High intensity focused ultrasound in clinical tumor ablation

Computational predictions of magnetic resonance acoustic radiation force imaging for breast cancer focused ultrasound therapy

PURPOSE

In magnetic resonance-guided focused ultrasound (MRgFUS) breast therapies, the focal location must be characterized to guide successful treatment. Focal characterization is difficult because heterogeneous breast tissues introduce phase aberrations that blur and shift the focus and traditional guidance methods do not work in adipose tissues. The purpose of this work is to evaluate numerical simulations of MRgFUS that predict the focal location. Those simulations are compared to clinical magnetic resonance acoustic radiation force imaging (MR-ARFI) data collected during in vivo treatment of breast tumors.

METHODS

The focal location was evaluated before MRgFUS treatment with MR-ARFI in five patients. The hybrid angular spectrum method (HAS) was applied to simulate pressure fields which were converted to forces, then convolved with a 3D Green's function (with time-of-arrival weighting) to produce a simulation of the MR-ARFI tissue displacement.

RESULTS

The focal locations found by the simulations and the MR-ARFI measurements were on average separated by 3.7 mm (SD: 0.9 mm). Characterization of the focal zone spatial distributions had a normalized root mean squared difference of 8.1% (SD: 2.5%). The displacement magnitudes of the simulations underestimated the MR-ARFI measurements by 82% (SD: 5.6%).

CONCLUSIONS

The agreement between MR-ARFI measurements and simulations demonstrates that HAS can predict the in vivo focal location in heterogeneous tissues, though accurate patient-specific properties are needed to improve predictions of tissue displacement magnitude. Tools developed in this study could be used to streamline MRgFUS treatment planning and optimization, for biomechanical property estimation, and in developing phase aberration correction techniques.

Ultrasound-guided high-intensity focused ultrasound for symptomatic uterine fibroids: clinical outcome of two European centers

OBJECTIVES

The aim of this study is to assess the clinical outcome and mid-term efficacy of ultrasound-guided high-intensity focused ultrasound (USgHIFU) as a treatment for symptomatic uterine fibroids at two major European HIFU centers.

MATERIALS AND METHODS

This bi-center longitudinal clinical study involved the treatment of 100 patients with symptomatic uterine fibroids using USgHIFU (n = 59 in Germany, n = 41 in Bulgaria). Clinical outcomes were evaluated at 6 weeks, 6 months, and 1 year follow-up utilizing the uterine fibroid symptoms-quality of life questionnaire for fibroid-related symptoms and health-related quality of life as well as MRI imaging for determining the fibroid volume.

RESULTS

The mean fibroid volume reduction rate was 33.2 ± 22.9%, 51.3 ± 24.2%, and 59.1 ± 28.0% at 6 weeks, 6 months, and 1 year, respectively (each p < 0.001). The mean symptom severity score decreased from 43.9 ± 18.8 at baseline to 35.4 ± 18.2 at 6 weeks, 31.1 ± 20.0 at 6 months, and 23.1 ± 14.0 at 1 year (each p < 0.001). The mean QOL score improved from 56.5 ± 23.4 at baseline to 65.4 ± 22.2 at 6 weeks, 72.5 ± 19.5 at 6 months, and 79.4 ± 15.3 at 1 year (each p < 0.001). No major complications were observed, though two patients experienced temporary sciatic nerve irritation following the procedure. Four patients had pregnancies and deliveries without any complications after USgHIFU therapy.

CONCLUSION

To our knowledge, this is the first longitudinal study conducted in two major European HIFU centers that reveals the clinical efficacy of USgHIFU ablation on symptomatic uterine fibroids. Our results confirm that USgHIFU is a non-invasive approach with a low risk of complications, offering an innovative treatment option for affected women.

KEY POINTS

Question To evaluate mid-term clinical efficacy and safety of US-guided high-intensity focused ultrasound (HIFU) for treating symptomatic uterine fibroids and patient outcomes across two European centers. Findings US-guided HIFU treatment resulted in significant fibroid volume reduction (up to 59.1% after 1 year) improving symptoms and quality of life with no major complications. Clinical relevance This prospective longitudinal study provides preliminary data assessing mid-term efficacy and clinical outcomes of ultrasound-guided HIFU. It is shown to be a low-risk, non-invasive treatment option for symptomatic uterine fibroids that reduces fibroid size and improves patients' quality of life.

Immunogenic cell death as interplay between physical anticancer modalities and immunotherapy

Current cancer treatment strategies in practice nowadays often face limitations in effectiveness due to factors such as resistance, recurrence, or suboptimal outcomes. Traditional approaches like chemotherapy often come with severe systemic side effects due to their non-specific action, prompting the development of more targeted therapies. Among these, physical ablation techniques such as radiotherapy (RT) and focused ultrasound (FUS) have gained attention for their ability to precisely target malignant tissues, reduce physical and mental stress for the patients, and minimize recovery time. These therapies also aim to stimulate the immune system through a process referred to as immunogenic cell death (ICD), enhancing the body's ability to fight cancer, explaining abscopal effects. RT has been the most established of the abovementioned techniques for decades, and will not be included in the review. While initially focused on complete tumor ablation, these techniques are now shifting towards milder, more controlled applications that induce ICD without extensive tissue damage. This review explores how physical ablation therapies can harness ICD to boost anticancer immunity, emphasizing their potential to complement immunotherapies and improve outcomes for cancer patients.

In vivo simultaneous proton resonance frequency shift thermometry and single reference variable flip angle T1 measurements

PURPOSE

The single reference variable flip angle sequence with a multi-echo stack of stars acquisition (SR-VFA-SoS) simultaneously measures temperature change using proton resonance frequency (PRF) shift and T1-based thermometry methods. This work evaluates SR-VFA-SoS thermometry in MR-guided focused ultrasound in an in vivo rabbit model.

METHODS

Simultaneous PRF shift thermometry and T1-based thermometry were obtained in a New Zealand white rabbit model (n = 7) during MR-guided focused ultrasound surgery using the SR-VFA-SoS sequence at 3 T. Distinct locations in muscle (n = 16), fat (n = 12), or the interface of both tissues (n = 23) were heated. The T1-temperature coefficient of fat was determined using least-squares fitting of inversion recovery-based T1 maps of untreated fat harvested from the animal and was applied to the in vivo measured heat-induced T1 changes to create temperature maps.

RESULTS

Using k-space weighted image contrast reconstruction, temporal resolution of 1.71 s was achieved for simultaneous thermometry at 1.5 × 1.5 × 2 mm voxel resolution. PRF shift thermometry was not sensitive to heating in fat. T1 changes were observed in fat at the ultrasound focus. The mean T1-temperature coefficient for fat was determined to be 1.9%/°C ± 0.2%/°C. Precision was 0.76°C ± 0.18°C for PRF shift thermometry in muscle and 1.93°C ± 0.60°C for T1-based thermometry in fat. Sonications in muscle showed an increase in T1 of 2.4%/°C ± 0.9%/°C.

CONCLUSION

The SR-VFA-SoS sequence was shown to simultaneously measure temperature change using PRF shift and T1-based methods in an in vivo model, providing thermometry for both aqueous and fat tissues.

Therapeutic Ultrasound for Multimodal Cancer Treatment: A Spotlight on Breast Cancer

Cancer remains a leading cause of mortality worldwide, and the demand for improved efficacy, precision, and safety of management options has never been greater. Focused ultrasound (FUS) is a rapidly emerging strategy for nonionizing, noninvasive intervention that holds promise for the multimodal treatment of solid cancers. Owing to its versatile array of bioeffects, this technology is now being evaluated across preclinical and clinical oncology trials for tumor ablation, therapeutic delivery, radiosensitization, sonodynamic therapy, and enhancement of tumor-specific immune responses. Given the breadth of this burgeoning domain, this review places a spotlight on recent advancements in breast cancer care to exemplify the multifaceted role of FUS technology for oncology indications-outlining physical principles of FUS-mediated thermal and mechanical bioeffects, giving an overview of results from recent preclinical and clinical studies investigating FUS with and without adjunct therapeutics in primary or disseminated breast cancer settings, and offering perspectives on the future of the field.

Development of a contrast-enhanced ultrasound-guided high-intensity focused ultrasound system for coagulation of liver parenchyma

BACKGROUND

The liver is the most common organ injured in blunt abdominal trauma and makes up roughly 5% of all trauma admissions. Current treatments are invasive and resource intensive, which may delay care. We aim to develop and validate a contrast-enhanced ultrasound (CEUS)-guided noninvasive tool to treat liver lacerations at the bedside.

METHODS

Two 1.8-MHz high-intensity focused ultrasound (HIFU) elements were coupled to a C1-6 diagnostic ultrasound probe and a Logiq E10 scanner (GE HealthCare, Waukesha, WI) using a custom enclosure for coregistered imaging and ablation. A phantom was created from polyacrylamide gel combined with thermochromic ink whose color changes above biological ablative temperatures (60°C). The HIFU wave was focused approximately 0.5 cm below the surface using a 50% duty cycle generating 11.9 MPa for 20, 30, 40, 50, and 60 seconds. Experiments were repeated on ex vivo chicken livers in a water bath. Finally, the livers of four live swine underwent up to six CEUS-guided treatments using parameters optimized from in vitro work.

RESULTS

Treatment of the phantom between 20 and 60 seconds produced ablation sizes from 0.016 to 0.4 cm 3 . The relationship between time and size was exponential ( R2 = 0.992). Ablation areas were also well visualized on with ultrasound imaging. The ex vivo liver ablation size at 20 seconds was 0.37 cm 3 , at 30 seconds was 0.66 cm 3 , and at 100 seconds was 5.0 cm 3 . For the in vivo swine experiments, the average ablation area measured 2.0 × 0.75 cm with a maximum of 3.5 × 1.5 cm. Contrast-enhanced ultrasound was used with the contrast agent Definity (Lantheus Medical Imaging, North Billerica, MA) for identification of lacerations and immediate postoperative evaluation of therapy.

CONCLUSION

These experiments demonstrate the feasibility of CEUS-guided transdermal HIFU ablation and the time-dependent size of ablation. This work warrants future investigations into using ultrasound to detect active bleeding and HIFU to coagulate grades III and IV liver laceration.

Optothermal-Stimulated Persistent Luminescence Imaging and Therapy (OSPLIT)

Persistent luminescent nanomaterials have significantly advanced in vivo bioimaging and biosensing by emitting photons after excitation ceases, effectively minimizing tissue autofluorescence. However, their application in biomedical fields such as tumor theranostics is limited by low brightness and rapid signal decay. To address these issues, OSPLIT (optothermal-stimulated persistent luminescence imaging therapy), a dual-function strategy for imaging and treatment is introduced. The OSPLIT approach enhances the release of charge carriers from deep traps in lanthanide-doped nanoparticles, resulting in a 73 fold increase in persistent luminescence within the second near-infrared (NIR-II) window. In living mice, it enables high-contrast imaging of lymph node metastases, with a signal-to-background ratio 11.8 times greater than conventional NIR-II fluorescence. Optothermal-boosted nanoparticles are effective in ablating lymph node metastasis and preventing tumor spread. These findings highlight the potential of optothermal stimulation to enhance persistent luminescence for both imaging and therapeutic applications.

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.

Neuromodulation with Ultrasound: Hypotheses on the Directionality of Effects and Community Resource

Low-intensity Transcranial Ultrasound Stimulation is a promising non-invasive technique for brain stimulation and focal neuromodulation. Research with humans and animal models has raised the possibility that TUS can be biased towards enhancing or suppressing neural function. Here, we first collate a set of hypotheses on the directionality of TUS effects and conduct an initial meta-analysis on the available healthy human participant TUS studies reporting stimulation parameters and outcomes (n = 47 studies, 52 experiments). In these initial exploratory analyses, we find that parameters such as the intensity and continuity of stimulation (duty cycle) with univariate tests show only statistical trends towards likely enhancement or suppressed of function with TUS. Multivariate machine learning analyses are currently limited by the small sample size. Given that human TUS sample sizes will continue to increase, predictability on the directionality of TUS effects could improve if this database can continue to grow as TUS studies more systematically explore the TUS stimulation parameter space and report outcomes. Therefore, we establish an inTUS database and resource for the systematic reporting of TUS parameters and outcomes to assist in greater precision in TUS use for brain stimulation and neuromodulation. The paper concludes with a selective review of human clinical TUS studies illustrating how hypotheses on the directionality of TUS effects could be developed for empirical testing in the intended clinical application, not limited to the examples provided.

Diagnostic ultrasound enhances, then reduces, exogenously induced brain activity of mice

Transcranially delivered diagnostic ultrasound (tDUS) applied to the human brain can modulate those brains such that they became more receptive to external stimulation relative to sham ultrasound exposure. Here, we sought to directly measure the effect of tDUS on mouse brain activity subjected to an external stimulation-a blinking light. Using electrocorticography, we observed a substantial increase in median brain activity due to tDUS plus a blinking light relative to baseline and relative to sham tDUS plus a blinking light. Subsequent brain activity decreased after cessation of tDUS but with continuation of the blinking light, though it remained above that demonstrated by mice exposed to only a blinking light. In a separate experiment, we showed that tDUS alone, without a blinking light, had no observable effect on median brain activity, but upon its cessation, brain activity decreased. These results demonstrate that simultaneous exposure to tDUS and blinking light can increase the receptivity of the visual cortex of mice exposed to that light, and that prior exposure to tDUS can reduce subsequent brain activity. In each case, these results are consistent with published data. Our results on mice echo published human results but do not directly explain them, since their test subjects received less intense diagnostic ultrasound than did our mice. Given the near ubiquity of diagnostic ultrasound systems, further progress along this line of research could one day lead to the widespread use of diagnostic ultrasound to intentionally modulate human brain function during exogenous stimulation.

Using the Tissue Impulse Response Function to Streamline Fractionated MRgFUS-Induced Hyperthermia

Background/Objectives: Combining radiation therapy with mild hyperthermia, especially via magnetic resonance-guided focused ultrasound (MRgFUS), holds promise for enhancing tumor control and alleviating symptoms in cancer patients. However, current clinical applications of MRgFUS focus primarily on ablative treatments, and using MRI guidance for each radiation session increases treatment costs and logistical demands. This study aimed to test a streamlined workflow for repeated hyperthermia treatments that reduces the need for continuous MRI monitoring, using an approach based on impulse response function (Green's function) to optimize acoustic power settings in advance. Methods: We implemented the Green's function approach in a perfused, tissue-mimicking phantom, conducting 30 experiments to simulate hyperthermia delivery via MRgFUS. Pre-calculated acoustic power settings were applied to maintain a stable hyperthermia target without the need for real-time feedback control from MRI thermometry. Additionally, a retrospective analysis of patient thermometry data from MRgFUS sonications was performed to assess feasibility in clinical contexts. Results: Our experiments demonstrated consistent, stable hyperthermia (+7 °C) for 15 min across varying perfusion rates, outperforming conventional closed-loop MRI feedback methods in maintaining temperature stability. The retrospective analysis confirmed that this method is noise-robust and clinically applicable. Conclusions: This off-line approach to hyperthermia control could simplify the integration of MRgFUS hyperthermia in cancer treatment, reducing costs and logistical barriers. These findings suggest that our method may enable the broader adoption of hyperthermia in radiation therapy, supporting its role as a viable adjuvant treatment in oncology.

Breaking Barriers in Huntington's Disease Therapy: Focused Ultrasound for Targeted Drug Delivery

Huntington's disease (HD) is a progressive neurodegenerative disease resulting from a mutation in the huntingtin (HTT) gene and characterized by progressive motor dysfunction, cognitive decline, and psychiatric disturbances. Currently, no disease-modifying treatments are available. Recent research has developed therapeutic agents that may have the potential to directly target the disease pathology, such as gene silencing or clearing the mutant protein. However, these agents are limited by their inability to cross the blood-brain barrier (BBB), preventing optimal therapeutic effects. Although various techniques have been explored to overcome the BBB, focused ultrasound (FUS) has emerged as a promising non-invasive therapeutic modality offering the potential for targeted intervention in neurodegenerative diseases, including HD. Preclinical studies demonstrated the safety and efficacy of FUS in delivering therapeutic agents, such as siRNAs and AAV vector-based gene therapy, resulting in significant reductions in mutant HTT expression and improvements in motor function in HD mouse models. Furthermore, the safety profile of FUS-induced BBB opening has been established in clinical trials on human patients of neurodegenerative diseases other than HD, showing no adverse effects on brain structure or function. This review provides a comprehensive overview of the current state of FUS research in HD and connects existing evidence from neurodegenerative disease studies with its promise in establishing disease-modifying therapies for HD.

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.

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.

High-Intensity Focus Ultrasound Ablation in Prostate Cancer: A Systematic Review

Background/Objectives: Prostate cancer (PCa) outcomes vary significantly across risk groups. In early-stage localized PCa, the functional outcomes following radical prostatectomy (RP) can be severe, prompting increased interest in focal therapy, particularly High-Intensity Focused Ultrasound (HIFU). This study is to summarize the current clinical trials of HIFU on PCa. Methods: We reviewed clinical trials from major databases, including PubMed, MEDLINE, Scopus, and EMBASE, to summarize the current research on HIFU in PCa treatment. Results: The literature highlights that HIFU may offer superior functional outcomes, particularly in continence recovery, compared to RP and radiation therapy. However, the oncological efficacy of HIFU remains inadequately supported by high-quality studies. Focal and hemigland ablations carry a risk of residual significant cancer, necessitating comprehensive patient counseling before treatment. For post-HIFU monitoring, we recommend 3T magnetic resonance imaging (MRI) with biopsy at 6 to 12 months to reassess the cancer status. Biochemical recurrence should be defined using the Phoenix criteria, and PSMA PET/CT can be considered for identifying recurrence in biopsy-negative patients. Conclusions: Whole-gland ablation is recommended as the general approach, as it provides a lower PSA nadir and avoids the higher positive biopsy rates observed after focal and hemigland ablation in both treated and untreated lobes. Future study designs should address heterogeneity, including variations in recurrence definitions and surveillance strategies, to provide more robust evidence for HIFU's oncological outcomes.

Revolutionizing cardiovascular care: the power of histotripsy

Histotripsy, an innovative ultrasonic technique, is poised to transform the landscape of cardiovascular disease management. This review explores the multifaceted applications of histotripsy across various domains of cardiovascular medicine. In thrombolysis, histotripsy presents a non-invasive, drug-free, and precise method for recanalizing blood vessels obstructed by clots, minimizing the risk of vessel damage and embolism. Additionally, histotripsy showcases its potential in congenital heart defect management, offering a promising alternative to invasive procedures by creating intracardiac communications noninvasively. For patients with calcified aortic stenosis, histotripsy demonstrates its effectiveness in softening calcified bioprosthetic valves, potentially revolutionizing valve interventions. In the realm of arrhythmias, histotripsy could play an important role in scar-based ventricular tachycardia ablation, eliminating channel-like isthmuses of slowly conducting myocardium. Histotripsy`s potential applications also extend to structural heart interventions, enabling the safe sectioning of basal chordae and potentially addressing mitral regurgitation. Furthermore, it showcases its versatility by safely generating ventricular septal defects, providing a non-invasive means of creating intracardiac communications in neonates with congenital heart disease. Yet, most supporting studies are in-vitro or animal studies and there are possible challenges in translating experimental data on cardiac histotripsy to the clinical level. As histotripsy continues to evolve and mature, its remarkable potential in cardiovascular disease management holds promise for improving patient outcomes and reducing the burden of invasive procedures in the field of cardiology.

An update on the role of focused ultrasound in neuro-oncology

PURPOSE OF REVIEW

Brain tumor treatment presents challenges for patients and clinicians, with prognosis for many of the most common brain tumors being poor. Focused ultrasound (FUS) can be deployed in several ways to circumvent these challenges, including the need to penetrate the blood-brain barrier and spare healthy brain tissue. This article reviews current FUS applications within neuro-oncology, emphasizing ongoing or recently completed clinical trials.

RECENT FINDINGS

Most clinical interest in FUS for neuro-oncology remains focused on exploring BBB disruption to enhance the delivery of standard-of-care therapeutics. More recently, the application of FUS for radiosensitization, liquid biopsy, and sonodynamic therapy is garnering increased clinical attention to assist in tumor ablation, early detection, and phenotypic diagnosis. Preclinical studies show encouraging data for the immunomodulatory effects of FUS, but these findings have yet to be tested clinically.

SUMMARY

FUS is a burgeoning area of neuro-oncology research. Data from several forthcoming large clinical trials should help clarify its role in neuro-oncology care.

Application of high intensity focused ultrasound combined with nanomaterials in anti-tumor therapy

High intensity focused ultrasound (HIFU) has demonstrated its safety, efficacy and noninvasiveness in the ablation of solid tumor. However, its further application is limited by its inherent deficiencies, such as postoperative recurrence caused by incomplete ablation and excessive intensity affecting surrounding healthy tissues. Recent research has indicated that the integration of nanomaterials with HIFU exhibits a promising synergistic effect in tumor ablation. The concurrent utilization of nanomaterials with HIFU can help overcome the limitations of HIFU by improving targeting and ablation efficiency, expanding operation area, increasing operation accuracy, enhancing stability and bio-safety during the process. It also provides a platform for multi-therapy and multi-mode imaging guidance. The present review comprehensively expounds upon the synergistic mechanism between nanomaterials and HIFU, summarizes the research progress of nanomaterials as cavitation nuclei and drug carriers in combination with HIFU for tumor ablation. Furthermore, this review highlights the potential for further exploration in the development of novel nanomaterials that enhance the synergistic effect with HIFU on tumor ablation.

Prediction of high-intensity focused ultrasound (HIFU)-induced lesion size using the echo amplitude from the focus in tissue

In the realm of high-intensity focused ultrasound (HIFU) therapy, the precise prediction of lesion size during treatment planning remains a challenge, primarily due to the difficulty in quantitatively assessing energy deposition at the target site and the acoustic properties of the tissue through which the ultrasound wave propagates. This study investigates the hypothesis that the echo amplitude originating from the focus is indicative of acoustic attenuation and is directly related to the resultant lesion size. Echoes from multi-layered tissues, specifically porcine tenderloin and bovine livers, with varying fat thickness from 0 mm to 35 mm were collected using a focused ultrasound (FUS) transducer operated at a low power output and short duration. Subsequent to HIFU treatment under clinical conditions, the resulting lesion areas in the ex vivo tissues were meticulously quantified. A novel treatment strategy that prioritizes treatment spots based on descending echo amplitudes was proposed and compared with the conventional raster scan approach. Our findings reveal a consistent trend of decreasing echo amplitudes and HIFU-induced lesion areas with the increasing fat thickness. For porcine tenderloin, the values decreased from 2541.7 ± 641.9 mV and 94.4 ± 17.9 mm2 to 385(342.5) mV and 24.9 ± 18.7 mm2, and for bovine liver, from 1406(1202.5) mV and 94.4 ± 17.9 mm2 to 502.1 ± 225.7 mV and 9.4 ± 6.3 mm2, respectively, as the fat thickness increases from 0 mm to 35 mm. Significant correlations were identified between preoperative echo amplitudes and the HIFU-induced lesion areas (R = 0.833 and 0.784 for the porcine tenderloin and bovine liver, respectively). These correlations underscore the potential for an accurate and dependable prediction of treatment outcomes. Employing the proposed treatment strategy, the ex vivo experiment yielded larger lesion areas in bovine liver at a penetration depth of 8 cm compared to the conventional approach (58.84 ± 17.16 mm2 vs. 44.28 ± 15.37 mm2, p < 0.05). The preoperative echo amplitude from the FUS transducer is shown to be a reflective measure of acoustic attenuation within the wave propagation window and is closely correlated with the induced lesion areas. The proposed treatment strategy demonstrated enhanced efficiency in ex vivo settings, affirming the feasibility and accuracy of predicting HIFU-induced lesion size based on echo amplitude.

Medical Ultrasound Application Beyond Diagnosis: Insights From Ultrasound Sensing and Biological Response

Ultrasound (US) can easily penetrate media with excellent spatial precision corresponding to its wavelength. Naturally, US plays a pivotal role in the echolocation abilities of certain mammals such as bats and dolphins. In addition, medical US generated by transducers interact with tissues via delivering ultrasonic energy in the modes of heat generation, exertion of acoustic radiation force (ARF), and acoustic cavitation. Based on the principle of echolocation, various assistive devices for visual impairment people have been developed. High-Intensity Focused Ultrasound (HIFU) are developed for targeted ablation and tissue destruction. Besides thermal ablation, histotripsy with US is designed to damage tissue purely via mechanical effect without thermal coagulation. Low-Intensity Focused Ultrasound (LIFU) has been proven to be an effective stimulation method for neuromodulation. Furthermore, US has been reported to transiently increase the permeability of biological membranes, enabling acoustic transfection and blood-brain barrier open. All of these advances in US are changing the clinic. This review mainly introduces the advances in these aspects, focusing on the physical and biological principles, challenges, and future direction.

Sonodynamic and Acoustically Responsive Nanodrug Delivery System: Cancer Application

The advent of acoustically responsive nanodrugs that are specifically optimized for sonodynamic therapy (SDT) is a novel approach for clinical applications. Examining the therapeutic applications of sono-responsive drug delivery systems, understanding their dynamic response to acoustic stimuli, and their crucial role in enhancing targeted drug delivery are intriguing issues for current cancer treatment. Specifically, the suggested review covers SDT, a modality that enhances the cytotoxic activity of specific compounds (sonosensitizers) using ultrasound (US). Notably, SDT offers significant advantages in cancer treatment by utilizing US energy to precisely target and activate sonosensitizers toward deep-seated malignant sites. The potential mechanisms underlying SDT involve the generation of radicals from sonosensitizers, physical disruption of cell membranes, and enhanced drug transport into cells via US-assisted sonoporation. In particular, SDT is emerging as a promising modality for noninvasive, site-directed elimination of solid tumors. Given the complexity and diversity of tumors, many studies have explored the integration of SDT with other treatments to enhance the overall efficacy. This trend has paved the way for SDT-based multimodal synergistic cancer therapies, including sonophototherapy, sonoimmunotherapy, and sonochemotherapy. Representative studies of these multimodal approaches are comprehensively presented, with a detailed discussion of their underlying mechanisms. Additionally, the application of audible sound waves in biological systems is explored, highlighting their potential to influence cellular processes and enhance therapeutic outcomes. Audible sound waves can modulate enzyme activities and affect cell behavior, providing novel avenues for the use of sound-based techniques in medical applications. This review highlights the current challenges and prospects in the development of SDT-based nanomedicines in this rapidly evolving research field. The anticipated growth of this SDT-based therapeutic approach promises to significantly improve the precision of cancer treatment.

Monitoring focused ultrasound ablation surgery (FUAS) using echo amplitudes of the therapeutic focused transducer

OBJECTIVE

B-mode sonography is commonly used to monitor focused ultrasound ablation surgery (FUAS), but has limitations in sensitivity. More accurate and reliable prediction of coagulation is required.

METHODS

The focused ultrasound (FUS) transducer was adapted for echo reception. Numerical simulations compared the normalized echo amplitudes from the FUS transducer and imaging probe at varying tissue depths and frequencies with a 3 mm necrosis at focus. An ex vivo experiment then evaluated echo changes from the FUS transducer and ultrasound imaging probe under different settings. Finally, coagulation prediction using FUS echo data was compared to sonography in a clinical ex vivo context.

RESULTS

The echo amplitudes from the FUS transducer exhibit a less pronounced decline with increasing tissue penetration depth compared to the ultrasound imaging probe. In ex vivo bovine liver experiments at depths of 2 cm and 4 cm, the FUS transducer detected normalized echo amplitudes that were significantly larger (i.e., 2∼3 folds) than those received by the ultrasound imaging probe. Moreover, multi-layered ex vivo tissue experiments that replicate clinical conditions revealed that coagulation prediction utilizing the FUS transducer's echo amplitudes achieved superior accuracy (91.2% vs. 60.3 %), sensitivity (92.1% vs. 54.5 %), and negative prediction (78.9% vs. 30.6 %), but similar specificity (88.2% vs. 84.6 %) and positive prediction (95.9% vs. 93.8 %) in comparison to sonography.

CONCLUSION

The echo amplitude of the FUS transducer serves as a sensitive and dependable metric for monitoring the FUAS outcomes. Its utilization may augment the procedure's safety and efficacy.

Minimally invasive interventional guided imaging therapies of musculoskeletal tumors

Historically, musculoskeletal (MSK) tumors, which include both bone and soft tissue tumors, have been managed as distinct entities. The incidence of metastases, particularly bone metastasis, in patients with MSK tumors can result in the emergence of significant complications such as pain, impairment of vital anatomical structures, or pathological fractures. Given these issues, a diverse team of experts is typically engaged in intricate treatment decision-making concerning the necessity of surgery, radiation, chemotherapy, or a mix of these methodologies. Nevertheless, percutaneous image-guided minimally invasive interventional therapy for MSK tumors represent a promising approach for treating such tumors. Over the past decade, significant progress has been made in this technique, leading to its growing acceptance in ordinary clinical practice. MSK tumors can be effectively treated by the use of ablation techniques, either as standalone procedures or in conjunction with other percutaneous treatments. Various image-guided techniques have been employed to observe the ablation zone and nearby structures, such as fluoroscopy, ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI). However, CT is the favored method due to its widespread availability and ability to visualize the tumor and its environs. The procedures employed include ethanol injection, radiofrequency ablation, microwave ablation, cryoablation, and magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU). The technique can be performed in combination with cementation, with or without additional metallic stabilizing devices, depending on the location of the lesion. Improved local tumor control can be attained by combining ablation with bland embolization or transarterial chemoembolization. This article provides an overview of the fundamental elements of minimally invasive interventional guided imaging therapy for MSK malignancies.

Optimized Schlieren imaging for real-time visualization of high-intensity focused ultrasound waves

OBJECTIVES

This article presents an low-cost experimental setup for visualizing refraction anomalies caused by high-intensity focused ultrasound (HIFU). The technique is based on Schlieren imaging, commonly used to visualize temperature and pressure differences in a medium. With this setup, double images of the Schlieren or their shadows to be investigated occur, so that the experimental setup is modified to avoid these double image artifacts.

METHODS

The optical setup mainly consists of a point light source, a parabolic mirror, and a camera. Birefringence artifacts are avoided by placing the point light source at a certain vertical distance to the camera, so that the light beam passes through the medium only once. The soundfield is generated by a HIFU transducer in a water tank placed in the beam path of the optical setup.

RESULTS

The experimental setup is capable of capturing Schlieren or shadow images. These images show the soundfield without disturbing double images and enable further analysis and qualitative assessment of the soundfield.

CONCLUSIONS

The presented setup provides a reliable and efficient method for visualizing refraction anomalies caused by the sonic field of a HIFU transducer and allows for accurate depiction of the refraction anomalies. The double images that usually occur are avoided.

Therapeutic ultrasound: an innovative approach for targeting neurological disorders affecting the basal ganglia

The basal ganglia are involved in motor control and action selection, and their impairment manifests in movement disorders such as Parkinson's disease (PD) and dystonia, among others. The complex neuronal circuitry of the basal ganglia is located deep inside the brain and presents significant treatment challenges. Conventional treatment strategies, such as invasive surgeries and medications, may have limited effectiveness and may result in considerable side effects. Non-invasive ultrasound (US) treatment approaches are becoming increasingly recognized for their therapeutic potential for reversibly permeabilizing the blood-brain barrier (BBB), targeting therapeutic delivery deep into the brain, and neuromodulation. Studies conducted on animals and early clinical trials using ultrasound as a therapeutic modality have demonstrated promising outcomes for controlling symptom severity while preserving neural tissue. These results could improve the quality of life for patients living with basal ganglia impairments. This review article explores the therapeutic frontiers of ultrasound technology, describing the brain mechanisms that are triggered and engaged by ultrasound. We demonstrate that this cutting-edge method could transform the way neurological disorders associated with the basal ganglia are managed, opening the door to less invasive and more effective treatments.

A comprehensive numerical procedure for high-intensity focused ultrasound ablation of breast tumour on an anatomically realistic breast phantom

High-Intensity Focused Ultrasound (HIFU) as a promising and impactful modality for breast tumor ablation, entails the precise focalization of high-intensity ultrasonic waves onto the tumor site, culminating in the generation of extreme heat, thus ablation of malignant tissues. In this paper, a comprehensive three-dimensional (3D) Finite Element Method (FEM)-based numerical procedure is introduced, which provides exceptional capacity for simulating the intricate multiphysics phenomena associated with HIFU. Furthermore, the application of numerical procedures to an anatomically realistic breast phantom (ARBP) has not been explored before. The integrity of the present numerical procedure has been established through rigorous validation, incorporating comparative assessments with previous two-dimensional (2D) simulations and empirical data. For ARBP ablation, the administration of a 0.1 MPa pressure input pulse at a frequency of 1.5 MHz, sustained at the focal point for 10 seconds, manifests an ensuing temperature elevation to 80°C. It is noteworthy that, in contrast, the prior 2D simulation using a 2D phantom geometry reached just 72°C temperature under the identical treatment regimen, underscoring the insufficiency of 2D models, ascribed to their inherent limitations in spatially representing acoustic energy, which compromises their overall effectiveness. To underscore the versatility of this numerical platform, a simulation of a more clinically relevant HIFU therapy procedure has been conducted. This scenario involves the repositioning of the ultrasound focal point to three separate lesions, each spaced at 3 mm intervals, with ultrasound exposure durations of 6 seconds each and a 5-second interval for movement between focal points. This approach resulted in a more uniform high-temperature distribution at different areas of the tumour, leading to the ablation of almost all parts of the tumour, including its verges. In the end, the effects of different abnormal tissue shapes are investigated briefly as well. For solid mass tumors, 67.67% was successfully ablated with one lesion, while rim-enhancing tumors showed only 34.48% ablation and non-mass enhancement tumors exhibited 20.32% ablation, underscoring the need for multiple lesions and tailored treatment plans for more complex cases.

An Updated Review of Thermal Ablation Technology for Uterine Fibroids and Adenomyosis: Focusing on Protecting Fertility

There is a growing trend towards minimally invasive or noninvasive alternatives for gynecological disorders due to their rapid alleviation of symptom, expedited recovery, and minimal risks of postoperative complications. Thermal ablation technology has been commonly advocated as a minimally invasive therapeutic methods in recent years, including microwave ablation, radiofrequency ablation, and high-intensity focused ultrasound. The increasing application scenarios require updated and systematic research, and more evidence to promote their appropriate use. The objective of this review is to summarize the latest views of ablation from a prospective of fertility protection, endeavor to clarify the clinical value of thermal ablation technology in protecting fertility by assessing parameters such as ablation rates, alleviation of disease symptoms, re-intervention rates and post-treatment pregnancy rates. We review the clinical studies of ablation for uterine fibroids and adenomyosis treatment in the past 10 years, summarize the limitation and the prospects of its development in the treatment process, so as to provide clinicians with advice on the best practice. In the management of uterine fibroids and adenomyosis, thermal ablation technology offers improved fertility preservation and minimizes normal tissue injury compared to traditional surgical approaches for patients pursuing reproductive goals. In the future, thermal ablation technology will play a significantly enhanced role in preserving fertility for individuals requiring treatment for uterine fibroids and adenomyosis, guided by indications. But further research is still needed in the form of more extensive randomized prospective trials to provide stronger evidence supporting this perspective.

Deep Brain Ultrasound Ablation Thermal Dose Modeling with in Vivo Experimental Validation

Intracorporeal needle-based therapeutic ultrasound (NBTU) is a minimally invasive option for intervening in malignant brain tumors, commonly used in thermal ablation procedures. This technique is suitable for both primary and metastatic cancers, utilizing a high-frequency alternating electric field (up to 10 MHz) to excite a piezoelectric transducer. The resulting rapid deformation of the transducer produces an acoustic wave that propagates through tissue, leading to localized high-temperature heating at the target tumor site and inducing rapid cell death. To optimize the design of NBTU transducers for thermal dose delivery during treatment, numerical modeling of the acoustic pressure field generated by the deforming piezoelectric transducer is frequently employed. The bioheat transfer process generated by the input pressure field is used to track the thermal propagation of the applicator over time. Magnetic resonance thermal imaging (MRTI) can be used to experimentally validate these models. Validation results using MRTI demonstrated the feasibility of this model, showing a consistent thermal propagation pattern. However, a thermal damage isodose map is more advantageous for evaluating therapeutic efficacy. To achieve a more accurate simulation based on the actual brain tissue environment, a new finite element method (FEM) simulation with enhanced damage evaluation capabilities was conducted. The results showed that the highest temperature and ablated volume differed between experimental and simulation results by 2.1884°C (3.71%) and 0.0631 cm3 (5.74%), respectively. The lowest Pearson correlation coefficient (PCC) for peak temperature was 0.7117, and the lowest Dice coefficient for the ablated area was 0.7021, indicating a good agreement in accuracy between simulation and experiment.

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.

Study of Biological Effects Induced in Solid Tumors by Shortened-Duration Thermal Ablation Using High-Intensity Focused Ultrasound

The HIFU ablation technique is limited by the long duration of the procedure, which results from the large difference between the size of the HIFU beam's focus and the tumor size. Ablation of large tumors requires treating them with a sequence of single HIFU beams, with a specific time interval in-between. The aim of this study was to evaluate the biological effects induced in a malignant solid tumor of the rat mammary gland, implanted in adult Wistar rats, during HIFU treatment according to a new ablation plan which allowed researchers to significantly shorten the duration of the procedure. We used a custom, automated, ultrasound imaging-guided HIFU ablation device. Tumors with a 1 mm thickness margin of healthy tissue were subjected to HIFU. Three days later, the animals were sacrificed, and the HIFU-treated tissues were harvested. The biological effects were studied, employing morphological, histological, immunohistochemical, and ultrastructural techniques. Massive cell death, hemorrhages, tissue loss, influx of immune cells, and induction of pro-inflammatory cytokines were observed in the HIFU-treated tumors. No damage to healthy tissues was observed in the area surrounding the safety margin. These results confirmed the efficacy of the proposed shortened duration of the HIFU ablation procedure and its potential for the treatment of solid tumors.

Generating and monitoring mild hyperthermia using a ring array ultrasound transducer

OBJECTIVE

To demonstrate the feasibility of using a ring array ultrasound (US) transducer, guided by ultrasound tomography (UST), for generating and monitoring mild hyperthermia (MHTh).

METHODS

In silico and in vitro experiments were designed to evaluate the efficacy of a ring array US transducer for generating MHTh and monitoring changes in temperature. In a series of in silico studies, we compared the acoustic focal profiles produced by a ring array US transducer transmitting at different frequencies and further investigated the effectiveness of UST-guidance in implementing aberration correction to enhance the focal profile. In vitro experiments evaluated the capability of using a ring array US transducer to generate and maintain MHTh and the accuracy of using UST to monitor temperature changes.

RESULTS

The simulations demonstrated that a ring array US transducer achieves symmetrical and localized acoustic focusing. In a heterogenous tissue model, a ring array US transducer achieved a superior acoustic focus by implementing aberration correction with guidance from UST. In vitro experiments demonstrated the capability of a ring array US transducer to generate MHTh in a tissue-mimicking phantom in an average of 117 ± 18 s and subsequently maintain MHTh. Lastly, a ring array US transducer utilized UST to track temperature changes in a preheated water-filled inclusion while it passively cooled from 45 °C to 25 °C, with a maximum error of 0.58 °C.

CONCLUSION

A ring array US transducer can noninvasively generate and monitor MHTh, overcoming many limitations of current clinical systems. The closed geometry of the transducer is optimal for acoustic focusing and UST-guidance allows for improved aberration correction in a heterogenous medium. Utilizing UST thermometry with the same ring array US transducer will allow for implementing an image-guided, temperature-controlled, all-acoustic MHTh system.

Ultrasound-responsive theranostic platform for the timely monitoring and efficient thrombolysis in thrombi of tPA resistance

There is no effective and noninvasive solution for thrombolysis because the mechanism by which certain thrombi become tissue plasminogen activator (tPA)-resistant remains obscure. Endovascular thrombectomy is the last option for these tPA-resistant thrombi, thus a new noninvasive strategy is urgently needed. Through an examination of thrombi retrieved from stroke patients, we found that neutrophil extracellular traps (NETs), ε-(γ-glutamyl) lysine isopeptide bonds and fibrin scaffolds jointly comprise the key chain in tPA resistance. A theranostic platform is designed to combine sonodynamic and mechanical thrombolysis under the guidance of ultrasonic imaging. Breakdown of the key chain leads to a recanalization rate of more than 90% in male rat tPA-resistant occlusion model. Vascular reconstruction is observed one month after recanalization, during which there was no thrombosis recurrence. The system also demonstrates noninvasive theranostic capabilities in managing pigs' long thrombi (>8 mm) and in revascularizing thrombosis-susceptible tissue-engineered vascular grafts, indicating its potential for clinical application. Overall, this noninvasive theranostic platform provides a new strategy for treating tPA-resistant thrombi.

Numerical studies on shortening the duration of HIFU ablation therapy and their experimental validation

High Intensity Focused Ultrasound (HIFU) is used in clinical practice for thermal ablation of malignant and benign solid tumors located in various organs. One of the reason limiting the wider use of this technology is the long treatment time resulting from i.a. the large difference between the size of the focal volume of the heating beam and the size of the tumor. Therefore, the treatment of large tumors requires scanning their volume with a sequence of single heating beams, the focus of which is moved in the focal plane along a specific trajectory with specific time and distance interval between sonications. To avoid an undesirable increase in the temperature of healthy tissues surrounding the tumor during scanning, the acoustic power and exposure time of each HIFU beam as well as the time intervals between sonications should be selected in such a way as to cover the entire volume of the tumor with necrosis as quickly as possible. This would reduce the costs of treatment. The aim of this study was to quantitatively evaluate the hypothesis that selecting the average acoustic power and exposure time for each individual heating beam, as well as the temporal intervals between sonications, can significantly shorten treatment time. Using 3D numerical simulations, the dependence of the duration of treatment of a tumor with a diameter of 5 mm or 9 mm (requiring multiple exposure to the HIFU beam) on the sonication parameters (acoustic power, exposure time) of each single beam capable of delivering the threshold thermal dose (CEM43 = 240 min) to the treated tissue volume was examined. The treatment duration was determined as the sum of exposure times to individual beams and time intervals between sonications. The tumor was located inside the ex vivo tissue sample at a depth of 12.6 mm. The thickness of the water layer between the HIFU transducer and the tissue was 50 mm. The sonication and scanning parameters selected using the developed algorithm shortened the duration of the ablation procedure by almost 14 times for a 5-mm tumor and 20 times for a 9-mm tumor compared to the duration of the same ablation plan when a HIFU beam was used of a constant acoustic power, constant exposure time (3 s) and constant long time intervals (120 s) between sonications. Results of calculations of the location and size of the necrotic lesion formed were experimentally verified on ex vivo pork loin samples, showing good agreement between them. In this way, it was proven that the proper selection of sonication and scanning parameters for each HIFU beam allows to significantly shorten the time of HIFU therapy.

Advances in Image-Guided Ablation Therapies for Solid Tumors

Image-guided solid tumor ablation methods have significantly advanced in their capability to target primary and metastatic tumors. These techniques involve noninvasive or percutaneous insertion of applicators to induce thermal, electrochemical, or mechanical stress on malignant tissue to cause tissue destruction and apoptosis of the tumor margins. Ablation offers substantially lower risks compared to traditional methods. Benefits include shorter recovery periods, reduced bleeding, and greater preservation of organ parenchyma compared to surgical intervention. Due to the reduced morbidity and mortality, image-guided tumor ablation offers new opportunities for treatment in cancer patients who are not candidates for resection. Currently, image-guided ablation techniques are utilized for treating primary and metastatic tumors in various organs with both curative and palliative intent, including the liver, pancreas, kidneys, thyroid, parathyroid, prostate, lung, breast, bone, and soft tissue. The invention of new equipment and techniques is expanding the criteria of eligible patients for therapy, as now larger and more high-risk tumors near critical structures can be ablated. This article provides an overview of the different imaging modalities, noninvasive, and percutaneous ablation techniques available and discusses their applications and associated complications across various organs.

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.

Ultrasound and neuroinflammation: immune modulation via the heat shock response

Current pharmacological therapeutic approaches targeting chronic inflammation exhibit transient efficacy, often with adverse effects, limiting their widespread use - especially in the context of neuroinflammation. Effective interventions require the consideration of homeostatic function, pathway dysregulation, and pleiotropic effects when evaluating therapeutic targets. Signalling molecules have multiple functions dependent on the immune context, and this complexity results in therapeutics targeting a single signalling molecule often failing in clinical translation. Additionally, the administration of non-physiologic levels of neurotrophic or anti-inflammatory factors can alter endogenous signalling, resulting in unanticipated effects. Exacerbating these challenges, the central nervous system (CNS) is isolated by the blood brain barrier (BBB), restricting the infiltration of many pharmaceutical compounds into the brain tissue. Consequently, there has been marked interest in therapeutic techniques capable of modulating the immune response in a pleiotropic manner; ultrasound remains on this frontier. While ultrasound has been used therapeutically in peripheral tissues - accelerating healing in wounds, bone fractures, and reducing inflammation - it is only recently that it has been applied to the CNS. The transcranial application of low intensity pulsed ultrasound (LIPUS) has successfully mitigated neuroinflammation in vivo, in models of neurodegenerative disease across a broad spectrum of ultrasound parameters. To date, the underlying biological effects and signalling pathways modulated by ultrasound are poorly understood, with a diverse array of reported molecules implicated. The distributed nature of the beneficial response to LIPUS implies the involvement of an, as yet, undetermined upstream signalling pathway, homologous to the protective effect of febrile range hyperthermia in chronic inflammation. As such, we review the heat shock response (HSR), a protective signalling pathway activated by thermal and mechanical stress, as the possible upstream regulator of the anti-inflammatory effects of ultrasound.

Advances in Tumor Management: Harnessing the Potential of Histotripsy

Tissue ablation techniques have long been used in clinical settings to treat various oncologic diseases. However, many of these techniques are invasive and can cause substantial adverse effects. Histotripsy is a noninvasive, nonionizing, nonthermal tissue ablation technique that has the potential to replace surgical interventions in various clinical settings. Histotripsy works by delivering high-intensity focused ultrasound waves to target tissue. These waves create cavitation bubbles within tissues that rapidly expand and collapse, thereby mechanically fractionating the tissue into acellular debris that is subsequently absorbed by the body's immune system. Preclinical and clinical studies have demonstrated the efficacy of histotripsy in treating a range of diseases, including liver, pancreatic, renal, and prostate tumors. Safety outcomes of histotripsy have been generally favorable, with minimal adverse effects reported. However, further studies are needed to optimize the technique and understand its long-term effects. This review aims to discuss the importance of histotripsy as a noninvasive tissue ablation technique, the preclinical and clinical literature on histotripsy and its safety, and the potential applications of histotripsy in clinical practice. Keywords: Tumor Microenvironment, Ultrasound-High-Intensity Focused (HIFU), Ablation Techniques, Abdomen/GI, Genital/Reproductive, Nonthermal Tissue Ablation, Histotripsy, Clinical Trials, Preclinical Applications, Focused Ultrasound © RSNA, 2024.

Breast Tomographic Ultrasound: The Spectrum from Current Dense Breast Cancer Screenings to Future Theranostic Treatments

This review provides unique insights to the scientific scope and clinical visions of the inventors and pioneers of the SoftVue breast tomographic ultrasound (BTUS). Their >20-year collaboration produced extensive basic research and technology developments, culminating in SoftVue, which recently received the Food and Drug Administration's approval as an adjunct to breast cancer screening in women with dense breasts. SoftVue's multi-center trial confirmed the diagnostic goals of the tissue characterization and localization of quantitative acoustic tissue differences in 2D and 3D coronal image sequences. SoftVue mass characterizations are also reviewed within the standard cancer risk categories of the Breast Imaging Reporting and Data System. As a quantitative diagnostic modality, SoftVue can also function as a cost-effective platform for artificial intelligence-assisted breast cancer identification. Finally, SoftVue's quantitative acoustic maps facilitate noninvasive temperature monitoring and a unique form of time-reversed, focused US in a single theranostic device that actually focuses acoustic energy better within the highly scattering breast tissues, allowing for localized hyperthermia, drug delivery, and/or ablation. Women also prefer the comfort of SoftVue over mammograms and will continue to seek out less-invasive breast care, from diagnosis to treatment.

Sonogenetics for Monitoring and Modulating Biomolecular Function by Ultrasound

Ultrasound technology, synergistically harnessed with genetic engineering and chemistry concepts, has started to open the gateway to the remarkable realm of sonogenetics-a pioneering paradigm for remotely orchestrating cellular functions at the molecular level. This fusion not only enables precisely targeted imaging and therapeutic interventions, but also advances our comprehension of mechanobiology to unparalleled depths. Sonogenetic tools harness mechanical force within small tissue volumes while preserving the integrity of the surrounding physiological environment, reaching depths of up to tens of centimeters with high spatiotemporal precision. These capabilities circumvent the inherent physical limitations of alternative in vivo control methods such as optogenetics and magnetogenetics. In this review, we first discuss mechanosensitive ion channels, the most commonly utilized sonogenetic mediators, in both mammalian and non-mammalian systems. Subsequently, we provide a comprehensive overview of state-of-the-art sonogenetic approaches that leverage thermal or mechanical features of ultrasonic waves. Additionally, we explore strategies centered around the design of mechanochemically reactive macromolecular systems. Furthermore, we delve into the realm of ultrasound imaging of biomolecular function, encompassing the utilization of gas vesicles and acoustic reporter genes. Finally, we shed light on limitations and challenges of sonogenetics and present a perspective on the future of this promising technology.

In vivo evaluation of focused ultrasound ablation surgery (FUAS)-induced coagulation using echo amplitudes of the therapeutic focused ultrasound transducer

OBJECTIVE

Monitoring sensitivity of sonography in focused ultrasound ablation surgery (FUAS) is limited (no hyperechoes in ∼50% of successful coagulation in uterine fibroids). A more accurate and sensitive approach is required.

METHOD

The echo amplitudes of the focused ultrasound (FUS) transducer in a testing mode (short pulse duration and low power) were found to correlate with the ex vivo coagulation. To further evaluate its coagulation prediction capabilities, in vivo experiments were carried out. The liver, kidney, and leg muscles of three adult goats were treated using clinical FUAS settings, and the echo amplitude of the FUS transducer and grayscale in sonography before and after FUAS were collected. On day 7, animals were sacrificed humanely, and the treated tissues were dissected to expose the lesion. Echo amplitude changes and lesion areas were analyzed statistically, as were the coagulation prediction metrics.

RESULTS

The echo amplitude changes of the FUS transducer correlate well with the lesion areas in the liver (R = 0.682). Its prediction in accuracy (94.4% vs. 50%), sensitivity (92.9% vs. 35.7%), and negative prediction (80% vs. 30.8%) is better than sonography, but similar in specificity (80% vs. 100%) and positive prediction (100% vs. 100%). In addition, the correlation between tissue depth and the lesion area is not good (|R| < 0.2). Prediction performances in kidney and leg muscles are similar.

CONCLUSION

The FUS echo amplitudes are sensitive to the tissue properties and their changes after FUAS. They are sensitive and reliable in evaluating and predicting FUAS outcomes.

The Assessment of a Novel Endoscopic Ultrasound-Compatible Cryocatheter to Ablate Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal disease that may be treated utilizing thermal therapies. Cryoablation is an effective, minimally invasive therapy that has been utilized for the treatment of various cancers, offering patients a quicker recovery and reduced side effects. Cryoablation has been utilized on a limited basis for the treatment of PDAC. With the recent reports on the success of cryoablation, there is a growing interest in the use of cryoablation as a standalone, minimally invasive procedure to treat PDAC. While offering a promising path, the application of cryoablation to PDAC is limited by current technologies. As such, there is a need for the development of new devices to support advanced treatment strategies for PDAC. To this end, this study investigated the performance of a new endoscopic ultrasound-compatible cryoablation catheter technology, FrostBite. We hypothesized that FrostBite would enable the rapid, effective, minimally invasive delivery of ultra-cold temperatures to target tissues, resulting in effective ablation via an endoscopic approach. Thermal properties and ablative efficacy were evaluated using a heat-loaded gel model, tissue-engineered models (TEMs), and an initial in vivo porcine study. Freeze protocols evaluated included single and repeat 3 and 5 min applications. Isotherm assessment revealed the generation of a 2.2 cm diameter frozen mass with the -20 °C isotherm reaching a diameter of 1.5 cm following a single 5 min freeze. TEM studies revealed the achievement of temperatures ≤ -20 °C at a diameter of 1.9 cm after a 5 min freeze. Fluorescent imaging conducted 24 h post-thaw demonstrated a uniformly shaped ellipsoidal ablative zone with a midline diameter of 2.5 cm, resulting in a total ablative volume of 6.9 cm3 after a single 5 min freeze. In vivo findings consistently demonstrated the generation of ablative areas measuring 2.03 cm × 3.2 cm. These studies demonstrate the potential of the FrostBite cryocatheter as an endoscopic ultrasound-based treatment option. The data suggest that FrostBite may provide for the rapid, effective, controllable freezing of cancerous pancreatic and liver tissues. This ablative power also offers the potential of improved safety margins via the minimally invasive nature of an endoscopic ultrasound-based approach or natural orifice transluminal endoscopic surgery (NOTES)-based approach. The results of this pre-clinical feasibility study show promise, affirming the need for further investigation into the potential of the FrostBite cryocatheter as an advanced, minimally invasive cryoablative technology.

MRI-Guided Focused Ultrasound for the Treatment of Dystonia: A Narrative Review

Contemporary surgical management of dystonia includes neuromodulation via deep brain stimulation (DBS) or ablative techniques such as radiofrequency (RF) ablation. MRI-guided focused ultrasound (MRgFUS) is an emerging modality that uses high-intensity ultrasound to precisely ablate targets in the brain; this is incisionless, potentially avoiding the surgical risks of a burr hole and transcortical tract to reach the anatomical target. There is some evidence of efficacy in essential tremor and Parkinson's disease (PD), but, to date, there is no study aggregating the evidence of MRgFUS in dystonia. In this narrative review, we searched Medline, Embase, CINAHL, EBSCO, and ClinicalTrials.gov for primary studies and clinical trials on MRgFUS in the treatment of dystonia. Data were analyzed concerning dystonia phenotype, reported outcomes, and complications. PD-related dystonia was also included within the scope of the review. Using our search criteria, six articles on the use of MRgFUS in adult dystonia and three articles on the use of FUS in dystonia in PD were included. Four trials on the use of FUS in dystonia were also found on ClinicalTrials.gov, one of which was completed in December 2013. All included studies showed evidence of symptomatic improvement, mostly in focal hand dystonia; improvements were also found in dystonia-associated tremor, cervicobrachial dystonia, and dystonia-associated chronic neuropathic pain as well as PD-related dystonia. Reported complications included transient neurological deficits and persistent arm pain in one study. However, the evidence is limited to level-4 case series at present. MRgFUS is an emerging modality that appears to be safe and effective, particularly in focal hand dystonia, without major adverse effects. However, the quality of evidence is low at present, and long-term outcomes are unknown. High-quality prospective studies comparing MRgFUS to other surgical techniques will be useful in determining its role in the management of dystonia.

Aptamer-Based Smart Targeting and Spatial Trigger-Response Drug-Delivery Systems for Anticancer Therapy

In recent years, the field of drug delivery has witnessed remarkable progress, driven by the quest for more effective and precise therapeutic interventions. Among the myriad strategies employed, the integration of aptamers as targeting moieties and stimuli-responsive systems has emerged as a promising avenue, particularly in the context of anticancer therapy. This review explores cutting-edge advancements in targeted drug-delivery systems, focusing on the integration of aptamers and stimuli-responsive platforms for enhanced spatial anticancer therapy. In the aptamer-based drug-delivery systems, we delve into the versatile applications of aptamers, examining their conjugation with gold, silica, and carbon materials. The synergistic interplay between aptamers and these materials is discussed, emphasizing their potential in achieving precise and targeted drug delivery. Additionally, we explore stimuli-responsive drug-delivery systems with an emphasis on spatial anticancer therapy. Tumor microenvironment-responsive nanoparticles are elucidated, and their capacity to exploit the dynamic conditions within cancerous tissues for controlled drug release is detailed. External stimuli-responsive strategies, including ultrasound-mediated, photo-responsive, and magnetic-guided drug-delivery systems, are examined for their role in achieving synergistic anticancer effects. This review integrates diverse approaches in the quest for precision medicine, showcasing the potential of aptamers and stimuli-responsive systems to revolutionize drug-delivery strategies for enhanced anticancer therapy.

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.

Improved source localization in passive acoustic mapping using delay-multiply-and-sum beamforming with virtually augmented aperture

High-intensity focused ultrasound (HIFU) is a promising non-invasive treatment method whose applications include tissue ablation, hemostasis, thrombolysis and blood-brain barrier opening etc. Its therapeutic effects come from the thermal necrosis and the mechanical destruction associated with acoustic cavitation. Passive acoustic mapping (PAM) is capable of simultaneous monitoring of HIFU-induced cavitation events using only receive beamforming. Nonetheless, conventional time exposure acoustics (TEA) algorithm has poor spatial resolution and suffers from the X-shaped artifacts. These factors lead to difficulties in precise localization of cavitation source. In this study, we proposed a novel adaptive PAM method which combines Delay-Multiply-and-Sum (DMAS) beamforming with virtual augmented aperture (VA) to overcome the problem. In DMAS-VA beamforming, the magnitude of each channel waveform is scaled by p-th root while the phase is multiplied by L. The p and L correspond respectively to the degree of signal coherence in DMAS beamforming and the augmentation factor of aperture size. After channel sum, p-th power is applied to restore the dimensionality of source strength and then the PAM image is reconstructed by accumulating the signal power over the observation time. Based on simulation and experimental results, the proposed DMAS-VA has better image resolution and image contrast compared with the conventional TEA. Moreover, since the VA method may introduce grating lobes into PAM because of the virtually augmented pitch size, DMAS coherent factor (DCF) is further developed to alleviate these image artifacts. Results indicate that, with DCF weighting, the PAM image of DMAS-VA beamforming could be constructed without detectable image artifacts from grating lobes and false main lobes.

Present and future of metal nanoparticles in tumor ablation therapy

Cancer is an important factor affecting the quality of human life as well as causing death. Tumor ablation therapy is a minimally invasive local treatment modality with unique advantages in treating tumors that are difficult to remove surgically. However, due to its physical and chemical characteristics and the limitation of equipment technology, ablation therapy cannot completely kill all tumor tissues and cells at one time; moreover, it inevitably damages some normal tissues in the surrounding area during the ablation process. Therefore, this technology cannot be the first-line treatment for tumors at present. Metal nanoparticles themselves have good thermal and electrical conductivity and unique optical and magnetic properties. The combination of metal nanoparticles with tumor ablation technology, on the one hand, can enhance the killing and inhibiting effect of ablation technology on tumors by expanding the ablation range; on the other hand, the ablation technology changes the physicochemical microenvironment such as temperature, electric field, optics, oxygen content and pH in tumor tissues. It helps to stimulate the degree of local drug release of nanoparticles and increase the local content of anti-tumor drugs, thus forming a synergistic therapeutic effect with tumor ablation. Recent studies have found that some specific ablation methods will stimulate the body's immune response while physically killing tumor tissues, generating a large number of immune cells to cause secondary killing of tumor tissues and cells, and with the assistance of metal nanoparticles loaded with immune drugs, the effect of this anti-tumor immunotherapy can be further enhanced. Therefore, the combination of metal nanoparticles and ablative therapy has broad research potential. This review covers common metallic nanoparticles used for ablative therapy and discusses in detail their characteristics, mechanisms of action, potential challenges, and prospects in the field of ablation.

Advancements in Microwave Ablation Techniques for Managing Pancreatic Lesions

Thermal ablation, including microwave ablation, has become increasingly important in the management of many solid tumors, including primary and metastatic tumors of the liver, kidney, and lung. However, its adoption to treat pancreatic lesions has been slowed due to concerns about potential adverse events. The success of radiofrequency ablation (RFA) in inoperable pancreatic cancers paved the way for its use in pancreatic neuroendocrine tumors and pancreatic cystic neoplasms (PCLs). In the last decade, other thermal ablation techniques, like microwave ablation, have emerged as alternatives to RFA. Microwaves, with frequencies ranging from 900 to 2450 MHz, generate heat by rapidly oscillating water molecules. Microwave ablation's advantage lies in its ability to achieve higher intra-lesion temperatures and uniform heating compared with RFA. Microwave ablation's application in pancreatic cancer and pancreatic neuroendocrine tumors has demonstrated promise with similar technical success to RFA. Yet, concern for peri-procedure complications, as well as a dearth of studies comparing RFA and microwave ablation, emphasize the need for further research. No studies have evaluated microwave ablation in PCLs. We herein review thermal ablation's potential to treat pancreatic lesions.

Successful In Situ Targeting of Pancreatic Tumors in a Novel Orthotopic Porcine Model Using Histotripsy

OBJECTIVE

New therapeutic strategies and paradigms are direly needed to treat pancreatic cancer. The absence of a suitable pre-clinical animal model of pancreatic cancer is a major limitation to biomedical device and therapeutic development. Traditionally, pigs have proven to be ideal models, especially in the context of designing human-sized instruments, perfecting surgical techniques and optimizing clinical procedures for use in humans. However, pig studies have typically focused on healthy tissue assessments and are limited to general safety evaluations because of the inability to effectively model human tumors.

METHODS

Here, we establish an orthotopic porcine model of human pancreatic cancer using RAG2/IL2RG double-knockout immunocompromised pigs and treat the tumors ex vivo and in vivo with histotripsy.

RESULTS

Using these animals, we describe the successful engraftment of Panc-1 human pancreatic cancer cell line tumors and characterize their development. To illustrate the utility of these animals for therapeutic development, we determine for the first time, the successful targeting of in situ pancreatic tumors using histotripsy. Treatment with histotripsy resulted in partial ablation in vivo and reduction in collagen content in both in vivo tumor in pig pancreas and ex vivo patient tumor.

CONCLUSION

This study presents a first step toward establishing histotripsy as a non-invasive treatment method for pancreatic cancer and exposes some of the challenges of ultrasound guidance for histotripsy ablation in the pancreas. Simultaneously, we introduce a highly robust model of pancreatic cancer in a large mammal model that could be used to evaluate a variety biomedical devices and therapeutic strategies.