Cavitation-induced pressure saturation: a mechanism governing bubble nucleation density in histotripsy.

Objective.Histotripsy is a noninvasive focused ultrasound therapy that mechanically disintegrates tissue by acoustic cavitation clouds. In this study, we investigate a mechanism limiting the density of bubbles that can nucleate during a histotripsy pulse. In this mechanism, the pressure generated by the initial bubble expansion effectively negates the incident pressure in the vicinity of the bubble. From this effect, the immediately adjacent tissue is prevented from experiencing the transient tension to nucleate bubbles. Approach.A Keller-Miksis-type single-bubble model was employed to evaluate the dependency of this effect on ultrasound pressure amplitude and frequency, viscoelastic medium properties, bubble nucleus size, and transducer geometric focusing. This model was further combined with a spatial propagation model to predict the peak negative pressure field as a function of position from a cavitating bubble.Main results. The single-bubble model showed the peak negative pressure near the bubble surface is limited to the inertial cavitation threshold. The predicted bubble density increased with increasing frequency, tissue viscosity, and transducer focusing angle. The simulated results were consistent with the trends observed experimentally in prior studies, including changes in density with ultrasound frequency and transducerF-number.Significance.The efficacy of the therapy is dependent on several factors, including the density of bubbles nucleated within the cavitation cloud formed at the focus. These results provide insight into controlling the density of nucleated bubbles during histotripsy and the therapeutic efficacy.

Inducing cavitation within hollow cylindrical radially polarized transducers for intravascular applications.

Thrombotic occlusions of large blood vessels are increasingly treated with catheter based mechanical approaches, one of the most prominent being to employ aspiration to extract clots through a hollow catheter lumen. A central technical challenge for aspiration catheters is to achieve sufficient suction force to overcome the resistance of clot material entering into the distal tip. In this study, we examine the feasibility of inducing cavitation within hollow cylindrical transducers with a view to ultimately using them to degrade the mechanical integrity of thrombus within the tip of an aspiration catheter. Hollow cylindrical radially polarized PZT transducers with 3.3/2.5 mm outer/inner diameters were assessed. Finite element simulations and hydrophone experiments were used to investigate the pressure field distribution as a function of element length and resonant mode (thickness, length). Operating in thickness mode (∼5 MHz) was found to be associated with the highest internal pressures, estimated to exceed 23 MPa. Cavitation was demonstrated to be achievable within the transducer under degassed water (10 %) conditions using hydrophone detection and high-frequency ultrasound imaging (40 MHz). Cavitation clouds occupied a substantial portion of the transducer lumen, in a manner that was dependent on the pulsing scheme employed (10 and 100 µs pulse lengths; 1.1, 11, and 110 ms pulse intervals). Collectively the results support the feasibility of achieving cavitation within a transducer compatible with mounting in the tip of an aspiration format catheter.

Optimized treatment parameter by computer simulation for high-intensity focused ultrasound treatment of uterine adenomyosis: Short-term and long-term results.

This study aimed to investigate the efficacy and safety of using optimized parameters obtained by computer simulation for ultrasound-guided high-intensity focused ultrasound (HIFU) treatment of uterine adenomyosis in comparison with conventional parameters. We retrospectively assessed a single-institution, prospective study that was registered at Clinical Research Information Service (CRiS) of Republic of Korea (KCT0003586). Sixty-six female participants (median age: 44 years) with focal uterine adenomyosis were prospectively enrolled. All participants were treated with a HIFU system by using treatment parameters either for treating uterine fibroids (Group A, first 20 participants) or obtained via computer simulation (Group B, later 46 participants). To assess the treatment efficacy of HIFU, qualitative indices, including the clinically effective dysmenorrhea improvement index (DII), were evaluated up to 3 years after treatment, whereas quantitative indices, such as the nonperfused volume ratio and adenomyosis volume shrinkage ratio (AVSR), on MRI were evaluated up to 3 months after treatment. Quantitative/qualitative indices were compared between Groups A and B by using generalized linear mixed effect model. A safety assessment was also performed. Results showed that clinically effective DII was more frequently observed in Group B than in Group A (odds ratio, 3.69; P = 0.025), and AVSR were higher in Group B than in Group A (least-squares means, 21.61; P = 0.001). However, two participants in Group B developed skin burns at the buttock and sciatic nerve pain and required treatment. In conclusion, parameters obtained by computer simulation were more effective than the conventional parameters for treating uterine adenomyosis by using HIFU in terms of clinically effective DII and AVSR. However, care should be taken because of the risk of adverse events.

An 8 mm endoscopic histotripsy array with integrated high-resolution ultrasound imaging.

An 8 mm diameter, image-guided, annular array histotripsy transducer was fabricated and characterized. The array was laser etched on a 5 MHz, 1-3 dice and fill, PZT-5H/epoxy composite with a 45 % volume fraction. Flexible PCBs were used to electrically connect to the array elements using wirebonds. The array was backed with a low acoustic impedance epoxy mixture. A 3.6 by 3.8 mm, 64-element, 30 MHz phased array imaging probe was positioned in the center hole, to co-align the imaging plane with the bubble cloud produced by the therapy array. A custom 16-channel high voltage pulse generator was used to test the annular array for focal lengths ranging from 3- to 8-mm. An aluminum lens-focussed transducer with a 7 mm focal length was fabricated using the same piezocomposite and backing material and tested along with the histotripsy array. Simulated results from COMSOL FEM models were compared to measured results for low voltage characterization of the array and lens-focussed transducer. The measured transmit sensitivity of the array ranged from 0.113 to 0.167 MPa/V, while the lens-focussed transducer was 0.192 MPa/V. Simulated values were 0.160 to 0.174 MPa/V and 0.169 MPa/V, respectively. The measured acoustic fields showed a significantly increased depth-of-field compared the lens-focussed transducer, while the beamwidths of the array focus were comparable to the lens. The measured cavitation voltage in water was between 254 V and 498 V depending on the focal length, and 336 V for the lens-focussed transducer. The array had a lower cavitation voltage than the lens-focussed transducer for a comparable operating depth. The histotripsy array was tested in a tissue phantom and an in vivo rat brain. It was used to produce an elongated lesion in the brain by electronically steering the focal length from 3- to 8-mm axially. Real time ultrasound imaging with a Doppler overlay was used to target the tissue and monitor ablation progress, and histology confirmed the targeted tissue was fully homogenized.

Multiple ultrasonic parametric imaging for the detection and monitoring of high-intensity focused ultrasound ablation.

Numerous quantitative ultrasound imaging techniques have demonstrated superior monitoring performance for thermal ablation when compared to conventional ultrasonic B-mode imaging. However, the absence of comparative studies involving various quantitative ultrasound imaging techniques hinders further clinical exploration. In this study, we simultaneously reconstructed ultrasonic Nakagami imaging, ultrasonic horizontally normalized Shannon entropy (hNSE) imaging, and ultrasonic differential attenuation coefficient intercept (DACI) imaging from ultrasound backscattered envelope data collected during high-intensity focused ultrasound ablation treatment. We comprehensively investigated their performance differences through qualitative and quantitative analyses, including the calculation of contrast-to-noise ratios (CNR) for ultrasonic images, receiver operating characteristic (ROC) analysis with corresponding indicators, the analysis of lesion area fitting relationships, and computational time consumption comparison. The mean CNR of hNSE imaging was 10.98 ± 4.48 dB, significantly surpassing the 3.82 ± 1.40 dB (p < 0.001, statistically significant) of Nakagami imaging and the 2.45 ± 0.74 dB (p < 0.001, statistically significant) of DACI imaging. This substantial difference underscores that hNSE imaging offers the highest contrast resolution for lesion recognition. Furthermore, we evaluated the ability of multiple ultrasonic parametric imaging to detect thermal ablation lesions using ROC curves. The area under the curve (AUC) for hNSE was 0.874, exceeding the values of 0.848 for Nakagami imaging and 0.832 for DACI imaging. Additionally, hNSE imaging exhibited the strongest linear correlation coefficient (R = 0.92) in the comparison of lesion area fitting, outperforming Nakagami imaging (R = 0.87) and DACI imaging (R = 0.85). hNSE imaging also performs best in real-time monitoring with each frame taking 6.38 s among multiple ultrasonic parametric imaging. Our findings unequivocally demonstrate that hNSE imaging excels in monitoring HIFU ablation treatment and holds the greatest potential for further clinical exploration.

Ultrasound-guided high-intensity focused ultrasound ablation for uterine arteriovenous fistula: a case series.

PURPOSE: To evaluate the efficacy and safety of high-intensity focused ultrasound (HIFU) ablation in the treatment of uterine arteriovenous fistula (UAVF). MATERIALS AND METHODS: This case series included three patients diagnosed with acquired UAVF. All patients underwent routine laboratory tests, electrocardiography (ECG), chest X-ray, ultrasound, and pelvic contrast-enhanced magnetic resonance imaging (MRI). HIFU treatment was performed under sedation and analgesia using a Model JC Focused Ultrasound Tumor Therapeutic System (made by Chongqing Haifu Medical Technology Co. Ltd., China) with a B mode ultrasound device for treatment guidance. The treatment time, sonication power, sonication time, and complications were recorded. Follow-up evaluations were scheduled at 1-, 3-, 6-, and 12-month to assess symptom improvement and evaluate the post-treatment imaging. RESULTS: All patients completed HIFU treatment in a single session without any major complication. All patients complained of mild lower abdominal and sacrococcygeal pain. Typically, no special treatment is required. Following HIFU treatment, there was a significant relief in clinical symptoms, particularly abnormal uterine bleeding. Ultrasound examinations conducted one month after the treatment revealed a notable reduction in the volume of the lesion, ranging from 57% to 100%. Moreover, the efficacy and safety of HIFU treatment remained consistent during the 12-month follow-up period. CONCLUSION: HIFU ablation appears to be an effective and safe treatment modality for UAVF. It provides a noninvasive approach with favorable clinical outcomes.

Efficacy and influencing factor analysis of high-intensity focused ultrasound therapy for abdominal wall endometriosis: a case series.

OBJECTIVE: The aim of this retrospective study was to investigate the short-term and long-term efficacy of high-intensity focused ultrasound (HIFU) therapy for abdominal wall endometriosis (AWE) and explore its potential influencing factors. MATERIALS AND METHODS: A total of 80 patients with AWE who underwent HIFU therapy were retrospectively analyzed. Follow-ups were also conducted to evaluate the changes in lesion size and pain relief. Multivariate logistic regression analysis was applied to investigate factors influencing HIFU therapy for AWE. RESULTS: Among the 80 patients with AWE who received HIFU therapy, the effective rates were 76.3%, 80.5%, and 90.5% after 3, 12 and 24 months of follow-up, respectively. Multivariate logistic regression analysis revealed that the AWE lesion diameter and sonication intensity had statistically significant effects on the 3-month and 12-month efficacy of HIFU therapy for AWE, while age, BMI, disease duration, average sonication power and grey-scale changes did not have statistically significant effects. Four patients with AWE experienced recurrence after HIFU therapy, for a three-year cumulative recurrence rate of 6.3%. Furthermore, ten patients required reintervention after treatment, for a five-year cumulative reintervention rate of 13.9%. CONCLUSIONS: This study further confirmed the safety and effectiveness of HIFU therapy for AWE. Factors such as AWE lesion diameter and sonication intensity have been identified as key influencers affecting the short-term and long-term efficacy of HIFU therapy for AWE. The first two years following HIFU therapy constitute crucial periods for observation, and judiciously extending follow-up intervals during this timeframe is advised.

Shape-recovery of implanted shape-memory devices remotely triggered via image-guided ultrasound heating.

Shape-memory materials hold great potential to impart medical devices with functionalities useful during implantation, locomotion, drug delivery, and removal. However, their clinical translation is limited by a lack of non-invasive and precise methods to trigger and control the shape recovery, especially for devices implanted in deep tissues. In this study, the application of image-guided high-intensity focused ultrasound (HIFU) heating is tested. Magnetic resonance-guided HIFU triggered shape-recovery of a device made of polyurethane urea while monitoring its temperature by magnetic resonance thermometry. Deformation of the polyurethane urea in a live canine bladder (5 cm deep) is achieved with 8 seconds of ultrasound-guided HIFU with millimeter resolution energy focus. Tissue sections show no hyperthermic tissue injury. A conceptual application in ureteral stent shape-recovery reduces removal resistance. In conclusion, image-guided HIFU demonstrates deep energy penetration, safety and speed.

Analysis of related factors influencing postoperative recurrence of adenomyosis treated with HIFU.

OBJECTIVE: To analyze the efficacy of high-intensity focused ultrasound (HIFU) for adenomyosis and postoperative recurrence and its influencing factors. METHODS: Clinical and follow-up data of 308 patients with adenomyosis who were treated with HIFU in Haifu Center, Affiliated Hospital of Chengdu University of Traditional Chinese Medicine from September 2017 to January 2022 were retrospectively analyzed. The recurrence of adenomyosis and the efficacy of HIFU at 6 months after surgery were followed up. To explore factors influencing postoperative prognosis and recurrence, the following variables were analyzed: patients' age, course of disease, gravidity and parity, size of the uterus, duration of HIFU, duration of irradiation, treatment intensity, dysmenorrhea score, time of follow-up, combined treatment of traditional Chinese medicine (TCM), western medicine adjuvant treatment, lesion location and type, and menorrhagia. RESULTS: Among the 308 patients, 238 (77%) were followed up from 6 to 36 months, with an average follow-up time of 15.24 ± 9.97 months. The other 70 (23%) were lost to follow-up. At 6-month after surgery, efficacy rates of dysmenorrhea and menorrhagia management were 86.7% and 89.3%, respectively. Postoperative recurrence rates were 4.8% (1-12 months), 9.0% (12-24 months), and 17.0% (24-36 months) for dysmenorrhea; and 6.3% (1-12 months), 2.4% (12-24 months), and 12.2% (24-36 months) for menorrhagia. Multivariate logistic regression analyses showed that parity (P = 0.043, OR = 1.773, 95% CI 1.018-3.087), uterine size (P = 0.019, OR = 1.004, 95% CI 1.001-1.007), combined treatment of TCM (P = 0.047, OR = 1.846, 95% CI 1.008-3.381), diffuse lesion type (P = 0.013, OR = 0.464, 95% CI 0.254-0.848) and ablation rate (P = 0.015, OR = 0.481, 95%CI 0.267-0.868) were prognostic factors (P < 0.05). Age, course of disease, gravidity, duration of HIFU, duration of irradiation, treatment intensity, preoperative dysmenorrhea score, time of follow-up, western medicine adjuvant therapy, lesion location, and preoperative menstrual volume had no effect on prognosis (P > 0.05). CONCLUSION: HIFU can effectively relieve dysmenorrhea and reduce menstrual volume in patients with adenomyosis. Parity, uterine size, lesion type (diffuse), and ablation rate are risk factors for symptom recurrence after HIFU, while the combination of TCM therapy is a protective factor for relapse. We, therefore, recommend TCM in the adjuvant setting after HIFU according to patient condition.

Characterization of Blood-Brain Barrier Opening Induced by Transcranial Histotripsy in Murine Brains.

OBJECTIVE: Transcranial histotripsy has shown promise as a non-invasive neurosurgical tool, as it has the ability to treat a wide range of locations in the brain without overheating the skull. One important effect of histotripsy in the brain is the blood-brain barrier (BBB) opening (BBBO) at the ablation site, but there is a knowledge gap concerning the extent of histotripsy-induced BBBO. Here we describe induction of BBBO by transcranial histotripsy and use of magnetic resonance imaging (MRI) and histology to quantify changes in BBBO at the periphery of the histotripsy ablation zone over time in the healthy mouse brain. METHODS: An eight-element, 1 MHz histotripsy transducer with a focal distance of 32.5 mm was used to treat the brains of 23 healthy female BL6 mice. T1-gadolinium (T1-Gd) MR images were acquired immediately following histotripsy treatment and during each of the subsequent 4 wk to quantify the size and intensity of BBB leakage. RESULTS: The T1-Gd MRI results revealed that the hyperintense BBBO volume increased over the first week and subsided gradually over the following 3 wk. Histology revealed complete loss of tight junction proteins and blood vessels in the center of the ablation region immediately after histotripsy, partial recovery in the periphery of the ablation zone 1 wk following histotripsy and near-complete recovery of tight junction complex after 4 wk. CONCLUSION: These results provide the first evidence of transcranial histotripsy-induced BBBO and repair at the periphery of the ablation zone.

Management of Uterine Fibroids and Sarcomas: The Palermo Position Paper.

BACKGROUND: Uterine fibroids are benign monoclonal tumors originating from the smooth muscle cells of the myometrium, constituting the most prevalent pathology within the female genital tract. Uterine sarcomas, although rare, still represent a diagnostic challenge and should be managed in centers with adequate expertise in gynecological oncology. OBJECTIVES: This article is aimed to summarize and discuss cutting-edge elements about the diagnosis and management of uterine fibroids and sarcomas. METHODS: This paper is a report of the lectures presented in an expert meeting about uterine fibroids and sarcomas held in Palermo in February 2023. OUTCOME: Overall, the combination of novel molecular pathways may help combine biomarkers and expert ultrasound for the differential diagnosis of uterine fibroids and sarcomas. On the one hand, molecular and cellular maps of uterine fibroids and matched myometrium may enhance our understanding of tumor development compared to histologic analysis and whole tissue transcriptomics, and support the development of minimally invasive treatment strategies; on the other hand, ultrasound imaging allows in most of the cases a proper mapping the fibroids and to differentiate between benign and malignant lesions, which need appropriate management. CONCLUSIONS AND OUTLOOK: The choice of uterine fibroid management, including pharmacological approaches, surgical treatment, or other strategies, such as high-intensity focused ultrasound (HIFU), should be carefully considered, taking into account the characteristics of the patient and reproductive prognosis.

Suppressing HIFU interference in ultrasound images using 1D U-Net-based neural networks.

Objective.One big challenge with high-intensity focused ultrasound (HIFU) is that the intense acoustic interference generated by HIFU irradiation overwhelms the B-mode monitoring images, compromising monitoring effectiveness. This study aims to overcome this problem using a one-dimensional (1D) deep convolutional neural network.Approach. U-Net-based networks have been proven to be effective in image reconstruction and denoising, and the two-dimensional (2D) U-Net has already been investigated for suppressing HIFU interference in ultrasound monitoring images. In this study, we propose that the one-dimensional (1D) convolution in U-Net-based networks is more suitable for removing HIFU artifacts and can better recover the contaminated B-mode images compared to 2D convolution.Ex vivoandinvivoHIFU experiments were performed on a clinically equivalent ultrasound-guided HIFU platform to collect image data, and the 1D convolution in U-Net, Attention U-Net, U-Net++, and FUS-Net was applied to verify our proposal.Main results.All 1D U-Net-based networks were more effective in suppressing HIFU interference than their 2D counterparts, with over 30% improvement in terms of structural similarity (SSIM) to the uncontaminated B-mode images. Additionally, 1D U-Nets trained usingex vivodatasets demonstrated better generalization performance ininvivoexperiments.Significance.These findings indicate that the utilization of 1D convolution in U-Net-based networks offers great potential in addressing the challenges of monitoring in ultrasound-guided HIFU systems.

Focused ultrasound ablation of melanoma with boiling histotripsy yields abscopal tumor control and antigen-dependent dendritic cell activation.

Background: Boiling histotripsy (BH), a mechanical focused ultrasound ablation strategy, can elicit intriguing signatures of anti-tumor immunity. However, the influence of BH on dendritic cell function is unknown, compromising our ability to optimally combine BH with immunotherapies to control metastatic disease. Methods: BH was applied using a sparse scan (1 mm spacing between sonications) protocol to B16F10-ZsGreen melanoma in bilateral and unilateral settings. Ipsilateral and contralateral tumor growth was measured. Flow cytometry was used to track ZsGreen antigen and assess how BH drives dendritic cell behavior. Results: BH monotherapy elicited ipsilateral and abscopal tumor control in this highly aggressive model. Tumor antigen presence in immune cells in the tumor-draining lymph nodes (TDLNs) was ~3-fold greater at 24h after BH, but this abated by 96h. B cells, macrophages, monocytes, granulocytes, and both conventional dendritic cell subsets (i.e. cDC1s and cDC2s) acquired markedly more antigen with BH. BH drove activation of both cDC subsets, with activation being dependent upon tumor antigen acquisition. Our data also suggest that BH-liberated tumor antigen is complexed with damage-associated molecular patterns (DAMPs) and that cDCs do not traffic to the TDLN with antigen. Rather, they acquire antigen as it flows through afferent lymph vessels into the TDLN. Conclusion: When applied with a sparse scan protocol, BH monotherapy elicits abscopal melanoma control and shapes dendritic cell function through several previously unappreciated mechanisms. These results offer new insight into how to best combine BH with immunotherapies for the treatment of metastatic melanoma.

Magnetic resonance-guided focused ultrasound versus percutaneous thermal ablation in local control of bone oligometastases: a systematic review and meta-analysis.

BACKGROUND: The percutaneous thermal ablation techniques (pTA) are radiofrequency ablation, cryoablation, and microwave ablation, suitable for the treatment of bone oligometastases. Magnetic resonance-guided focused ultrasound (MRgFUS) is a noninvasive ablation technique. OBJECTIVES: To compare the effectiveness and safety of MRgFUS and pTA for treating bone oligometastases and their complications. METHODS: Studies were selected with a PICO/PRISMA protocol: pTA or MRgFUS in patients with bone oligometastases; non-exclusive curative treatment. Exclusion criteria were: primary bone tumor; concurrent radiation therapy; palliative therapy; and absence of imaging at follow-up. PubMed, BioMed Central, and Scopus were searched. The modified Newcastle-Ottawa Scale assessed articles quality. For each treatment (pTA and MRgFUS), we conducted two separate random-effects meta-analyses to estimate the pooled effectiveness and safety. The effectiveness was assessed by combining the proportions of treated lesions achieving local tumor control (LTC); the safety by combining the complications rates of treated patients. Meta-regression analyses were performed to identify any outcome predictor. RESULTS: A total of 24 articles were included. Pooled LTC rate for MRgFUS was 84% (N = 7, 95% CI 66-97%, I2 = 74.7%) compared to 65% of pTA (N = 17, 95% CI 51-78%, I2 = 89.3%). Pooled complications rate was similar, respectively, 13% (95% CI 1-32%, I2 = 81.0%) for MRgFUS and 12% (95% CI 8-18%, I2 = 39.9%) for pTA, but major complications were recorded with pTA only. The meta-regression analyses, including technique type, study design, tumor, and follow-up, found no significant predictors. DISCUSSION: The effectiveness and safety of the two techniques were found comparable, even though MRgFUS is a noninvasive treatment that did not cause any major complication. Limited data availability on MRgFUS and the lack of direct comparisons with pTA may affect these findings. CONCLUSIONS: MRgFUS can be a valid, safe, and noninvasive treatment for bone oligometastases. Direct comparison studies are needed to confirm its promising benefits.

Evaluating the Effects of Water Balloons on High-Intensity Focused Ultrasound for Treating Uterine Fibroids.

OBJECTIVE: In the treatment of uterine fibroids with ultrasound-guided high-intensity focused ultrasound (HIFU), water balloons are considered to be a valuable aid for improving safety and efficiency. However, the water balloons worsen the pathway for acoustic transmission, causing degraded performance both in ultrasound therapy and in ultrasound imaging. This study was aimed at establishing a protocol to evaluate the effects of the water balloon. METHODS: Simulations and experiments were carefully conducted to quantitatively investigate the effects of water ballons on the efficiency of HIFU energy delivery and on the quality of ultrasound guiding images. More specifically, HIFU-induced temperature increases in the focal region, together with spatial resolution, contrast and signal-to-noise ratio in the ultrasound guiding images, were compared under the conditions with and without the water balloon. RESULTS: Experiment results revealed that the use of water balloons led to decreases in temperature up to 10ºC within the focal region in some specific situations, but the quality of the guiding images was relatively less affected. CONCLUSION: The study provided knowledge on what influence the water balloon could have in ultrasound-guided HIFU treatment; it also established a practical and standardized evaluation scheme for further optimizing the water balloon, for example, its material and internal liquid compositions. This study can potentially help improve the efficiency and safety of treating uterine fibroids with ultrasound-guided HIFU systems.

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.

Long-term outcome and risk factors of reintervention after high intensity focused ultrasound ablation for uterine fibroids: a systematic review and meta-analysis.

OBJECTIVES: To quantify the reintervention rate and analyze the risk factors for reintervention after high-intensity focused ultrasound (HIFU) ablation of uterine fibroids. METHODS: Eighteen studies were selected from the seven databases. A meta-analysis was applied to synthesize the reintervention rates for fibroids across various follow-up durations. Subgroup-analysis was conducted based on the year of surgery, sample size, guide methods, and non-perfusion volume ratio (NPVR). Signal intensity of T2-weighted imaging (T2WI) was independently evaluated for reintervention risk. RESULTS: The study enrolled 5216 patients with fibroids treated with HIFU. There were 3247, 1239, 1762, and 2535 women reaching reintervention rates of 1% (95% confidence interval (CI): 1-1), 7% (95% CI: 4-11), 19% (95% CI: 11-27), and 29% (95% CI: 14-44) at 12, 24, 36, and 60-month after HIFU. The reintervention rates of patients treated with US-guided HIFU (USgHIFU) were significantly lower than those of patients treated with MR-guided focused ultrasound surgery (MRgFUS). When the NPVR of fibroids was over 50%, the reintervention rates at 12, 36 and 60-month after HIFU were 1% (95% CI: 0.3-2), 5% (95% CI: 3-8), and 15% (95% CI: 9-20). The reintervention risk for hyper-intensity fibroids on T2WI was 3.45 times higher (95% CI: 2.7-4.39) for hypo-/iso-intensity fibroids. CONCLUSION: This meta-analysis showed that the overall reintervention rates after HIFU were acceptable and provided consultative suggestions regarding treatment alternatives for patients with fibroids. Subgroup-analysis revealed that USgHIFU, NPVR ≥ 50%, and hypo-/iso-intensity of fibroids on T2WI were significant factors in reducing reintervention. SYSTEMATIC REVIEW REGISTRATION: PROSPERO, CRD42023456094.

Non-contrast enhanced MRI for efficiency evaluation of high-intensity focused ultrasound in adenomyosis ablation.

OBJECTIVE: To investigate the value of T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) in evaluating the therapeutic effect of high-intensity focused ultrasound (HIFU) in adenomyosis ablation. MATERIAL AND METHODS: One hundred eighty-nine patients with adenomyosis were treated with HIFU. The ablation areas on T2WI and DWI sequences were classified into different types: type I, relatively ill-defined rim or unrecognizable; subtype IIa, well-defined rim with hyperintensity; subtype IIb, well-defined rim with hypointensity. The volume of ablation areas on T2WI (VT2WI) and DWI (VDWI) was measured and compared with the non-perfused volume (NPV), and linear regression was conducted to analyze their correlation with NPV. RESULTS: The VT2WI of type I and type II (subtype IIa and subtype IIb) were statistically different from the corresponding NPV (p = 0.004 and 0.024, respectively), while no significant difference was found between the VDWI of type I and type II with NPV (p = 0.478 and 0.561, respectively). In the linear regression analysis, both VT2WI and VDWI were positively correlated with NPV, with R2 reaching 0.96 and 0.97, respectively. CONCLUSIONS: Both T2WI and DWI have the potential for efficient evaluation of HIFU treatment in adenomyosis, and DWI can be a replacement for CE-T1WI to some extent.