High intensity focused ultrasound: physical principles and devices

Acoustic holography in biomedical applications

Acoustic holography can be used to construct an arbitrary wavefront at a desired 2D plane or 3D volume by beam shaping an emitted field and is a relatively new technique in the field of biomedical applications. Acoustic holography was first theorized in 1985 following Gabor's work in creating optical holograms in the 1940s. Recent developments in 3D printing have led to an easier and faster way to manufacture monolithic acoustic holographic lenses that can be attached to single-element transducers. As ultrasound passes through the lens material, a phase shift is applied to the waves, causing an interference pattern at the 2D image plane or 3D volume, which forms the desired pressure field. This technology has many applications already in use and has become of increasing interest for the biomedical community, particularly for treating regions that are notoriously difficult to operate on, such as the brain. Acoustic holograms could provide a non-invasive, precise, and patient specific way to deliver drugs, induce hyperthermia, or create tissue cell patterns. However, there are still limitations in acoustic holography, such as the difficulties in creating 3D holograms and the passivity of monolithic lenses. This review aims to outline the biomedical applications of acoustic holograms reported to date and discuss their current limitations and the future work that is needed for them to reach their full potential in the biomedical community.

Overview of Therapeutic Ultrasound Applications and Safety Considerations: 2024 Update

A 2012 review of therapeutic ultrasound was published to educate researchers and physicians on potential applications and concerns for unintended bioeffects (doi: 10.7863/jum.2012.31.4.623). This review serves as an update to the parent article, highlighting advances in therapeutic ultrasound over the past 12 years. In addition to general mechanisms for bioeffects produced by therapeutic ultrasound, current applications, and the pre-clinical and clinical stages are outlined. An overview is provided for image guidance methods to monitor and assess treatment progress. Finally, other topics relevant for the translation of therapeutic ultrasound are discussed, including computational modeling, tissue-mimicking phantoms, and quality assurance protocols.

High-intensity focused ultrasound ablation to increase tumor-specific lymphocytes in prostate cancer

Treatment options for localized prostate cancer have been expanded by FDA-approval of High-Intensity Focused Ultrasound (HIFU). Prostate cancer typically has few tumor-infiltrating lymphocytes, which are crucial for antitumor immunity. This study investigated the use of HIFU to increase lymphocyte infiltration into the tumor and enhance antitumor immunity. RM1 prostate tumors were implanted onto both flanks of syngeneic C57BL/6 J mice, with one tumor subjected to HIFU treatment. The growth of the contralateral tumor was monitored. Blood samples were obtained from patients both before and after prostatectomy or HIFU treatment. Peripheral blood mononuclear cells (PBMCs) were then isolated to analyze the immune cells. In murine experiments, the application of HIFU to one tumor decreased the growth of the contralateral (non-HIFU treated) tumor, when the contralateral tumor was the same tumor type, but not when it was a different tumor type. HIFU increased infiltration of CD4+ and CD8+ lymphocytes into the contralateral, same-type tumor. Lymphocyte depletion studies affirmed that the antitumor immune response triggered by HIFU relies on CD4+ and CD8+ lymphocytes. Addition of cholesterol-lowering intervention further increased antitumor immunity generated by HIFU in mice. In human subjects, HIFU, but not prostatectomy, stimulated anti-tumor CD4+ and CD8+ lymphocytes. We concluded that HIFU induced a potent cellular antitumor immune response that inhibited the progression of murine prostate tumors. HIFU stimulated tumor-specific cellular immunity in patients. Future clinical trials should explore the clinical benefits of HIFU, possibly in combination with existing immunotherapies, as immune modulators for both localized and metastatic disease.

Gamma Knife Radiosurgery, Central Lateral Thalamotomy, and Chronic Neuropathic Pain: A Prospective Single-Center Study With Long-Term Follow-Up

OBJECTIVE

We present our experience in using Gamma knife surgery (GKS) on the posterior part of the central lateral nucleus (CLp) for refractory neuropathic pain, examining its long-term efficacy and safety in patients with one of the longest pretreatment pain duration in the literature. Furthermore, we examined certain factors that might influence the outcome of this technique.

METHODS

We conducted a prospective study involving 9 patients who underwent GKS between 2020 and 2023. We employed Icon model GKS and Vantage stereotactic frame. The planning process encompassed a dual localization system. The assessments involved the use of both the visual analog and Barrow Neurological Institute (BNI) scales (6 months, 12 months, and then annually). Data analysis was developed using SPSS 25.

RESULTS

Our series consisted of 6 women and 3 men with an average age of 52.3 ± 17.4 years. A maximum dose of 130 Gy was administered. The mid-term postoperative period (1 year) showed that 8 patients (88.9%) experienced significant pain relief (visual analog scale P = 0.011; BNI IIIa). The median follow-up time was 24.8 ± 8.2. At the last assessment, all patients maintained their improvement (visual analog scale P = 0.018; BNI IIIa). We found no association between patient age (P = 0.329), duration of pretreatment pain (P = 0.469), multiple previous surgical treatments (P = 0.750) or the pain's etiology (P = 0.25), and poorer outcomes post CLp thalamotomy. None of the cases has experienced a recurrence so far. Both morbidity and mortality were 0%.

CONCLUSIONS

Our findings suggest that bilateral ablation of the CLp using GKS is both effective and safe for treating drug-resistant neuropathic pain. This simple, accurate, and noninvasive surgical technique effectively achieves pain control across various localized areas and sustains a lasting clinical response, even in patients with multiple previous surgical interventions or prolonged pain duration.

Current role of focal therapy in prostate cancer

BACKGROUND

Thanks to the improved accuracy of multiparametric Magnetic Resonance Imaging (mpMRI) to detect and localize the dominant index lesion on prostate cancer (PCa), the concept of minimally invasive focal treatments (FT) has gained popularity. Nevertheless, although high-quality evidence that FT has favorable functional outcomes, definitive proof of its oncological effectiveness compared to standard treatments remains underreported.

OBJECTIVE

This study aims to explore the efficacy, safety, oncologic and functional outcomes of different type of FT for PCa.

EVIDENCE ACQUISITION

A non-systematic literature review was conducted by searching on PubMed "prostate cancer" AND "focal treatment" OR "HIFU" OR "irreversible electroporation" OR "cryoablation" OR "focal laser ablation." Overall, 22 articles published in English literature from 2018 to 2023 describing FT techniques for PCa were included.

EVIDENCE SYNTHESIS

Related to the field ablated, focal therapies include hemiablation (half gland), focal ablation (zonal-base) or targeted therapy (lesion-based). FT modalities can be categorized in thermal and non-thermal energy: thermal energy techniques include high-intensity focused ultrasound (HIFU), cryotherapy, radiofrequency ablation (RFA), and focal laser ablation (FLA). Focal brachytherapy, irreversible electroporation (IRE), and vascular-targeted photodynamic therapy (VTP) are classified as non-thermal ablation. Each focal ablative treatments could be promising alternative to conventional radical therapies to treat PCa in term of mid-term oncologic and functional outcomes, however, limited data are available in comparison with standardized radical treatments. HIFU and Cryo are the most studied techniques and seem to be superior to radical treatments in term of functional outcomes despite associated with higher recurrence and retreatment rate.

CONCLUSIONS

Current evidences of oncologic and functional outcomes of FT are based mainly on retrospective, non-comparative and single center studies. Thus, none of the focal therapies available should be considered safe alternative to standardized treatments in routine practice and should be offered only for well selected PCa patients with low or at least favorable-intermediate risk disease, unfit for radical options.

Multi-sequence magnetic resonance imaging radiomics combined with imaging features predicts the difficulty of HIFU treatment of uterine fibroids

To establish a multivariate linear regression model for predicting the difficulty of high-intensity focused ultrasound (HIFU) ablation of uterine fibroids based on multi-sequence magnetic resonance imaging radiomics features. A retrospective analysis was conducted on 218 patients with uterine fibroids who underwent HIFU treatment, including 178 cases from Yongchuan Hospital of Chongqing Medical University and 40 cases from the Second Affiliated Hospital of Chongqing Medical University (external validation set). Radiomics features were extracted and selected from magnetic resonance images, and potentially related imaging features were collected. The energy efficiency factor (EEF) was used as the dependent variable. Imaging models, radiomics models, and joint models were established using a stepwise approach. The model with the highest R2 value was selected for external validation. The R2 value of the combined model was 0.642, higher than that of other models. Spearman correlation analysis showed a correlation coefficient of R = 0.824 (P < 0.001) between predicted EEF and actual EEF. External validation yielded a correlation coefficient of R = 0.645 (P < 0.001). A model for predicting EEF has been developed, which is clinically important for predicting the difficulty of HIFU treatment of uterine fibroids.

A temperature-inducible protein module for control of mammalian cell fate

Inducible protein switches are currently limited for use in tissues and organisms because common inducers cannot be controlled with precision in space and time in optically dense settings. Here, we introduce a protein that can be reversibly toggled with a small change in temperature, a stimulus that is both penetrant and dynamic. This protein, called Melt (Membrane localization using temperature) oligomerizes and translocates to the plasma membrane when temperature is lowered. We generated a library of Melt variants with switching temperatures ranging from 30 °C to 40 °C, including two that operate at and above 37 °C. Melt was a highly modular actuator of cell function, permitting thermal control over diverse processes including signaling, proteolysis, nuclear shuttling, cytoskeletal rearrangements and cell death. Finally, Melt permitted thermal control of cell death in a mouse model of human cancer. Melt represents a versatile thermogenetic module for straightforward, non-invasive and spatiotemporally defined control of mammalian cells with broad potential for biotechnology and biomedicine.

Study of Histotripsy With Subsequent Heating on In Vitro VX2 Cancer Cells

OBJECTIVE

Focused ultrasound has emerged as a precise and minimally invasive modality for effective cancer treatment. In this study, we propose a novel method that integrates the mechanical effects of focused ultrasound, known as histotripsy, with heating to enhance both the immediate and sustained cytotoxic effects on cancer cells.

METHODS

Our investigation focused on VX2 cancer cells in suspension, examining five experimental groups: blank control, negative control, heating alone, histotripsy alone, and histotripsy with subsequent heating. B-mode ultrasound imaging was utilized to visualize cavitation bubble cloud formation and its motion during histotripsy. The suspension was contained in individually sealed compartments obtained from bubble wrap (referred to as bubble wrap compartments) embedded within the agarose phantom. Residual living cells were examined immediately after treatment and cultured for 96 hours to analyze the growth patterns. Additionally, CFDA SE staining was employed to assess cell proliferation. Furthermore, both intracellular and extracellular heat shock protein 70 (HSP70) levels were measured to investigate the potential initiation of an immune response.

RESULTS

The combination of histotripsy and subsequent heating significantly reduced the normalized concentration of living cells immediately after treatment. It also decreased the proliferation rate of residual cells compared with the other experimental groups. Histotripsy with subsequent heating also increased the generation and release of HSP70, which might potentially enhance an innate anti-tumor immune response in vivo.

CONCLUSION

Histotripsy and subsequent heating improved the immediate lethal impact on VX2 cancer cells and curtailed the proliferation of residual cancer cells in suspension. This study presents a promising strategy for cancer therapy in the future.

Thyroid-Targeted Nano-Bombs Empower HIFU for Graves' Disease

Graves' disease (GD) is an autoimmune disorder with a high incidence rate, particularly affecting women of reproductive age. Current treatment modalities for GD carry significant disadvantages, especially for pregnant or nursing women. As a novel extracorporeal therapeutic technique, high-intensity focused ultrasound (HIFU) shows great promise for treating GD; however, its low treatment efficacy impedes clinical application. In this study, a thyroid-targeted nano-bomb system (PD-PLGA@Si-Ab/PDA-I, PSAPI) is developed to enhance HIFU efficacy and improve therapeutic outcomes for GD. The core structure of PSAPI encapsulates a phase-transition material, perfluorohexane, and the anti-inflammatory drug diclofenac within a poly(lactide-co-glycolide) (PLGA) and silica shell. A polydopamine coating enhances biocompatibility, while iodine loading and thyroid-stimulating hormone receptor (TSHR) antibodies grafting ensure targeted delivery to the thyroid. Robust in vitro and in vivo results demonstrated that PSAPI is highly biocompatible, accumulates in the thyroid within 24 h after administration, and significantly potentiates the therapeutic efficacy of HIFU, resulting in markedly reduced inflammatory responses. Transcriptomic analysis revealed a cellular defense mechanism activated in PSAPI-treated cells following HIFU irradiation, highlighting potential molecular targets for the future development of HIFU-sensitizing agents. The biocompatible PSAPI nano-bomb developed in this study holds great transformative potential, addressing critical gaps in current therapeutic practices for GD.

High-intensity focused ultrasound: an innovative approach for micro-manipulation of demineralized dentine

BACKGROUND

Treatment of deep carious lesions poses significant challenges in dentistry, as complete lesion removal risks compromising pulp vitality, while selective removal often reduces the longevity of restorations. Herein, we propose a minimally invasive approach using High-Intensity Focused Ultrasound (HIFU) for microscale removal of carious dentine. Concurrently, HIFU's antimicrobial effects against associated cariogenic biofilms and the corresponding thermal and biological impacts on surrounding tissues were investigated.

METHODS

A total of 238 sound human molars were utilized, with 203 samples of artificial carious-simulated dentine (ACSD) prepared for HIFU exposure. HIFU (250 kHz) was applied at 20 W for varying durations (60, 120, and 180 s). The acoustic waves were administered via a collimated cone coupled to the dentine surface using ultrasonic gel.

RESULTS

Advanced characterization techniques including scanning electron microscopy (n = 5/group), Raman spectroscopy, atomic force microscopy, and nano-indentation (n = 5/group), demonstrated HIFU's effectiveness in removing demineralized collagen-fibrils. This was reflected in the increased mineral content, nano-hardness, and reduced elastic-modulus of ACSD lesions. Micro-CT (n = 6/group) confirmed the increase in mineral density post-HIFU exposure. Confocal microscopy of Rhodamine-B stained ACSD (n = 5/group) quantified the depth of dentine microscale removal post-HIFU exposure in a time-dependent manner. HIFU's potent anti-biofilm effect (n = 9/group) against Streptococcus mutans biofilms was evidenced by microscopic characterizations and significant reductions in metabolic-activity and colony-forming units. Furthermore, HIFU promoted the proliferation of dental pulp stem cells (n = 3/group) while maintaining the associated temperature-rise within the physiological tolerance.

CONCLUSION

HIFU's potential as an innovative, minimally invasive, non-ionizing tool for dentine carious lesion micromanipulation was demonstrated through the interaction between focused acoustic waves and dentine, warranting further studies for future clinical translation in restorative and/or preventive dentistry.

HIFU-CCL19/21 Axis Enhances Dendritic Cell Vaccine Efficacy in the Tumor Microenvironment

BACKGROUND/OBJECTIVES

Effectively targeting treatment-resistant tumor cells, particularly cancer stem cells (CSCs) involved in tumor recurrence, remains a major challenge in immunotherapy. This study examines the potential of combining mechanical high-intensity focused ultrasound (M-HIFU) with dendritic cell (DC) vaccines to enhance immune responses against OLFM4-expressing tumors, a CSC marker linked to immune evasion and tumor growth.

METHODS

M-HIFU was applied to induce immunogenic cell death by mechanically disrupting tumor cells, releasing tumor-associated antigens and creating an immunostimulatory environment. DC vaccines loaded with OLFM4 were then administered to boost the immune response within this primed environment.

RESULTS

The combination of M-HIFU and DC vaccine significantly inhibited tumor growth and metastasis, with enhanced T-cell activation and increased recruitment of immune cells due to elevated chemokines CCL19 and CCL21. This synergy promoted immune memory, reducing the likelihood of recurrence.

CONCLUSIONS

M-HIFU effectively promotes the migration of DC vaccines through CCL19/21, presenting a promising approach for cancer treatment. Further studies are recommended to optimize this combination for clinical applications, with potential to improve patient outcomes in challenging cancer types.

Focused Ultrasound in Cancer Immunotherapy: A Review of Mechanisms and Applications

Ultrasound is well-perceived for its diagnostic application. Meanwhile, ultrasound, especially focused ultrasound (FUS), has also demonstrated therapeutic capabilities, such as thermal tissue ablation, hyperthermia, and mechanical tissue ablation, making it a viable therapeutic approach for cancer treatment. Cancer immunotherapy is an emerging cancer treatment approach that boosts the immune system to fight cancer, and it has also exhibited enhanced effectiveness in treating previously considered untreatable conditions. Currently, cancer immunotherapy is regarded as one of the four pillars of cancer treatment because it has fewer adverse effects than radiation and chemotherapy. In recent years, the unique capabilities of FUS in ablating tumors, regulating the immune system, and enhancing anti-tumor responses have resulted in a new field of research known as FUS-induced/assisted cancer immunotherapy. In this work, we provide a comprehensive overview of this new research field by introducing the basics of focused ultrasound and cancer immunotherapy and providing the state-of-the-art applications of FUS in cancer immunotherapy: the mechanisms and preclinical and clinical studies. This review aims to offer the scientific community a reliable reference to the exciting field of FUS-induced/assisted cancer immunotherapy, hoping to foster the further development of related technology and expand its medical applications.

Magnetoelectric nanodiscs enable wireless transgene-free neuromodulation

Deep brain stimulation with implanted electrodes has transformed neuroscience studies and treatment of neurological and psychiatric conditions. Discovering less invasive alternatives to deep brain stimulation could expand its clinical and research applications. Nanomaterial-mediated transduction of magnetic fields into electric potentials has been explored as a means for remote neuromodulation. Here we synthesize magnetoelectric nanodiscs (MENDs) with a core-double-shell Fe3O4-CoFe2O4-BaTiO3 architecture (250 nm diameter and 50 nm thickness) with efficient magnetoelectric coupling. We find robust responses to magnetic field stimulation in neurons decorated with MENDs at a density of 1 µg mm-2 despite individual-particle potentials below the neuronal excitation threshold. We propose a model for repetitive subthreshold depolarization that, combined with cable theory, supports our observations in vitro and informs magnetoelectric stimulation in vivo. Injected into the ventral tegmental area or the subthalamic nucleus of genetically intact mice at concentrations of 1 mg ml-1, MENDs enable remote control of reward or motor behaviours, respectively. These findings set the stage for mechanistic optimization of magnetoelectric neuromodulation towards applications in neuroscience research.

The Thermal Ablation with MRgFUS: From Physics to Oncological Applications

The growing interest in minimal and non-invasive therapies, especially in the field of cancer treatment, highlights a significant shift toward safer and more effective options. Ablative therapies are well-established tools in cancer treatment, with known effects including locoregional control, while their role as modulators of the systemic immune response against cancer is emerging. The HIFU developed with magnetic resonance imaging (MRI) guidance enables treatment precision, improves real-time procedural control, and ensures accurate outcome assessment. Magnetic Resonance-guided Focused Ultrasound (MRgFUS) induces deep coagulation necrosis within an elliptical focal area, effectively encompassing the entire tumor site and allowing for highly targeted radical ablation. The applications of MRgFUS in oncology are rapidly expanding, offering pain relief and curative treatment options for bone metastatic lesions. Additionally, the MRgFUS plays an effective role in targeted optional therapies for early prostate and breast cancers. Emerging research also focuses on the potential uses in treating abdominal cancers and harnessing capabilities to stimulate immune responses against tumors or to facilitate the delivery of anticancer drugs. This evolving landscape presents exciting opportunities for improving patient outcomes and advancing cancer treatment methodologies. In neuro-oncology, MRgFUS utilizes low-intensity focused ultrasound (LIFU) along with intravenous microbubbles to open the blood-brain barrier (BBB) and enhance the intra-tumoral delivery of chemotherapy drugs.

Innovative Approaches to Brain Cancer: The Use of Magnetic Resonance-guided Focused Ultrasound in Glioma Therapy

Gliomas are a wide group of common brain tumors, with the most aggressive type being glioblastoma multiforme (GBM), with a 5-year survival rate of less than 5% and a median survival time of approximately 12-14 months. The standard treatment of GBM includes surgical excision, radiotherapy, and chemotherapy with temozolomide (TMZ). However, tumor recurrence and progression are common. Therefore, more effective treatment for GBM should be found. One of the main obstacles to the treatment of GBM and other gliomas is the blood-brain barrier (BBB), which impedes the penetration of antitumor chemotherapeutic agents into glioblastoma cells. Nowadays, one of the most promising novel methods for glioma treatment is Magnetic Resonance-guided Focused Ultrasound (MRgFUS). Low-intensity FUS causes the BBB to open transiently, which allows better drug delivery to the brain tissue. Under magnetic resonance guidance, ultrasound waves can be precisely directed to the tumor area to prevent side effects in healthy tissues. Through the open BBB, we can deliver targeted chemotherapeutics, anti-tumor agents, immunotherapy, and gene therapy directly to gliomas. Other strategies for MRgFUS include radiosensitization, sonodynamic therapy, histotripsy, and thermal ablation. FUS can also be used to monitor the treatment and progression of gliomas using blood-based liquid biopsy. All these methods are still under preclinical or clinical trials and are described in this review to summarize current knowledge and ongoing trials.

A Comprehensive Overview of the Current Status and Advancements in Various Treatment Strategies against Epilepsy

Epilepsy affects more than 70 million individuals of all ages worldwide and remains one of the most severe chronic noncommunicable neurological diseases globally. Several neurotransmitters, membrane protein channels, receptors, enzymes, and, more recently noted, various pathways, such as inflammatory and mTORC complexes, play significant roles in the initiation and propagation of seizures. Over the past two decades, significant developments have been made in the diagnosis and treatment of epilepsy. Various pharmacological drugs with diverse mechanisms of action and other treatment options have been developed to control seizures and treat epilepsy. These options include surgical treatment, nanomedicine, gene therapy, natural products, nervous stimulation, a ketogenic diet, gut microbiota, etc., which are in various developmental stages. Despite a plethora of drugs and other treatment options, one-third of affected individuals are resistant to current medications, while the majority of approved drugs have severe side effects, and significant changes can occur, such as pharmacoresistance, effects on cognition, long-term problems, drug interactions, risks of poor adherence, specific effects for certain medications, and psychological complications. Therefore, the development of new drugs and other treatment options that have no or minimal adverse effects is needed to combat this deadly disease. In this Review, we comprehensively summarize and explain all of the treatment options that have been approved or are in developmental stages for epilepsy as well as their status in clinical trials and advancements.

AI-powered ultrasonic thermometry for HIFU therapy in deep organ

High-intensity focused ultrasound (HIFU) is considered as an important non-invasive way for tumor ablation in deep organs. However, accurate real-time monitoring of the temperature field within HIFU focal area remains a challenge. Although ultrasound technology, compared with other approaches, is a good choice for noninvasive and real-time monitoring on the temperature distribution, traditional ultrasonic thermometry mainly relies on the backscattered signal, which is difficult for high temperature (>50 °C) measurement. Given that artificial intelligence (AI) shows significant potential for biomedical applications, we propose an AI-powered ultrasonic thermometry using an end-to-end deep neural network termed Breath-guided Multimodal Teacher-Student (BMTS), which possesses the capability to elucidate the interaction between HIFU and complex heterogeneous biological media. It has been demonstrated experimentally that two-dimension temperature distribution within HIFU focal area in deep organ can be accurately reconstructed with an average error and a frame speed of 0.8 °C and 0.37 s, respectively. Most importantly, the maximum measurable temperature for ultrasonic technology has been successfully expanded to a record value of 67 °C. This breakthrough indicates that the development of AI-powered ultrasonic thermometry is beneficial for precise HIFU therapy planning in the future.

Optogenetic Control of Condensates: Principles and Applications

Biomolecular condensates appear throughout cell physiology and pathology, but the specific role of condensation or its dynamics is often difficult to determine. Optogenetics offers an expanding toolset to address these challenges, providing tools to directly control condensation of arbitrary proteins with precision over their formation, dissolution, and patterning in space and time. In this review, we describe the current state of the field for optogenetic control of condensation. We survey the proteins and their derivatives that form the foundation of this toolset, and we discuss the factors that distinguish them to enable appropriate selection for a given application. We also describe recent examples of the ways in which optogenetic condensation has been used in both basic and applied studies. Finally, we discuss important design considerations when engineering new proteins for optogenetic condensation, and we preview future innovations that will further empower this toolset in the coming years.

Experimental Evaluation of an Ultrasound-Guided High-Intensity-Focused Ultrasound Probe for Sonication of Artery

OBJECTIVES

This study aimed to develop an ultrasound-guided high-intensity-focused ultrasound (USgHIFU) probe for arterial sonication and to evaluate vascular contraction.

METHODS

The USgHIFU probe comprised two confocal spherical transducers for sonication and a US color Doppler flow imaging probe for guidance. A vessel-mimicking phantom was sonicated in two directions. In the vascular radial direction, an isolated rabbit aorta embedded in ex vivo pork liver was sonicated at different acoustic powers (245 and 519 W), flow rates (25, 30, and 50 mL/minute), and sonication energies (519, 980, and 1038 J). Changes in the postsonication vessels were evaluated using US imaging, microscopic observation, and histopathological analysis.

RESULTS

Beam focusing along the vascular radial direction caused significant deformation of both tube walls (n = 4), whereas focusing along the axial direction only affected the contraction of the anterior wall (n = 4). The contraction index (Dc) of the vessel sonicated at 245 W and 980 J was 56.2 ± 9.7% (n = 12) with 25 mL/minute. The Dc of the vessel sonicated at 519 W and 1038 J was 56.5 ± 7.8% (n = 17). The Dc of the vessel sonicated at 519 J total energy was 18.3 ± 5.1% (n = 12).

CONCLUSION

The developed USgHIFU probe induced greater vascular contractions by covering a larger area of the vessel wall in the radial direction. Sonication energy affects vascular contraction through temperature elevation of the vessel wall. When the acoustic power was high, an increase in acoustic power, even with comparable sonication energy, did not result in greater vessel contraction.

Revealing physical interactions of ultrasound waves with the body through photoelasticity imaging

Ultrasound is a ubiquitous technology in medicine for screening, diagnosis, and treatment of disease. The functionality and efficacy of different ultrasound modes relies strongly on our understanding of the physical interactions between ultrasound waves and biological tissue structures. This article reviews the use of photoelasticity imaging for investigating ultrasound fields and interactions. Physical interactions are described for different ultrasound technologies, including those using linear and nonlinear ultrasound waves, as well as shock waves. The use of optical modulation of light by ultrasound is presented for shadowgraphic and photoelastic techniques. Investigations into shock wave and burst wave lithotripsy using photoelastic methods are summarized, along with other endoscopic forms of lithotripsy. Photoelasticity in soft tissue surrogate materials is reviewed, and its deployment in investigating tissue-bubble interactions, generated ultrasound waves, and traumatic brain injury, are discussed. With the continued growth of medical ultrasound, photoelasticity imaging can play a role in elucidating the physical mechanisms leading to useful bioeffects of ultrasound for imaging and therapy.

High-Intensity Focused Ultrasound in Dentistry: A Literature Review

Although high-intensity focused ultrasound (HIFU) has been applied widely in medicine, utilising its non-invasive dual ablation and thermal coagulation properties, its application in dentistry has primarily remained in the research phase, predominantly in in vitro studies. Nonetheless, there has been a consistent increase in the number of publications on this subject in recent decades, focusing on areas such as remineralisation of dentine surfaces, removal of smear layers, drug delivery, and microbial elimination. The number of advantages HIFU can offer, such as its non-surgical nature, absence of ionising radiation, lack of residue, and absence of aerosols, is driving this upward trend, indicating the potential for HIFU in clinical dentistry and ongoing efforts towards developing HIFU-based devices for routine dental use. This succinct review aims to outline the historical context, operational mechanisms of HIFU, summarise recent dental research, and provide a forward-looking perspective on the role of HIFU in modern clinical dentistry.

Optimization of ultrasound heating with Pickering droplets using core-shell scattering theory

Nanoparticles find widespread application in various medical contexts, including targeted nanomedicine and enhancing therapeutic efficacy. Moreover, they are employed to stabilize emulsions, giving rise to stabilized droplets known as Pickering droplets. Among the various methods to improve anti-cancer treatment, ultrasound hyperthermia stands out as an efficient approach. This research proposes Pickering droplets as promising sonosensitizer candidates, to enhance the attenuation of ultrasound with simultaneous potential to act as drug carriers. The enhanced ultrasound energy dissipation could be, therefore, optimized by changing the parameters of Pickering droplets. The ultrasound scattering theory, based on the core-shell model, was employed to calculate theoretical ultrasound properties such as attenuation and velocity. Additionally, computer simulations, based on a bioheat transfer model, were utilized to compute heat generation in agar-based phantoms of tissues under different ultrasound wave frequencies. Two types of phantoms were simulated: a pure agar phantom and an agar phantom incorporating spherical inclusions. The spherical inclusions, with a diameter of 10 mm, were doped with various sizes of Pickering droplets, considering their core radius and shell thickness. Computer simulation of these spherical inclusions incorporated within agar phantom resulted in different enhancement of achieved temperature elevation, which depending on the core radius, shell thickness, and the material properties of the system. Notably, spherical inclusions doped with Pickering droplets stabilized by magnetite nanoparticles exhibited a higher temperature rise compared to droplets stabilized by silica nanoparticles. Moreover, nanodroplets with a core radius below 400 nm demonstrated better heating performance compared to microdroplets. Furthermore, Pickering droplets incorporated into agar phantom could allow obtaining a similar effect of local heating as sophisticated focused ultrasound devices.

Model based deep learning method for focused ultrasound pathway scanning

The primary purpose of high-intensity focused ultrasound (HIFU), a non-invasive medical therapy, is to precisely target and ablate tumors by focusing high-frequency ultrasound from an external power source. A series of ablations must be performed in order to treat a big volume of tumors, as a single ablation can only remove a small amount of tissue. To maximize therapeutic efficacy while minimizing adverse side effects such as skin burns, preoperative treatment planning is essential in determining the focal site and sonication duration for each ablation. Here, we introduce a machine learning-based approach for designing HIFU treatment plans, which makes use of a map of the material characteristics unique to a patient alongside an accurate thermal simulation. A numerical model was employed to solve the governing equations of HIFU process and to simulate the HIFU absorption mechanism, including ensuing heat transfer process and the temperature rise during the sonication period. To validate the accuracy of this numerical model, a series of tests was conducted using ex vivo bovine liver. The findings indicate that the developed models properly represent the considerable variances observed in tumor geometrical shapes and proficiently generate well-defined closed treated regions based on imaging data. The proposed strategy facilitated the formulation of high-quality treatment plans, with an average tissue over- or under-treatment rate of less than 0.06%. The efficacy of the numerical model in accurately predicting the heating process of HIFU, when combined with machine learning techniques, was validated through quantitative comparison with experimental data. The proposed approach in cooperation with HIFU simulation holds the potential to enhance presurgical HIFU plan.

Five-year follow-up after a single US-guided high intensity focused ultrasound treatment of breast fibroadenoma

The aim of this study was to evaluate the long-term efficacy of a single ultrasound-guided high-intensity focused ultrasound (US-HIFU) treatment in patients with breast fibroadenoma (FA) in terms of volume and pain reduction as well as palpation findings. From december 2013 until november 2014 27 women with a symptomatic FA were treated in one HIFU-session. Follow-up visits were performed after 7 days, 6 months and 1, 2, 3 and 5 years with clinical examination and ultrasound. One year after the procedure, a core needle biopsy of the residual lesion was offered. There was a significant volume reduction 6 months after HIFU from 1083.10 to 347.13 mm3 (p < 0.0001) with a mean volume reduction ratio (VRR) of 61.63%. Thereafter the FAs showed a further, but no longer significant decrease in size. One patient with an initial incomplete ablation and histologically confirmed persistent vital cells after 1 year showed a strong regrowth after 3 years. Excluding this patient from analysis, the mean VRR at months 12, 24, 36, and 60 was 86.44%, 94.44%, 94.90%, and 97.85%, respectively. Before HIFU, 59.26% of the patients had pain (22.33/100 VAS) which decreased to 6.56/100 after 12 months and remained reduced over the 5 year follow up period. A decrease in palpability from 85.19 to 7.69% was observed within 24 months. A single HIFU intervention let to a substantial reduction in size, pain, and palpability with its most potential effect during the first 12 months. Subsequently, the observed effect remained stable over a 5 year follow up period. Incomplete initial treatment was associated with the risk of regrowth.

Tissue Ablation: Applications and Perspectives

Tissue ablation techniques have emerged as a critical component of modern medical practice and biomedical research, offering versatile solutions for treating various diseases and disorders. Percutaneous ablation is minimally invasive and offers numerous advantages over traditional surgery, such as shorter recovery times, reduced hospital stays, and decreased healthcare costs. Intra-procedural imaging during ablation also allows precise visualization of the treated tissue while minimizing injury to the surrounding normal tissues, reducing the risk of complications. Here, the mechanisms of tissue ablation and innovative energy delivery systems are explored, highlighting recent advancements that have reshaped the landscape of clinical practice. Current clinical challenges related to tissue ablation are also discussed, underlining unmet clinical needs for more advanced material-based approaches to improve the delivery of energy and pharmacology-based therapeutics.

Image-guided Ablative Procedures

Various image-guided ablative procedures include chemical and thermal ablation techniques and irreversible electroporation. These have been used for curative intent for small tumours and palliative intent for debulking, immunogenicity and pain control. Understanding these techniques is critical to avoiding complications and achieving superior clinical outcomes. Additionally, combination with immunotherapy and chemotherapies is rapidly evolving. There are numerous opportunities in interventional radiology to advance ablation techniques and seamlessly integrate into current treatment regimens for both benign and malignant tumours.

High-Intensity Focused Ultrasound Enhances Drug Penetration into the Human Skin in the Franz Diffusion Cell

Purpose

High-intensity focused ultrasound (HIFU)-assisted drug delivery is a non-invasive tool to deliver drugs to targeted areas, currently used mainly for treating cancer and cardiovascular diseases. However, in terms of transdermal drug delivery, HIFU technology is still poorly understood. Accordingly, this study sought to investigate the effectiveness of HIFU on drug penetration into the skin using human skin tissues.

Methods

Gel-type drugs whose ingredient is glutathione were labelled with fluorescein isothiocyanate, in turn the drugs were allowed to penetrate to the human skin tissue in the Franz diffusion cell for 24 hours in control and HIFU treatment groups, and their fluorescence intensity was measured using a multiple microplate reader at one, two, six, and 24 hours after drug application. In addition, tissue slice analysis was performed in each tissue slice at 24 hours post-drug application. The % area, fluorescence intensity per area, and penetration depth of the drug were measured using a fluorescence microscope.

Results

The fluorescence intensity increased with time in all groups. Specifically, at 24 hours after drug application, the fluorescence intensity (a.u). of the 10-shot HIFU treatment group was significantly enhanced compared to that of the control group (p < 0.05). The tissue slice analysis demonstrated that the % area of fluorescent drug and the fluorescence intensity per area (a.u.) were all significantly increased in both HIFU treatment groups compared to the control group (p < 0.05, p < 0.001). In addition, the penetration depth (μm) also markedly rose in both HIFU treatment groups compared to the control group (p < 0.01, p < 0.05).

Conclusion

It was demonstrated for the first time that HIFU significantly facilitated topical drug penetration into the human skin, strongly implying that HIFU can be a useful option for transdermal drug delivery.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

A Systematic Review and Single-Arm Meta-Analysis on the Efficacy of High-Intensity, Focused Ultrasound for Benign Prostatic Hyperplasia Treatment: A Forgotten Option?

Benign prostatic hyperplasia (BPH) is a non-cancerous enlargement of prostate tissue, commonly affecting older men. This condition leads to lower urinary tract symptoms (LUTS), which significantly affect the quality of life. Over time, extensive research has been conducted regarding BPH treatment, exploring various treatment options. High-intensity focused ultrasound (HIFU) is a non-invasive treatment modality that has shown promise in initial studies. However, evidence regarding its long-term efficacy and safety remains inconclusive. This study evaluates HIFU's safety and efficacy for BPH treatment, identifying gaps for future research. The study conducted comprehensive searches across the PubMed, Google Scholar, Cochrane Central, and ClinicalTrials.gov databases, covering English-language articles from 1994 to 2023. Inclusion criteria focused on peer-reviewed studies, with more than 10 patients utilizing ultrasound image-guided HIFU for BPH while excluding other HIFU modalities lacking ultrasound image guidance. Data extraction targeted primary outcomes (peak flow rate, International Prostate Symptom Score (IPSS), postvoid residual volume) and secondary outcomes (treatment time, follow-up duration). Statistical analysis utilized a random effects model with heterogeneity assessed by I² statistics and the Q test, alongside subgroup analysis based on study design. The risk of bias assessment employed the Cochrane Collaboration tool for randomized controlled trials and the methodological index for nonrandomized studies. Among 560 identified articles, 12 studies with 522 patients met the inclusion criteria. Primary outcomes showed improvements in Qmax (1 month: 2.50 ml/s, 12 months: 6.22 ml/s) and IPSS (1 month: -9.37 points, 12 months: -11.60 points). Reported complications included transient hematuria, hematospermia, and urinary retention. HIFU presents significant clinical improvements in treating BPH, albeit with slow progression attributed to specific techniques and the ablative approach. Manageable complication profiles are observed, yet study design flaws hinder a comprehensive evaluation of HIFU efficacy. The authors suggest areas for clinical optimization, emphasizing the necessity of further research.

The emergence of cancer sono-immunotherapy

Owing to its remarkable ease of use, ultrasound has recently been explored for stimulating or amplifying immune responses during cancer therapy, termed 'sono-immunotherapy'. Ultrasound can cause immunogenic cell death in cancer cells via thermal and nonthermal effects to regulate the tumor microenvironment, thereby priming anticancer immunity; by integrating well-designed biomaterials, novel sono-immunotherapy approaches with augmented efficacy can also be developed. Here, we review the advances in sono-immunotherapy for cancer treatment and summarize existing limitations along with potential trends. We offer emerging insights into this realm, which might prompt breakthroughs and expand its potential applications to other diseases.

Complications and adverse events of high-intensity focused ultrasound in its application to gynecological field - a systematic review and meta-analysis

OBJECTIVE

To analyze and summarize the types, incidence rates and relevant influencing factors of adverse events (AEs) after high-intensity focused ultrasound ablation of gynecological diseases and provide reference and basis for handling such events in clinical practice.

METHOD

We searched PubMed, Cochrane Library, Web of Science and Embase databases to retrieve all literature since its establishment until February 2024. We evaluated the quality of included literature and publication bias and conducted a meta-analysis of single group rates for various AEs using Stata 17.0.

RESULTS

This systematic review finally included 41 articles. We summarized 34 kinds of AEs in 7 aspects and conducted a single group rate meta-analysis and sub-group analysis of 16 kinds of AEs. Among the common AEs of High-Intensity Focused Ultrasound (HIFU), the incidence of lower abdominal pain/pelvic pain is 36.1% (95% CI: 24.3%∼48.8%), vaginal bleeding is 20.6% (95% CI: 13.9%∼28.0%), vaginal discharge is 14.0% (95% CI: 9.6%∼19.1%), myoma discharge is 24% (95% CI: 14.6%∼34.8%), buttock pain is 10.8% (95% CI: 6.0%∼16.5%) and sacral pain is 10% (95% CI: 8.8%∼11.2%). Serious complications include uterine rupture, necrotic tissue obstruction requiring surgical intervention, third degree skin burns and persistent lower limb pain or movement disorders.

CONCLUSION

The common AEs after HIFU surgery are mostly mild and controllable, and the incidence of serious complications is extremely low. By reasonable prevention and active intervention, these events can be further reduced, making it a safe and effective treatment method. It is a good choice for patients who crave noninvasive treatment or have other surgical contraindications.

Safety and efficacy of histotripsy delivery through overlying gas-filled small bowel in an ex vivo swine model

PURPOSE

To evaluate the safety and efficacy of performing histotripsy through overlying gas-filled bowel in an ex vivo swine model.

METHODS

An ex vivo model was created to simulate histotripsy treatment of solid organs through gas-filled bowel. Spherical 2.5 cm histotripsy treatments were performed in agar phantoms for each of five treatment groups: 1) control with no overlying bowel (n = 6), 2) bowel 0 cm above phantom (n = 6), 3) bowel 1 cm above phantom (n = 6), 4) bowel 2 cm above phantom (n = 6), and 5) bowel 0 cm above the phantom with increased treatment amplitude (n = 6). Bowel was inspected for gross and microscopic damage, and treatment zones were measured. A ray-tracing simulation estimated the percentage of therapeutic beam path blockage by bowel in each scenario.

RESULTS

All histotripsy treatments through partial blockage were successful (24/24). No visible or microscopic damage was observed to intervening bowel. Partial blockage resulted in a small increase in treatment volume compared to controls (p = 0.002 and p = 0.036 for groups with bowel 0 cm above the phantom, p > 0.3 for bowel 1 cm and 2 cm above the phantom). Gas-filled bowel was estimated to have blocked 49.6%, 35.0%, and 27.3% of the therapeutic beam at 0, 1, and 2 cm, respectively.

CONCLUSION

Histotripsy has the potential to be applied through partial gas blockage of the therapeutic beam path, as shown by this ex vivo small bowel model. Further work in an in vivo survival model appears indicated.

Feasibility study of focused ultrasound in the treatment of vulvar low-grade squamous intraepithelial lesions with persistent symptoms

OBJECTIVE

This study aimed to investigate the feasibility, efficacy, and safety of focused ultrasound (FUS) for the treatment of vulvar low-grade squamous intraepithelial lesions (VLSIL) with persistent symptoms.

METHODS

This retrospective analysis included 24 VLSIL patients who underwent FUS treatment. At each follow-up visit, the clinical response was assessed including changes in symptoms and signs. In addition, the histological response was assessed based on the vulvar biopsy results of the 3rd follow-up. Clinical and histological response were assessed to elucidate the efficacy.

RESULTS

A total of 22 patients completed follow-up and post-treatment pathological biopsies. After treatment, the clinical scores of itching decreased from 2.55 ± 0.51 to 0.77 ± 0.81 (p < 0.05). Furthermore, the clinical response rate and histological response rate were 86.4% and 81.8%, respectively. Only two cured patients indicated recurrence in the 3rd and 4th year during the follow-up period and achieved cure after re-treatment. In terms of adverse effects, only one patient developed ulcers after treatment, which healed after symptomatic anti-inflammatory treatment without scarring, and no other treatment complications were found in any patients. None of the patients developed a malignant transformation during the follow-up period.

CONCLUSION

This study revealed that FUS is feasible, effective, and safe for treating VLSIL patients with persistent symptoms, providing a new solution for the noninvasive treatment of symptomatic VLSIL.

Evaluation of Dual-Frequency Switching HIFU for Optimizing Superficial Ablation

OBJECTIVE

Dual-frequency high-intensity focused ultrasound (HIFU) thermal ablation is an exceptionally promising technique for treating tumors due to its precision and effectiveness. However, there are still a few studies on improving the accuracy and efficiency of HIFU in superficial ablation applications. This study proposes a method utilizing dual frequency switching ultrasound (DFSU) to enhance the efficiency and precision of superficial treatments.

METHODS

A dual-frequency HIFU transducer operating at 4.5 MHz and 13.7 MHz was designed, and a dual-frequency impedance matching network was designed to optimize electro-acoustic conversion efficiency. Phantom and ex vivo tests were conducted to measure and compare thermal lesion areas and temperature rises caused by single-frequency ultrasound (SFU) and DFSU.

RESULTS

In both phantom and ex vivo tests, the utilization of DFSU resulted in larger lesion areas compared to SFU. Moreover, DFSU provided improved control and versatility, enabling precise and efficient ablation.

CONCLUSION

DFSU exhibits the ability to generate larger ablation areas in superficial tissue compared to SFU, and DFSU allows flexible control over the ablation area and temperature rise rate. The acoustic power deposition of HIFU can be optimized to achieve precise ablation.

Biomechanical testing of ex vivo porcine tendons following high intensity focused ultrasound thermal ablation

INTRODUCTION

Magnetic resonance-guided focused ultrasound (MRgFUS) has been demonstrated to be able to thermally ablate tendons with the aim to non-invasively disrupt tendon contractures in the clinical setting. However, the biomechanical changes of tendons permitting this disrupting is poorly understood. We aim to obtain a dose-dependent biomechanical response of tendons following magnetic resonance-guided focused ultrasound (MRgFUS) thermal ablation.

METHODS

Ex vivo porcine tendons (n = 72) were embedded in an agar phantom and randomly assigned to 12 groups based on MRgFUS treatment. The treatment time was 10, 20, or 30s, and the applied acoustic power was 25, 50, 75, or 100W. Following each MRgFUS treatment, tendons underwent biomechanical tensile testing on an Instron machine, which calculated stress-strain curves during tendon elongation. Rupture rate, maximum treatment temperature, Young's modulus and ultimate strength were analyzed for each treatment energy.

RESULTS

The study revealed a dose-dependent response, with tendons rupturing in over 50% of cases when energy delivery exceeded 1000J and 100% disruption at energy levels beyond 2000J. The achieved temperatures during MRgFUS were directly proportional to energy delivery. The highest recorded temperature was 56.8°C ± 9.34 (3000J), while the lowest recorded temperate was 18.6°C ± 0.6 (control). The Young's modulus was highest in the control group (47.3 MPa ± 6.5) and lowest in the 3000J group (13.2 MPa ± 5.9). There was no statistically significant difference in ultimate strength between treatment groups.

CONCLUSION

This study establishes crucial thresholds for reliable and repeatable disruption of tendons, laying the groundwork for future in vivo optimization. The findings prompt further exploration of MRgFUS as a non-invasive modality for tendon disruption, offering hope for improved outcomes in patients with musculotendinous contractures.

Growing Trend to Adopt Speckle Variance Optical Coherence Tomography for Biological Tissue Assessments in Pre-Clinical Applications

Speckle patterns are a generic feature in coherent imaging techniques like optical coherence tomography (OCT). Although speckles are granular like noise texture, which degrades the image, they carry information that can be benefited by processing and thereby furnishing crucial information of sample structures, which can serve to provide significant important structural details of samples in in vivo longitudinal pre-clinical monitoring and assessments. Since the motions of tissue molecules are indicated through speckle patterns, speckle variance OCT (SV-OCT) can be well-utilized for quantitative assessments of speckle variance (SV) in biological tissues. SV-OCT has been acknowledged as a promising method for mapping microvasculature in transverse-directional blood vessels with high resolution in micrometers in both the transverse and depth directions. The fundamental scope of this article reviews the state-of-the-art and clinical benefits of SV-OCT to assess biological tissues for pre-clinical applications. In particular, focus on precise quantifications of in vivo vascular response, therapy assessments, and real-time temporal vascular effects of SV-OCT are primarily emphasized. Finally, SV-OCT-incorporating pre-clinical techniques with high potential are presented for future biomedical applications.

High-quality Agar and Polyacrylamide Tumor-mimicking Phantom Models for Magnetic Resonance-guided Focused Ultrasound Applications

Background

Tissue-mimicking phantoms (TMPs) have been used extensively in clinical and nonclinical settings to simulate the thermal effects of focus ultrasound (FUS) technology in real tissue or organs. With recent technological developments in the FUS technology and its monitoring/guided techniques such as ultrasound-guided FUS and magnetic resonance-guided FUS (MRgFUS) the need for TMPs are more important than ever to ensure the safety of the patients before being treated with FUS for a variety of diseases (e.g., cancer or neurological). The purpose of this study was to prepare a tumor-mimicking phantom (TUMP) model that can simulate competently a tumor that is surrounded by healthy tissue.

Methods

The TUMP models were prepared using polyacrylamide (PAA) and agar solutions enriched with MR contrast agents (silicon dioxide and glycerol), and the thermosensitive component bovine serum albumin (BSA) that can alter its physical properties once thermal change is detected, therefore offering real-time visualization of the applied FUS ablation in the TUMPs models. To establish if these TUMPs are good candidates to be used in thermoablation, their thermal properties were characterized with a custom-made FUS system in the laboratory and a magnetic resonance imaging (MRI) setup with MR-thermometry. The BSA protein's coagulation temperature was adjusted at 55°C by setting the pH of the PAA solution to 4.5, therefore simulating the necrosis temperature of the tissue.

Results

The experiments carried out showed that the TUMP models prepared by PAA can change color from transparent to cream-white due to the BSA protein coagulation caused by the thermal stress applied. The TUMP models offered a good MRI contrast between the TMPs and the TUMPs including real-time visualization of the ablation area due to the BSA protein coagulation. Furthermore, the T2-weighted MR images obtained showed a significant change in T2 when the BSA protein is thermally coagulated. MR thermometry maps demonstrated that the suggested TUMP models may successfully imitate a tumor that is present in soft tissue.

Conclusion

The TUMP models developed in this study have numerous uses in the testing and calibration of FUS equipment including the simulation and validation of thermal therapy treatment plans with FUS or MRgFUS in oncology applications.

Experimental and Computational Analysis of High-Intensity Focused Ultrasound Thermal Ablation in Breast Cancer Cells: Monolayers vs. Spheroids

High-intensity focused ultrasound (HIFU) is a non-invasive therapeutic modality that uses precise acoustic energy to ablate cancerous tissues through coagulative necrosis. In this context, we investigate the efficacy of HIFU ablation in two distinct cellular configurations, namely 2D monolayers and 3D spheroids of epithelial breast cancer cell lines (MDA-MB 231 and MCF7). The primary objective is to compare the response of these two in vitro models to HIFU while measuring their ablation percentages and temperature elevation levels. HIFU was systematically applied to the cell cultures, varying ultrasound intensity and duty cycle during different sonication sessions. The results indicate that the degree of ablation is highly influenced by the duty cycle, with higher duty cycles resulting in greater ablation percentages, while sonication duration has a minimal impact. Numerical simulations validate experimental observations, highlighting a significant disparity in the response of 2D monolayers and 3D spheroids to HIFU treatment. Specifically, tumor spheroids require lower temperature elevations for effective ablation, and their ablation percentage significantly increases with elevated duty cycles. This study contributes to a comprehensive understanding of acoustic energy conversion within the biological system during HIFU treatment for 2D versus 3D ablation targets, holding potential implications for refining and personalizing breast cancer therapeutic strategies.

Safety Review of Therapeutic Ultrasound for Spinal Cord Neuromodulation and Blood-Spinal Cord Barrier Opening

New focused ultrasound spinal cord applications have emerged, particularly those improving therapeutic agent delivery to the spinal cord via blood-spinal cord barrier opening and the neuromodulation of spinal cord tracts. One hurdle in the development of these applications is safety. It may be possible to use safety trends from seminal and subsequent works in focused ultrasound to guide the development of safety guidelines for spinal cord applications. We collated data from decades of pre-clinical studies and illustrate a clear relationship between damage, time-averaged spatial peak intensity and exposure duration. This relationship suggests a thermal mechanism underlies ultrasound-induced spinal cord damage. We developed minimum and mean thresholds for damage from these pre-clinical studies. When these thresholds were plotted against the parameters used in recent pre-clinical ultrasonic spinal cord neuromodulation studies, the majority of the neuromodulation studies were near or above the minimum threshold. This suggests that a thermal neuromodulatory effect may exist for ultrasonic spinal cord neuromodulation, and that the thermal dose must be carefully controlled to avoid damage to the spinal cord. By contrast, the intensity-exposure duration threshold had no predictive value when applied to blood-spinal cord barrier opening studies that employed injected contrast agents. Most blood-spinal cord barrier opening studies observed slight to severe damage, except for small animal studies that employed an active feedback control method to limit pressures based on measured bubble oscillation behavior. The development of new focused ultrasound spinal cord applications perhaps reflects the recent success in the development of focused ultrasound brain applications, and recent work has begun on the translation of these technologies from brain to spinal cord. However, a great deal of work remains to be done, particularly with respect to developing and accepting safety standards for these applications.

Blood-Brain Barrier Disruption for the Treatment of Primary Brain Tumors: Advances in the Past Half-Decade

PURPOSE OF REVIEW

To review relevant advances in the past half-decade in the treatment of primary brain tumors via modification of blood-brain barrier (BBB) permeability.

RECENT FINDINGS

BBB disruption is becoming increasingly common in the treatment of primary brain tumors. Use of mannitol in BBB disruption for targeted delivery of chemotherapeutics via superselective intra-arterial cerebral infusion (SIACI) is the most utilized strategy to modify the BBB. Mannitol is used in conjunction with chemotherapeutics, oligonucleotides, and other active agents. Convection-enhanced delivery has become an attractive option for therapeutic delivery while bypassing the BBB. Other technologic innovations include laser interstitial thermal therapy (LITT) and focused ultrasound (FUS) which have emerged as prime modalities to directly target tumors and cause significant local BBB disruption. In the past 5 years, interest has significantly increased in studying modalities to disrupt the BBB in primary brain tumors to enhance treatment responses and improve clinical outcomes.

Treatment Planning and Aberration Correction Algorithm for HIFU Ablation of Renal Tumors

High-intensity focused ultrasound (HIFU) applications for thermal or mechanical ablation of renal tumors often encounter challenges due to significant beam aberration and refraction caused by oblique beam incidence, inhomogeneous tissue layers, and presence of gas and bones within the beam. These losses can be significantly mitigated through sonication geometry planning, patient positioning, and aberration correction using multielement phased arrays. Here, a sonication planning algorithm is introduced, which uses the simulations to select the optimal transducer position and evaluate the effect of aberrations and acoustic field quality at the target region after aberration correction. Optimization of transducer positioning is implemented using a graphical user interface (GUI) to visualize a segmented 3-D computed tomography (CT)-based acoustic model of the body and to select sonication geometry through a combination of manual and automated approaches. An HIFU array (1.5 MHz, 256 elements) and three renal cell carcinoma (RCC) cases with different tumor locations and patient body habitus were considered. After array positioning, the correction of aberrations was performed using a combination of backpropagation from the focus with an ordinary least squares (OLS) optimization of phases at the array elements. The forward propagation was simulated using a combination of the Rayleigh integral and k-space pseudospectral method (k-Wave toolbox). After correction, simulated HIFU fields showed tight focusing and up to threefold higher maximum pressure within the target region. The addition of OLS optimization to the aberration correction method yielded up to 30% higher maximum pressure compared to the conventional backpropagation and up to 250% higher maximum pressure compared to the ray-tracing method, particularly in strongly distorted cases.

In vivo exposure of the bladder using a non-invasive high intensity focused ultrasound toroidal transducer

A toroidal high-intensity focused ultrasound (HIFU) transducer was used to expose normal bladder wall tissues non-invasively in vivo in a porcine model in order to investigate the potential to treat bladder tumors. The transducer was divided into 32 concentric rings with equal surface areas, operating at 2.5 MHz. Eight animals were split into two groups of 4. In the first group, post-mortem evaluation was performed immediately after ultrasound exposure. In the second group, animals survived for up to seven days before post-mortem evaluation. The ultrasound imaging guided HIFU device was hand-held during the procedure using optical tracking to ensure correct targeting. One thermal lesion in each animal was created using a 40 s exposure at 80 acoustic Watts (free-field) in the trigone region of the bladder wall. The average (±Standard Deviation) abdominal wall and bladder wall thicknesses were 10.3 ± 1.4 mm and 1.1 ± 0.4 mm respectively. The longest and shortest axes of the HIFU ablations were 7.7 ± 2.9 mm and 6.0 ± 1.8 mm, respectively, resulting in an ablation of the whole thickness of the bladder wall in most cases. Ablation were performed at an average depth (distance from the skin surface to the centre of the HIFU lesion) of 42.5 ± 3.8 mm and extended throughout the thickness of the bladder. There were two cases of injury to tissues immediately adjacent to the bladder wall but without signs of perforation, as confirmed by histological analysis. Non-invasive HIFU ablation using a hand-held toroidal transducer was successfully performed to destroy regions of the bladder wall in vivo.

Healing Process after High-Intensity Focused Ultrasound Treatment of Benign Skin Lesions: Dermoscopic Analysis and Treatment Guidelines

Background: High-Intensity Focused Ultrasound (HIFU) has emerged as a precise and non-invasive modality for tissue ablation and healing. This study presents a detailed dermoscopic analysis of skin healing post-High-Intensity Focused Ultrasound (HIFU) treatment, focusing on common benign skin lesions, such as seborrheic keratosis, sebaceous hyperplasia, vascular lesions, and sebaceous nevi. Methods: Prior to HIFU treatment, a comprehensive assessment was conducted, integrating ultrasound scanning and clinical evaluations. The TOOsonix System ONE-M was employed for HIFU treatments, with parameters tailored to each lesion type. Results: A common pattern observed across all lesions includes initial whitening post treatment, followed by scab formation and the development of a pink area with reparative vessels. This study, however, highlights distinct differences in fibrosis patterns and healing timelines across different lesion types. Each lesion type exhibited unique fibrosis patterns post treatment. Flatter variants of seborrheic keratosis healed within a month, displaying hypopigmentation and reparative vessels, alongside a distinct lattice fibrosis pattern in more verrucous forms, which took about two months to heal. Sebaceous hyperplasia, characterized by rapid healing within three weeks, demonstrated fibrosis with pink areas and perpendicular white lines, concluding with a slight depression. Vascular lesions varied in healing time based on depth, with superficial ones showing whitening and crust formation, while deeper lesions had vessel occlusion and size reduction accompanied by concentric fibrotic bands. Sebaceous nevi presented the longest healing duration of three months, characterized by amorphous white-gray structures, scab formation, and the emergence of pink areas with branching vessels, leading to clear skin with reduced white lines. Conclusions: in conclusion, this meticulous clinical evaluation highlights the unique healing characteristics and timelines for each skin lesion type treated with HIFU. These insights are invaluable for optimizing follow-up assessments, identifying potential complications, and refining treatment protocols. By providing detailed insights into the healing timelines and patterns for different types of lesions, patients can be better informed about their post-treatment journey.

Unraveling lipid and inflammation interplay in cancer, aging and infection for novel theranostic approaches

The synergistic relationships between Cancer, Aging, and Infection, here referred to as the CAIn Triangle, are significant determinants in numerous health maladies and mortality rates. The CAIn-related pathologies exhibit close correlations with each other and share two common underlying factors: persistent inflammation and anomalous lipid concentration profiles in the membranes of affected cells. This study provides a comprehensive evaluation of the most pertinent interconnections within the CAIn Triangle, in addition to examining the relationship between chronic inflammation and specific lipidic compositions in cellular membranes. To tackle the CAIn-associated diseases, a suite of complementary strategies aimed at diagnosis, prevention, and treatment is proffered. Our holistic approach is expected to augment the understanding of the fundamental mechanisms underlying these diseases and highlight the potential of shared features to facilitate the development of novel theranostic strategies.

Ultrasound robotics for precision therapy

In recent years, the application of microrobots in precision therapy has gained significant attention. The small size and maneuverability of these micromachines enable them to potentially access regions that are difficult to reach using traditional methods; thus, reducing off-target toxicities and maximizing treatment effectiveness. Specifically, acoustic actuation has emerged as a promising method to exert control. By harnessing the power of acoustic energy, these small machines potentially navigate the body, assemble at the desired sites, and deliver therapies with enhanced precision and effectiveness. Amidst the enthusiasm surrounding these miniature agents, their translation to clinical environments has proven difficult. The primary objectives of this review are threefold: firstly, to offer an overview of the fundamental acoustic principles employed in the field of microrobots; secondly, to assess their current applications in medical therapies, encompassing tissue targeting, drug delivery or even cell infiltration; and lastly, to delve into the continuous efforts aimed at integrating acoustic microrobots into in vivo applications.

High-intensity focused ultrasound in adenomyosis treatment: Insights on safety, efficacy, and reproductive prospects

The management of adenomyosis has undergone significant evolution, moving from traditional surgical interventions like hysterectomy to more conservative methods aimed at preserving fertility. Essential roles have been played by uterine-sparing surgeries and uterine artery embolization. Despite these advancements, there is a growing interest in less invasive alternatives. This review delves into the potential of high-intensity focused ultrasound (HIFU). HIFU employs focused ultrasound waves for precise ablation of adenomyotic lesions. The review conducts a thorough analysis of HIFU principles, safety, efficacy, and its possible synergies with other therapies. HIFU seems to be effective for adenomyosis treatment, demonstrating a favorable adverse effect profile and suitability for fertility preservation. Combining HIFU with hormonal treatment appears to enhance long-term symptom control, presenting a promising and comprehensive approach for managing adenomyosis. The goal of this article is to develop a comprehensive understanding of HIFU's role in contemporary adenomyosis management and to explore areas requiring further research.

Sono-activated materials for enhancing focused ultrasound ablation: Design and application in biomedicine

The ablation effect of focused ultrasound (FUS) has played an increasingly important role in the biomedical field over the past decades, and its non-invasive features have great advantages, especially for clinical diseases where surgical treatment is not available or appropriate. Recently, rapid advances in the adjustable morphology, enzyme-mimetic activity, and biostability of sono-activated materials have significantly promoted the medical application of FUS ablation. However, a systematic review of sono-activated materials based on FUS ablation is not yet available. This progress review focuses on the recent design, fundamental principles, and applications of sono-activated materials in the FUS ablation biomedical field. First, the different ablation mechanisms and the key factors affecting ablation are carefully determined. Then, the design of sono-activated materials with high FUS ablation efficiencies is comprehensively discussed. Subsequently, the representative biological applications are summarized in detail. Finally, the primary challenges and future perspectives are also outlined. We believe this timely review will provide key information and insights for further exploration of focused ultrasound ablation and new inspiration for designing future sono-activated materials. STATEMENT OF SIGNIFICANCE: The ablation effect of focused ultrasound (FUS) has played an increasingly important role in the biomedical field over the past decades. However, there are also some challenges of FUS ablation, such as skin burns, tumour recurrence after thermal ablation, and difficulty in controlling cavitation ablation. The rapid advance in adjustable morphology, enzyme-mimetic activity, and biostability of sono-activated materials has significantly promoted the medical application of FUS ablation. However, the systematic review of sono-activated materials based on FUS ablation is not yet available. This progress review focuses on the recent design, fundamental principles, and applications in the FUS ablation biomedical field of sono-activated materials. We believe this timely review will provide key information and insights for further exploration of FUS ablation.

Head-to-Head Comparison of Acoustic Properties of Lead-Free and PZT-Based HIFU Transducers Operating at 12 MHz

A direct comparison of performance and acoustic properties of high-intensity focused ultrasonic transducers utilizing lead-free (sodium bismuth titanate-NBT) and lead-based (lead zirconate titanate-PZT) piezoceramics is discussed. All transducers operate at 12 MHz at third harmonic frequency, having an outer diameter of 20 mm, a central hole of 5 mm in diameter, and a radius of curvature of 15 mm. The electroacoustic efficiency determined by a radiation force balance is evaluated in a range of input power levels up to 15 W. Schlieren tomography as well as hydrophone measurements are used for evaluation of the acoustic field distribution. It is found that the average electroacoustic efficiency of NBT-based transducers is approximately 40%, while it is around 80% in the PZT-based devices. NBT devices show significantly higher inhomogeneity of the acoustic field under schlieren tomography compared to PZT devices. From pressure measurements in the prefocal plane, it was found that the inhomogeneity could be attributed to depoling of significant areas of the NBT piezo-component during the fabrication process. In conclusion, PZT-based devices performed significantly better than those using lead-free material. However, the NBT devices show promise for this application and their electroacoustic efficiency as well as the uniformity of the acoustic field could be improved by employing a low-temperature fabrication process or repoling after processing.

Magnetoelectric Nanodiscs Enable Wireless Transgene-Free Neuromodulation

Deep-brain stimulation (DBS) with implanted electrodes revolutionized treatment of movement disorders and empowered neuroscience studies. Identifying less invasive alternatives to DBS may further extend its clinical and research applications. Nanomaterial-mediated transduction of magnetic fields into electric potentials offers an alternative to invasive DBS. Here, we synthesize magnetoelectric nanodiscs (MENDs) with a core-double shell Fe3O4-CoFe2O4-BaTiO3 architecture with efficient magnetoelectric coupling. We find robust responses to magnetic field stimulation in neurons decorated with MENDs at a density of 1 μg/mm2 despite individual-particle potentials below the neuronal excitation threshold. We propose a model for repetitive subthreshold depolarization, which combined with cable theory, corroborates our findings in vitro and informs magnetoelectric stimulation in vivo. MENDs injected into the ventral tegmental area of genetically intact mice at concentrations of 1 mg/mL enable remote control of reward behavior, setting the stage for mechanistic optimization of magnetoelectric neuromodulation and inspiring its future applications in fundamental and translational neuroscience.

Local-Nonlinearity-Enabled Deep Subdiffraction Control of Acoustic Waves

Diffraction sets a natural limit for the spatial resolution of acoustic wave fields, hindering the generation and recording of object details and manipulation of sound at subwavelength scales. We propose to overcome this physical limit by utilizing nonlinear acoustics. Our findings indicate that, contrary to the commonly utilized cumulative nonlinear effect, it is in fact the local nonlinear effect that is crucial in achieving subdiffraction control of acoustic waves. We theoretically and experimentally demonstrate a deep subwavelength spatial resolution up to λ/38 in the far field at a distance 4.4 times the Rayleigh distance. This Letter represents a new avenue towards deep subdiffraction control of sound, and may have far-reaching impacts on various applications such as acoustic holograms, imaging, communication, and sound zone control.