High-intensity Focused Ultrasound System Research Articles

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.

Real-Time Reconstruction of HIFU Focal Temperature Field Based on Deep Learning.

Objective and Impact Statement: High-intensity focused ultrasound (HIFU) therapy is a promising noninvasive method that induces coagulative necrosis in diseased tissues through thermal and cavitation effects, while avoiding surrounding damage to surrounding normal tissues. Introduction: Accurate and real-time acquisition of the focal region temperature field during HIFU treatment marked enhances therapeutic efficacy, holding paramount scientific and practical value in clinical cancer therapy. Methods: In this paper, we initially designed and assembled an integrated HIFU system incorporating diagnostic, therapeutic, and temperature measurement functionalities to collect ultrasound echo signals and temperature variations during HIFU therapy. Furthermore, we introduced a novel multimodal teacher-student model approach, which utilizes the shared self-expressive coefficients and the deep canonical correlation analysis layer to aggregate each modality data, then through knowledge distillation strategies, transfers the knowledge from the teacher model to the student model. Results: By investigating the relationship between the phantoms, invitro, and invivo ultrasound echo signals and temperatures, we successfully achieved real-time reconstruction of the HIFU focal 2D temperature field region with a maximum temperature error of less than 2.5 °C. Conclusion: Our method effectively monitored the distribution of the HIFU temperature field in real time, providing scientifically precise predictive schemes for HIFU therapy, laying a theoretical foundation for subsequent personalized treatment dose planning, and providing efficient guidance for noninvasive, nonionizing cancer treatment.

A theragnostic HIFU transducer and system for inherently registered imaging and therapy.

One big challenge with high intensity focused ultrasound (HIFU) is the difficulty in accurate prediction of focal location due to the complex wave propagation in heterogeneous medium even with imaging guidance. This study aims to overcome this by combining therapy and imaging guidance with one single HIFU transducer using the vibro-acoustography (VA) strategy. Based on the VA imaging method, a HIFU transducer consisting of 8 transmitting elements was proposed for therapy planning, treatment and evaluation. Inherent registration between the therapy and imaging created unique spatial consistence in HIFU transducer's focal region in the above three procedures. Performance of this imaging modality was first evaluated through in-vitro phantoms. In-vitro and ex-vivo experiments were then designed to demonstrate the proposed dual-mode system's ability in conducting accurate thermal ablation. Point spread function of the HIFU-converted imaging system had a full wave half maximum of about 1.2 mm in both directions at a transmitting frequency of 1.2 MHz, which outperformed the conventional ultrasound imaging (3.15 MHz) in in-vitro situation. Image contrast was also tested on the in-vitro phantom. Various geometric patterns could be accurately 'burned out' on the testing objects by the proposed system both in vitro and ex vivo. Implementation of imaging and therapy with one HIFU transducer in this manner is feasible and it has potential as a novel strategy for addressing the long-standing problem in the HIFU therapy, possibly pushing this non-invasive technique forward towards wider clinical applications.

Technical note: Evaluation of the acoustic radiation force imaging for predicting HIFU focus with in vitro and ex vivo experiments.

High-intensity focused ultrasound (HIFU) is currently used for the treatment of various diseases, but it still lacks a reliable technique in the preoperative stage to accurately place its "energy blade" onto diseased targets. Acoustic radiation force imaging (ARFI) was recently introduced to tackle this issue, but its applicability and limitations were not clear. The aim of this study was to evaluate the performance of ARFI method in prediction of HIFU focal location at the preoperative stage. A point spread function (PSF) localization method, which was borrowed from the ultrasound super resolution field, was used to validate the core autocorrelation-based motion estimation algorithm in the ARFI procedure. Accuracy of the ARFI method for estimating the HIFU focus were tested with in vitro and ex vivo experiments with a clinically equivalent HIFU system. Comparisons were made between the estimated focal locations and those of the damaged area after the testing objects were cut open. Results showed that the PSF localization was able to serve as a validating method for motion detection only when the tissue displacement was large. With the ARFI method, location of the HIFU focus could be accurately predicted by a 2D motion map preoperatively, and the axial spatial errors were less than 0.5mm. However, the derived 2D motion maps can only be valuable when the acoustic stimulation in ARFI were strong enough, which was probably due to the fact that the HIFU focal locations were at large depths and the ultrasound imaging signal had low signal to noise ratio. The ARFI method was indeed an accurate technique for preoperatively predicting HIFU focus in vitro and ex vivo. If clinical applications were to be considered, particularly in deep tissues, efforts might need to be made to improve ability of the ultrasound motion estimation technique.

MR-guided ultrasound-stimulated microbubble therapy enhances radiation-induced tumor response

High intensity focused ultrasound (HIFU) systems have been approved for therapeutic ultrasound delivery to cause tissue ablation or induced hyperthermia. Microbubble agents have also been used in combination with sonication exposures. These require temperature feedback and monitoring to prevent unstable cavitation and prevent excess tissue heating. Previous work has utilized lower power and pressure to oscillate microbubbles and transfer energy to endothelial cells in the absence of thermally induced damage that can radiosensitize tumors. This work investigated whether reduced acoustic power and pressure on a commercial available MR-integrated HIFU system could result in enhanced radiation-induced tumor response after exposure to ultrasound-stimulated microbubbles (USMB) therapy. A commercially available MR-integrated HIFU system was used with a hyperthermia system calibration provided by the manufacturer. The ultrasound transducer was calibrated to reach a peak negative pressure of − 750 kPa. Thirty male New Zealand white rabbits bearing human derived PC3 tumors were grouped to receive no treatment, 14 min of USMB, 8 Gy of radiation in a separate irradiation cabinet, or combined treatments. In vivo temperature changes were collected using MR thermometry at the tumor center and far-field muscle region. Tissues specimens were collected 24 h post radiation therapy. Tumor cell death was measured and compared to untreated controls through hematoxylin and eosin staining and immunohistochemical analysis. The desired peak negative pressure of − 750 kPa used for previous USMB occurred at approximately an input power of 5 W. Temperature changes were limited to under 4 °C in ten of twelve rabbits monitored. The median temperature in the far-field muscle region of the leg was 2.50 °C for groups receiving USMB alone or in combination with radiation. Finally, statistically significant tumor cell death was demonstrated using immunohistochemical analysis in the combined therapy group compared to untreated controls. A commercial MR-guided therapy HIFU system was able to effectively treat PC3 tumors in a rabbit model using USMB therapy in combination with radiation exposures. Future work could find the use of reduced power and pressure levels in a commercial MR-guided therapy system to mechanically stimulate microbubbles and damage endothelial cells without requiring high thermal doses to elicit an antitumor response.

Array-based high-intensity focused ultrasound therapy system integrated with real-time ultrasound and photoacoustic imaging.

High-intensity focused ultrasound (HIFU) is a promising non-invasive therapeutic technique in clinical applications. Challenges in stimulation or ablation HIFU therapy are to accurately target the treatment spot, flexibly deliver or fast-move focus points in the treatment region, and monitor therapy progress in real-time. In this paper, we develop an array-based HIFU system integrated with real-time ultrasound (US) and photoacoustic (PA) imaging. The array-based HIFU transducer can be dynamically focused in a lateral range of ∼16 mm and an axial range of ∼40 mm via electronically adjusting the excitation phase map. To monitor the HIFU therapy progress in real-time, sequential HIFU transmission, PA imaging, PA thermometry, and US imaging are implemented to display the dual-modal images and record the local temperature changes. Co-registered dual-modal images show structural and functional information and thus can guide the HIFU therapy for precise positioning and dosage control. Besides therapy, the multi-element HIFU transducer can also be used to acquire US images to precisely align the imaging coordinates with the HIFU coordinates. Phantom experiments validate the precise and dynamic steering capability of HIFU ablation. We also show that dual-modal imaging can guide HIFU in the designated region and monitor the temperature in biological tissue in real-time.

Experimental evaluation of high intensity focused ultrasound for fat reduction of ex vivo porcine adipose tissue.

The present study was stimulated by the continuous growth of commercially available high intensity focused ultrasound (HIFU) systems for fat reduction. Herein, HIFU was utilised for fat ablation using a single-element ultrasonic transducer operating in thermal mode. The custom-made concave transducer that operates at 1.1MHz was assessed on excised porcine adipose tissue for its ability to reduce fat. Ultrasonic sonications were executed on the adipose tissue utilising acoustical power between 14 and 75W and sonication time in the range of 1-10min. The mass of the adipose tissue sample was weighed afore and after ultrasonic sonications and the effect of the sonication on the mass change was recorded. Mass change was linearly dependent with either increasing acoustical power or sonication time and was in the range of 0.46-1.9g. High acoustical power of 62.5W for a sonication time of 1min and a power of 75W for a sonication time of 5min, respectively resulted in the formation of a lesion or possible cavitation on the piece of excised adipose tissue. The study demonstrated the efficacy of the proposed transducer in achieving a reduction of excised fat tissue. The present findings indicate the potential use of the transducer in a HIFU system indicated for the reduction of subcutaneous adipose tissue where increased values of acoustical power can result in increased amounts of fat reduction.

Characterization and Ex Vivo evaluation of an extracorporeal high-intensity focused ultrasound (HIFU) system.

BackgroundHigh‐intensity focused ultrasound (HIFU) has been in clinical use for a variety of solid tumors and cancers. Accurate and reliable calibration is in a great need for clinical applications. An extracorporeal clinical HIFU system applied for the investigational device exemption (IDE) to the Food and Drug Administration (FDA) so that evaluation of its characteristics, performance, and safety was required.MethodsThe acoustic pressure and power output was characterized by a fiber optic probe and a radiation force balance, respectively, with the electrical power up to 2000 W. An in situ acoustic energy was established as the clinical protocol at the electrical power up to 500 W. Temperature elevation inside the tissue sample was measured by a thermocouple array. Generated lesion volume at different in situ acoustic energies and pathological examination of the lesions was evaluated ex vivo.ResultsAcoustic pressure mapping showed the insignificant presence of side/grating lobes and pre‐ or post‐focal peaks (≤−12 dB). Although distorted acoustic pressure waveform was found in the free field, the nonlinearity was reduced significantly after the beam propagating through tissue samples (i.e., the second harmonic of −11.8 dB at 500 W). Temperature elevation was <10°C at a distance of 10 mm away from a 20‐mm target, which suggests the well‐controlled HIFU energy deposition and no damage to the surrounding tissue. An acoustic energy in the range of 750–1250 J resulted in discrete lesions with an interval space of 5 mm between the treatment spots. Histology confirmed that the lesions represented a region of permanently damaged cells by heat fixation, without causing cell lysis by either cavitation or boiling.ConclusionsOur characterization and ex vivo evaluation protocol met the IDE requirement. The in‐situ acoustic energy model will be used in clinical trials to deliver almost consistent energy to the various targets.

Design of a High-Power Multilevel Sinusoidal Signal and High-Frequency Excitation Module Based on FPGA for HIFU Systems

High-intensity focused ultrasound (HIFU) is a noninvasive therapy that uses focused ultrasound to treat a part of the tissue; high temperatures can damage tissues by heat. HIFU has many applications in the field of surgery and aesthetics and is used increasingly in everyday life. In this article, we discuss the mainboard design that controls the HIFU system with the ability to create a multistep sine wave compatible with many different applications. The signal used to trigger the transducer is a sinusoidal signal with a frequency adjustable from 0.1 to 3 MHz. In addition, the power supplied to the HIFU transducer is also controlled easily by the configuration parameters installed in the control circuit board. The proposed control and design method generates a voltage signal that doubles the supply voltage, thereby reducing the current on the MOSFET. The hardware design is optimized for a surface-mounted device-type MOSFET without the need for an external heat sink. In tests, we conducted a harmonious combination of two output signals to activate the same HIFU probe. The results showed that the energy transferred to the HIFU transducer increased by 1.5 times compared to a single channel. This means that the HIFU treatment time is reduced when using this method, with absolutely no changes in the system structure.

Fuzzy Logic Control-Based HIFU System Integrated with Photoacoustic Imaging Module for Ex Vivo Artificial Tumor Treatment

The objective of this study is to design a therapeutic method combining a portable high intensity focused ultrasound (HIFU) design which is suitable for the laboratory environment and a tailored integrated photo-acoustic imaging (PAI) system for monitoring thermal treatment. The electrical HIFU design is fabricated with changeable operating frequency and justified output power for resonating with different kinds of commercial transducers. The system’s control interface is built based on a touch screen to create a companionable interaction for users. The embedded fuzzy logic controller using the thermal input from the thermocouple sensor precisely drives the target temperature during HIFU exposure to achieve the expectedly coagulating results. The PAI system with 532-nm laser excitation is also integrated to define the affected region before and after HIFU treatment. The proposed fuzzy controller-integrated HIFU setup compatible with the PAI system is a feasible instrument in thermal therapy for ex vivo artificial tumors management.

The Use of High-Intensity Focused Ultrasound for the Rewarming of Cryopreserved Biological Material.

High-intensity focused ultrasound (HIFU) has been used in different medical applications in the last years. In this work, we present for the first time the use of HIFU in the field of cryopreservation, the preservation of biological material at low temperatures. An HIFU system has been designed with the objective of achieving a fast and uniform rewarming in organs, key to overcome the critical problem of devitrification. The finite-element simulations have been carried out using COMSOL Multiphysics software. An array of 26 ultrasonic transducers was simulated, achieving an HIFU focal area in the order of magnitude of a model organ (ovary). A parametric study of the warming rate and temperature gradients, as a function of the frequency and power of ultrasonic waves, was performed. An optimal value for these parameters was found. The results validate the appropriateness of the technique, which is of utmost importance for the future creation of cryopreserved organ banks.

HIFU for the treatment of difficult colorectal liver metastases with unsuitable indications for resection and radiofrequency ablation: A phase I clinical trial.

e16715 Background: Previous studies showed that high intensity focused ultrasound (HIFU) treatment could treat liver tumor and pancreatic cancer, with fewer serious adverse reactions.To evaluate the safety and efficacy of HIFU for patients with colorectal liver metastases(CRLM) that were contraindicated for resection and radiofrequency ablation. Methods: Patients between 20 to 80 years of age with 1-3 liver metastases from colorectal cancer were included. The primary colorectal lesions were thoroughly resected and any case with extra-hepatic metastasis was excluded. Ultrasound guided HIFU system was employed and target region ablation was achieved with repeated sonications from the deep to shallow regions of the tumor section by section. Results: Thirteen patients were enrolled. Pain was the most common adverse events(AEs) (n = 8), followed by fatigue (n = 7), increased aspartate aminotransferase (AST) (n = 7), increased alanine aminotransferase(ALT) (n = 5), and skin edema (n = 4). No grade≥3 AEs occurred.The majority of patients (76.9%) had a complete response and the remaining three patients achieved partial response. The objective response rate was 100% after the first HIFU treatment. Nine patients relapsed but most were isolated only in the liver (8/9). The median follow-up was 25 months. The 2-year progression-free survival (PFS) was 16.7%, and median PFS was 9 months. Notably, the 2-year overall survival (OS) was 77.8%, and median OS was 25 months. Conclusions: This study indicates that HIFU treatment is safe, has an excellent tumor response and long-termprognosis even when the foci in risky locations, and is probably a considerable option for patients who were unsuitable for other local treatments.

An MRI-Guided Ring High-Intensity Focused Ultrasound System for Noninvasive Breast Ablation.

High-intensity focused ultrasound (HIFU) has been used for noninvasive treatment of breast tumors, but the present magnetic resonance imaging (MRI)-guided HIFU (MRI-HIFU) systems encounter skin burn. In this study, a novel MRI-HIFU breast ablation system was developed to improve the above problem. The system consisted of the ring HIFU phased-array transducer, a commercial power amplifier, the mechanical positioner, and the graphical user interface control software. MRI thermometry was also established to monitor the temperature in the HIFU-treated tissue. Ablation of pork and the in vivo rabbit leg were carried out to validate the developed system. Results of fat-surrounding pork ablation showed that the ring HIFU system reached a safe margin of 3 mm without fat burn. Moreover, precision of the positioner moving the HIFU focal zone was within 6% error under MRI circumstances. The representative MRI temperature images show that the peak temperatures among the five ablations ranged between 66 °C and 91 °C, and their thermal doses were over 10000. The system could also ablate the biceps femoris of a rabbit without skin burn to form a lesion of 2.5 mm beneath the skin. With the HIFU dose of 315 W/10 s, the MRI temperature map revealed that the maximum temperature and the thermal dose were 60 °C and 3380, respectively. The MRI-guided ring HIFU system can ablate the target tissue near subcutaneous fat without fat burn. The system prototype is a promising tool for clinical implementation.

Magnetic nanoparticles-enhanced focused ultrasound heating: size effect, mechanism, and performance analysis

High intensity focused ultrasound (HIFU) has attracted great interest as a new energy-based technique to treat disordered tissues, such as tumors, through a hyperthermal mechanism using ultrasonic waves. However, long treatment times and collateral damage to healthy tissues due to high acoustic powers are still challenges for the clinical application of HIFU. One possible strategy to enhance the deposition efficiency of HIFU at the tumor site is to employ magnetic nanoparticles (MNPs) as ultrasound absorption agents for the thermal therapy. The objectives of the current study are threefold: (i) to examine the effects of MNP features, including the size and volume concentration, on the thermal mechanism of HIFU (ii) to investigate the performance of MNPs as they were exposed to ultrasound fields at different ranges of power and frequency (iii) and to study the interaction mechanism between MNPs and ultrasonic waves during the MNPs-enhanced HIFU process. To this end, we developed an ultrasound-guided HIFU system to conduct an in vitro experimental study on tissue phantoms containing MNPs of different sizes and volume concentrations. A set of HIFU parameters such as temperature rise and the rate of absorbed energy was monitored to examine the role of MNPs during the NPs-enhanced HIFU thermal procedure. Results showed that the MNPs significantly improved the thermal effect of HIFU by enhancing the rate of energy converted to heat and the temperature rise at the focal region. Moreover, it was demonstrated that the increase of MNP size and volume concentration greatly enhanced the HIFU parameters; the effects of MNPs were further improved by increasing the power and frequency of acoustic field.

Sonodynamic Therapy With Anticancer Micelles and High-Intensity Focused Ultrasound in Treatment of Canine Cancer.

Sonodynamic therapy (SDT) is a minimally invasive anticancer therapy involving a chemical sonosensitizer and high-intensity focused ultrasound (HIFU). SDT enables the reduction of drug dose and HIFU irradiation power compared to those of conventional monotherapies. In our previous study, mouse models of colon and pancreatic cancer were used to confirm the effectiveness of SDT vs. drug-only or HIFU-only therapy. To validate its usefulness, we performed a clinical trial of SDT using an anticancer micelle (NC-6300) and our HIFU system in four pet dogs with spontaneous tumors, including chondrosarcoma, osteosarcoma, hepatocellular cancer, and prostate cancer. The fact that no adverse events were observed, suggests the usefulness of SDT.

High-frequency (20-MHz) high-intensity focused ultrasound (HIFU) system for dermal intervention: Preclinical evaluation in skin equivalents.

High-intensity focused ultrasound (HIFU) for non-invasive treatment of a range of internal pathologies including cancers of major organs and cerebral pathologies is in exponential growth. Systems, however, operate at relatively low frequencies, in the range of 200-2000kHz as required for deep axial penetration of the body. HIFU utilizing frequencies in excess of 15MHz has so far not been explored, but presents an opportunity to extend the HIFU modality to target specific dermal lesions and small animal research. A new 20-MHz HIFU system (TOOsonix ONE-R) with narrow focus corresponding to the dermis was studied in acoustic skin equivalents, for example, in a tissue-mimicking gel and in bovine liver. HIFU lesion geometry, depth, and diameter were determined. The temperature increase in the focal point was measured as a function of acoustic power and the duration of HIFU exposure. The system produces highly reproducible ultrasound lesions with predictable and configurable depths of 1-2mm, thus corresponding to the depth of the human dermis. The lesion geometry was elongated triangular and sized 0.1-0.5mm, convergent to a focal point skin deep. Focal point temperature ranged between 40 and 90°C depending on the chosen setting. Observations were confirmed ex vivo in bovine liver and porcine muscle. Variation of acoustic power and duration of exposure produced linear effects in the range of the settings studied. Thus, effects could be adjusted within the temperature interval and spatial field relevant for clinical therapy and experimental intervention targeting the dermal layer of human skin. The tested 20-MHz HIFU system for dermal applications fulfilled key prerequisite of narrow-field HIFU dedicated to cutaneous applications regarding reproducibility, geometry, and small size of the applied ultrasound lesions. Controlled adjustment of acoustic lesions within the temperature range 40-90°C qualifies the system for a range of non-ablative and ablative applications in dermatological therapy.

Controllable Nucleation of Cavitation from Plasmonic Gold Nanoparticles for Enhancing High Intensity Focused Ultrasound Applications.

In this study, plasmonic gold nanoparticles were simultaneously exposed to pulsed near-infrared laser light and high intensity focused ultrasound (HIFU) for the controllable nucleation of cavitation in tissue-mimicking gel phantoms. This in vitro protocol was developed to demonstrate the feasibility of this approach, for both enhancement of imaging and therapeutic applications for cancer. The same apparatus can be used for both imaging and therapeutic applications by varying the exposure duration of the HIFU system. For short duration exposures (10 µs), broadband acoustic emissions were generated through the controlled nucleation of inertial cavitation around the gold nanoparticles. These emissions provide direct localization of nanoparticles. For future applications, these particles may be functionalized with molecular-targeting antibodies (e.g. anti-HER2 for breast cancer) and can provide precise localization of cancerous regions, complementing routine diagnostic ultrasound imaging. For continuous wave (CW) exposures, the cavitation activity was used to increase the localized heating from the HIFU exposures resulting in larger thermal damage in the gel phantoms. The acoustic emissions generated from inertial cavitation activity during these CW exposures was monitored using a passive cavitation detection (PCD) system to provide feedback of cavitation activity. Increased localized heating was only achieved through the unique combination of nanoparticles, laser light and HIFU. Further validation of this technique in pre-clinical models of cancer is necessary.

Controllable Nucleation of Cavitation from Plasmonic Gold Nanoparticles for Enhancing High Intensity Focused Ultrasound Applications

In this study, plasmonic gold nanoparticles were simultaneously exposed to pulsed near-infrared laser light and high intensity focused ultrasound (HIFU) for the controllable nucleation of cavitation in tissue-mimicking gel phantoms. This in vitro protocol was developed to demonstrate the feasibility of this approach, for both enhancement of imaging and therapeutic applications for cancer. The same apparatus can be used for both imaging and therapeutic applications by varying the exposure duration of the HIFU system. For short duration exposures (10 µs), broadband acoustic emissions were generated through the controlled nucleation of inertial cavitation around the gold nanoparticles. These emissions provide direct localization of nanoparticles. For future applications, these particles may be functionalized with molecular-targeting antibodies (e.g. anti-HER2 for breast cancer) and can provide precise localization of cancerous regions, complementing routine diagnostic ultrasound imaging. For continuous wave (CW) exposures, the cavitation activity was used to increase the localized heating from the HIFU exposures resulting in larger thermal damage in the gel phantoms. The acoustic emissions generated from inertial cavitation activity during these CW exposures was monitored using a passive cavitation detection (PCD) system to provide feedback of cavitation activity. Increased localized heating was only achieved through the unique combination of nanoparticles, laser light and HIFU. Further validation of this technique in pre-clinical models of cancer is necessary.

A High-Precision US-Guided Robot-Assisted HIFU Treatment System for Breast Cancer

Abstract Breast cancer is the most commonly diagnosed cancer in women. A strong treatment candidate is high-intensity focused ultrasound (HIFU), a non-invasive therapeutic method that has already demonstrated its promise. To improve the precision and lower the cost of HIFU treatment, our group has developed an ultrasound (US)-guided, five-degree-of-freedom (DOF), robot-assisted HIFU system. We constructed a fully functional prototype enabling easy three-dimensional (3D) US image reconstruction, target segmentation, treatment path generation, and automatic HIFU irradiation. The position was calibrated using a wire phantom and the coagulated area was assessed on heterogeneous tissue phantoms. Under the US guidance, the centroids of the HIFU-ablated area deviated by less than 2 mm from the planned treatment region. The overshoot around the planned region was well below the tolerance of clinical usage. Our system is considered to be sufficiently accurate for breast cancer treatment.

Value of diffusion-weighted imaging for monitoring tissue change during magnetic resonance-guided high-intensity focused ultrasound therapy in bone applications: an ex-vivo study

BackgroundMagnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) can palliate metastatic bone pain by periosteal neurolysis. We investigated the value of diffusion-weighted imaging (DWI) for monitoring soft tissue changes adjacent to bone during MR-guided HIFU. We evaluated the repeatability of the apparent diffusion coefficient (ADC) measurement, the temporal evolution of ADC change after sonication, and its relationship with thermal parameters.MethodsEx-vivo experiments in lamb legs (n = 8) were performed on a Sonalleve MR-guided HIFU system. Baseline proton resonance frequency shift (PRFS) thermometry evaluated the accuracy of temperature measurements and tissue cooling times after exposure. PRFS acquired during sonication (n = 27) was used to estimate thermal dose volume and temperature. After repeat baseline measurements, DWI was assessed longitudinally and relative ADC changes were derived for heated regions.ResultsBaseline PRFS was accurate to 1 °C and showed that tissues regained baseline temperatures within 5 min. Before sonication, coefficient of variation for repeat ADC measurements was 0.8%. After sonication, ADC increased in the muscle adjacent to the exposed periosteum, it was maximal 1–5 min after sonication, and it significantly differed between samples with persistent versus non-persistent ADC changes beyond 20 min. ADC increases at 20 min were stable for 2 h and correlated significantly with thermal parameters (ADC versus applied acoustic energy at 16–20 min: r = 0.77, p < 0.001). A 20% ADC increase resulted in clear macroscopic tissue damage.ConclusionsOur preliminary results suggest that DWI can detect intra-procedural changes in ex-vivo muscle overlying the periosteum. This could be useful for studying the safety and efficacy of clinical MR-guided HIFU bone treatments.