High-intensity Focused Ultrasound Research Articles

Propensity score matched analysis of functional outcome in five thousand cases of robot-assisted radical prostatectomy versus high-intensity focused ultrasound

BackgroundTo evaluate functional outcome after robot-assisted radical prostatectomy (RARP) and high-intensity focused ultrasound (HIFU) ablation for prostate cancer. MethodsWe retrospectively reviewed 4,983 RARP and 230 HIFU procedures performed at a single tertiary center. A 1:4 ratio propensity score matching (PSM) was performed to achieve baseline equivalence in age, body mass index (BMI), comorbidities, clinical stage, prostate specific antigen (PSA), prostate volume, biopsy grade, and number of positive cores. Functional outcomes based on International Prostate Symptom Score (IPSS), International Index of Erectile Function (IIEF-5) scores, and incontinence rates were evaluated at 6, 12, and 24 months. Resultstotal of 193 HIFU cases matched to 760 cases of RARP, were included. No differences were observed in perioperative IPSS at all follow-up periods. Despite comparative erectile function at baseline, HIFU showed significantly better erectile function preservation compared to RARP, with mean IIEF-5 scores of 9.5 versus 4.8, 9.5 versus 5.8, and 8.4 versus 6.7 at 6, 12, and 24 months, respectively (all P < 0.001). Pad-free rates at 6 and 12 months were comparable, with over 96% achieving continence at 12 months in both groups, although the rate of ≤1 pad/day at last follow-up was slightly better in HIFU (98.9% vs. 96.7%, P = 0.049). Subgroup analysis on partial (PGA) and whole gland ablation (WGA) showed no differences in IIEF-5 and incontinence but increased voiding difficulty in WGA versus PGA after 12 months of therapy (P < 0.05). Preoperative IIEF-5 ≥17 and HIFU were significant predictors of early erectile function recovery at 6 months (HR 4.4 and 5.0; all P < 0.001). No differences were observed in treatment-free survival between PGA, WGA, and RARP. ConclusionHIFU shows better performance in early recovery and preservation of erectile function after treatment for prostate cancer without increasing the risk of treatment failure. Patients with moderate to severe erectile dysfunction (IIEF-5 <17) prior to surgery should be warned of poor recovery after treatment.

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

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

Enhancing electrochemiluminescence for chloramphenicol detection based on the synergistic effect of doped Ti3C2 with ultrasound

Chloramphenicol (CAP) is known to be harmful to the environment and food, posing a threat to human health. Developing an effective and convenient method for detecting CAP is crucial. An electrochemiluminescence (ECL) biosensor has been designed for sensitive detection of CAP. The improved ECL behavior was attributed to the synergistic effect of N and P co-doped Ti3C2-Apt1 (N, P-Ti3C2-Apt1) nanoprobes and high intensity focused ultrasound (HIFU) pretreatment. The doping of N and P could improve the electrochemical performance of Ti3C2. HIFU pretreatment generated more reactive oxygen species (ROS) in the luminol-O2 system. N, P-Ti3C2 could aggregate and catalyze ROS, causing an increase in ECL intensity. Furthermore, N, P-Ti3C2 as a carrier loaded more aptamer, which could recognize CAP with high specificity. The detection limit was 0.01 ng/mL. This biosensor has been successfully applied in milk and environmental water samples, highlighting its potential in the field of food and environmental analysis.

Abstract 3845: High-intensity focused ultrasound ablation increases tumor specific lymphocytes in prostate cancer

Abstract The treatment of localized prostate cancer has been revolutionized by High-Intensity Focused Ultrasound (HIFU), an FDA-approved procedure. Thermal HIFU achieves the destruction of tumor tissue through the noninvasive delivery of ultrasonic energy, causing rapid heating of the targeted area. Given that prostate cancer typically exhibits a low presence of tumor-infiltrating lymphocytes crucial for antitumor immunity, this study aimed to investigate whether HIFU has the potential to activate antitumor immunity and enhance lymphocyte infiltration within the tumor. RM1 tumors were implanted on the flanks of syngeneic C57BL/6J mice, with one tumor subjected to HIFU treatment. The growth of the contralateral tumor was monitored, and at the end of the study, tumors were collected to evaluate immune cell infiltration. 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 cell population. In murine experiments, the application of HIFU to one tumor resulted in a reduction in the growth of the contralateral (untreated) tumor, specifically when the contralateral tumor was of the same type, but not when it was a different tumor type. Notably, HIFU led to an augmented infiltration of CD4+ and CD8+ lymphocytes into the contralateral (untreated) tumor. Depletion studies further affirmed that the antitumor immune response triggered by HIFU relies on CD4+ and CD8+ lymphocytes. In human subjects, HIFU was observed to elevate the CD4+ and CD8+ lymphocyte populations in PBMCs. HIFU induces a potent antitumor immune response that effectively inhibits the progression of murine prostate tumors. This immune response is contingent upon CD4+ and CD8+ lymphocytes. HIFU demonstrates significant promise in activating antitumor immune responses in patients diagnosed with prostate cancer. Subsequent research endeavors should delve into models of metastatic prostate cancer, exploring the potential synergy of cytoreductive prostate tumor ablation with systemic immunotherapies to elicit a robust and comprehensive antitumor immune response. Citation Format: Shengchen Su, Yanping Wang, Eric M. Lo, Hyung L. Kim. High-intensity focused ultrasound ablation increases tumor specific lymphocytes in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3845.

High-intensity focused ultrasound for endometrial ablation in adenomyosis: a clinical study.

The present study aimed to investigate the clinical efficacy of endometrial ablation with high-intensity focused ultrasound (HIFU) for symptom relief in women with adenomyosis. Between July 2014 and July 2020, 167 patients with adenomyosis treated at the Zhongshan City People's Hospital were enrolled in this study. Patients were divided into two groups according to patient aspirations: the control group, including patients who only underwent ablation of adenomyosis lesions (group A) and the treatment group, including patients who underwent removal of adenomyosis lesions and endometrial ablation (group B). The reduced dysmenorrhea scores (visual analog scale) and menstrual volume scores (pictorial blood assessment chart) were measured before and after treatment. The scores were obtained by subtracting the postoperative scores from the preoperative scores and were compared to determine whether the symptoms had alleviated. Compared with the menstrual volume of group A, that in group B showed significant improvements. The average relief rates of dysmenorrhea in the two groups also showed significant improvement. However, the scores in group B showed a more significant improvement than those in group A. Therefore, our findings suggest that endometrial ablation using HIFU may be superior to conventional therapy with regard to alleviating the symptoms of increased menstruation in women with adenomyosis.

Expansion of the cavitation region using ultrasound focus scanning in the direction of ultrasound propagation for an efficient method of histotripsy

Histotripsy is a non-invasive high-intensity focused ultrasound (HIFU) based therapy using the mechanical effect of cavitation bubbles. In this paper, we experimentally examined the effectiveness of a proposed method of scanning the HIFU focus in the direction of propagation to expand the region of the bubble cloud and increase the treatment throughput. First, the continuous generation of cavitation bubbles was observed with a high-speed camera, and it was confirmed that the region of bubble cloud generation could be expanded by focus scanning. Next, we performed ex vivo experiments. Tissue treated with histotripsy is disrupted and homogenized at the subcellular level, resulting in a decrease in the backscatter intensity of the ultrasound. Therefore, we observed the progression of tissue homogenization with histotripsy by evaluating the reduction of echo intensity in ultrasound imaging. The results suggest that focus scanning can improve the time efficiency of treatment.

Fluoroscopy-guided high-intensity focused ultrasound ablation of the lumbar medial branch nerves: dose escalation study and comparison with radiofrequency ablation in a porcine model

BackgroundRadiofrequency ablation (RFA) is a common method for alleviating chronic back pain by targeting and ablating of facet joint sensory nerves. High-intensity focused ultrasound (HIFU) is an emerging, non-invasive, image-guided...

High-intensity focused ultrasound with visually directed power adjustment for focal treatment of localized prostate cancer: systematic review and meta-analysis

PurposeTo characterize patient outcomes following visually directed high-intensity focused ultrasound (HIFU) for focal treatment of localized prostate cancer.MethodsWe performed a systematic review of cancer-control outcomes and complication rates among men with localized prostate cancer treated with visually directed focal HIFU. Study outcomes were calculated using a random-effects meta-analysis model.ResultsA total of 8 observational studies with 1,819 patients (median age 67 years; prostate-specific antigen 7.1 mg/ml; prostate volume 36 ml) followed over a median of 24 months were included. The mean prostate-specific antigen nadir following visually directed focal HIFU was 2.2 ng/ml (95% CI 0.9–3.5 ng/ml), achieved after a median of 6 months post-treatment. A clinically significant positive biopsy was identified in 19.8% (95% CI 12.4–28.3%) of cases. Salvage treatment rates were 16.2% (95% CI 9.7–23.8%) for focal- or whole-gland treatment, and 8.6% (95% CI 6.1–11.5%) for whole-gland treatment. Complication rates were 16.7% (95% CI 9.9–24.6%) for de novo erectile dysfunction, 6.2% (95% CI 0.0–19.0%) for urinary retention, 3.0% (95% CI 2.1–3.9%) for urinary tract infection, 1.9% (95% CI 0.1–5.3%) for urinary incontinence, and 0.1% (95% CI 0.0–1.4%) for bowel injury.ConclusionLimited evidence from eight observational studies demonstrated that visually directed HIFU for focal treatment of localized prostate cancer was associated with a relatively low risk of complications and acceptable cancer control over medium-term follow-up. Comparative, long-term safety and effectiveness results with visually directed focal HIFU are lacking.

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 vivo and in vivo HIFU 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 using ex vivo datasets demonstrated better generalization performance in in vivo experiments. 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.

A Review of High-Intensity Focused Ultrasound

For 80 years, high-intensity focused ultrasound (HIFU) has been the subject of interest in medical research. It is a non-invasive procedure that causes the death of cells in a very select area through one of two mechanisms, either heat or cavitation. While diagnostic ultrasound is well known in the medical profession and ultrasound is also used in physiotherapy, high-intensity focused ultrasound is less known but is becoming increasingly important as a non-invasive tool that can be used in many ways, including in the treatment of several cancers as well as benign uterine fibroids. Other interesting developments are underway, including its use in the treatment through an intact skull of essential tremors and the tremor associated with Parkinson’s disease, and in a modified form, it is used to target drug delivery to the brain due to its potential opening of the blood–brain barrier. The depth of penetration of HIFU is variable depending on the type of transducer used and the distance from it. Clinical trials of abdominal malignancies and benign uterine fibroids are reviewed in this article along with potential side effects of the procedure. Over the past two decades, the technology has improved considerably, and the clinical indications have broadened. The current limitations of the technology are also discussed, along with the potential advances in the field that may be made over the next decade.

Focal high-intensity focused ultrasound therapy for localized prostate cancer: An interim analysis of the multinational FASST study.

High-intensity focused ultrasound (HIFU) emerged as a novel approach for the treatment of localized prostate cancer (PCa). However, prospective studies on HIFU-related outcomes and predictors of treatment failure (TF) remain scarce. We conducted a multinational prospective cohort study among patients undergoing HIFU therapy for localized, low- to intermediate-risk PCa. Follow-up data on serial prostate specific antigen (PSA), multi-parametric magnetic resonance imaging (mpMRI), targeted/systematic biopsies, adverse events and functional outcomes were collected. The primary endpoint was TF, defined as histologically confirmed PCa requiring whole-gland salvage treatment. Uni- and multi-variable adjusted hazard ratios (HRs) were calculated using Cox proportional hazard regression models. At baseline, mean (standard deviation) age was 64.14 (7.19) years, with the majority of patients showing T-stage 1 (73.9%) and International Society of Urological Pathology grading system Grade 2 (58.8%). PSA nadir (median, 1.70 ng/mL) was reached after 6 months. Of all patients recruited, 16% had clinically significant PCa, as confirmed by biopsy, of which 13.4% had TF. Notably, T-stage and number of positive cores at initial biopsy were independent predictors of TF during follow-up (HR [95% CI] 1.27 [1.02-1.59] and 5.02 [1.80-14.03], respectively). Adverse events were minimal (17% and 8% early and late adverse events, respectively), with stable or improved functional outcomes in the majority of patients. This interim analysis of a multinational study on HIFU therapy for the management of low-to-intermediate-risk PCa reveals good functional outcomes, minimal adverse events and low incidence of TF over the short-term. Data on long-term outcomes, specifically as it relates to oncological outcomes, are awaited eagerly.

Prediction of Ablation Rate for High-Intensity Focused Ultrasound Therapy of Adenomyosis in MR Images Based on Multi-model Fusion.

This study aimed to develop a model based on radiomics and deep learning features to predict the ablation rate in patients with adenomyosis undergoing high-intensity focused ultrasound (HIFU) therapy. A total of 119 patients with adenomyosis who received HIFU therapy were retrospectively analyzed. Participants were included in the training and testing queues in a 7:3 ratio. Radiomics features were extracted from T2-weighted imaging (T2WI) images, and VGG-19 was used to extract advanced deep features. An ensemble model based on multi-model fusion for predicting the efficacy of HIFU in adenomyosis was proposed, which consists of four base classifiers and was evaluated using accuracy, precision, recall, F-score, and area under the receiver operating characteristic curve (AUC). The predictive performance of the combined model combining radiomics and deep learning features outperformed the radiomics and deep learning feature models alone, with accuracy of 0.848 and 0.814 in training and test sets, and AUC of 0.916 and 0.861, respectively. Compared with the base classifiers that make up the multi-model fusion model, the fusion model also exhibited better prediction performance. The fusion model incorporating both radiomics and deep learning features had certain predictive value for the ablation rate of adenomyosis under HIFU therapy and could help select patients with adenomyosis who would benefit from HIFU therapy.

Histotripsy: an innovative approach for minimally invasive tumour and disease treatment.

Histotripsy is a noninvasive medical technique that uses high-intensity focused ultrasound (HIFU) to treat liver tumours. The two main histotripsy methods are boiling histotripsy and cavitation cloud histotripsy. Boiling histotripsy uses prolonged ultrasound pulses to create small boiling bubbles in the tissue, which leads to the breakdown of the tissue into smaller subcellular fragments. Cavitation cloud histotripsy uses the ultrasonic cavitation effect to disintegrate target tissue into precisely defined liquefied lesions. Both methods show similar treatment effectiveness; however, boiling histotripsy ensures treatment stability by producing a stable boiling bubble with each pulse. The therapeutic effect is ascribed to mechanical damage at the subcellular level rather than thermal damage. This article discusses the mechanisms, treatment parameters, and potential of histotripsy as a minimally invasive procedure that provides precise and controlled subcellular damage.

Changes of serum CA125 and PGE2 before and after high-intensity focused ultrasound combined with GnRH-a in treatment of patients with adenomyosis.

This study aimed to investigate the changes of serum carbohydrate antigen 125 (CA125) and prostaglandin E2 (PGE2) in patients with adenomyosis before and after treatment with high-intensity focused ultrasound (HIFU) combined with gonadotropin-releasing hormone agonist (GnRH-a). One hundred and sixty-five patients with adenomyosis who received HIFU combined with GnRH-a were selected as case group. Sixty-five healthy women who underwent physical examination at the same time were taken as normal control group. At the end of follow-up 6 months after treatment, the case group were divided into effective subgroup and ineffective subgroup according to clinical efficacy. Changes of serum CA125 and PGE2 were analyzed. Serum CA125 and PGE2 levels in the case group were higher than those in the normal control group before treatment (both P < 0.001). Serum CA125 and PGE2 levels in the case group 6 months after treatment were lower than those before treatment (both P < 0.001). There was no difference in serum CA125 and PGE2 levels between effective subgroup and ineffective subgroup before treatment (P = 0.351, 0.284, respectively). Serum CA125 and PGE2 levels in the effective subgroup were lower than those in the ineffective subgroup 6 months after treatment (both P < 0.001). Serum CA125 and PGE2 may be involved in the development of adenomyosis, and their expression levels may be related to the prognosis of patients. Levels of serum CA125 and PGE2 in patients with adenomyosis decrease after treatment with HIFU combined with GnRH-a. The detection of serum CA125 and PGE2 may be used as an index to diagnose adenomyosis and evaluate the therapeutic effect of HIFU combined with GnRH-a.

A spatiotemporal deconvolution approach for measurements of therapeutic ultrasound pressures, intensities, and beamwidths

Complete characterization of high intensity focused ultrasound (HIFU) systems includes measurements of transmitted pressure at the focal plane with a hydrophone. However, highly focused, nonlinear HIFU beams can result in considerable spatial averaging artifacts due to finite area of the hydrophone active element. Spatiotemporal deconvolution (STD) can correct for hydrophone spatial averaging (Wear, IEEE Trans. UFFC 69, 1243–1256 (2021)]. The objective of the present work is to extend validation of STD from diagnostic levels (6 MPa) to therapeutic levels (49 MPa). Three HIFU transducers (1.45 MHz F/1, 1.53 MHz F/1.5, and 3.91 MHz F/1) were driven in tone bursts (Agilent HP3314A function generator, ENI 240L amplifier) to generate HIFU fields in a degassed, deionized water tank with focal compressional pressures of 49, 16, and 29 MPa. Fields were measured in focal planes with two hydrophones (Onda HFO 100-μm fiber-optic; Onda HNA-0400 400-μm robust needle). STD reduced inter-hydrophone differences from −18 ± 11% to 0 ± 8% (peak compressional pressure), −8 ± 4% to −5 ± 5% (peak rarefactional pressure), −20% ± 7% to −3 ± 8% (pulse intensity integral), and 21 ± 12% to −2 ± 3% (beam FWHM). STD reduces dependence of measurements on hydrophone active element size. STD reduces reliance on fiber optic hydrophones, which can be expensive, difficult to use, and prone to radiation-force-induced sensor misalignment.

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.

Evaluation of Dual-Frequency Switching HIFU for Optimizing Superficial Ablation

ObjectiveDual-frequency high-intensity focused ultrasound (HIFU) thermal ablation is an exceptionally promising technique for treating tumors due to its precision and effectiveness. However, there are still a few studies on improving the accuracy and efficiency of HIFU in superficial ablation applications. This study proposes a method utilizing dual frequency switching ultrasound (DFSU) to enhance the efficiency and precision of superficial treatments. MethodsA dual-frequency HIFU transducer operating at 4.5 MHz and 13.7 MHz was designed, and a dual-frequency impedance matching network was designed to optimize electro-acoustic conversion efficiency. Phantom and ex vivo tests were conducted to measure and compare thermal lesion areas and temperature rises caused by single-frequency ultrasound (SFU) and DFSU. ResultsIn both phantom and ex vivo tests, the utilization of DFSU resulted in larger lesion areas compared to SFU. Moreover, DFSU provided improved control and versatility, enabling precise and efficient ablation. ConclusionDFSU exhibits the ability to generate larger ablation areas in superficial tissue compared to SFU, and DFSU allows flexible control over the ablation area and temperature rise rate. The acoustic power deposition of HIFU can be optimized to achieve precise ablation.

Optical method for direct temperature measurement of high intensity focused ultrasound heating

The acoustic pressure field or heat deposition from the passage of an ultrasonic wave can produce a perceptible alteration in the medium’s optical refractive index. With proper placement of the light source and imaging camera, the optical effect can be recorded. This talk describes an optical temperature measurement methodology dubbed laser-ray-bundle (LRB) of the heat deposition from a high intensity focused ultrasound (HIFU) transducer in a transparent tissue phantom. The method does not require calibration, and directly converts the thermo-optic signal to temperature without recourse to any iterative computations. LRB boasts of excellent temporal and spatial resolutions and high temperature sensitivity better than any fine wire thermocouple. Furthermore, it is completely non-invasive. The LRB method is demonstrated with the heat deposition from single millisecond long HIFU pulses in a PDMS tissue phantom or from a train of single pulses with very good performance. The method represents a new capability for quickly assess a HIFU transducer output, and for laboratory and preclinical studies of heating near tissue interfaces including bone, air, or fat. A preliminary experimental setup for measuring the acoustic pressure field is presented.

Effect of intended shift in propagation direction of cavitation generation position on coagulation position in bubble-enhanced ultrasonic heating

High-intensity focused ultrasound (HIFU) is a noninvasive cancer treatment that uses powerful focused ultrasound energy to coagulate tissue. However, due to its small focal region, this treatment is time-consuming. Therefore, we have focused on the heating effect of cavitation bubbles. The safe utilization of bubbles requires that they are consistently generated and maintained in the treatment area. In this study, the effects of the HIFU focal shift in the direction of ultrasound propagation on the bubble and coagulation regions were investigated by high-speed camera and ultrasound imaging. As a result, the appropriate focal shift of pulses that generates the bubbles prevented expansion of bubble regions and generated coagulation regions with good reproducibility near the treatment target.

Noninvasive Monitoring of Tissue Temperature Changes Induced by Focused Ultrasound Exposure using Sparse Expression of Ultrasonic Radio Frequency Echo Signals.

Noninvasive therapies such as focused ultrasound were developed to be used for cancer therapies, vessel bleeding, and drug delivery. The main purpose of focused ultrasound therapy is to affect regions of interest (ROI) of tissues without any injuries to surrounding tissues. In this regard, an appropriate monitoring method is required to control the treatment. This study is aimed to develop a noninvasive monitoring technique of focused ultrasound (US) treatment using sparse representation of US radio frequency (RF) echo signals. To this end, reasonable results in temperature change estimation in the tissue under focused US radiation were obtained by utilizing algorithms related to sparse optimization as orthogonal matching pursuit (OMP) and accompanying Shannon's entropy. Consequently, ex vivo tissue experimental tests yielded two datasets, including low-intensity focused US (LIFU) and high-intensity focused US (HIFU) data. The proposed processing method analyzed the ultrasonic RF echo signal and expressed it as a sparse signal and calculated the entropy of each frame. The results indicated that the suggested approach could noninvasively estimate temperature changes between 37°C and 47°C during LIFU therapy. In addition, it represented temperature changes during HIFU ablation at various powers, ranging from 10 to 130 W. The normalized mean square error of the proposed method is 0.28, approximately 2.15 on previous related methods. These results demonstrated that this novel proposed approach, including the combination of sparsity and Shanoon's entropy, is more feasible and effective in temperature change estimation than its predecessors.