letter reports on a tip-sensitive all-silica fiber-optic Fabry–Perot (TAFOFP) ultrasonic hydrophone for measuring high intensity focused ultrasound (HIFU) fields. The all-silica fiber-optic structure ensures that the TAFOFP ultrasonic hydrophone can withstand HIFU fields and the tip-sensitive configuration ensures that the TAFOFP ultrasonic hydrophone can achieve a high spatial resolution of 125 μm. The experimental results have shown that the TAFOFP ultrasonic hydrophone could stably measure the peak positive ultrasonic pressure as high as 4.34 MPa, and the measured ultrasonic pressure distributions of the HIFU field by the fabricated TAFOFP ultrasonic hydrophone agreed well with those by the piezoceramic needle hydrophone.

High intensity focused ultrasound (HIFU) focusing precision is limited by conventional focusing ultrasound methods. The aim of this study is to develop an ultrasonic focusing modality by using a spherical cavity transducer with open ends. Experimental measurements and numerical simulations were performed to study the acoustic field and the induced tissue lesion using this transducer. The results demonstrate that the focusing zone is smaller while the focusing gain of sound pressure is higher (about 3 times) than the conventional concave focusing method. The results demonstrate great clinical potentials of enhancing the precision of HIFU therapy to the sub-wavelength level.

A novel and general in situ hydrophobic shell-protected selective etching strategy has been developed to synchronously synthesize and modify hollow mesoporous silica nanoparticles (HMSNs) and rattle-type mesoporous silica nanoparticles (RMSNs) with well-defined morphology, effectively avoiding the drawbacks of post-modification. The key point of the strategy lies in the hydrophilicity differences between the pure silica inner core and the organic hybrid silica shell, which results in the preferential etching of the pure silica inner core. Except that amino group functionalized HMSNs (amino-HMSNs) can be synthesized via this strategy, it can be readily applied for the synthesis of HMSNs and RMSNs synchronously grafted with different kinds of functional groups by employing other silane coupling agents, directly indicating the generality of this strategy. Furthermore, adding no additional reduction agents, the amino-HMSNs can be regarded as nanoreactors, and a distinctively heterogeneous rattle-type structure, Au@HMSN/Au, with an entrapped size-tunable Au nanoparticle and some small Au nanocrystals embedded in the hollow cavity and shell of each nanoparticle, respectively, is obtained. As hybrid ultrasound contrast agents (UCAs), unlike micro-sized organic UCAs merely confined to blood pool imaging, the as-synthesized nano-sized amino-HMSNs can achieve excellent in vitro ultrasound imaging, and potentially be applied in cell-level imaging. More importantly, relying on the process merits of our strategy, such as the doping of silane coupling agents and no calcination treatment, amino-HMSNs exhibit enhanced ultrasound imaging to some certain extent compared to the calcined ones.