Role of acoustic cavitation in the delivery and monitoring of cancer treatment by high-intensity focused ultrasound (HIFU)

Optimizing high-intensity focused ultrasound-induced immunogenic cell-death using passive cavitation mapping as a monitoring tool

Over the past decade, ultrasound (US) has gathered significant attention and research focus in the realm of medical treatments, particularly within the domain of anti-cancer therapies. This growing interest can be attributed to its non-invasive nature, precision in delivery, availability, and safety. While the conventional objective of US-based treatments to treat breast, prostate, and liver cancer is the ablation of target tissues, the introduction of the concept of immunogenic cell death (ICD) has made clear that inducing cell death can take different non-binary pathways through the activation of the patient's anti-tumor immunity. Here, we investigate high-intensity focused ultrasound (HIFU) to induce ICD by unraveling the underlying physical phenomena and resulting biological effects associated with HIFU therapy using an automated and fully controlled experimental setup. Our in-vitro approach enables the treatment of adherent cancer cells (B16F10 and CT26), analysis for ICD hallmarks and allows to monitor and characterize in real time the US-induced cavitation activity through passive cavitation detection (PCD). We demonstrate HIFU-induced cell death, CRT exposure, HMGB1 secretion and antigen release. This approach holds great promise in advancing our understanding of the therapeutic potential of HIFU for anti-cancer strategies.

Mechanical Disruption by Focused Ultrasound Re-sensitizes ER+ Breast Cancer Cells to Hormone Therapy

OBJECTIVE

Tamoxifen is the most used agent to treat estrogen receptor-positive (ER+) breast cancer (BC). While it decreases the risk of cancer recurrence by 50%, many patients develop resistance to this treatment, culminating in highly aggressive disease. Tamoxifen resistance comes from the repression of ER transcriptional activity that switches the cancer cells to proliferation via nonhormonal signaling pathways. Here, we evaluate a potential strategy to overcome tamoxifen resistance by focused ultrasound (FUS), a noninvasive approach for the mechanical excitation of cancer cells.

METHODS

Resistant and nonresistant ER+ BC cells and xenografts from patients with ER+ BC were treated with tamoxifen, FUS or their combination. The apoptosis, proliferation rate, gene expression and activity of estrogen receptor, and morphological changes were measured in treated cells and tissues.

RESULTS

FUS caused the mechanical disruption of tamoxifen-resistant BC cells that in turn led to the upregulation of ERα-encoding gene expression and long-term re-sensitization of the cells to tamoxifen. Patient-derived xenografts treated with Tamoxifen and FUS demonstrated a significant reduction in tumor viability and proliferation and a strong structural damage to tumor cells and extracellular matrix.

CONCLUSION

FUS can improve ER+ BC treatment by re-sensitizing the cancer cells to tamoxifen.

Propulsion mechanisms of micro/nanorobots: a review

Micro/nanomotors (MNMs) are intelligent, efficient and promising micro/nanorobots (MNR) that can respond to external stimuli (e.g., chemical energy, temperature, light, pH, ultrasound, magnetic, biosignals, ions) and perform specific tasks. The MNR can adapt to different external stimuli and transform into various functional forms to match different application scenarios. So far, MNR have found extensive application in targeted therapy, drug delivery, tissue engineering, environmental remediation, and other fields. Despite the promise of MNR, there are few reviews that focus on them. To shed new light on the further development of the field, it is necessary to provide an overview of the current state of development of these MNR. Therefore, this paper reviews the research progress of MNR in terms of propulsion mechanisms, and points out the pros and cons of different stimulus types. Finally, this paper highlights the current challenges faced by MNR and proposes possible solutions to facilitate the practical application of MNR.

Microbubble-enhanced transcranial MR-guided focused ultrasound brain hyperthermia: heating mechanism investigation using finite element method

Recently, our group developed a synergistic brain drug delivery method to achieve simultaneous transcranial hyperthermia and localized blood-brain barrier opening via MR-guided focused ultrasound (MRgFUS). In a rodent model, we demonstrated that the ultrasound power required for transcranial MRgFUS hyperthermia was significantly reduced by injecting microbubbles (MBs). However, the specific mechanisms underlying the power reduction caused by MBs remain unclear. The present study aims to elucidate the mechanisms of MB-enhanced transcranial MRgFUS hyperthermia through numerical studies using the finite element method. The microbubble acoustic emission (MAE) and the viscous dissipation (VD) were hypothesized to be the specific mechanisms. Acoustic wave propagation was used to model the FUS propagation in the brain tissue, and a bubble dynamics equation for describing the dynamics of MBs with small shell thickness was used to model the MB oscillation under FUS exposures. A modified bioheat transfer equation was used to model the temperature in the rodent brain with different heat sources. A theoretical model was used to estimate the bubble shell's surface tension, elasticity, and viscosity losses. The simulation reveals that MAE and VD caused a 40.5% and 52.3% additional temperature rise, respectively. Compared with FUS only, MBs caused a 64.0% temperature increase, which is consistent with our previous animal experiments. Our investigation showed that MAE and VD are the main mechanisms of MB-enhanced transcranial MRgFUS hyperthermia.

Harmonic Motion Imaging-Guided Focused Ultrasound Ablation: Comparison of Three Focused Ultrasound Interference Filtering Methods

OBJECTIVE

Harmonic motion imaging (HMI) is an acoustic radiation force-based elasticity imaging technique, which can be used to monitor changes in tissue mechanical properties caused by focused ultrasound (FUS)-induced thermal ablation. In conventional HMI, the amplitude-modulated FUS sequence and imaging pulse are transmitted simultaneously. With this method, the high-amplitude FUS signal must be separated from the imaging data for tissue displacement estimation. Frequency domain notch filtering and bandpass filtering were previously used to filter FUS interference from imaging data. However, FUS interference becomes more pronounced at the increased intensities and durations necessary for thermal ablation, rendering frequency domain filtering challenging. In this study, three methods for FUS interference filtering during HMI-guided FUS ablation (HMIgFUS) were compared. The methods were notch filtering; interleaved HMIgFUS, with interleaved FUS and imaging pulses; and FUS-net, a convolutional neural network-based U-Net autoencoder developed by our group for FUS interference filtering in radiofrequency data. FUS-net was applied here for the first time for the purpose of ablation displacement monitoring.

METHODS

The three filtering methods were tested during 20 HMIgFUS acquisitions in an ex vivo canine liver using a range of peak positive pressures from 11 to 18 MPa and durations ranging from 60 to 180 seconds. The B-mode mean squared errors (MSEs) and displacement amplitude contrast-to-noise ratios (CNRs) of the three methods were calculated and compared.

RESULTS

The interleaved method for HMIgFUS was found to be significantly robust in avoiding FUS interference in all tested cases for FUS ablation monitoring, especially cases with high FUS pressure and long durations, as opposed to traditional notch filtering and FUS-net filtering. CNRs obtained from displacement amplitude maps in the interleaved data set were significantly higher in all cases than those obtained from the notch filtered and FUS-net data sets. There was not a significant trend in displacement CNR between the FUS-net and notch filtered data sets. However, B-mode MSE was found to be significantly higher when comparing the FUS-net and interleaved data sets as opposed to the notch filtered and interleaved data sets, suggesting further potential of FUS-net as an FUS interference filtering method.

CONCLUSION

These findings indicate the robustness of interleaved HMIgFUS in avoiding FUS interference during HMIgFUS monitoring and the advantages, limitations and future potential of FUS-net and notch filtering.

Safety of Sonazoid in Assisting High-Intensity Focused Ultrasound Ablation Therapy for Advanced Liver Malignant Lesions: A Single-Arm Clinical Study

OBJECTIVE

The aim of the study described here was to evaluate the safety of Sonazoid-assisted high-intensity focused ultrasound (HIFU) in the treatment of advanced malignant liver lesions.

METHODS

A single-arm study was designed to enroll participants who were diagnosed with advanced primary liver cancer or liver metastases and proposed to receive Sonazoid assistance during HIFU treatment. Serological examination was conducted within 1 wk, and side effects in each patient were monitored for 1 mo. To evaluate therapeutic efficacy, the contrast-enhanced magnetic resonance imaging was performed 1 mo after treatment, and short-term follow-up was conducted a year later.

RESULTS

A total of 17 participants (12 male, 5 female) with an average age of 58 y (range: 46-73 y) were enrolled, including 11 patients with hepatocellular carcinoma, 2 patients with hepatic metastasis and 4 patients with cholangiocarcinoma. The total volume of tumor mass was 111.82 (11.01-272.30) cm3. The average total ablation time for a patient was 2021 ± 1030 s, and the energy efficiency factor was 5979.7 (3108.0, 45634.5) J/cm3. Immediately after HIFU treatment, 1 patient (5.9%) achieved complete response (CR), 4 patients (23.5%) had a moderate response, 8 patients (47.1%) had partial reperfusion and 4 patients (23.5%) had stable disease (SD). The average ablation rate for all the tumors was 51.5 ± 26.7%. The level of glutamic-pyruvic transaminase (ALT) was mildly increased in 71.6% (12/17) of patients after HIFU therapy. Mean ALT values before and after treatment were 22 (14, 35) U/L and 36 (25, 41) U/L, respectively (Z = 1.947, p = 0.051). Mild or obvious edema in skin and subcutaneous soft tissues were observed in 76.5% of patients, but no serious side effects were found. Twelve months after treatment, the follow-up results revealed that 1 patient (5.8%) achieved a CR, 8 patients (47.1%) had SD and 8 patients (47.1%) had progressive disease. The estimated median time to progression was 11 mo after treatment, with a 95% confidence interval of 6, 11 for all involved patients.

CONCLUSION

Use of Sonazoid is safe and feasible for improving HIFU ablation efficiency during the treatment of advanced malignant liver lesions. The therapeutic efficacy of Sonazoid-assisted HIFU needs to be explored in additional controlled clinical investigations.

Mapping of 20 L capacity ultrasonic reactor using cavitation activity meter and dye degradation

Mapping of a novel 20 L capacity ultrasonic (US) reactor having a total of 44 transducers was done by measuring the local cavitation intensity using a cavitation activity meter at different horizontal planes and subsequent validation based on dye degradation. A fixed frequency of 33 kHz and temperature of 30 °C was used during the mapping performed at two different power levels of 250 W and 400 W. In addition, the mapping of specific plane 2 was also performed with transducers operating on walls 1 and 3, while switching the transducers on walls 2 and 4 off and vice versa so as to establish the role of using multiple transducers. Degradation of RO4 dye was also measured at the plane 2 at various powers as 250 W, 400 W, and 1000 W. The degradation of the RO4 dye directly correlated to the cavitation intensity measured at the various location inside the US reactor. The average cavitation intensity was 265.38, 317.25, 185, and 300.5 Cavins for power dissipations of 250 W, 400 W, 250 W (wall 1 and 3 transducers in operation), and 400 W (wall 2 and 4 transducers in operation), respectively. Correspondingly, the average degradation was 10.35 %, 13.03 %, 5.52 %, and 8.9 % for same sequence of operational power and transducers. The investigation amply illustrated dependency of the cavitational activity on the location, power dissipation, and operating mode elucidating important design related information useful for scale up of sonochemical reactors.

Stimuli-Responsive Functional Micro-/Nanorobots: A Review

Stimuli-responsive functional micro-/nanorobots (srFM/Ns) are a class of intelligent, efficient, and promising microrobots that can react to external stimuli (such as temperature, light, ultrasound, pH, ion, and magnetic field) and perform designated tasks. Through adaptive transformation into the corresponding functional forms, they can perfectly match the demands depending on different applications, which manifest extremely important roles in targeted therapy, biological detection, tissue engineering, and other fields. Promising as srFM/Ns can be, few reviews have focused on them. It is therefore necessary to provide an overview of the current development of these intelligent srFM/Ns to provide clear inspiration for further development of this field. Hence, this review summarizes the current advances of stimuli-responsive functional microrobots regarding their response mechanism, the achieved functions, and their applications to highlight the pros and cons of different stimuli. Finally, we emphasize the existing challenges of srFM/Ns and propose possible strategies to help accelerate the study of this field and promote srFM/Ns toward actual applications.

Excitation of a Single Compound by Light and Ultrasound Enhanced the Long-Term Cure of Mice Bearing Prostate Tumors

Current treatment for prostate cancer is dependent on the stages of the cancer, recurrence, and genetic factors. Treatment varies from active surveillance or watchful waiting to prostatectomy, chemotherapy, and radiation therapy in combination or alone. Although radical prostate cancer therapy reduces the advancement of the disease and its mortality, the increased disease treatment associated morbidity, erectile dysfunction, and incontinence affect the quality of life of cancer survivors. To overcome these problems, photodynamic therapy (PDT) has previously been investigated using Photofrin^TM as a photosensitizer (PS). However, Photofrin-PDT has shown limitations in treating prostate cancer due to its limited tumor-specificity and the depth of light penetration at 630 nm (the longest wavelength absorption of Photofrin^TM). The results presented herein show that this limitation can be solved by using a near infrared (NIR) compound as a photosensitizer (PS) for PDT and the same agent also acts as a sonosensitizer for SDT (using ultrasound to activate the compound). Compared to light, ultrasound has a stronger penetration ability in biological tissues. Exposing the PS (or sonosensitizer) to ultrasound (US) initiates an electron-transfer process with a biological substrate to form radicals and radical ions (type I reaction). In contrast, exposure of the PS to light (PDT) generates singlet oxygen (type II reaction). Therefore, the reactive oxygen species (ROS) produced by SDT and PDT follow two distinct pathways, i.e., type I (oxygen independent) and type II (oxygen dependent), respectively, and results in significantly enhanced destruction of tumor cells. The preliminary in vitro and in vivo results in a PC3 cell line and tumor model indicate that the tumor specificality of the therapeutic agent(s) can be increased by targeting galectin-1 and galectin-3, known for their overexpression in prostate cancer.

Choroidal neovascularization removal with photo-mediated ultrasound therapy

BACKGROUND

Age-related macular degeneration (AMD) is a major cause of irreversible central vision loss. The main reason for lost vision due to AMD is choroidal neovascularization (CNV). In the clinic, current treatments for CNV include photodynamic therapy, laser photocoagulation, and anti-vascular endothelial growth factor (VEGF) therapy.

PURPOSE

This study evaluates a novel treatment technique combining synchronized nanosecond laser pulses and ultrasound bursts, namely photo-mediated ultrasound therapy (PUT) as a potential treatment method for CNV, for its efficacy and safety in the treatment of CNV via the experiments in a clinically-relevant rabbit model in vivo.

METHODS

CNV was created by subretinal injection of Matrigel and vascular endothelial growth factor (M&V) in 10 New Zealand white rabbits. Six rabbits were used in the PUT group. In the control groups, two rabbits were treated by laser-only, and two rabbits were treated by ultrasound-only. The treatment efficacy was evaluated through fundus photography and fluorescein angiography (FA) longitudinally for up to 4 weeks. Rabbits were sacrificed for histopathology 3 months after treatment to examine the safety of PUT.

RESULTS

The fluorescein leakage on FA was quantified to longitudinally evaluate treatment outcome. Compared with baseline, the relative intensity index was reduced by 26.57% ± 8.66% at 3 days after treatment, 27.24% ± 6.21% at 1 week after treatment, 27.79% ± 2.61% at 2 weeks after treatment, and 32.12% ± 3.23% at 4 weeks after treatment, all with a statistically significant difference of p < 0.01. The comparison between the relative intensity indexes from the two control groups (laser-only treatment and ultrasound-only treatment) did not show any statistically significant difference at all time points. Safety evaluation at 3 months with histopathology demonstrated that the PUT did not result in morphologic changes to the neurosensory retina.

CONCLUSIONS

This study introduces PUT for the first time for the treatment of CNV. The results demonstrated good efficacy and safety of PUT to treat CNV in a clinically-relevant rabbit model. With a single session of treatment, PUT can safely reduce the leakage of CNV for at least 1 month after treatment.

Real-time assessment of high-intensity focused ultrasound heating and cavitation with hybrid optoacoustic ultrasound imaging

High-intensity focused ultrasound (HIFU) enables localized ablation of biological tissues by capitalizing on the synergistic effects of heating and cavitation. Monitoring of those effects is essential for improving the efficacy and safety of HIFU interventions. Herein, we suggest a hybrid optoacoustic-ultrasound (OPUS) approach for real-time assessment of heating and cavitation processes while providing an essential anatomical reference for accurate localization of the HIFU-induced lesion. Both effects could clearly be observed by exploiting the temperature dependence of optoacoustic (OA) signals and the strong contrast of gas bubbles in pulse-echo ultrasound (US) images. The differences in temperature increase and its rate, as recorded with a thermal camera for different HIFU pressures, evinced the onset of cavitation at the expected pressure threshold. The estimated temperatures based on OA signal variations were also within 10-20 % agreement with the camera readings for temperatures below the coagulation threshold (∼50 °C). Experiments performed in excised tissues as well as in a post-mortem mouse demonstrate that both heating and cavitation effects can be effectively visualized and tracked using the OPUS approach. The good sensitivity of the suggested method for HIFU monitoring purposes was manifested by a significant increase in contrast-to-noise ratio within the ablated region by > 10 dB and > 5 dB for the OA and US images, respectively. The hybrid OPUS-based monitoring approach offers the ease of handheld operation thus can readily be implemented in a bedside setting to benefit several types of HIFU treatments used in the clinics.

An in-vivo study of the combined therapeutic effects of pulsed non-thermal focused ultrasound and radiation for prostate cancer

PURPOSE

The purpose of this study was to investigate the in vivo combined effects of pulsed focused ultrasound (pFUS) and radiation (RT) for prostate cancer treatment.

MATERIALS AND METHODS

An animal prostate tumor model was developed by implanting human LNCaP tumor cells in the prostates of nude mice. Tumor-bearing mice were treated with pFUS, RT or both (pFUS + RT) and compared with a control group. Non-thermal pFUS treatment was delivered by keeping the body temperature below 42 °C as measured real-time by MR thermometry and using a pFUS protocol (1 MHz, 25 W focused ultrasound; 1 Hz pulse rate with a 10% duty cycle for 60 sec for each sonication). Each tumor was covered entirely using 4-8 sonication spots. RT treatment with a dose of 2 Gy was delivered using an external beam (6 MV photon energy with dose rate 300MU/min). Following the treatment, mice were scanned weekly with MRI for tumor volume measurement.

RESULTS

The results showed that the tumor volume in the control group increased exponentially to 142 ± 6%, 205 ± 12%, 286 ± 22% and 410 ± 33% at 1, 2, 3 and 4 weeks after treatment, respectively. In contrast, the pFUS group was 29% (p < 0.05), 24% (p < 0.05), 8% and 9% smaller, the RT group was 7%, 10%, 12% and 18% smaller, and the pFUS + RT group was 32%, 39%, 41% and 44% (all with p < 0.05) smaller than the control group at 1, 2, 3, and 4 weeks post treatment, respectively. Tumors treated by pFUS showed an early response (i.e. the first 2 weeks), while the RT group showed a late response. The combined pFUS + RT treatment showed consistent response throughout the post-treatment weeks.

CONCLUSIONS

These results suggest that RT combined with non-thermal pFUS can significantly delay the tumor growth. The mechanism of tumor cell killing between pFUS and RT may be different. Pulsed FUS shows early tumor growth delay, while RT contributes to the late effect on tumor growth delay. The addition of pFUS to RT significantly enhanced the therapeutic effect for prostate cancer treatment.

Comparing Phantom and Animal Metrics Applied in the Determination of Focused Ultrasound Stable and Inertial Cavitation Levels

OBJECTIVE

The opening of the blood-brain barrier (BBB) to allow therapeutic drug passage can be achieved by inducing microbubble cavitation using focused ultrasound (FUS). This approach can be monitored through analysis of the received signal to distinguish between stable cavitation associated with safe BBB opening and inertial cavitation associated with blood vessel damage. In this study, FUS phantom and animal studies were used to evaluate the experimental conditions that generate several cross-consistent metrics having the potential to be combined for the reliable, automatic control of cavitation levels.

METHODS

Typical metrics for cavitation monitoring involve observing changes in the spectrum generated by applying the discrete Fourier transform (DFT) to the time domain signal detected using a hydrophone during FUS. A confocal hydrophone was used to capture emissions during a 10 ms FUS burst, sampled at 32 ns intervals, to produce 321,500 points and a high-resolution spectrum when transformed. The FUS spectra were analyzed to show the impact that equipment-transients and well-known DFT-related distortions had on the metrics used for cavitation control. A new approach, physical sparsification (PH-SP), was introduced to sharpen FUS spectral peaks and minimize the effect of these distortions.

DISCUSSION

It was demonstrated that the general spectral signal-to-noise ratio (SNR) could be improved by removing the initial noisy phantom hydrophone signal transient. Minor changes in the transient length digitally removed from the sampled values significantly changed the spectral bandwidths of all the harmonically related FUS signals. We evaluated signal processing techniques to minimize the impact these DFT-related distortions on area-under-the-curve (AUC) metric calculations, and we identified the advantages of using PH-SP and proposed new metrics when characterizing FUS spectral properties. The results show many second, third and sub-harmonic metrics provide cross-consistent evidence of changes between stable and inertial cavitation levels. Removing the first harmonic signal component with a hardware low-pass filter allowed the hydrophone gain to be boosted without introducing distortion, leading to an improved analysis of the sub-harmonic signal orders of magnitude smaller in intensity. Metrics that optimized the energy in the real component of the complex-valued PH-SP spectra provided a 32% increase in the sub-harmonic sensitivity compared to standard metrics.

CONCLUSION

A preliminary investigation of existing and proposed metrics showed that system noise could be large enough to mask the transition between stable and inertial cavitation. Strong narrowing of sub-harmonic peak shapes on applying physical sparsification (PH-SP) were seen in both phantom and animal studies. However, validating equivalent trends of the metrics with pressure were limited by the increased system noise level in the animal study combined with the natural variability between subjects studied. The combined use of hardware low-pass filters and physical sparsification to selectively removing distortions in the spectrum allowed the optimization of metrics for cavitation monitoring by improving the sub-harmonic sensitivity.

Holographic Focused Ultrasound Hyperthermia System for Uniform Simultaneous Thermal Exposure of Multiple Tumor Spheroids

Hyperthermia is currently used to treat cancer due to its ability to radio- and chemo-sensitize and to stimulate the immune response. While ultrasound is non-ionizing and can induce hyperthermia deep within the body non-invasively, achieving uniform and volumetric hyperthermia is challenging. This work presents a novel focused ultrasound hyperthermia system based on 3D-printed acoustic holograms combined with a high-intensity focused ultrasound (HIFU) transducer to produce a uniform iso-thermal dose in multiple targets. The system is designed with the aim of treating several 3D cell aggregates contained in an International Electrotechnical Commission (IEC) tissue-mimicking phantom with multiple wells, each holding a single tumor spheroid, with real-time temperature and thermal dose monitoring. System performance was validated using acoustic and thermal methods, ultimately yielding thermal doses in three wells that differed by less than 4%. The system was tested in vitro for delivery of thermal doses of 0-120 cumulative equivalent minutes at 43 °C (CEM43) to spheroids of U87-MG glioma cells. The effects of ultrasound-induced heating on the growth of these spheroids were compared with heating using a polymerase chain reaction (PCR) thermocycler. Results showed that exposing U87-MG spheroids to an ultrasound-induced thermal dose of 120 CEM43 shrank them by 15% and decreased their growth and metabolic activity more than seen in those exposed to a thermocycler-induced heating. This low-cost approach of modifying a HIFU transducer to deliver ultrasound hyperthermia opens new avenues for accurately controlling thermal dose delivery to complex therapeutic targets using tailored acoustic holograms. Spheroid data show that thermal and non-thermal mechanisms are implicated in the response of cancer cells to non-ablative ultrasound heating.

Robotic system for magnetic resonance imaging-guided high-intensity focus ultrasound application: Feasibility of breast fibroadenoma treatment

PURPOSE

This paper presents a high-intensity focus ultrasound (HIFU) robotic system for treating breast fibroadenoma under the guidance of magnetic resonance imaging (MRI). Based on the thermal and mechanical effects of ultrasound, the system aims to deliver ultrasound energy to a target precisely without damaging the normal tissue. The temperature elevation can be monitored in real time by MRI, and the treatment plan can be adjusted during the procedure. The requirements, design specifications, control system and registration of the robotic system are specified.

METHODS

The robotic system was designed with a 3 degrees of freedom manipulator with limit switches and encoders, a customised MRI-compatible breast coil, a water bladder with sets of breast-conforming brackets, and a probe capable of generating ultrasound. Twenty volunteers were recruited for this study, and their data were analysed to provide more precise data for the design. The accuracy of the robot was evaluated in free space using a coordinate measuring machine, phantom and ex vivo porcine tissue in MRI room. The study also verified the signal-to-noise ratio (SNR) of the MRI with the effect of the robotic system.

RESULTS

The research findings revealed that the manipulator exhibited a translational precision of 0.10 ± 0.14 mm, a rotational fidelity around the X direction of 0.11 ± 0.09°, and an oscillatory exactness around the Y direction of 0.10 ± 0.08°. The investigation of positioning accuracy demonstrated that the robot's error in free space was 0.26 ± 0.07 mm. When subjected to MRI room with agar-silica phantom and ex vivo porcine tissue, the positioning accuracy amounted to 1.11 ± 0.47 mm and 1.57 ± 0.52 mm. In the presence of the robotic system, the SNR of the MRI experienced a 4.2% reduction, which had a negligible impact on image quality.

CONCLUSIONS

The conducted experiments validate the efficacy of the proposed MRI-guided HIFU robotic system in executing agar-silica phantom and ex vivo porcine tissue investigations with adequate positioning accuracy. Consequently, this system exhibits certain feasibility for the treatment of breast fibroadenomas.

Photo-/piezo-activated ultrathin molybdenum disulfide nanomedicine for synergistic tumor therapy

Molybdenum disulfide (MoS₂), as a transition metal dichalcogenide, has attracted tremendous attention owing to its remarkable electronic, physical, and chemical properties. In this study, based on the energy-converting nanomedicine, we report multifunctional two-dimensional (2D) MoS₂ nanosheets with inherent plasmonic property and piezocatalytic activity for imaging-guided synergistic tumor therapy. MoS₂ nanosheets display strong plasmon resonances in the near-infrared (NIR) region, especially in the second NIR biological window, possessing a notable light energy to heat effect under 1064 nm laser irradiation, which not only serves as a robust photothermal agent for cancer cell ablation but also acts as a contrast-enhanced agent for thermal imaging and photoacoustic imaging. Meanwhile, MoS₂ nanosheets feature a remarkable piezotronic effect, exhibiting mechanical vibration energy to electricity under the stimulation of ultrasound-mediated microscopic pressure for reactive oxygen species generation to further kill cancer cells. The new function for old materials may open up the in-depth exploration of MoS₂-based functional biomaterials in the future clinical application of imaging-guided photothermal and piezocatalytic synergetic treatment.

Sonoprocessing: mechanisms and recent applications of power ultrasound in food

There is a growing interest in using green technologies in the food industry. As a green processing technique, ultrasound has a great potential to be applied in many food applications. In this review, the basic mechanism of ultrasound processing technology has been discussed. Then, ultrasound technology was reviewed from the application of assisted food processing methods, such as assisted gelation, assisted freezing and thawing, assisted crystallization, and other assisted applications. Moreover, ultrasound was reviewed from the aspect of structure and property modification technology, such as modification of polysaccharides and fats. Furthermore, ultrasound was reviewed to facilitate beneficial food reactions, such as glycosylation, enzymatic cross-linking, protein hydrolyzation, fermentation, and marination. After that, ultrasound applications in the food safety sector were reviewed from the aspect of the inactivation of microbes, degradation of pesticides, and toxins, as well inactivation of some enzymes. Finally, the applications of ultrasound technology in food waste disposal and environmental protection were reviewed. Thus, some sonoprocessing technologies can be recommended for the use in the food industry on a large scale. However, there is still a need for funding research and development projects to develop more efficient ultrasound devices.

Evaluation of the dual-frequency transducer for controlling thermal ablation morphology using frequency shift keying signal

PURPOSE

The catheter-based ultrasound (CBUS) can reach the target tissue directly and achieve rapid treatment. The frequency shift keying (FSK) signal is proposed to regulate and evaluate tumor ablation by a miniaturized dual-frequency transducer.

METHODS

A dual-frequency transducer prototype (3 × 7 × 0.4 mm) was designed and fabricated for the CBUS applicator (OD: 3.8 mm) based on the fundamental frequency of 5.21 MHz and the third harmonic frequency of 16.88 MHz. Then, the acoustic fields and temperature field distributions using the FSK signals (with 0, 25, 50, 75, and 100% third harmonic frequency duty ratios) were simulated by finite element analysis. Finally, tissue ablation and temperature monitoring were performed in phantom and ex vivo tissue, respectively.

RESULTS

At the same input electrical power (20 W), the output acoustic power of the fundamental frequency of the transducer was 10.03 W (electroacoustic efficiencies: 50.1%), and that of the third harmonic frequency was 6.19 W (30.6%). As the third harmonic frequency duty ratios increased, the shape of thermal lesions varied from strip to droplet in simulated and phantom experimental results. The same trend was observed in ex vivo tests.

CONCLUSION

Dual-frequency transducers excited by the FSK signal can control the morphology of lesions.

SIGNIFICANCE

The acoustic power deposition of CBUS was optimized to achieve precise ablation.

Ultrasound-Induced Drug Release from Stimuli-Responsive Hydrogels

Stimuli-responsive hydrogel drug delivery systems are designed to release a payload when prompted by an external stimulus. These platforms have become prominent in the field of drug delivery due to their ability to provide spatial and temporal control for drug release. Among the different external triggers that have been used, ultrasound possesses several advantages: it is non-invasive, has deep tissue penetration, and can safely transmit acoustic energy to a localized area. This review summarizes the current state of understanding about ultrasound-responsive hydrogels used for drug delivery. The mechanisms of inducing payload release and activation using ultrasound are examined, along with the latest innovative formulations and hydrogel design strategies. We also report on the most recent applications leveraging ultrasound activation for both cancer treatment and tissue engineering. Finally, the future perspectives offered by ultrasound-sensitive hydrogels are discussed.

Shockwaves Increase In Vitro Resilience of Rhizopus oryzae Biofilm under Amphotericin B Treatment

Acoustical biophysical therapies, including ultrasound, radial pressure waves, and shockwaves, have been shown to harbor both a destructive and regenerative potential depending on physical treatment parameters. Despite the clinical relevance of fungal biofilms, little work exits comparing the efficacy of these modalities on the destruction of fungal biofilms. This study evaluates the impact of acoustical low-frequency ultrasound, radial pressure waves, and shockwaves on the viability and proliferation of in vitro Rhizopus oryzae biofilm under Amphotericin B induced apoptosis. In addition, the impact of a fibrin substrate in comparison with a traditional polystyrene well-plate one is explored. We found consistent, mechanically promoted increased Amphotericin B efficacy when treating the biofilm in conjunction with low frequency ultrasound and radial pressure waves. In contrast, shockwave induced effects of mechanotransduction results in a stronger resilience of the biofilm, which was evident by a marked increase in cellular viability, and was not observed in the other types of acoustical pressure waves. Our findings suggest that fungal biofilms not only provide another model for mechanistical investigations of the regenerative properties of shockwave therapies, but warrant future investigations into the clinical viability of the therapy.

Investigation of hardware and software techniques to enhance the characteristics of focused ultrasound (FUS) spectra

Objective. Microbubble cavitation generated by focused ultrasound (FUS) can induce safe blood-brain-barrier (BBB) opening allowing therapeutic drug passage. Spectral changes in the hydrophone sensor signal are currently used to distinguish stable cavitation from inertial cavitation that can damage the BBB. Gibbs’ ringing, peak intensity loss and peak width increase are well-known distortions evident when using the discrete Fourier transform (DFT) to transform data containing a few hundred points. We investigate overcoming the fact that FUS time signals (10 ms providing 312 500 points sampled at 32 ns intervals) can generate such sharp spectral peaks that variations in their DFT-related distortions can significantly impact the values of the key metrics used for cavitation characterization. Approach. We introduce low-pass filter hardware to improve how the analogue to digital convertor handles high-frequency noise components and the orders of magnitude differences between FUS harmonic intensities. We investigate the enhanced FUS spectral stability and resolution obtained from a new technique, physical sparsification (PH-SP), customized to the a-priori information that all key FUS components are harmonically related. Results are compared with standard DFT optimizations involving time data windowing and Fourier interpolation. Main results. A new simulation model showed peak intensity, widths and metrics modified by small changes in the transformed signal’s length when removing the noisy starting transient of the FUS hydrophone signal or following minor excitation frequency or sampling rate adjustments. 25%–60% area-under-the-curve changes occurred in phantom studies at different pressure levels. Spectral peak sharpness was best optimized and stabilized with PH-SP. Significance. Special FUS characteristics mean starting transients and minor variations in experimental procedures lead to significant changes in the spectral metrics used to monitor cavitation levels. Customizing PH-SP to these characteristics led to sharper, more stable spectra with the potential to track the impact of microbubble environment changes.

Neuroinflammation associated with ultrasound-mediated permeabilization of the blood-brain barrier

The blood-brain barrier (BBB) continues to represent one of the most significant challenges for successful drug-based treatments of neurological disease. Mechanical modulation of the BBB using focused ultrasound (FUS) and microbubbles (MBs) has shown considerable promise in enhancing the delivery of therapeutics to the brain, but questions remain regarding possible long-term effects of such forced disruption. This review examines the evidence for inflammation associated with ultrasound-induced BBB disruption and potential strategies for managing such inflammatory effects to improve both the efficacy and safety of therapeutic ultrasound in neurological applications.

Ultrasound Triggers Hypericin Activation Leading to Multifaceted Anticancer Activity

The use of ultrasound (US) in combination with a responsive chemical agent (sonosensitizer) can selectively trigger the agent's anticancer activity in a process called sonodynamic therapy (SDT). SDT shares some properties with photodynamic therapy (PDT), which has been clinically approved, but sets itself apart because of its use of US rather than light to achieve better tissue penetration. SDT provides anticancer effects mainly via the sonosensitizer-mediated generation of reactive oxygen species (ROS), although the precise nature of the underpinning mechanism is still under debate. This work investigates the SDT anticancer activity of hypericin (Hyp) in vitro in two- (2D) and three-dimensional (3D) HT-29 colon cancer models, and uses PDT as a yardstick due to its well-known Hyp phototoxicity. The cancer cell uptake and cellular localization of Hyp were investigated first to determine the proper noncytotoxic concentration and incubation time of Hyp for SDT. Furthermore, ROS production, cell proliferation, and cell death were evaluated after Hyp was exposed to US. Since cancer relapse and transporter-mediated multidrug resistance (MDR) are important causes of cancer treatment failure, the US-mediated ability of Hyp to elicit immunogenic cell death (ICD) and overcome MDR was also investigated. SDT showed strong ROS-mediated anticancer activity 48 h after treatment in both the HT-29 models. Specific damage-associated molecular patterns that are consistent with ICD, such as calreticulin (CRT) exposure and high-mobility group box 1 protein (HMGB1) release, were observed after SDT with Hyp. Moreover, the expression of the ABC transporter, P-glycoprotein (P-gp), in HT-29/MDR cells was not able to hinder cancer cell responsiveness to SDT with Hyp. This work reveals, for the first time, the US responsiveness of Hyp with significant anticancer activity being displayed, making it a full-fledged sonosensitizer for the SDT of cancer.

Ultrasound-Responsive Aqueous Two-Phase Microcapsules for On-Demand Drug Release

Traditional implanted drug delivery systems cannot easily change their release profile in real time to respond to physiological changes. Here we present a microfluidic aqueous two-phase system to generate microcapsules that can release drugs on demand as triggered by focused ultrasound (FUS). The biphasic microcapsules are made of hydrogels with an outer phase of mixed molecular weight (MW) poly(ethylene glycol) diacrylate that mitigates premature payload release and an inner phase of high MW dextran with payload that breaks down in response to FUS. Compound release from microcapsules could be triggered as desired; 0.4 μg of payload was released across 16 on-demand steps over days. We detected broadband acoustic signals amidst low heating, suggesting inertial cavitation as a key mechanism for payload release. Overall, FUS-responsive microcapsules are a biocompatible and wirelessly triggerable structure for on-demand drug delivery over days to weeks.

Three birds with one stone: co-encapsulation of diclofenac and DL-menthol for realizing enhanced energy deposition, glycolysis inhibition and anti-inflammation in HIFU surgery

Despite attracting increasing attention in clinic, non-invasive high-intensity focused ultrasound (HIFU) surgery still commonly suffers from tumor recurrence and even matastasis due to the generation of thermo-resistance in non-apoptotic tumor cells and adverse therapy-induced inflammation with enhanced secretion of growth factors in irradiated region. In this work, inspired by the intrinsic property that the expression of thermo-resistant heat shock proteins (HSPs) is highly dependent with adenosine triphosphate (ATP), dual-functionalized diclofenac (DC) with anti-inflammation and glycolysis-inhibition abilities was successfully co-encapsulated with phase-change dl-menthol (DLM) in poly(lactic-co-glycolic acid) nanoparticles (DC/DLM@PLGA NPs) to realize improved HIFU surgery without causing adverse inflammation. Both in vitro and in vivo studies demonstrated the great potential of DC/DLM@PLGA NPs for serving as an efficient synergistic agent for HIFU surgery, which can not only amplify HIFU ablation efficacy through DLM vaporization-induced energy deposition but also simultaneously sensitize tumor cells to hyperthermia by glycolysis inhibition as well as diminished inflammation. Thus, our study provides an efficient strategy for simultaneously improving the curative efficiency and diminishing the harmful inflammatory responses of clinical HIFU surgery.

Multifunctional Theranostic Nanoparticles for Enhanced Tumor Targeted Imaging and Synergistic FUS/Chemotherapy on Murine 4T1 Breast Cancer Cell

Purpose

Triple negative breast cancer (TNBC) is challenging for effective remission due to its very aggressive, extremely metastatic and resistant to conventional chemotherapy. Herein, a multifunctional theranostic nanoparticle was fabricated to enhance tumor targeted imaging and promote focused ultrasound (FUS) ablation and chemotherapy and sonodynamic therapy (SDT). A multi-modal synergistic therapy can improve the therapeutic efficacy and prognosis of TNBC.

Methods

AS1411 aptamer modified PEG@PLGA nanoparticles encapsulated with perfluorohexane (PFH) and anti-cancer drug doxorubicin (DOX) were constructed (AS1411-DOX/PFH-PEG@PLGA) to enhance tumor targeted imaging to guide ablation and synergistic effect of FUS/chemotherapy. FUS was utilized to trigger the co-release of doxorubicin and simultaneously PFH phase transition and activate DOX for SDT effect. The physicochemical, phase-changeable imaging capability, biosafety of nanoparticles and multi-mode synergistic effects on growth of TNBC were thoroughly evaluated in vivo and in vitro.

Results

The synthesized AS1411-DOX/PFH-PEG@PLGA (A-DPPs) nanoparticles are uniformly round with an average diameter of 306.03 ± 5.35 nm and the zeta potential of −4.05 ± 0.13 mV, displaying high biosafety and FUS-responsive drug release in vitro and in vivo. AS1411 modified NPs specifically bind to 4T1 cells and elevate the ultrasound contrast agent (UCA) image contrast intensity via PFH phase-transition after FUS exposure. Moreover, the combined treatment of A-DPPs nanoparticles with FUS exhibited significantly higher apoptosis rate, stronger inhibitory effect on 4T1 cell invasion in vitro, induced more reactive oxygen species (ROS), and enhanced anti-tumor effect compared to a single therapy (p < 0.05). Additionally, the joint strategy resulted in more intense cavitation effect and larger ablated areas and reduced energy efficiency factor (EEF) both in vitro and in vivo.

Conclusion

The multifunctional AS1411-DOX/PFH-PEG@PLGA nanoparticles can perform as a marvelous synergistic agent for enhanced FUS/chemotherapy, promote real-time contrast enhanced US imaging and improve the therapeutic efficacy and prognosis of TNBC.

Ultrasound and nanomaterial: an efficient pair to fight cancer

Ultrasounds are often used in cancer treatment protocols, e.g. to collect tumor tissues in the right location using ultrasound-guided biopsy, to image the region of the tumor using more affordable and easier to use apparatus than MRI and CT, or to ablate tumor tissues using HIFU. The efficacy of these methods can be further improved by combining them with various nano-systems, thus enabling: (i) a better resolution of ultrasound imaging, allowing for example the visualization of angiogenic blood vessels, (ii) the specific tumor targeting of anti-tumor chemotherapeutic drugs or gases attached to or encapsulated in nano-systems and released in a controlled manner in the tumor under ultrasound application, (iii) tumor treatment at tumor site using more moderate heating temperatures than with HIFU. Furthermore, some nano-systems display adjustable sizes, i.e. nanobubbles can grow into micro-bubbles. Such dual size is advantageous since it enables gathering within the same unit the targeting properties of nano bubbles via EPR effect and the enhanced ultrasound contrasting properties of micro bubbles. Interestingly, the way in which nano-systems act against a tumor could in principle also be adjusted by accurately selecting the nano-system among a large choice and by tuning the values of the ultrasound parameters, which can lead, due to their mechanical nature, to specific effects such as cavitation that are usually not observed with purely electromagnetic waves and can potentially help destroying the tumor. This review highlights the clinical potential of these combined treatments that can improve the benefit/risk ratio of current cancer treatments.

Numerical Study of Bubble Cloud and Thermal Lesion Evolution During Acoustic Droplet Vaporization Enhanced HIFU Treatment

Acoustic droplet vaporization (ADV) has been proven to enhance high intensity focused ultrasound (HIFU) thermal ablation of tumor. It has also been demonstrated that triggering droplets before HIFU exposure could be a potential way to control both the size and the shape of the thermal lesion. In this paper, a numerical model is proposed to predict the thermal lesion created in ADV enhanced HIFU treatment. Bubble oscillation was coupled into a viscoelastic medium in the model to more closely represent real applications in tissues. Several physical processes caused by continuous wave ultrasound and elevated temperature during the HIFU exposure were considered, including rectified diffusion, gas solubility variation with temperature in the medium, and boiling. Four droplet concentrations spanning two orders of magnitude were calculated. The bubble cloud formed from triggering of the droplets by the pulse wave ultrasound, along with the evolution of the shape and location of the bubble cloud and thermal lesion during the following continuous wave exposure was obtained. The increase of bubble void fraction caused by continuous wave exposure was found to be consistent with the experimental observation. With the increase of droplet concentration, the predicted bubble cloud shapes vary from tadpole to triangular and double triangular, while the thermal lesions move toward the transducer. The results show that the assumptions used in this model increased the accuracy of the results. This model may be used for parametrical study of ADV enhanced HIFU treatment and be further used for treatment planning and optimization in the future.

Radial oscillation and translational motion of a gas bubble in a micro-cavity

According to classical nucleation theory, a gas nucleus can grow into a cavitation bubble when the ambient pressure is negative. Here, the growth process of a gas nucleus in a micro-cavity was simplified to two "events", and the full confinement effect of the surrounding medium of the cavity was considered by including the bulk modulus in the equation of state. The Rayleigh-Plesset-like equation of the cavitation bubble in the cavity was derived to model the radial oscillation and translational motion of the cavitation bubble in the local acoustic field. The numerical results show that the nucleation time of the cavitation bubble is sensitive to the initial position of the gas nucleus. The cavity size affects the duration of the radial oscillation of the cavitation bubble, where the duration is shorter for smaller cavities. The equilibrium radius of a cavitation bubble grown from a gas nucleus increases with increasing size of the cavity. There are two possible types of translational motion: reciprocal motion around the center of the cavity and motion toward the cavity wall. The growth process of gas nuclei into cavitation bubbles is also dependent on the compressibility of the surrounding medium and the magnitude of the negative pressure. Therefore, gas nuclei in a liquid cavity can be excited by acoustic waves to form cavitation bubbles, and the translational motion of the cavitation bubbles can be easily observed owing to the confining influence of the medium outside the cavity.

Experimental Demonstration of Trans-Skull Volumetric Passive Acoustic Mapping With the Heterogeneous Angular Spectrum Approach

Real-time, 3-D, passive acoustic mapping (PAM) of microbubble dynamics during transcranial focused ultrasound (FUS) is essential for optimal treatment outcomes. The angular spectrum approach (ASA) potentially offers a very efficient method to perform PAM, as it can reconstruct specific frequency bands pertinent to microbubble dynamics and may be extended to correct aberrations caused by the skull. Here, we experimentally assess the abilities of heterogeneous ASA (HASA) to perform trans-skull PAM. Our experimental investigations demonstrate that the 3-D PAMs of a known 1-MHz source, constructed with HASA through an ex vivo human skull segment, reduced both the localization error (from 4.7 ± 2.3 to 2.3 ± 1.6 mm) and the number, size, and energy of spurious lobes caused by aberration, with the modest additional computational expense. While further improvements in the localization errors are expected with arrays with denser elements and larger aperture, our analysis revealed that experimental constraints associated with the array pitch and aperture (here, 1.8 mm and 2.5 cm, respectively) can be ameliorated by interpolation and peak finding techniques. Beyond the array characteristics, our analysis also indicated that errors in the registration (translation and rotation of ±5 mm and ±5°, respectively) of the skull segment to the array can lead to peak localization errors of the order of a few wavelengths. Interestingly, errors in the spatially dependent speed of sound in the skull (±20%) caused only subwavelength errors in the reconstructions, suggesting that registration is the most important determinant of point source localization accuracy. Collectively, our findings show that HASA can address source localization problems through the skull efficiently and accurately under realistic conditions, thereby creating unique opportunities for imaging and controlling the microbubble dynamics in the brain.

Effects of shell-integrated Sudan Black dye on the acoustic activity and ultrasound imaging properties of lipid-shelled nanoscale ultrasound contrast agents

SIGNIFICANCE

An effective contrast agent for concurrent multimodal photoacoustic (PA) and ultrasound (US) imaging must have both high optical absorption and high echogenicity. Integrating a highly absorbing dye into the lipid shell of gas core nanobubbles (NBs) adds PA contrast to existing US contrast agents but may impact agent ultrasonic response.

AIM

We report on the development and ultrasonic characterization of lipid-shell stabilized C3F8 NBs with integrated Sudan Black (SB) B dye in the shell as dual-modal PA-US contrast agents.

APPROACH

Perfluoropropane NBs stabilized with a lipid shell including increasing concentrations of SB B dye were formulated by amalgamation (SBNBs). Physical properties of SBNBs were characterized using resonant mass measurement, transmission electron microscopy and pendant drop tensiometry. Concentrated bubble solutions were imaged for 8 min to assess signal decay. Diluted bubble solutions were stimulated by a focused transducer to determine the response of individual NBs to long cycle (30 cycle) US. For assessment of simultaneous multimodal contrast, bulk populations of SBNBs were imaged using a PA and US imaging platform.

RESULTS

We produced high agent yield (∼1011) with a mean diameter of ∼200 to 300 nm depending on SB loading. A 40% decrease in bubble yield was measured for solutions with 0.3 and 0.4  mg  /  ml SB. The addition of SB to the shell did not substantially affect NB size despite an increase in surface tension by up to 8  mN  /  m. The bubble decay rate increased after prolonged exposure (8 min) by dyed bubbles in comparison to their undyed counterparts (2.5-fold). SB in bubble shells increased gas exchange across the shell for long cycle US. PA imaging of these agents showed an increase in power (up to 10 dB) with increasing dye.

CONCLUSIONS

We added PA contrast function to NBs. The addition of SB increased gas exchange across the NB shell. This has important implications in their use as multimodal agents.

Passive Cavitation Detection With a Needle Hydrophone Array

Therapeutic ultrasound and microbubble technologies seek to drive systemically administered microbubbles into oscillations that safely manipulate tissue or release drugs. Such procedures often detect the unique acoustic emissions from microbubbles with the intention of using this feedback to control the microbubble activity. However, most sensor systems reported introduce distortions to the acoustic signal. Acoustic shockwaves, a key emission from microbubbles, are largely absent in reported recording, possibly due to the sensors being too large or too narrowband, or having strong phase distortions. Here, we built a sensor array that countered such limitations with small, broadband sensors and a low-phase distorting material. We built eight needle hydrophones with polyvinylidene fluoride (PVDF, diameter: 2 mm) then fit them into a 3-D-printed scaffold in a two-layered, staggered arrangement. Using this array, we monitored microbubbles exposed to therapeutically relevant ultrasound pulses (center frequency: 0.5 MHz, peak-rarefactional pressure: 130-597 kPa, pulselength: four cycles). Our tests revealed that the hydrophones were broadband with the best having a sensitivity of -224.8 dB ± 3.2 dB re 1 V/ μ Pa from 1 to 15 MHz. The array was able to capture shockwaves generated by microbubbles. The signal-to-noise ratio (SNR) of the array was approximately two times higher than individual hydrophones. Also, the array could localize microbubbles (-3 dB lateral resolution: 2.37 mm) and determine the cavitation threshold (between 161 and 254 kPa). Thus, the array accurately monitored and localized microbubble activities, and may be an important technological step toward better feedback control methods and safer and more effective treatments.

Enhanced HIFU Theranostics with Dual-Frequency-Ring Focused Ultrasound and Activatable Perfluoropentane-Loaded Polymer Nanoparticles

High-intensity focused ultrasound (HIFU) has been widely used in tumor ablation in clinical settings. Meanwhile, there is great potential to increase the therapeutic efficiency of temporary cavitation due to enhanced thermal effects and combined mechanical effects from nonlinear vibration and collapse of the microbubbles. In this study, dual-frequency (1.1 and 5 MHz) HIFU was used to produce acoustic droplet vaporization (ADV) microbubbles from activatable perfluoropentane-loaded polymer nanoparticles (PFP@Polymer NPs), which increased the therapeutic outcome of the HIFU and helped realize tumor theranostics with ultrasound contrast imaging. Combined with PFP@Polymer NPs, dual-frequency HIFU changed the shape of the damage lesion and reduced the acoustic intensity threshold of thermal damage significantly, from 216.86 to 62.38 W/cm². It produced a nearly 20 °C temperature increase in half the irradiation time and exhibited a higher tumor inhibition rate (84.5% ± 3.4%) at a low acoustic intensity (1.1 MHz: 23.77 W/cm²; 5 MHz: 0.35 W/cm²) in vitro than the single-frequency HIFU (60.2% ± 11.9%). Moreover, compared with the traditional PFP@BSA NDs, PFP@Polymer NPs showed higher anti-tumor efficacy (81.13% vs. 69.34%; * p < 0.05) and better contrast-enhanced ultrasound (CEUS) imaging ability (gray value of 57.53 vs. 30.67; **** p < 0.0001), probably benefitting from its uniform and stable structure. It showed potential as a highly efficient tumor theranostics approach based on dual-frequency HIFU and activatable PFP@Polymer NPs.

Experimental Demonstration of a Stacked Hybrid Optoacoustic-Piezoelectric Transducer for Localized Heating and Enhanced Cavitation

Laser-generated focused ultrasound (LGFU) is an emerging modality for cavitation-based therapy. However, focal pressure amplitudes by LGFU alone to achieve pulsed cavitation are often lacking as a treatment depth increases. This requires a higher pressure from a transmitter surface and more laser energies that even approach to a damage threshold of transmitter. To mitigate the requirement for LGFU-induced cavitation, we propose LGFU configurations with a locally heated focal zone using an additional high-intensity focused ultrasound (HIFU) transmitter. After confirming heat-induced cavitation enhancement using two separate transmitters, we then developed a stacked hybrid optoacoustic-piezoelectric transmitter, which is a unique configuration made by coating an optoacoustic layer directly onto a piezoelectric substrate. This shared curvature design has great practical advantage without requiring the complex alignment of two focal zones. Moreover, this enabled the amplification of cavitation bubble density by 18.5-fold compared to the LGFU operation alone. Finally, the feasibility of tissue fragmentation was confirmed through a tissue-mimicking gel, using the combination of LGFU and HIFU (not via a stacked structure). We expect that the stacked transmitter can be effectively used for stronger and faster tissue fragmentation than the LGFU transmitter alone.

Effects of sub-atmospheric pressure and dissolved oxygen concentration on lesions generated in ex vivo tissues by high intensity focused ultrasound

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 (P_stat) can control the acoustic cavitation. But the question of how the decrease of P_stat 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 P_stat, 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 (I_sata) of 6500 W/cm² was used to expose two groups of in vitro bovine livers for 2 s; one group was under atmospheric pressure (P_stat = 1 bar) and the other was under sub-atmospheric pressure (P_stat = 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.

Photoacoustic computed tomography of mechanical HIFU-induced vascular injury

Mechanical high-intensity focused ultrasound (HIFU) has been used for cancer treatment and drug delivery. Existing monitoring methods for mechanical HIFU therapies such as MRI and ultrasound imaging often suffer from high cost, poor spatial-temporal resolution, and/or low sensitivity to tissue's hemodynamic changes. Evaluating vascular injury during mechanical HIFU treatment, therefore, remains challenging. Photoacoustic computed tomography (PACT) is a promising tool to meet this need. Intrinsically sensitive to optical absorption, PACT provides high-resolution imaging of blood vessels using hemoglobin as the endogenous contrast. In this study, we have developed an integrated HIFU-PACT system for detecting vascular rupture in mechanical HIFU treatment. We have demonstrated singular value decomposition for enhancing hemorrhage detection. We have validated the HIFU-PACT performance on phantoms and in vivo animal tumor models. We expect that PACT-HIFU will find practical applications in oncology research using small animal models.

Bursting Microbubbles: How Nanobubble Contrast Agents Can Enable the Future of Medical Ultrasound Molecular Imaging and Image-Guided Therapy

The field of medical ultrasound has undergone a significant evolution since the development of microbubbles as contrast agents. However, due to their size, microbubbles remain in the vasculature, and therefore have limited clinical applications. Building a better - and smaller - bubble can expand the applications of contrast-enhanced ultrasound by allowing bubbles to extravasate from blood vessels - creating new opportunities. In this review, we summarize recent research on the formulation and use of NBs as imaging agents and as therapeutic vehicles. We discuss the ongoing debates in the field and reluctance to accepting NBs as an acoustically active construct and a potentially impactful clinical tool that can help shape the future of medical ultrasound. We hope that the overview of key experimental and theoretical findings in the NB field presented in this paper provides a fundamental framework that will help clarify NB-ultrasound interactions and inspire engagement in the field.

Equivalent time active cavitation imaging

RATIONALE

Despite the development of a large number of neurologically active drugs, brain diseases are difficult to treat due to the inability of many drugs to penetrate the blood-brain barrier. High-intensity focused ultrasound blood-brain barrier opening in a site-specific manner could significantly expand the spectrum of available drug treatments. However, without monitoring, brain damage and off target effects can occur during these treatments. While some methods can monitor inertial cavitation, temperature increase, or passively monitor cavitation events, to the best of our knowledge none of them can actively and spatiotemporally map the high intensity focused ultrasound pressure field during treatment.

METHODS

Here we detail the development of a novel ultrasound imaging modality called Equivalent Time Active Cavitation Imaging capable of characterizing the high-intensity focused ultrasound pressure field through stable cavitation events across the field of view with an ultrafast active imaging setup. This work introduces 1) a novel plane wave sequence whose transmit delays increase linearly with transmit events enabling the sampling of high-frequency cavitation events, and 2) an algorithm allowing the filtration of the microbubble signal for pressure field mapping. The pressure measurements with our modality were first carried out in vitro for hydrophone comparison and then in vivo during blood-brain barrier opening treatment in mice.

RESULTS

This study demonstrates the ability of our modality to spatiotemporally characterize a modulation pressure field with an active imaging setup. The resulting pressure field mapping reveals a good correlation with hydrophone measurements. Further proof is provided experimentally in vivo with promising results.

CONCLUSION

This proof of concept establishes the first steps towards a novel ultrasound modality for monitoring focused ultrasound blood-brain barrier opening, allowing new possibilities for a safe and precise monitoring method.

Heating technology for malignant tumors: a review

The therapeutic application of heat is very effective in cancer treatment. Both hyperthermia, i.e., heating to 39-45 °C to induce sensitization to radiotherapy and chemotherapy, and thermal ablation, where temperatures beyond 50 °C destroy tumor cells directly are frequently applied in the clinic. Achievement of an effective treatment requires high quality heating equipment, precise thermal dosimetry, and adequate quality assurance. Several types of devices, antennas and heating or power delivery systems have been proposed and developed in recent decades. These vary considerably in technique, heating depth, ability to focus, and in the size of the heating focus. Clinically used heating techniques involve electromagnetic and ultrasonic heating, hyperthermic perfusion and conductive heating. Depending on clinical objectives and available technology, thermal therapies can be subdivided into three broad categories: local, locoregional, or whole body heating. Clinically used local heating techniques include interstitial hyperthermia and ablation, high intensity focused ultrasound (HIFU), scanned focused ultrasound (SFUS), electroporation, nanoparticle heating, intraluminal heating and superficial heating. Locoregional heating techniques include phased array systems, capacitive systems and isolated perfusion. Whole body techniques focus on prevention of heat loss supplemented with energy deposition in the body, e.g., by infrared radiation. This review presents an overview of clinical hyperthermia and ablation devices used for local, locoregional, and whole body therapy. Proven and experimental clinical applications of thermal ablation and hyperthermia are listed. Methods for temperature measurement and the role of treatment planning to control treatments are discussed briefly, as well as future perspectives for heating technology for the treatment of tumors.

The safety of echo contrast-enhanced ultrasound in high-intensity focused ultrasound ablation for abdominal wall endometriosis: a retrospective study

Background

We aimed to investigate the efficacy and safety of echo contrast-enhanced ultrasound (CEUS) during high-intensity focused ultrasound (HIFU) ablation therapy for abdominal wall endometriosis (AWE).

Methods

A total of 67 patients with AWE were treated with HIFU ablation, and their demographic characteristics were retrospectively analysed. Blood perfusion of the focal lesion was assessed before the operation, during ablation and after the operation with the use of an ultrasound contrast agent, and the effect of the ultrasound contrast agent on treatment was assessed over a 1-year follow-up period. The degree of symptom relief and adverse effects were evaluated after HIFU ablation.

Results

Eighty-two lesions were ablated in 67 patients. CEUS showed that all lesions were successfully ablated with HIFU. The shrinkage ratio of the lesions significantly increased over the follow-up period. Intermittent pain disappeared at 1 month after the operation, and the patients' pain scores significantly decreased at the 1-year follow-up. The mean [± standard deviation (SD)] lesion volume was 7.64±8.95 cm³ on B-mode ultrasound. The post-HIFU non-perfused volume was 18.34±24.08 cm³, and the rate of massive changes on greyscale imaging was 96.16%±5.44% at 12 months. During the procedure, the main complications were a prickling sensation and tenderness in the treatment area and/or a transient "hot" sensation on the skin. After the procedure, there was no obvious discomfort except for pain. Two patients developed an approximately 1-cm area of skin that exhibited a waxy appearance. Seven patients had haematuria. No severe complications were observed.

Conclusions

Ultrasound contrast agents are effective and safe for evaluating the effect of HIFU ablation on AWE, and this approach provides significant guidance and evaluation benefits for the use of HIFU treatment for AWE without obvious side effects.

Evaluation of Pseudorandom Sonications for Reducing Cavitation With a Clinical Neurosurgery HIFU Device

Transcranial high-intensity focused ultrasound is used in clinics for treating essential tremor (ET) and proposed for many other brain disorders. This promising treatment modality requires high energy resulting eventually in undesired cavitation and potential side effects. The goals of the present work were: 1) to evaluate the potential increase of the cavitation threshold using pseudorandom gated sonications and 2) to assess the heating capabilities with such sonications. The experiments were performed with the transcranial magnetic resonance (MR)-compatible ExAblate Neuro system (InSightec, Haifa, Israel) operating at a frequency of 670 kHz, either in continuous wave (CW) or with pseudorandom gated sonications of 50% duty cycle. Cavitation activity with the two types of sonications was compared using chemical dosimetry of hydroxyl radical production at the focus of the transducer, after propagation in water or through a human skull. Heating trials were performed in a hydrogel tissue-mimicking material embedded in a human skull to mimic a clinical situation. The temperature was measured by MR-thermometry when focusing at the geometrical focus and steering off focus up to 15 mm. Compared with CW sonications, the use of gated sonication did not affect the efficiency (60%) nor the steering abilities of the transducer. After propagation through a human skull, gated sonication required a higher pressure level (10 MPa) to initiate cavitation as compared with CW (5.8 MPa). Moreover, at equivalent acoustic power above the cavitation threshold, the level of cavitation activity initiated with gated sonications was much lower with gated sonication than with continuous sonications, almost half after propagation through water and one-third after propagation through a skull. This lowered cavitation activity may be attributed to a breaking of the dynamic of the bubbles moving from monochromatic to more broadband sonications and to the removal of residual cavitation nuclei between pulses with gated sonications. The heating capability was not affected by the gated sonications, and similar temperature increases were reached at focus with both types of sonications when sonicating at equivalent acoustic power, both in water or after propagation through a human skull (+15 °C at 325 W for 10 s). These data, acquired with a clinical system, suggest that gated sonication could be an alternative to continuous sonications when cavitation onset is an issue.

Evaluation of the properties of daughter bubbles generated by inertial cavitation of preformed microbubbles

Inertial cavitation (IC) of the preformed microbubbles is being investigated for ultrasound imaging and therapeutic applications. However, microbubbles rupture during IC, creating smaller daughter bubbles (DBs), which may cause undesired bioeffects in the target region. Thus, it is important to determine the properties of DBs to achieve controllable cavitation activity for applications. In this study, we theoretically calculated the dissolution dynamics of sulfur hexafluoride bubbles. Then, we applied a 1-MHz single tone burst with different peak negative pressures (PNPs) and pulse lengths (PLs), and multiple 5-MHz tone bursts with fixed acoustic conditions to elicit IC of the preformed SonoVue microbubbles and scattering of DBs, respectively. After the IC and scattering signals were received by a 7.5-MHz transducer, time- and frequency-domain analysis was performed to obtain the IC dose and scattering intensity curve. The theoretical dissolution curves and measured scattering intensity curves were combined to determine the effect of the incident pulse parameters on the lifetime, mean radius and distribution range of DBs. Increased PNP reduced the lifetime and mean size of the DBs population and narrowed the size distribution. The proportion of small DBs (less than resonance size) increased from 36.83% to 85.98% with an increase in the PNP from 0.6 to 1.6 MPa. Moreover, increased PL caused a shift of the DB population to the smaller bubbles with shorter lifetime and narrower distribution. The proportion of small bubbles increased from 25.74% to 95.08% as the PL was increased from 5 to 100 µs. Finally, increased IC dose caused a smaller mean size, shorter lifetime and narrower distribution in the DB population. These results provide new insight into the relationship between the incident acoustic parameters and the properties of DBs, and a feasible strategy for achieving controllable cavitation activity in applications.

The effect of ultrasound cavitation on endothelial cells

Acoustic cavitation has been widely explored for both diagnostic and therapeutic purposes. Ultrasound-induced cavitation, including inertial cavitation and non-inertial cavitation, can cause microstreaming, microjet, and free radical formation. The acoustic cavitation effects on endothelial cells have been studied for drug delivery, gene therapy, and cancer therapy. Studies have demonstrated that the ultrasound-induced cavitation effect can treat cancer, ischaemia, diabetes, and cardiovascular diseases. In this minireview, we will review the impact of ultrasound-induced cavitation on the endothelial cells such as cell permeability, cell proliferation, gene expression regulation, cell viability, hemostasis interaction, oxygenation, and variation in the level of calcium ions, ceramide, nitric oxide (NO) and nitric oxide synthase (NOS) activity. The applications of these effects and the cavitation mechanism involved will be summarized, demonstrating the important role of acoustic cavitation in non-invasive ultrasound treatment of various physiological conditions.

Improved therapeutic antibody delivery to xenograft tumors using cavitation nucleated by gas-entrapping nanoparticles

Aims: Testing ultrasound-mediated cavitation for enhanced delivery of the therapeutic antibody cetuximab to tumors in a mouse model. Methods: Tumors with strong EGF receptor expression were grown bilaterally. Cetuximab was coadministered intravenously with cavitation nuclei, consisting of either the ultrasound contrast agent Sonovue or gas-stabilizing nanoscale SonoTran Particles. One of the two tumors was exposed to focused ultrasound. Passive acoustic mapping localized and monitored cavitation activity. Both tumors were then excised and cetuximab concentration was quantified. Results: Cavitation increased tumoral cetuximab concentration. When nucleated by Sonovue, a 2.1-fold increase (95% CI 1.3- to 3.4-fold) was measured, whereas SonoTran Particles gave a 3.6-fold increase (95% CI 2.3- to 5.8-fold). Conclusions: Ultrasound-mediated cavitation, especially when nucleated by nanoscale gas-entrapping particles, can noninvasively increase site-specific delivery of therapeutic antibodies to solid tumors.

Ultrasound for the Brain: A Review of Physical and Engineering Principles, and Clinical Applications

The emergence of new ultrasound technologies has improved our understanding of the brain functions and offered new opportunities for the treatment of brain diseases. Ultrasound has become a valuable tool in preclinical animal and clinical studies as it not only provides information about the structure and function of brain tissues but can also be used as a therapy alternative for brain diseases. High-resolution cerebral flow images with high sensitivity can be acquired using novel functional ultrasound and super-resolution ultrasound imaging techniques. The noninvasive treatment of essential tremors has been clinically approved and it has been demonstrated that the ultrasound technology can revolutionize the currently existing treatment methods. Microbubble-mediated ultrasound can remotely open the blood-brain barrier enabling targeted drug delivery in the brain. More recently, ultrasound neuromodulation received a great amount of attention due to its noninvasive and deep penetration features and potential therapeutic benefits. This review provides a thorough introduction to the current state-of-the-art research on brain ultrasound and also introduces basic knowledge of brain ultrasound including the acoustic properties of the brain/skull and engineering techniques for ultrasound. Ultrasound is expected to play an increasingly important role in the diagnosis and therapy of brain diseases.