The safety and feasibility of extracorporeal high-intensity focused ultrasound (HIFU) for the treatment of liver and kidney tumours in a Western population

ROS-generating TiO2 nanoparticles for non-invasive sonodynamic therapy of cancer

The non-invasive photodynamic therapy has been limited to treat superficial tumours, primarily ascribed to poor tissue penetration of light as the energy source. Herein, we designed a long-circulating hydrophilized titanium dioxide nanoparticle (HTiO2 NP) that can be activated by ultrasound to generate reactive oxygen species (ROS). When administered systemically to mice, HTiO2 NPs effectively suppressed the growth of superficial tumours after ultrasound treatments. In tumour tissue, the levels of proinflammatory cytokines were elevated several fold and intense vascular damage was observed. Notably, ultrasound treatments with HTiO2 NPs also suppressed the growth of deeply located liver tumours at least 15-fold, compared to animals without ultrasound treatments. This study provides the first demonstration of the feasibility of using HTiO2 NPs as sensitizers for sonodynamic therapy in vivo.

An implantable compound-releasing capsule triggered on demand by ultrasound

Implantable devices have a large potential to improve human health, but they are often made of biofouling materials that necessitate special coatings, rely on electrical connections for external communication, and require a continuous power source. This paper demonstrates an alternative platform, which we call iTAG (implantable thermally actuated gel), where an implanted capsule can be wirelessly controlled by ultrasound to trigger the release of compounds. We constructed a millimeter-sized capsule containing a co-polymer gel (NiPAAm-co-AAm) that contracts above body temperature (i.e. at 45 °C) to release compounds through an opening. This gel-containing capsule is biocompatible and free of toxic electronic or battery components. An ultrasound hardware, with a focused ultrasound (FUS) transducer and a co-axial A-mode imaging transducer, was used to image the capsule (to monitor in real time its position, temperature, and effectiveness of dose delivery), as well as to trigger a rapid local rise in temperature, contraction of gel, and release of compounds in vitro and in vivo. The combination of this gel-based capsule and compact ultrasound hardware can serve as a platform for triggering local release of compounds, including potentially in deep tissue, to achieve tailored personalized therapy.

One-lung flooding reduces the ipsilateral diaphragm motion during mechanical ventilation

BACKGROUND

Diaphragm motion during spontaneous or mechanical respiration hinders image-guided percutaneous interventions of tumours in lung and upper abdomen. Motion-tracking methods can be applied but increase procedure complexity and procedure time. One-lung flooding (OLF) generates a suitable acoustic pathway to lung tumours and likely suppress diaphragm motion. The aim of this study was to quantify the effect of OLF on ipsilateral diaphragm motion during contralateral one-lung ventilation.

METHODS

To measure the diaphragm motion, M-mode ultrasonography of the right hemidiaphragm was performed during spontaneous breathing and mechanical ventilation, as well as after right-side lung flooding, in three pigs. Diaphragm motion was analysed using magnetic resonance images during left-side lung flooding and mechanical ventilation, in four pigs.

RESULTS

Double-lung ventilation increased the diaphragm movement in comparison with spontaneous breathing (17.8 ± 4.4 vs. 12.2 ± 3.4 mm, p = 0.014). Diaphragm movement on the flooded side during contralateral one-lung ventilation was significantly reduced compared to that during double-lung ventilation (3.9 ± 1.0 vs. 17.8 ± 4.4 mm, p = 0.041). By analysing the magnetic resonance images, the hemidiaphragm on the flooded side showed an average displacement of 4.2 mm, a maximum displacement of 15 mm close to the ventilated lung and no displacement at the lateral side.

CONCLUSION

OLF leads to a drastic reduction of diaphragm motion on the ipsilateral side which implies that targeting and motion compensation algorithms for interventions like high-intensity focused ultrasound ablation of intrapulmonary and hepatic lesions might not be required.

High-intensity focused ultrasound (HIFU) for pancreatic carcinoma: evaluation of feasibility, reduction of tumour volume and pain intensity

OBJECTIVES

Prognosis of patients with locally advanced pancreatic adenocarcinoma is extremely poor. They often suffer from cancer-related pain reducing their quality of life. This prospective observational study aimed to evaluate feasibility, local tumour response, and changes in quality of life and symptoms in Caucasian patients with locally advanced pancreatic cancer treated by ultrasound-guided high-intensity focused ultrasound (HIFU).

METHODS

Thirteen patients underwent HIFU, five with stage III, eight with stage IV UICC disease. Ten patients received simultaneous palliative chemotherapy. Postinterventional clinical assessment included evaluation of quality of life and symptom changes using standardized questionnaires. CT and MRI follow-up evaluated the local tumour response.

RESULTS

HIFU was successfully performed in all patients. Average tumour reduction was 34.2 % at 6 weeks and 63.9 % at 3 months. Complete or partial relief of cancer-related pain was achieved in 10 patients (77 %), five of whom required less analgesics for pain control. Quality of life was improved revealing increased global health status and alleviated symptoms. HIFU treatment was well tolerated. Eight patients experienced transient abdominal pain directly after HIFU.

CONCLUSIONS

HIFU ablation of pancreatic carcinoma is a feasible, safe and effective treatment with a crucial benefit in terms of reduction of tumour volume and pain intensity.

KEY POINTS

• US-guided HIFU is feasible and safe for patients with unresectable pancreatic cancer. • HIFU can considerably reduce tumour volume and cancer-related pain. • Patients treated with HIFU experienced significant and lasting reduction of pain intensity. • HIFU has a crucial clinical benefit for patients with pancreatic cancer.

A Multifunctional Theranostic Nanoagent for Dual-Mode Image-Guided HIFU/Chemo- Synergistic Cancer Therapy

High-intensity focused ultrasound (HIFU) is deemed to be a promising noninvasive therapeutic modality for cancers as well as non-neoplastic diseases. However, the accuracy of the technique in the diagnosis and treatment of tumors remains unsatisfactory. HIFU, when combined with multifunctional synergistic agents (SAs), has the potential to be of greater diagnostic and therapeutic efficacy. Here we describe a smart and multifunctional hollow mesoporous Prussian blue (HMPBs) theranostic nanoplatform, the hollow structure of which is capable of encapsulating doxorubicin (DOX) and perfluorohexane (HMPBs-DOX/PFH). In vitro and in vivo studies validated that HMPBs-DOX/PFH can be used as an amplifiable dual-mode imaging contrast agent, which can simultaneously enhance ultrasound (US) and photoacoustic (PA) imaging for guiding and monitoring tumor therapy. When exposed to HIFU, this versatile HMPBs-DOX/PFH agent could increase the cavitation effect and use lower HIFU intensity to achieve coagulative necrosis. Furthermore, it significantly accelerated the release of DOX thereby enhancing chemotherapeutic efficacy and avoiding systemic side effects of the drug. Such a novel theranostic nanoplatform is expected to integrate dual-mode guided imaging with greater therapeutic efficacy and fewer side effects and is very promising for the noninvasive synergistic tumor therapy.

Low-Intensity Focused Ultrasound Induces Reversal of Tumor-Induced T Cell Tolerance and Prevents Immune Escape

Immune responses against cancer cells are often hindered by immunosuppressive mechanisms that are developed in the tumor microenvironment. Induction of a hyporesponsive state in tumor Ag-specific T cells is one of the major events responsible for the inability of the adaptive immune system to mount an efficient antitumor response and frequently contributes to lessen the efficacy of immunotherapeutic approaches. Treatment of localized tumors by focused ultrasound (FUS) is a minimally invasive therapy that uses a range of input energy for in situ tumor ablation through the generation of thermal and cavitation effect. Using a murine B16 melanoma tumor model, we show that a variant of FUS that delivers a reduced level of energy at the focal point and generates mild mechanical and thermal stress in target cells has the ability to increase immunogenic presentation of tumor Ags, which results in reversal of tumor-induced T cell tolerance. Furthermore, we show that the combination of nonablative low-energy FUS with an ablative hypofractionated radiation therapy results in synergistic control of primary tumors and leads to a dramatic reduction in spontaneous pulmonary metastases while prolonging recurrence-free survival only in immunocompetent mice.

HIFU Tissue Ablation: Concept and Devices

High intensity focused ultrasound (HIFU) is rapidly gaining clinical acceptance as a technique capable of providing non-invasive heating and ablation for a wide range of applications. Usually requiring only a single session, treatments are often conducted as day case procedures, with the patient either fully conscious, lightly sedated or under light general anesthesia. HIFU scores over other thermal ablation techniques because of the lack of necessity for the transcutaneous insertion of probes into the target tissue. Sources placed either outside the body (for treatment of tumors or abnormalities of the liver, kidney, breast, uterus, pancreas brain and bone), or in the rectum (for treatment of the prostate), provide rapid heating of a target tissue volume, the highly focused nature of the field leaving tissue in the ultrasound propagation path relatively unaffected. Numerous extra-corporeal, transrectal and interstitial devices have been designed to optimize application-specific treatment delivery for the wide-ranging areas of application that are now being explored with HIFU. Their principle of operation is described here, and an overview of their design principles is given.

Ultrasound Transducers

Diagnostic medical ultrasound transducers have evolved through the years and have contributed significantly to improved patient care. This article discusses the history and types of transducers and the elements that have changed over time. There has been a sharp transition from natural to human-made elements and from one to many in a single transducer. Ergonomics also now plays a role in transducer design and will continue to do so; the grip, weight, and size of transducers are in the forefront of design considerations. The evolution of transducers has changed not only how well we visualize anatomy and what anatomy we see but also how the patient’s care is managed. Different, new, and emerging technologies certainly will continue to be identified within the sonography community.

High-Intensity Focused Ultrasound: Current Status for Image-Guided Therapy

Image-guided high-intensity focused ultrasound (HIFU) is an innovative therapeutic technology, permitting extracorporeal or endocavitary delivery of targeted thermal ablation while minimizing injury to the surrounding structures. While ultrasound-guided HIFU was the original image-guided system, MR-guided HIFU has many inherent advantages, including superior depiction of anatomic detail and superb real-time thermometry during thermoablation sessions, and it has recently demonstrated promising results in the treatment of both benign and malignant tumors. HIFU has been employed in the management of prostate cancer, hepatocellular carcinoma, uterine leiomyomas, and breast tumors, and has been associated with success in limited studies for palliative pain management in pancreatic cancer and bone tumors. Nonthermal HIFU bioeffects, including immune system modulation and targeted drug/gene therapy, are currently being explored in the preclinical realm, with an emphasis on leveraging these therapeutic effects in the care of the oncology patient. Although still in its early stages, the wide spectrum of therapeutic capabilities of HIFU offers great potential in the field of image-guided oncologic therapy.

An improved optical flow tracking technique for real-time MR-guided beam therapies in moving organs

Magnetic resonance (MR) guided high intensity focused ultrasound and external beam radiotherapy interventions, which we shall refer to as beam therapies/interventions, are promising techniques for the non-invasive ablation of tumours in abdominal organs. However, therapeutic energy delivery in these areas becomes challenging due to the continuous displacement of the organs with respiration. Previous studies have addressed this problem by coupling high-framerate MR-imaging with a tracking technique based on the algorithm proposed by Horn and Schunck (H and S), which was chosen due to its fast convergence rate and highly parallelisable numerical scheme. Such characteristics were shown to be indispensable for the real-time guidance of beam therapies. In its original form, however, the algorithm is sensitive to local grey-level intensity variations not attributed to motion such as those that occur, for example, in the proximity of pulsating arteries.In this study, an improved motion estimation strategy which reduces the impact of such effects is proposed. Displacements are estimated through the minimisation of a variation of the H and S functional for which the quadratic data fidelity term was replaced with a term based on the linear L(1)norm, resulting in what we have called an L(2)-L(1) functional.The proposed method was tested in the livers and kidneys of two healthy volunteers under free-breathing conditions, on a data set comprising 3000 images equally divided between the volunteers. The results show that, compared to the existing approaches, our method demonstrates a greater robustness to local grey-level intensity variations introduced by arterial pulsations. Additionally, the computational time required by our implementation make it compatible with the work-flow of real-time MR-guided beam interventions.To the best of our knowledge this study was the first to analyse the behaviour of an L(1)-based optical flow functional in an applicative context: real-time MR-guidance of beam therapies in moving organs.

A review of high intensity focused ultrasound in relation to the treatment of renal tumours and other malignancies

For 60 years, high-intensity focused ultrasound (HIFU) has been the subject of interest for medical research. HIFU causes tissue necrosis in a very well defined area, at a variable distance from the transducer, through heating or cavitation. Over the past two decades, the use of high-intensity focused ultrasound has been investigated in many clinical settings. This review summarises recent advances made in the field of renal cancer in particular, and gives an overview on the use of the extracorporeal machines in the treatment of other malignant tumours.

Respiration based steering for high intensity focused ultrasound liver ablation

PURPOSE

Respiratory motion makes hepatic ablation using high intensity focused ultrasound (HIFO) challenging. Previous HIFU liver treatment had required apnea induced during general anesthesia. We describe and test a system that allows treatment of the liver in the presence of breathing motion.

METHODS

Mapping a signal from an external respiratory bellow to treatment locations within the liver allows the ultrasound transducer to be steered in real time to the target location. Using a moving phantom, three metrics were used to compare static, steered, and unsteered sonications: the area of sonications once a temperature rise of 15°C was achieved, the energy deposition required to reach that temperature, and the average rate of temperature rise during the first 10 s of sonication. Steered HIFU in vivo ablations of the porcine liver were also performed and compared to breath-hold ablations.

RESULTS

For the last phantom metric, all groups were found to be statistically significantly different (P ≤ 0.003). However, in the other two metrics, the static and unsteered sonications were not statistically different (P > 0.9999). Steered in vivo HIFU ablations were not statistically significantly different from ablations during breath-holding.

CONCLUSIONS

A system for performing HIFU steering during ablation of the liver with breathing motion is presented and shown to achieve results equivalent to ablation performed with breath-holding.

Bubbles with shock waves and ultrasound: a review

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed 'acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics-bubble interactions, with a focus on shock wave-bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the 'resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave-bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead.

Molecular Imaging-Guided Interventional Hyperthermia in Treatment of Breast Cancer

Breast cancer is the most frequent malignancy in women worldwide. Although it is commonly treated via chemotherapy, responses vary among its subtypes, some of which are relatively insensitive to chemotherapeutic drugs. Recent studies have shown that hyperthermia can enhance the effects of chemotherapy in patients with refractory breast cancer or without surgical indications. Recent advances in molecular imaging may not only improve early diagnosis but may also facilitate the development and response assessment of targeted therapies. Combining advanced techniques such as molecular imaging and hyperthermia-integrated chemotherapy should open new avenues for effective management of breast cancer.

An Ultrasound Image-Based Dynamic Fusion Modeling Method for Predicting the Quantitative Impact of In Vivo Liver Motion on Intraoperative HIFU Therapies: Investigations in a Porcine Model

Organ motion is a key component in the treatment of abdominal tumors by High Intensity Focused Ultrasound (HIFU), since it may influence the safety, efficacy and treatment time. Here we report the development in a porcine model of an Ultrasound (US) image-based dynamic fusion modeling method for predicting the effect of in vivo motion on intraoperative HIFU treatments performed in the liver in conjunction with surgery. A speckle tracking method was used on US images to quantify in vivo liver motions occurring intraoperatively during breathing and apnea. A fusion modeling of HIFU treatments was implemented by merging dynamic in vivo motion data in a numerical modeling of HIFU treatments. Two HIFU strategies were studied: a spherical focusing delivering 49 juxtapositions of 5-second HIFU exposures and a toroidal focusing using 1 single 40-second HIFU exposure. Liver motions during breathing were spatially homogenous and could be approximated to a rigid motion mainly encountered in the cranial-caudal direction (f = 0.20 Hz, magnitude > 13 mm). Elastic liver motions due to cardiovascular activity, although negligible, were detectable near millimeter-wide sus-hepatic veins (f = 0.96 Hz, magnitude < 1 mm). The fusion modeling quantified the deleterious effects of respiratory motions on the size and homogeneity of a standard "cigar-shaped" millimetric lesion usually predicted after a 5-second single spherical HIFU exposure in stationary tissues (Dice Similarity Coefficient: DSC < 45%). This method assessed the ability to enlarge HIFU ablations during respiration, either by juxtaposing "cigar-shaped" lesions with spherical HIFU exposures, or by generating one large single lesion with toroidal HIFU exposures (DSC > 75%). Fusion modeling predictions were preliminarily validated in vivo and showed the potential of using a long-duration toroidal HIFU exposure to accelerate the ablation process during breathing (from 0.5 to 6 cm3 · min(-1)). To improve HIFU treatment control, dynamic fusion modeling may be interesting for assessing numerically focusing strategies and motion compensation techniques in more realistic conditions.

Nanoscale theranostics for physical stimulus-responsive cancer therapies

Physical stimulus-responsive therapies often employing multifunctional theranostic agents responsive to external physical stimuli such as light, magnetic field, ultra-sound, radiofrequency, X-ray, etc., have been widely explored as novel cancer therapy strategies, showing encouraging results in many pre-clinical animal experiments. Unlike conventional cancer chemotherapy which often accompanies with severe toxic side effects, physical stimulus-responsive agents usually are non-toxic by themselves and would destruct cancer cells only under specific external stimuli, and thus could offer greatly reduced toxicity and enhanced treatment specificity. In addition, physical stimulus-responsive therapies can also be combined with other traditional therapeutics to achieve synergistic anti-tumor effects via a variety of mechanisms. In this review, we will summarize the latest progress in the development of physical stimulus-responsive therapies, and discuss the important roles of nanoscale theranostic agents involved in those non-conventional therapeutic strategies.

Using the Promise of Sonodynamic Therapy in the Clinical Setting against Disseminated Cancers

Sonodynamic therapy (SDT) is a form of ultrasound therapy in which specialized chemotherapeutic agents known as sonosensitizers are administered to increase the efficacy of ultrasound-mediated preferential damage of neoplastic cells. Multiple in vitro and in vivo studies have indicated that SDT has the ability to exhibit profound physical and chemical changes on cellular structure. As supportive as the data have been, assessment of this method at the clinical level has been limited to only solid tumors. Although SDT has shown efficacy against multiple adherent neoplastic cell lines, it has also shown particular promise with leukemia-derived cell lines. Potential procedures to administer SDT to leukemia patients are heating the appendages as ultrasound is applied to these areas (Heat and Treat), using an ultrasound probe to scan the body for malignant growths (Target and Destroy), and extracorporeal blood sonication (EBS) through dialysis. Each method offers a unique set of benefits and concerns that will need to be evaluated in preclinical mammalian models of malignancy before clinical examination can be considered.

A clinically feasible treatment protocol for magnetic resonance-guided high-intensity focused ultrasound ablation in the liver

OBJECTIVES

Magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) allows for noninvasive thermal ablation under real-time temperature imaging guidance. The purpose of this study was to assess the feasibility and safety of MR-HIFU ablation of liver tissue in a clinically acceptable setting. The experimental protocol was designed with a clinical ablation procedure of a small malignant tumor in mind; the procedures were performed within a clinically feasible time frame and care was taken to avoid adverse events. The main outcome was the size and quality of the ablated liver tissue volume on imaging and histology. Secondary outcomes were safety and treatment time.

MATERIALS AND METHODS

Healthy pigs (n = 10) under general anesthesia were positioned on a clinical MR-HIFU system, which consisted of an HIFU tabletop with a skin cooling system integrated into a 1.5-T MR scanner. A liver tissue volume was ablated with multiple sonication cells (4 × 4 × 10 mm, 450 W). Both MR thermometry and sonication were respiratory-gated using a pencil beam navigator on the diaphragm. Contrast-enhanced T1-weighted (CE-T1w) imaging was performed for treatment evaluation. Targeted total treatment time was 3 hours. The abdominal wall, liver, and adjacent organs were inspected postmortem for thermal damage. Ablated tissue volumes were processed for cell viability staining. The ablated volumes were analyzed using MR imaging, MR thermometry, and cell viability histology.

RESULTS

Eleven volume ablations were performed in 10 animals, resulting in a median nonperfused volume (NPV) on CE-T1w imaging of 1.6 mL (interquartile range [IQR], 0.8-2.3; range, 0.7-3.0). Cell viability histology showed a damaged volume of 1.5 mL (IQR, 1.1-1.8; range, 0.7-2.3). The NPV was confluent in 10 of the 11 cases. The ablated tissue volume on cell viability histology was confluent in all 9 available cases. In all cases, there was a good correspondence between the aspects of the NPV on CE-T1w and the ablated volume on cell viability histology. Two treatment-related adverse events occurred: 1 animal had a 7-mm skin burn and 1 animal showed evidence of thermal damage on the surface of the spleen. Median ablation time was 108 minutes (IQR, 101-120; range, 96-181 minutes) and median total treatment time was 180 minutes (IQR, 165-224; 130-250 minutes).

CONCLUSIONS

Our results demonstrate the feasibility and safety of MR-HIFU ablation of liver tissue volumes. The imaging data and cell viability histology show, for the first time, that confluent ablation volumes can be achieved with motion-gated ablation and MR guidance. These results were obtained using a readily available MR-HIFU system with only minor modifications, within a clinically acceptable time frame, and with only minor adverse events. This shows that this technique is sufficiently reliable and safe to initiate a clinical trial.

High intensity focused ultrasound (HIFU) focal spot localization using harmonic motion imaging (HMI)

Several ultrasound-based imaging modalities have been proposed for image guidance and monitoring of high-intensity focused ultrasound (HIFU) treatment. However, accurate localization and characterization of the effective region of treatment (focal spot) remain important obstacles in the clinical implementation of HIFU ablation. Harmonic motion imaging for focused ultrasound (HMIFU) is a HIFU monitoring technique that utilizes radiation-force-induced localized oscillatory displacement. HMIFU has been shown to correctly identify the formation and extent of HIFU thermal ablation lesions. However a significant problem remains in identifying the location of the HIFU focus, which is necessary for treatment planning. In this study, the induced displacement was employed to localize the HIFU focal spot inside the tissue prior to treatment. Feasibility was shown with two separate systems. The 1D HMIFU system consisted of a HIFU transducer emitting an amplitude-modulated HIFU beam for mechanical excitation and a confocal single-element, pulse-echo transducer for simultaneous RF acquisition. The 2D HIFU system consists of a HIFU phased array, and a co-axial imaging phased array for simultaneous imaging. Initial feasibility was first performed on tissue-mimicking gelatin phantoms and the focal zone was defined as the region corresponding to the -3dB full width at half maximum of the HMI displacement. Using the same parameters, in vitro experiments were performed in canine liver specimens to compare the defined focal zone with the lesion. In vitro measurements showed good agreement between the HMI predicted focal zone and the induced HIFU lesion location. HMIFU was experimentally shown to be capable of predicting and tracking the focal region in both phantoms and in vitro tissues. The accuracy of focal spot localization was evaluated by comparing with the lesion location in post-ablative tissues, with a R(2) = 0.821 at p < 0.002 in the 2D HMI system. We demonstrated the feasibility of using this HMI-based technique to localize the HIFU focal spot without inducing thermal changes during the planning phase. The focal spot localization method has also been applied on ex vivo human breast tissue ablation and can be fully integrated into any HMI system for planning purposes.

The Value of Proton Magnetic Resonance Spectroscopy in High-Intensity Focused Ultrasound Treatment of Experimental Liver Cancer

High-intensity focused ultrasound (HIFU) is a rapidly developing, non-invasive technique for local treatment of solid tumors that produce coagulative tumor necrosis. This study is aimed to investigate the feasibility of proton magnetic resonance spectroscopy (MRS) on early assessing treatment of HIFU ablation in rabbit with VX2 liver tumor. HIFU ablation was performed on normal liver and VX2 tumor in rabbit, and MRS was performed on normal liver and VX2 tumor before and 2 days after 100% HIFU ablation or 80% ablation in tumor volume. Choline (Cho) and choline/lipid (Cho/Lip) ratios between complete and partial HIFU ablation of tumor were compared. Tissues were harvested and sequentially sliced to confirm the necrosis. In normal liver, the Cho value liver was not obviously changed after HIFU (P > .05), but the Cho/Lip ratio was decreased (P < .05). Cho in liver VX2 tumor was much higher than that in normal liver (P < .001). Cho and Cho/Lip ratio were significantly decreased in tumor after complete HIFU ablation and partial HIFU ablation, and the Cho value in complete HIFU tumor ablation did not show any difference from that in normal liver after HIFU (P > .05); however, the Cho value in partial ablation was still higher than that in normal liver before or in tumor after complete HIFU treatment due to the residual part of tumors, and Cho/Lip ratio is lower than that in complete HIFU treatment (P < .001). The changes in MRS parameters were consistent with histopathologic changes of the tumor tissues after treatment. MRS could differentiate the complete tumor necrosis from residual tumor tissue, when combined with magnetic resonance imaging. We conclude that MRS may be applied as an important, non-invasive biomarker for monitoring the thoroughness of HIFU ablation.

Modeling and predicting tissue movement and deformation for high intensity focused ultrasound therapy

Purpose

In ultrasound-guided High Intensity Focused Ultrasound (HIFU) therapy, the target tissue (such as a tumor) often moves and/or deforms in response to an external force. This problem creates difficulties in treating patients and can lead to the destruction of normal tissue. In order to solve this problem, we present a novel method to model and predict the movement and deformation of the target tissue during ultrasound-guided HIFU therapy.

Methods

Our method computationally predicts the position of the target tissue under external force. This prediction allows appropriate adjustments in the focal region during the application of HIFU so that the treatment head is kept aligned with the diseased tissue through the course of therapy. To accomplish this goal, we utilize the cow tissue as the experimental target tissue to collect spatial sequences of ultrasound images using the HIFU equipment. A Geodesic Localized Chan-Vese (GLCV) model is developed to segment the target tissue images. A 3D target tissue model is built based on the segmented results. A versatile particle framework is constructed based on Smoothed Particle Hydrodynamics (SPH) to model the movement and deformation of the target tissue. Further, an iterative parameter estimation algorithm is utilized to determine the essential parameters of the versatile particle framework. Finally, the versatile particle framework with the determined parameters is used to estimate the movement and deformation of the target tissue.

Results

To validate our method, we compare the predicted contours with the ground truth contours. We found that the lowest, highest and average Dice Similarity Coefficient (DSC) values between predicted and ground truth contours were, respectively, 0.9615, 0.9770 and 0.9697.

Conclusion

Our experimental result indicates that the proposed method can effectively predict the dynamic contours of the moving and deforming tissue during ultrasound-guided HIFU therapy.

New approach for local cancer treatment using pulsed high-intensity focused ultrasound and phase-change nanodroplets

PURPOSE

The aim of this study was to investigate the combination effects of pulsed HIFU (pHIFU) and phase-change nanodroplets (PCND) as a sensitizer on efficient induction of mechanical effects of pHIFU and chemically enhanced tumor growth inhibition for local anti-tumor therapy.

METHOD

Changes in growth of colon 26 tumor tissue inoculated onto CDF1 mice were evaluated by the following treatments. (1) pHIFU exposure (1.1 MHz, 3.2 kW/cm(2), 300 cycles, and 50 ms interval) for 60 s, (2) PCND (1 %) injection, (3) adriamycin (4 mg/kg) injection, (4) pHIFU exposure after PCND injection, and (5) pHIFU exposure after PCND + adriamycin injection simultaneously.

RESULTS

Significant changes in tumor growth were observed in the group with combination of pHIFU and PCND, although single therapy did not show any significant difference. PCND enhanced mechanical tissue fractionation by pHIFU, which was detectable by Real-time tissue elastography. Moreover, the combination of pHIFU and PCND + Adriamycin suppressed the tumor growth for 2 weeks, and 3 of 4 mice did not show any sign of regrowth during the 30-day observation.

CONCLUSION

The combination of pHIFU and PCND exerted a significant anti-tumor effect and may be a new candidate for treatment of locally advanced cancer.

Quality of MR thermometry during palliative MR-guided high-intensity focused ultrasound (MR-HIFU) treatment of bone metastases

BACKGROUND

Magnetic resonance (MR)-guided high-intensity focused ultrasound has emerged as a clinical option for palliative treatment of painful bone metastases, with MR thermometry (MRT) used for treatment monitoring. In this study, the general image quality of the MRT was assessed in terms of signal-to-noise ratio (SNR) and apparent temperature variation. Also, MRT artifacts were scored for their occurrence and hampering of the treatment monitoring.

METHODS

Analyses were performed on 224 MRT datasets retrieved from 13 treatments. The SNR was measured per voxel over time in magnitude images, in the target lesion and surrounding muscle, and was averaged per treatment. The standard deviation over time of the measured temperature per voxel in MRT images, in the muscle outside the heated region, was defined as the apparent temperature variation and was averaged per treatment. The scored MRT artifacts originated from the following sources: respiratory and non-respiratory time-varying field inhomogeneities, arterial ghosting, and patient motion by muscle contraction and by gross body movement. Distinction was made between lesion type, location, and procedural sedation and analgesic (PSA).

RESULTS

The average SNR was highest in and around osteolytic lesions (21 in lesions, 27 in surrounding muscle, n = 4) and lowest in the upper body (9 in lesions, 16 in surrounding muscle, n = 4). The average apparent temperature variation was lowest in osteolytic lesions (1.2°C, n = 4) and the highest in the upper body (1.7°C, n = 4). Respiratory time-varying field inhomogeneity MRT artifacts occurred in 85% of the datasets and hampered treatment monitoring in 81%. Non-respiratory time-varying field inhomogeneities and arterial ghosting MRT artifacts were most frequent (94% and 95%) but occurred only locally. Patient motion artifacts were highly variable and occurred less in treatments of osteolytic lesions and using propofol and esketamine as PSA.

CONCLUSIONS

In this study, the general image quality of MRT was observed to be higher in osteolytic lesions and lower in the upper body. Respiratory time-varying field inhomogeneity was the most prominent MRT artifact. Patient motion occurrence varied between treatments and seemed to be related to lesion type and type of PSA. Clinicians should be aware of these observed characteristics when interpreting MRT images.

Volume reduction of benign thyroid nodules 3 months after a single treatment with high-intensity focused ultrasound (HIFU)

Background

High-intensity focused ultrasound (HIFU) is a promising, non-invasive technique in treating benign thyroid nodules (TNs). The aim of this study was to evaluate the efficacy of HIFU to induce clinically meaningful shrinkage in benign predominantly solid TNs and to identify variables that influence or predict the magnitude of TN volume reduction.

Methods

For each of ten subjects, HIFU treatment was conducted on a single nodule. Nodular volume was measured sonographically at baseline and at 3 months post-procedure. Nodular function and early treatment assessment was done scintigraphically.

Results

Median nodular volume reduction was 0.7 ml absolute and 48.8% relative to pre-interventional size (p < 0.05). Absolute shrinkage was negatively correlated with the average treatment depth (τ = −0.61, p < 0.05). Absolute nodular volume was positively correlated with the scintigraphic nodular uptake reduction (τ = 0.66, p < 0.05).

Conclusions

HIFU treatment of benign predominantly solid TNs appears to be safe and effective for inducing nodular shrinkage. Despite potential for improvement, a single treatment session with HIFU is already a viable alternative to more standard methods. The feasibility of multiple HIFU treatments requires further investigation. Due to the small sample size, the findings of this analysis need conformation by larger studies.

Histotripsy methods in mechanical disintegration of tissue: towards clinical applications

In high intensity focused ultrasound (HIFU) therapy, an ultrasound beam is focused within the body to locally affect the targeted site without damaging intervening tissues. The most common HIFU regime is thermal ablation. Recently there has been increasing interest in generating purely mechanical lesions in tissue (histotripsy). This paper provides an overview of several studies on the development of histotripsy methods toward clinical applications. Two histotripsy approaches and examples of their applications are presented. In one approach, sequences of high-amplitude, short (microsecond-long), focused ultrasound pulses periodically produce dense, energetic bubble clouds that mechanically disintegrate tissue. In an alternative approach, longer (millisecond-long) pulses with shock fronts generate boiling bubbles and the interaction of shock fronts with the resulting vapour cavity causes tissue disintegration. Recent preclinical studies on histotripsy are reviewed for treating benign prostatic hyperplasia (BPH), liver and kidney tumours, kidney stone fragmentation, enhancing anti-tumour immune response, and tissue decellularisation for regenerative medicine applications. Potential clinical advantages of the histotripsy methods are discussed. Histotripsy methods can be used to mechanically ablate a wide variety of tissues, whilst selectivity sparing structures such as large vessels. Both ultrasound and MR imaging can be used for targeting and monitoring the treatment in real time. Although the two approaches utilise different mechanisms for tissue disintegration, both have many of the same advantages and offer a promising alternative method of non-invasive surgery.

Ultrasound-guided therapeutic focused ultrasound: current status and future directions

This paper reviews ultrasound imaging methods for the guidance of therapeutic focused ultrasound (USgFUS), with emphasis on real-time preclinical methods. Guidance is interpreted in the broadest sense to include pretreatment planning, siting of the FUS focus, real-time monitoring of FUS-tissue interactions, and real-time control of exposure and damage assessment. The paper begins with an overview and brief historical background of the early methods used for monitoring FUS-tissue interactions. Current imaging methods are described, and discussed in terms of sensitivity and specificity of the localisation of the FUS effects in both therapeutic and sub-therapeutic modes. Thermal and non-thermal effects are considered. These include cavitation-enhanced heating, tissue water boiling and cavitation. Where appropriate, USgFUS methods are compared with similar methods implemented using other guidance modalities, e.g. magnetic resonance imaging. Conclusions are drawn regarding the clinical potential of the various guidance methods, and the feasibility and current status of real-time implementation.

Quality assurance for clinical high intensity focused ultrasound fields

As the use of HIFU in the clinic becomes more widespread there is an ever increasing need to standardise quality assurance protocols, an important step in facilitating the wider acceptance of HIFU as a therapeutic modality. This article reviews pertinent aspects of HIFU treatment delivery, encompassing the closely related aspects of quality assurance and calibration. Particular attention is given to the description and characterisation of relevant acoustic field parameters and the measurement of acoustic power. Where appropriate, recommendations are made.

First clinical experience of intra-operative high intensity focused ultrasound in patients with colorectal liver metastases: a phase I-IIa study

BACKGROUND

Surgery is the only curative treatment in patients with colorectal liver metastases (CLM), but only 10-20% of patients are eligible. High Intensity Focused Ultrasound (HIFU) technology is of proven value in several indications, notably prostate cancer. Its intra-operative use in patients with CLM has not previously been studied. Preclinical work suggested the safety and feasibility of a new HIFU device capable of ablating volumes of up to 2cm x 2cm in a few seconds.

METHODS

We conducted a prospective, single-centre phase I-IIa trial. HIFU was delivered immediately before scheduled hepatectomy. To demonstrate the safety and efficacy of rapidly ablating liver parenchyma, ablations were performed on healthy tissue within the areas scheduled for resection.

RESULTS

In total, 30 ablations were carried out in 15 patients. These ablations were all generated within 40 seconds and on average measured 27.5mm x 21.0mm. The phase I study (n = 6) showed that use of the HIFU device was feasible and safe and did not damage neighbouring tissue. The phase IIa study (n = 9) showed both that the area of ablation could be precisely targeted on a previously implanted metallic mark (used to represent a major anatomical structure) and that ablations could be undertaken deliberately to avoid such a mark. Ablations were achieved with a precision of 1-2 mm.

CONCLUSION

HIFU was feasible, safe and effective in ablating areas of liver scheduled for resection. The next stage is a phase IIb study which will attempt ablation of small metastases with a 5 mm margin, again prior to planned resection.

TRIAL REGISTRATION

ClinicalTrials.govNCT01489787.

First clinical experience of intra-operative high intensity focused ultrasound in patients with colorectal liver metastases: a phase I-IIa study

Background

Surgery is the only curative treatment in patients with colorectal liver metastases (CLM), but only 10–20% of patients are eligible. High Intensity Focused Ultrasound (HIFU) technology is of proven value in several indications, notably prostate cancer. Its intra-operative use in patients with CLM has not previously been studied. Preclinical work suggested the safety and feasibility of a new HIFU device capable of ablating volumes of up to 2cm x 2cm in a few seconds.

Methods

We conducted a prospective, single-centre phase I-IIa trial. HIFU was delivered immediately before scheduled hepatectomy. To demonstrate the safety and efficacy of rapidly ablating liver parenchyma, ablations were performed on healthy tissue within the areas scheduled for resection.

Results

In total, 30 ablations were carried out in 15 patients. These ablations were all generated within 40 seconds and on average measured 27.5mm x 21.0mm. The phase I study (n = 6) showed that use of the HIFU device was feasible and safe and did not damage neighbouring tissue. The phase IIa study (n = 9) showed both that the area of ablation could be precisely targeted on a previously implanted metallic mark (used to represent a major anatomical structure) and that ablations could be undertaken deliberately to avoid such a mark. Ablations were achieved with a precision of 1–2 mm.

Conclusion

HIFU was feasible, safe and effective in ablating areas of liver scheduled for resection. The next stage is a phase IIb study which will attempt ablation of small metastases with a 5 mm margin, again prior to planned resection.

Trial Registration

ClinicalTrials.govNCT01489787

Random calibration for accelerating MR-ARFI guided ultrasonic focusing in transcranial therapy

Transcranial focused ultrasound is a promising therapeutic modality. It consists of placing transducers around the skull and emitting shaped ultrasound waves that propagate through the skull and then concentrate on one particular location within the brain. However, the skull bone is known to distort the ultrasound beam. In order to compensate for such distortions, a number of techniques have been proposed recently, for instance using Magnetic Resonance Imaging feedback. In order to fully determine the focusing distortion due to the skull, such methods usually require as many calibration signals as transducers, resulting in a lengthy calibration process. In this paper, we investigate how the number of calibration sequences can be significantly reduced, based on random measurements and optimization techniques. Experimental data with six human skulls demonstrate that the number of measurements can be up to three times lower than with the standard methods, while restoring 90% of the focusing efficiency.

Au nanoparticle-coated, PLGA-based hybrid capsules for combined ultrasound imaging and HIFU therapy

A simple method to prepare AuNPs@PDA/PLGA hybrid capsules for combined ultrasound imaging and HIFU therapy was presented.

Robotized High Intensity Focused Ultrasound (HIFU) system for treatment of mobile organs using motion tracking by ultrasound imaging: An in vitro study

High Intensity Focused Ultrasound (HIFU) therapy is a very promising method for ablation of solid tumors. However, intra-abdominal organ motion, principally due to breathing, is a substantial limitation that results in incorrect tumor targeting. The objective of this work is to develop an all-in-one robotized HIFU system that can compensate motion in real-time during HIFU treatment. To this end, an ultrasound visual servoing scheme working at 20 Hz was designed. It relies on the motion estimation by using a fast ultrasonic speckle tracking algorithm and on the use of an interleaved imaging/HIFU sonication sequence for avoiding ultrasonic wave interferences. The robotized HIFU system was tested on a sample of chicken breast undergoing a vertical sinusoidal motion at 0.25 Hz. Sonications with and without motion compensation were performed in order to assess the effect of motion compensation on thermal lesions induced by HIFU. Motion was reduced by more than 80% thanks to this ultrasonic visual servoing system.

Effective strategy of the combination of high-intensity focused ultrasound and transarterial chemoembolization for improving outcome of unresectable and metastatic hepatoblastoma: a retrospective cohort study

The combination of high-intensity focused ultrasound (HIFU) and transarterial chemoembolization (TACE) has been experimentally performed in a variety of malignant tumors, and its validity has not yet been evaluated for hepatoblastoma (HB). We evaluated the disease-response rate, resection rate, and toxicity in children with unresectable or metastatic HB (stage III and stage IV HB) after sequential treatment with TACE plus HIFU in a controlled clinical trial. The 35 patients with unresectable or metastatic HB were nonrandomly assigned to HIFU ablation (n = 12) or C5V chemotherapy (n = 23). The rates of complete resection, tumor response, and treatment toxicity were evaluated for both regimens. Nine patients who received C5V and 10 patients who received TACE plus HIFU became operable (P = .02). The 3-year event-free survival and overall survival rates were 43.03% and 56.68% in the C5V group and 38.57% and 57.86% in the TACE plus HIFU group, respectively. Acute grade 3 or 4 adverse events, including neutropenia, thrombocytopenia, and anemia, were more frequent in patients treated with C5V therapy than in patients receiving TACE plus HIFU. HIFU ablation achieved a higher rate of complete resection and a lower rate of severe complications compared with C5V treatment in children with advanced HB (Chinese Clinical Trials Registry No. ChiCTR-PRCH-08000182).

An in-vivo investigation of the therapeutic effect of pulsed focused ultrasound on tumor growth

PURPOSE

High-intensity focused ultrasound (HIFU) has been investigated for ablative therapy and drug enhancement for gene therapy and chemotherapy. The aim of this work is to explore the feasibility of pulsed focused ultrasound (pFUS) for cancer therapy using an in vivo animal model.

METHODS

A clinical HIFU system (InSightec ExAblate 2000) integrated with a 1.5 T GE MR scanner was used in this study. Suitable ultrasound parameters were investigated to perform nonthermal sonications, keeping the temperature elevation below 4 °C as measured in real time by MR thermometry. LNCaP cells (10(6)) were injected into the prostates of male mice (n = 20). When tumors reached a diameter of about 5 mm in 3D as measured on magnetic resonance imaging (MRI), the tumor-bearing mice (n = 8) were treated with pFUS (1 MHz frequency; 25 W acoustic power; 0.1 duty cycle; 60 s duration). A total of 4-6 sonications were used to cover the entire tumor volume under MR image guidance. The animals were allowed to survive for 4 weeks after the treatment. The tumor growth was monitored on high-resolution (0.2 mm) MRI weekly post treatment and was compared with that of the control group (n = 12).

RESULTS

Significant tumor growth delay was observed in the tumor-bearing mice treated with pFUS. The mean tumor volume for the pFUS treated mice remained the same 1 week after the treatment while the mean tumor volume of the control mice grew 42% over the same time. Two weeks after the pFUS treatment, the control group had a mean tumor volume 40% greater than that of the treated group. There was a greater variation in tumor volume at 4 weeks post treatment for both treated and control mice and a slightly faster tumor growth for the pFUS treated mice.

CONCLUSIONS

The authors' results demonstrated that pFUS may have a great potential for cancer therapy. Further experiments are warranted to understand the predominantly nonthermal cell killing mechanisms of pFUS and to derive optimal ultrasound parameters and fractionation schemes to maximize the therapeutic effect of pFUS.

Intrapleural fluid infusion for MR-guided high-intensity focused ultrasound ablation in the liver dome

RATIONALE AND OBJECTIVES

Magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) ablation of tumors in the liver dome is challenging because of the presence of air in the costophrenic angle. In this study, we used a porcine liver model and a clinical MR-HIFU system to assess the feasibility and safety of using intrapleural fluid infusion (IPI) to create an acoustic window for MR-HIFU ablation in the liver dome.

MATERIALS AND METHODS

Healthy adult Dalland land pigs (n = 6) under general anesthesia were used with animal committee approval. Degassed saline (200-800 mL) was infused into the intrapleural space under ultrasound guidance. A clinical 1.5-T MR-HIFU system was used to perform sonications (4-mm treatment cells, 300-450 W, 20-30 seconds) in the liver dome under real-time MR thermometry. An intercostal firing technique was used to prevent rib heating in one experiment. Technical success was defined as a temperature increase (>10°C) in the target area. After termination, the animal was examined for thermal damage to liver, diaphragm, pleura, lung, or intercostal muscle.

RESULTS

An acoustic window was established in all animals. A temperature increase in the target area was achieved in all animals (max. 47°C-67°C). MR thermometry showed no heating outside the target area. Intercostal firing effectively reduced rib heating (55°C vs. 42°C). Postmortem examination revealed no unwanted thermal damage. One complication occurred, in the first experiment, because of an ill-suited needle (displacement of the needle).

CONCLUSIONS

The results indicate that IPI may be used safely to assist MR-HIFU ablation of tumors in the liver dome. For reliable tissue coagulation, IPI must be combined with an intercostal sonication technique. Considering the proportion of patients with tumors in the liver dome, IPI widens the applicability of MR-HIFU ablation for liver tumors considerably.

High-intensity focused ultrasound: noninvasive treatment for local unresectable recurrence of osteosarcoma

OBJECTIVE

Local unresectable recurrence of osteosarcoma is one of the most challenging tumors to treat. High-intensity focused ultrasound (HIFU) is a new, noninvasive technique with potential to ablate and inactivate tumors. Treatment of solid tumors with HIFU has been reported. In this study, we assessed safety and efficacy of HIFU in treating local unresectable recurrence of osteosarcoma.

METHODS

We performed a retrospective analysis of 27 patients who had local unresectable recurrence of osteosarcoma from 2006 to 2010. Changes of biochemical markers and pain rating, response rate, disease control rate, local disease progression-free survival, progression-free survival (PFS) and overall survival (OS) were used to evaluate efficacy of HIFU treatment.

RESULTS

HIFU resulted in a significant change in alkaline phosphatase and lactic acid dehydrogenase and a remarkably relief in pain rating, without severe side effects. According to MRI examination 4-6 weeks after HIFU treatment, 2 (7.4%) patients had complete response (CR), 12 (44.4%) had partial response (PR), 9 (33.3%) had stable disease (SD) and 4 (14.8%) had progression disease (PD). The response rate was 51.8% and the local disease control rate was 85.2%. The 1-, 2-, and 3-year local disease control rates were 59.2%, 40.7% and 33.1%, respectively. The median local disease progression-free time was 14 months, the median progression-free time was 13 months and the median over-all survival time was 21 months. Patients without pulmonary metastasis had a better local disease control rate at 1-,2-,3-year and a longer local disease progression-free time, progression-free time, over-all survival time than patients with pulmonary metastasis.

CONCLUSION

HIFU is a safe and noninvasive treatment for local unresectable recurrence of osteosarcoma, with good local control and without severe complications.

Emerging HIFU applications in cancer therapy

High intensity focused ultrasound (HIFU), is a promising, non-invasive modality for treatment of tumours in conjunction with magnetic resonance imaging or diagnostic ultrasound guidance. HIFU is being used increasingly for treatment of prostate cancer and uterine fibroids. Over the last 10 years a growing number of clinical trials have examined HIFU treatment of both benign and malignant tumours of the liver, breast, pancreas, bone, connective tissue, thyroid, parathyroid, kidney and brain. For some of these emerging indications, HIFU is poised to become a serious alternative or adjunct to current standard treatments--including surgery, radiation, gene therapy, immunotherapy, and chemotherapy. Current commercially available HIFU devices are marketed for their thermal ablation applications. In the future, lower energy treatments may play a significant role in mediating targeted drug and gene delivery for cancer treatment. In this article we introduce currently available HIFU systems, provide an overview of clinical trials in emerging oncological targets, and briefly discuss selected pre-clinical research that is relevant to future oncological HIFU applications.

Evaluation of superparamagnetic iron oxide-polymer composite microcapsules for magnetic resonance-guided high-intensity focused ultrasound cancer surgery

Background

Superparamagnetic poly (lactic-co-glycolic acid) (PLGA)-coated Fe₃O₄ microcapsules are receiving increased attention as potential diagnostic and therapeutic modalities in the field of oncology. In this study, PLGA-coated Fe₃O₄ microcapsules were combined with a magnetic resonance imaging-guided high-intensity focused ultrasound (MR-guided HIFU) platform, with the objective of investigating the effects of these composite microcapsules regarding MR-guided HIFU liver cancer surgery in vivo.

Methods

PLGA-coated Fe₃O₄ microcapsules consisting of a liquid core and a PLGA-Fe₃O₄ shell were fabricated using a modified double emulsion evaporation method. Their acute biosafety was confirmed in vitro using MDA cells and in vivo using rabbits. To perform MR-guided HIFU surgery, the microcapsules were intravenously injected into a rabbit liver tumor model before MR-guided HIFU. T₂-weighted images and MR signal intensity in normal liver parenchyma and tumor tissue were acquired before and after injection, to assess the MR imaging ability of the microcapsules. After MR-guided HIFU ablation tissue temperature mapping, the coagulative volume and histopathology of the tumor tissue were analyzed to investigate the ablation effects of MR-guided HIFUs.

Results

Scanning and transmission electron microscopy showed that the microcapsules displayed a spherical morphology and a shell-core structure (mean diameter, 587 nm). The hysteresis curve displayed the typical superparamagnetic properties of the microcapsules, which are critical to their application in MR-guided HIFU surgery. In MR-guided HIFU surgery, these microcapsules functioned as an MRI contrast agent, induced significant hyperthermal enhancement (P < 0.05) and significantly enhanced the volume of coagulative necrosis (P < 0.05).

Conclusions

The administration of PLGA-coated Fe₃O₄ microcapsules is a potentially synergistic technique regarding the enhancement of MR-guided HIFU cancer surgery.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-800) contains supplementary material, which is available to authorized users.

High-Intensity Focused Ultrasound (HIFU) in Uterine Fibroid Treatment: Review Study

Background

High-intensity focused ultrasound (HIFU) is a highly precise medical procedure used locally to heat and destroy diseased tissue through ablation. This study intended to review HIFU in uterine fibroid therapy, to evaluate the role of HIFU in the therapy of leiomyomas as well as to review the actual clinical activities in this field including efficacy and safety measures beside the published clinical literature.

Material/Methods

An inclusive literature review was carried out in order to review the scientific foundation, and how it resulted in the development of extracorporeal distinct devices. Studies addressing HIFU in leiomyomas were identified from a search of the Internet scientific databases. The analysis of literature was limited to journal articles written in English and published between 2000 and 2013.

Results

In current gynecologic oncology, HIFU is used clinically in the treatment of leiomyomas. Clinical research on HIFU therapy for leiomyomas began in the 1990s, and the majority of patients with leiomyomas were treated predominantly with HIFUNIT 9000 and prototype single focus ultrasound devices. HIFU is a non-invasive and highly effective standard treatment with a large indication range for all sizes of leiomyomas, associated with high efficacy, low operative morbidity and no systemic side effects.

Conclusions

Uterine fibroid treatment using HIFU was effective and safe in treating symptomatic uterine fibroids. Few studies are available in the literature regarding uterine artery embolization (UAE). HIFU provides an excellent option to treat uterine fibroids.

Treatment envelope evaluation in transcranial magnetic resonance-guided focused ultrasound utilizing 3D MR thermometry

BACKGROUND

Current clinical targets for transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) are all located close to the geometric center of the skull convexity, which minimizes challenges related to focusing the ultrasound through the skull bone. Non-central targets will have to be reached to treat a wider variety of neurological disorders and solid tumors. Treatment envelope studies utilizing two-dimensional (2D) magnetic resonance (MR) thermometry have previously been performed to determine the regions in which therapeutic levels of FUS can currently be delivered. Since 2D MR thermometry was used, very limited information about unintended heating in near-field tissue/bone interfaces could be deduced.

METHODS

In this paper, we present a proof-of-concept treatment envelope study with three-dimensional (3D) MR thermometry monitoring of FUS heatings performed in a phantom and a lamb model. While the moderate-sized transducer used was not designed for transcranial geometries, the 3D temperature maps enable monitoring of the entire sonication field of view, including both the focal spot and near-field tissue/bone interfaces, for full characterization of all heating that may occur. 3D MR thermometry is achieved by a combination of k-space subsampling and a previously described temporally constrained reconstruction method.

RESULTS

We present two different types of treatment envelopes. The first is based only on the focal spot heating-the type that can be derived from 2D MR thermometry. The second type is based on the relative near-field heating and is calculated as the ratio between the focal spot heating and the near-field heating. This utilizes the full 3D MR thermometry data achieved in this study.

CONCLUSIONS

It is shown that 3D MR thermometry can be used to improve the safety assessment in treatment envelope evaluations. Using a non-optimal transducer, it is shown that some regions where therapeutic levels of FUS can be delivered, as suggested by the first type of envelope, are not necessarily safely treated due to the amount of unintended near-field heating occurring. The results presented in this study highlight the need for 3D MR thermometry in tcMRgFUS.

Local thyroid tissue ablation by high-intensity focused ultrasound: effects on thyroid function and first human feasibility study with hot and cold thyroid nodules

OBJECTIVE

The aim of this study was to assess whether high-intensity focused ultrasound (HIFU), a new and promising method for the treatment of benign hot and cold thyroid nodules using thermal ablation, has an impact on thyroid function, and to evaluate its feasibility in outpatient settings. Additionally, a possible difference in the treatment of solid and complex thyroid nodules was evaluated.

METHOD

Ten patients with one thyroid nodule each (six cold and four hot nodules) underwent HIFU in January 2014. Four nodules were solid and six nodules were complex. Serum levels of triiodothyronine (T3), thyroxine (T4), thyrotropin (TSH), thyroglobulin (hTg) and additionally antibodies against hTg (TAK), TSH receptors (TRAK) and thyroid peroxidase (TPO) were measured at enrolment and 24 h after the HIFU treatment. The pre- and post-thyroglobulin reduction was measured to evaluate the scale of ablation. In addition, patients' pain was recorded on a numeric rating scale from 0 to 10.

RESULTS

The HIFU treatment did not affect thyroid function, since hormone levels stayed stable (p < 0.05). No serious immune reaction was induced. Thyroglobulin serum levels increased significantly (p < 0.05) and were correlated to the total energy emitted by HIFU (p < 0.1). The results of complex thyroid nodules did not differ from solid thyroid nodules. Similarly, the results of hot thyroid nodules did not differ from cold thyroid nodules. All patients tolerated the whole treatment and no severe complications were observed.

CONCLUSION

HIFU is a safe and effective method to treat benign, solid, complex, hot and cold thyroid nodules preserving thyroid function. Further developments of the system are needed to gain suitability for daily use.

Early assessment of high-intensity focused ultrasound treatment of benign thyroid nodules by scintigraphic means

Background

High-intensity focused ultrasound (HIFU) allows to inflict intracorporal thermal lesions without penetrating the skin or damaging the surrounding tissue. This analysis intends to assess the magnitude of HIFU-induced ablations within benign thyroid nodules using scintigraphic imaging with ^99mTc.

Methods

Ten cold, hot, or indifferent nodules were treated using multiple pulses of HIFU to induce temperatures of around 85°C within the ablation zone. Pre- and posttreatment, uptake values of ^99mTc-pertechnetate or ^99mTc-MIBI were recorded. The pre-post reduction of nodular uptake was evaluated to assess ablation magnitude.

Results

Relative nodular uptake in relation to total thyroidal uptake decreased after one session of HIFU in all cases. Median ^99mTc-MIBI uptake reduction was 35.5% (ranging from 11% to 57%; p < 0.1), while ^99mTc-pertechnetate scintigraphy showed a median uptake reduction of 27% (range 10% to 44%; p < 0.1). No major complications were observed.

Conclusions

HIFU appears to be safe and is an easy to perform means of thermal ablation. This study shows that HIFU treatment in thyroidal nodules can be evaluated by scintigraphic means shortly after the intervention. Due to small sample size, the exact magnitude of HIFU ablation efficiency in thyroidal nodules remains a value to be assessed in a larger study.