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Abstract
Ultrasound therapy has been investigated for over half a century. Ultrasound can act on tissue through a variety of mechanisms, including thermal, shockwave and cavitation mechanisms, and through these can elicit different responses. Ultrasound therapy can provide a non-invasive or minimally invasive treatment option, and ultrasound technology has advanced to the point where devices can be developed to investigate a wide range of applications. This review focuses on non-cancer clinical applications of therapeutic ultrasound, with an emphasis on treatments that have recently reached clinical investigations, and preclinical research programmes that have great potential to impact patient care.
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52
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Wang TR, Dallapiazza R, Elias WJ. Neurological applications of transcranial high intensity focused ultrasound. Int J Hyperthermia 2015; 31:285-91. [PMID: 25703389 DOI: 10.3109/02656736.2015.1007398] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Advances in transcranial MRI-guided focused ultrasound have renewed interest in lesioning procedures in functional neurosurgery with a potential role in the treatment of neurological conditions such as chronic pain, brain tumours, movement disorders and psychiatric diseases. While the use of transcranial MRI-guided focused ultrasound represents a new innovation in neurosurgery, ultrasound has been used in neurosurgery for almost 60 years. This paper reviews the major historical milestones that have led to modern transcranial focused ultrasound and discusses current and evolving applications of ultrasound in the brain.
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Affiliation(s)
- Tony R Wang
- Department of Neurological Surgery, University of Virginia Health Sciences Center , Charlottesville, Virginia , USA
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53
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O'Reilly MA, Jones RM, Hynynen K. Three-dimensional transcranial ultrasound imaging of microbubble clouds using a sparse hemispherical array. IEEE Trans Biomed Eng 2014; 61:1285-94. [PMID: 24658252 DOI: 10.1109/tbme.2014.2300838] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
There is an increasing interest in bubble-mediated focused ultrasound (FUS) interventions in the brain. However, current technology lacks the ability to spatially monitor the interaction of the microbubbles with the applied acoustic field, something which is critical for safe clinical translation of these treatments. Passive acoustic mapping could offer a means for spatially monitoring microbubble emissions that relate to bubble activity and associated bioeffects. In this study, a hemispherical receiver array was integrated within an existing transcranial therapy array to create a device capable of both delivering therapy and monitoring the process via passive imaging of bubble clouds. A 128-element receiver array was constructed and characterized for varying bubble concentrations and source spacings. Initial in vivo feasibility testing was performed. The system was found to be capable of monitoring bubble emissions down to single bubble events through an ex vivo human skull. The lateral resolution of the system was found to be between 1.25 and 2 mm and the axial resolution between 2 and 3.5 mm, comparable to the resolution of MRI-based temperature monitoring during thermal FUS treatments in the brain. The results of initial in vivo experiments show that bubble activity can be mapped starting at pressure levels below the threshold for blood-brain barrier disruption. This study presents a feasible solution for imaging bubble activity during cavitation-mediated FUS treatments in the brain.
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Pajek D, Burgess A, Huang Y, Hynynen K. High-intensity focused ultrasound sonothrombolysis: the use of perfluorocarbon droplets to achieve clot lysis at reduced acoustic power. ULTRASOUND IN MEDICINE & BIOLOGY 2014; 40:2151-61. [PMID: 25023095 PMCID: PMC4130783 DOI: 10.1016/j.ultrasmedbio.2014.03.026] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Revised: 03/21/2014] [Accepted: 03/24/2014] [Indexed: 05/03/2023]
Abstract
The purpose of this study was to evaluate use of intravascular perfluorocarbon droplets to reduce the sonication power required to achieve clot lysis with high-intensity focused ultrasound. High-intensity focused ultrasound with droplets was initially applied to blood clots in an in vitro flow apparatus, and inertial cavitation thresholds were determined. An embolic model for ischemic stroke was used to illustrate the feasibility of this technique in vivo. Recanalization with intravascular droplets was achieved in vivo at 24 ± 5% of the sonication power without droplets. Recanalization occurred in 71% of rabbits that received 1-ms pulsed sonications during continuous intravascular droplet infusion (p = 0.041 vs controls). Preliminary experiments indicated that damage was confined to the ultrasonic focus, suggesting that tolerable treatments would be possible with a more tightly focused hemispheric array that allows the whole focus to be placed inside of the main arteries in the human brain.
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Affiliation(s)
- Daniel Pajek
- Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Canada; Department of Medical Biophysics, University of Toronto, Toronto, Canada.
| | - Alison Burgess
- Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Canada
| | - Yuexi Huang
- Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Canada
| | - Kullervo Hynynen
- Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Canada; Department of Medical Biophysics, University of Toronto, Toronto, Canada
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In vitro demonstration of focused ultrasound thrombolysis using bifrequency excitation. BIOMED RESEARCH INTERNATIONAL 2014; 2014:518787. [PMID: 25243147 PMCID: PMC4163449 DOI: 10.1155/2014/518787] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Revised: 06/05/2014] [Accepted: 06/25/2014] [Indexed: 11/20/2022]
Abstract
Focused ultrasound involving inertial cavitation has been shown to be an
efficient method to induce thrombolysis without any pharmacological agent. However,
further investigation of the mechanisms involved and further optimization of the
process are still required. The present work aims at studying the relevance of a
bifrequency excitation compared to a classical monofrequency excitation to achieve
thrombolysis without any pharmacological agent. In vitro human blood clots were
placed at the focus of a piezoelectric transducer. Efficiency of the thrombolysis
was assessed by weighing each clot before and after sonication. The efficiencies of
mono- (550 kHz) and bifrequency (535 and 565 kHz) excitations were compared for
peak power ranging from 70 W to 220 W. The thrombolysis efficiency appears to be
correlated to the inertial cavitation activity quantified by passive acoustic listening.
In the conditions of the experiment, the power needed to achieve 80% of thrombolysis
with a monofrequency excitation is reduced by the half with a bifrequency excitation.
The thermal effects of bifrequency and monofrequency excitations, studied using MR
thermometry measurements in turkey muscle samples where no cavitation occurred,
did not show any difference between both types of excitations when using the same
power level.
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56
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Pajek D, Hynynen K. The application of sparse arrays in high frequency transcranial focused ultrasound therapy: a simulation study. Med Phys 2014; 40:122901. [PMID: 24320540 DOI: 10.1118/1.4829510] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Transcranial focused ultrasound is an emerging therapeutic modality that can be used to perform noninvasive neurosurgical procedures. The current clinical transcranial phased array operates at 650 kHz, however the development of a higher frequency array would enable more precision, while reducing the risk of standing waves. However, the smaller wavelength and the skull's increased distortion at this frequency are problematic. It would require an order of magnitude more elements to create such an array. Random sparse arrays enable steering of a therapeutic array with fewer elements. However, the tradeoffs inherent in the use of sparsity in a transcranial phased array have not been systematically investigated and so the objective of this simulation study is to investigate the effect of sparsity on transcranial arrays at a frequency of 1.5 MHz that provides small focal spots for precise exposure control. METHODS Transcranial sonication simulations were conducted using a multilayer Rayleigh-Sommerfeld propagation model. Element size and element population were varied and the phased array's ability to steer was assessed. RESULTS The focal pressures decreased proportionally as elements were removed. However, off-focus hotspots were generated if a high degree of steering was attempted with very sparse arrays. A phased array consisting of 1588 elements 3 mm in size, a 10% population, was appropriate for steering up to 4 cm in all directions. However, a higher element population would be required if near-skull sonication is desired. CONCLUSIONS This study demonstrated that the development of a sparse, hemispherical array at 1.5 MHz could enable more precision in therapies that utilize lower intensity sonications.
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Affiliation(s)
- Daniel Pajek
- Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M4N3M5, Canada
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57
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Lipsman N, Mainprize TG, Schwartz ML, Hynynen K, Lozano AM. Intracranial applications of magnetic resonance-guided focused ultrasound. Neurotherapeutics 2014; 11:593-605. [PMID: 24850310 PMCID: PMC4121456 DOI: 10.1007/s13311-014-0281-2] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
The ability to focus acoustic energy through the intact skull on to targets millimeters in size represents an important milestone in the development of neurotherapeutics. Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel, noninvasive method, which--under real-time imaging and thermographic guidance--can be used to generate focal intracranial thermal ablative lesions and disrupt the blood-brain barrier. An established treatment for bone metastases, uterine fibroids, and breast lesions, MRgFUS has now been proposed as an alternative to open neurosurgical procedures for a wide variety of indications. Studies investigating intracranial MRgFUS range from small animal preclinical experiments to large, late-phase randomized trials that span the clinical spectrum from movement disorders, to vascular, oncologic, and psychiatric applications. We review the principles of MRgFUS and its use for brain-based disorders, and outline future directions for this promising technology.
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Affiliation(s)
- Nir Lipsman
- Division of Neurosurgery, University Health Network, University of Toronto, 399 Bathurst Street, 4W-431, Toronoto, M5T 2S8, Canada,
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Christian E, Yu C, Apuzzo MLJ. Focused ultrasound: relevant history and prospects for the addition of mechanical energy to the neurosurgical armamentarium. World Neurosurg 2014; 82:354-65. [PMID: 24952224 DOI: 10.1016/j.wneu.2014.06.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 06/08/2014] [Accepted: 06/10/2014] [Indexed: 10/25/2022]
Abstract
Although the concept of focused ultrasonography emerged more than 70 years ago, the need for a craniectomy obviated its development as a noninvasive technology. Since then advances in phased array transducers and magnetic resonance imaging technology have resurrected the ultrasound as a noninvasive therapeutic for a plethora of neurological conditions ranging from embolic stroke and intracranial hemorrhage to movement disorders and brain neoplasia. In the same way that stereotactic radiosurgery has fundamentally changed the scope and treatment paradigms of tumor and specifically skull base surgery, focused ultrasound has a similar potential to revolutionize the field of neurological surgery. In addition, focused ultrasound comes without the general complexity or the risks of ionizing radiation that accompany radiosurgery. As the quest for minimally invasive and noninvasive therapeutics continues to define the new neurosurgery, the focused ultrasound evolves to join the neurosurgical armamentarium.
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Affiliation(s)
- Eisha Christian
- Department of Neurosurgery, Keck School of Medicine of University of Southern California, Los Angeles, California, USA
| | - Cheng Yu
- Department of Neurosurgery, Keck School of Medicine of University of Southern California, Los Angeles, California, USA.
| | - Michael L J Apuzzo
- Department of Neurosurgery, Keck School of Medicine of University of Southern California, Los Angeles, California, USA
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59
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Dobrakowski PP, Machowska-Majchrzak AK, Labuz-Roszak B, Majchrzak KG, Kluczewska E, Pierzchała KB. MR-guided focused ultrasound: a new generation treatment of Parkinson's disease, essential tremor and neuropathic pain. Interv Neuroradiol 2014; 20:275-82. [PMID: 24976088 DOI: 10.15274/inr-2014-10033] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Accepted: 01/26/2014] [Indexed: 12/16/2022] Open
Abstract
The application of high intense focused ultrasound (HIFU) is currently the subject of many experimental and clinical trials. The combination of HIFU with MRI guidance known as MR-guided focused ultrasound (MRgFUS) appears to be particularly promising to ablate tissues located deep in the brain. The method can be the beginning of interventional neurology and an important alternative to neurosurgery. Studies conducted to date show the effectiveness of the method both in chronic diseases and in emergency cases. The safety and effectiveness of this method have been observed in parkinsonian and essential tremor as well as in neuropathic pain. The procedure does not require anaesthesia. Ionizing radiation is not used and there is no risk of cumulative dose. Such advantages may result in low complication rates and medical justification for further development of MRgFUS.
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Affiliation(s)
| | | | - Beata Labuz-Roszak
- Clinical Department of Neurology, Medical University of Silesia; Zabrze, Poland
| | | | - Ewa Kluczewska
- Clinical Department of Neurology, Medical University of Silesia; Zabrze, Poland
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60
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Unger E, Porter T, Lindner J, Grayburn P. Cardiovascular drug delivery with ultrasound and microbubbles. Adv Drug Deliv Rev 2014; 72:110-26. [PMID: 24524934 DOI: 10.1016/j.addr.2014.01.012] [Citation(s) in RCA: 124] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Revised: 01/23/2014] [Accepted: 01/29/2014] [Indexed: 01/14/2023]
Abstract
Microbubbles lower the threshold for cavitation of ultrasound and have multiple potential therapeutic applications in the cardiovascular system. One of the first therapeutic applications to enter into clinical trials has been microbubble-enhanced sonothrombolysis. Trials were conducted in acute ischemic stroke and clinical trials are currently underway for sonothrombolysis in treatment of acute myocardial infarction. Microbubbles can be targeted to epitopes expressed on endothelial cells and thrombi by incorporating targeting ligands onto the surface of the microbubbles. Targeted microbubbles have applications as molecular imaging contrast agents and also for drug and gene delivery. A number of groups have shown that ultrasound with microbubbles can be used for gene delivery yielding robust gene expression in the target tissue. Work has progressed to primate studies showing delivery of therapeutic genes to generate islet cells in the pancreas to potentially cure diabetes. Microbubbles also hold potential as oxygen therapeutics and have shown promising results as a neuroprotectant in an ischemic stroke model. Regulatory considerations impact the successful clinical development of therapeutic applications of microbubbles with ultrasound. This paper briefly reviews the field and suggests avenues for further development.
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61
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Wei CW, Xia J, Lombardo M, Perez C, Arnal B, Larson-Smith K, Pelivanov I, Matula T, Pozzo L, O’Donnell M. Laser-induced cavitation in nanoemulsion with gold nanospheres for blood clot disruption: in vitro results. OPTICS LETTERS 2014; 39:2599-602. [PMID: 24784055 PMCID: PMC9008802 DOI: 10.1364/ol.39.002599] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Optically activated cavitation in a nanoemulsion contrast agent is proposed for therapeutic applications. With a 56°C boiling point perfluorohexane core and highly absorptive gold nanospheres at the oil-water interface, cavitation nuclei in the core can be efficiently induced with a laser fluence below medical safety limits (70 mJ/cm2 at 1064 nm). This agent is also sensitive to ultrasound (US) exposure and can induce inertial cavitation at a pressure within the medical diagnostic range. Images from a high-speed camera demonstrate bubble formation in these nanoemulsions. The potential of using this contrast agent for blood clot disruption is demonstrated in an in vitro study. The possibility of simultaneous laser and US excitation to reduce the cavitation threshold for therapeutic applications is also discussed.
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Affiliation(s)
- Chen-wei Wei
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
- Corresponding author:
| | - Jinjun Xia
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
| | - Michael Lombardo
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
| | - Camilo Perez
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
| | - Bastien Arnal
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
| | - Kjersta Larson-Smith
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
| | - Ivan Pelivanov
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
- International Laser Center, Moscow State University, Moscow, Russia
| | - Thomas Matula
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
| | - Lilo Pozzo
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
| | - Matthew O’Donnell
- Departments of Bioengineering and Chemical Engineering, and Applied Physics Lab, University of Washington, Seattle, Washington 98195, USA
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62
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Lapchak PA, Kikuchi K, Butte P, Hölscher T. Development of transcranial sonothrombolysis as an alternative stroke therapy: incremental scientific advances toward overcoming substantial barriers. Expert Rev Med Devices 2014; 10:201-13. [DOI: 10.1586/erd.12.88] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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63
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Jones RM, O'Reilly MA, Hynynen K. Transcranial passive acoustic mapping with hemispherical sparse arrays using CT-based skull-specific aberration corrections: a simulation study. Phys Med Biol 2013; 58:4981-5005. [PMID: 23807573 DOI: 10.1088/0031-9155/58/14/4981] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The feasibility of transcranial passive acoustic mapping with hemispherical sparse arrays (30 cm diameter, 16 to 1372 elements, 2.48 mm receiver diameter) using CT-based aberration corrections was investigated via numerical simulations. A multi-layered ray acoustic transcranial ultrasound propagation model based on CT-derived skull morphology was developed. By incorporating skull-specific aberration corrections into a conventional passive beamforming algorithm (Norton and Won 2000 IEEE Trans. Geosci. Remote Sens. 38 1337-43), simulated acoustic source fields representing the emissions from acoustically-stimulated microbubbles were spatially mapped through three digitized human skulls, with the transskull reconstructions closely matching the water-path control images. Image quality was quantified based on main lobe beamwidths, peak sidelobe ratio, and image signal-to-noise ratio. The effects on the resulting image quality of the source's emission frequency and location within the skull cavity, the array sparsity and element configuration, the receiver element sensitivity, and the specific skull morphology were all investigated. The system's resolution capabilities were also estimated for various degrees of array sparsity. Passive imaging of acoustic sources through an intact skull was shown possible with sparse hemispherical imaging arrays. This technique may be useful for the monitoring and control of transcranial focused ultrasound (FUS) treatments, particularly non-thermal, cavitation-mediated applications such as FUS-induced blood-brain barrier disruption or sonothrombolysis, for which no real-time monitoring techniques currently exist.
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Affiliation(s)
- Ryan M Jones
- Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Canada.
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