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Hughes A, Khan DS, Alkins R. Current and Emerging Systems for Focused Ultrasound-Mediated Blood-Brain Barrier Opening. ULTRASOUND IN MEDICINE & BIOLOGY 2023; 49:1479-1490. [PMID: 37100672 DOI: 10.1016/j.ultrasmedbio.2023.02.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 02/09/2023] [Accepted: 02/23/2023] [Indexed: 05/17/2023]
Abstract
With an ever-growing list of neurological applications of focused ultrasound (FUS), there has been a consequent increase in the variety of systems for delivering ultrasound energy to the brain. Specifically, recent successful pilot clinical trials of blood-brain barrier (BBB) opening with FUS have generated substantial interest in the future applications of this relatively novel therapy, with divergent, purpose-built technologies emerging. With many of these technologies at various stages of pre-clinical and clinical investigation, this article seeks to provide an overview and analysis of the numerous medical devices in active use and under development for FUS-mediated BBB opening.
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Affiliation(s)
- Alec Hughes
- School of Medicine, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada
| | - Dure S Khan
- Centre for Neuroscience Studies, Queen's University, Kingston, ON, Canada
| | - Ryan Alkins
- Centre for Neuroscience Studies, Queen's University, Kingston, ON, Canada; Division of Neurosurgery, Department of Surgery, Kingston Health Sciences Centre, Queen's University, Kingston, ON, Canada.
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2
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Lu N, Hall TL, Sukovich JR, Choi SW, Snell J, McDannold N, Xu Z. Two-step aberration correction: application to transcranial histotripsy. Phys Med Biol 2022; 67:10.1088/1361-6560/ac72ed. [PMID: 35609619 PMCID: PMC9234948 DOI: 10.1088/1361-6560/ac72ed] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 05/24/2022] [Indexed: 11/11/2022]
Abstract
Objective: Phase aberration correction is essential in transcranial histotripsy to compensate for focal distortion caused by the heterogeneity of the intact skull bone. This paper improves the 2-step aberration correction (AC) method that has been previously presented and develops an AC workflow that fits in the clinical environment, in which the computed tomography (CT)-based analytical approach was first implemented, followed by a cavitation-based approach using the shockwaves from the acoustic cavitation emission (ACE).Approach:A 700 kHz, 360-element hemispherical transducer array capable of transmit-and-receive on all channels was used to transcranially generate histotripsy-induced cavitation and acquire ACE shockwaves. For CT-AC, two ray-tracing models were investigated: a forward ray-tracing model (transducer-to-focus) in the open-source software Kranion, and an in-house backward ray-tracing model (focus-to-transducer) accounting for refraction and the sound speed variation in skulls. Co-registration was achieved by aligning the skull CT data to the skull surface map reconstructed using the acoustic pulse-echo method. For ACE-AC, the ACE signals from the collapses of generated bubbles were aligned by cross-correlation to estimate the corresponding time delays.Main results:The performance of the 2-step method was tested with 3 excised human calvariums placed at 2 different locations in the transducer array. Results showed that the 2-step AC achieved 90 ± 7% peak focal pressure compared to the gold standard hydrophone correction. It also reduced the focal shift from 0.84 to 0.30 mm and the focal volume from 10.6 to 2.0 mm3on average compared to the no AC cases.Significance:The 2-step AC yielded better refocusing compared to either CT-AC or ACE-AC alone and can be implemented in real-time for transcranial histotripsy brain therapy.
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Affiliation(s)
- Ning Lu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, United States of America
| | - Timothy L Hall
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, United States of America
| | - Jonathan R Sukovich
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, United States of America
| | - Sang Won Choi
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, United States of America
| | - John Snell
- Focused Ultrasound Foundation, Charlottesville, United States of America
| | - Nathan McDannold
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Zhen Xu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, United States of America
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Mensah-Brown KG, Yang AI, Hitti FL, Henry L, Heman-Ackah SM, Chaibainou H, Baltuch GH. Magnetic Resonance-Guided Focused Ultrasound Thalamotomy for Essential Tremor Under General Anesthesia: Technical Note. Oper Neurosurg (Hagerstown) 2022; 22:255-260. [PMID: 35147587 DOI: 10.1227/ons.0000000000000119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Accepted: 11/03/2021] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an incisionless therapy for the treatment of medication-resistant essential tremor. Although its safety and efficacy has been demonstrated, MRgFUS is typically performed with the patient awake, with intraprocedural neurological assessments to guide lesioning. OBJECTIVE To report the first case of MRgFUS thalamotomy under general anesthesia in a patient whose medical comorbidities prohibit him from being in a supine position without a secured airway. METHODS The dentatorubrothalamic tract was directly targeted. Two sonications reaching lesional temperatures (≥54°C) were delivered without any complications. RESULTS Lesioning was confirmed on intraoperative magnetic resonance imaging, and the patient experienced 89% improvement in his tremor postoperatively. CONCLUSION This demonstrates the safety and feasibility of MRgFUS thalamotomy under general anesthesia without the benefit of intraprocedural neurological assessments.
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Affiliation(s)
- Kobina G Mensah-Brown
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Andrew I Yang
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Frederick L Hitti
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | | | - Sabrina M Heman-Ackah
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Hanane Chaibainou
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Gordon H Baltuch
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Yuen J, Miller KJ, Klassen BT, Lehman VT, Lee KH, Kaufmann TJ. Hyperostosis in Combination With Low Skull Density Ratio: A Potential Contraindication for Magnetic Resonance Imaging-Guided Focused Ultrasound Thalamotomy. Mayo Clin Proc Innov Qual Outcomes 2022; 6:10-15. [PMID: 34977470 PMCID: PMC8704442 DOI: 10.1016/j.mayocpiqo.2021.11.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Since its approval in treating a number of movement disorders, magnetic resonance imaging–guided focused ultrasound (MRgFUS) has been adopted rapidly as one of the standard treatment modalities internationally. However, the efficiency of the energy delivered by the ultrasonic waves is largely determined by the highly variable bone morphology and density characteristics of the skull. One of the widely accepted indices used to facilitate patient selection is the skull density ratio (SDR). Earlier literature suggested that an SDR of less than 0.4 would be unfavorable for MRgFUS treatment. Some prior studies have excluded patients with hyperostosis. However, there is little published data regarding the impact of other skull features such as hyperostosis on treatment success. We present the case of a 66-year-old man with medically refractory essential tremor who had an SDR of 0.38 and extensive hyperostosis frontalis interna and underwent attempted MRgFUS thalamotomy treatment. However, intraoperatively the treatment was unsuccessful in generating sufficiently elevated temperature to create a lesion of the usual desired volume, and as expected, there was minimal clinical improvement. For comparison, we also summarize a case series of 4 other patients with an SDR of less than 0.4 who had successful outcomes. We believe that SDR should not be used as the only means of selecting patients for MRgFUS. Instead, important factors such as hyperostosis should be taken into consideration for patient selection and pretreatment counseling.
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Yang AI, Alabi OO, Hitti FL, Henry L, Clanton R, Baltuch GH. Letter: Lesion Shape and Size in MRgFUS Thalamotomy: Predictors and Implications. Neurosurgery 2021; 89:E198-E200. [PMID: 34192743 DOI: 10.1093/neuros/nyab233] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Andrew I Yang
- Department of Neurosurgery University of Pennsylvania Philadelphia, Pennsylvania, USA
| | - Opeyemi O Alabi
- Department of Neurosurgery University of Pennsylvania Philadelphia, Pennsylvania, USA
| | - Frederick L Hitti
- Department of Neurosurgery University of Pennsylvania Philadelphia, Pennsylvania, USA
| | | | | | - Gordon H Baltuch
- Department of Neurosurgery University of Pennsylvania Philadelphia, Pennsylvania, USA
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McDannold N, Jason White P, Rees Cosgrove G. Using Phase Data From MR Temperature Imaging to Visualize Anatomy During MRI-Guided Focused Ultrasound Neurosurgery. IEEE TRANSACTIONS ON MEDICAL IMAGING 2020; 39:3821-3830. [PMID: 32746127 PMCID: PMC7749411 DOI: 10.1109/tmi.2020.3005631] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Neurosurgery targets in the thalamus can be challenging to identify during transcranial MRI-guided focused ultrasound (MRgFUS) thermal ablation due to poor image quality. They also neighbor structures that can result in side effects if damaged. Here we demonstrate that the phase data obtained during MRgFUS for MR temperature imaging (MRTI) contains anatomic information that could be useful in guiding this procedure. This approach was evaluated in 68 thalamotomies for essential tremor (ET). We found that we could readily visualize the red nucleus and subthalamic nucleus, and those nuclei were consistently aligned with the sonication target coordinates. We also could consistently visualize the internal capsule, which needs to be protected from thermal damage to prevent side effects. Preliminary results from four pallidotomies in Parkinson's disease patients suggest that this approach might also be useful in visualizing the optic tract in addition to the internal capsule. Overall, this approach can visualize anatomic landmarks that may be useful to refine atlas-based targeting for MRgFUS. Since the same data is used for MRTI and anatomic visualization, there are no errors induced by registration to previously obtained planning images or image distortion, and no additional time is needed.
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McDannold N, Jason White P, Rees Cosgrove G. MRI-based thermal dosimetry based on single-slice imaging during focused ultrasound thalamotomy. Phys Med Biol 2020; 65:235018. [PMID: 32916666 PMCID: PMC8019066 DOI: 10.1088/1361-6560/abb7c4] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Transcranial MRI-guided focused ultrasound (MRgFUS) is a noninvasive thermal ablation method approved for the treatment of essential tremor and tremor-dominant Parkinson's disease. This method uses MR temperature imaging (MRTI) to monitor the treatment. Accurately tracking the accumulated thermal dose is important for both safety and efficacy. Currently, MRTI is obtained in a single plane that varies between sonications, preventing direct tracking of the accumulated dose. In this work, we tested a method to estimate this dose during 120 MRgFUS treatments. This method used the MRTI to create simulated thermal images for sonications when the imaging plane was changed. This approach accurately predicted the lesion shapes. The mean Sørensen-Dice similarity coefficient between the lesion segmentations and dose regions at the 17 cumulative min at 43 °C (CEM43) threshold used by the device software was 0.82 but varied among different treatments (range: 0.34-0.95). Tissue swelling appeared to explain when mismatch occurred, although other errors probably contributed. Overall, the mean distance between the lesion segmentations and the 17 CEM43 dose contours was 0.37 ± 0.57 mm. The probability for thermal damage was estimated to be 50% at 13.6 CEM43 and a maximum temperature of 48.6 °C. Due to large thermal gradients, which exceeded 99 CEM43/mm on average, the area where the probability for thermal damage was uncertain was narrow. Overall these results show that the 17 CEM43 threshold is on average a good predictor for thermal lesions, although there will always be a narrow margin where the fate of the tissue is uncertain.
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Affiliation(s)
- Nathan McDannold
- Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States of America
| | - P Jason White
- Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States of America
| | - G Rees Cosgrove
- Department of Neurosurgery, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States of America
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8
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McDannold N, White PJ, Cosgrove R. Elementwise approach for simulating transcranial MRI-guided focused ultrasound thermal ablation. PHYSICAL REVIEW RESEARCH 2019; 1:033205. [PMID: 34164625 PMCID: PMC8218657 DOI: 10.1103/physrevresearch.1.033205] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
This work explored an elementwise approach to model transcranial MRI-guided focused ultrasound (TcMRgFUS) thermal ablation, a noninvasive approach to neurosurgery. Each element of the phased array transducer was simulated individually and could be simultaneously loaded into computer memory, allowing for rapid (~2.5 s) calculation of the pressure field for different phase offsets used for beam steering and aberration correction. We simulated the pressure distribution for 431 sonications in 32 patients, applied the phase and magnitude values used during treatment, and estimated the resulting temperature rise. We systematically varied the relationship between CT (computerized tomography)-derived skull density and the acoustic attenuation and sound speed to obtain the best agreement between the predictions and MR temperature imaging (MRTI). The optimization was validated with simulations of 396 sonications from 40 additional treatments. After optimization, the predicted and measured heating agreed well (R 2: 0.74 patients 1-32; 0.71 patients 33-72). The dimensions and obliquity of the heating in the simulated temperature maps were correlated with the MRTI (R 2: 0.62, 0.74, respectively), but the measured heating was more spatially diffuse. The energy needed to achieve ablation varied by an order of magnitude (3.3-36.1 kJ). While this elementwise approach required more computation time up front (the combined simulation matrices were approximately 4.6 times higher than a single large simulation), it could be performed in parallel on a computing cluster. It allows for rapid calculation of the three-dimensional heating at the focus for different phase and magnitude values on the array. We also show how this approach can be used to optimize the relationship between CT-derived skull density and acoustic properties. While the relationships found here need further validation in a larger patient population, these results demonstrate the promise of this approach to model TcMRgFUS.
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Affiliation(s)
- Nathan McDannold
- Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
| | - P Jason White
- Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Rees Cosgrove
- Department of Neurosurgery, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
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9
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Ferri M, Bravo JM, Redondo J, Jiménez-Gambín S, Jiménez N, Camarena F, Sánchez-Pérez JV. On the Evaluation of the Suitability of the Materials Used to 3D Print Holographic Acoustic Lenses to Correct Transcranial Focused Ultrasound Aberrations. Polymers (Basel) 2019; 11:E1521. [PMID: 31546807 PMCID: PMC6780887 DOI: 10.3390/polym11091521] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 09/13/2019] [Accepted: 09/16/2019] [Indexed: 11/16/2022] Open
Abstract
The correction of transcranial focused ultrasound aberrations is a relevant topic for enhancing various non-invasive medical treatments. Presently, the most widely accepted method to improve focusing is the emission through multi-element phased arrays; however, a new disruptive technology, based on 3D printed holographic acoustic lenses, has recently been proposed, overcoming the spatial limitations of phased arrays due to the submillimetric precision of the latest generation of 3D printers. This work aims to optimize this recent solution. Particularly, the preferred acoustic properties of the polymers used for printing the lenses are systematically analyzed, paying special attention to the effect of p-wave speed and its relationship to the achievable voxel size of 3D printers. Results from simulations and experiments clearly show that, given a particular voxel size, there are optimal ranges for lens thickness and p-wave speed, fairly independent of the emitted frequency, the transducer aperture, or the transducer-target distance.
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Affiliation(s)
- Marcelino Ferri
- Centro de Tecnologías Físicas, Universitat Politècnica de València, Camino de Vera S/N, 46020 Valencia, Spain.
| | - José María Bravo
- Centro de Tecnologías Físicas, Universitat Politècnica de València, Camino de Vera S/N, 46020 Valencia, Spain.
| | - Javier Redondo
- Instituto para la Gestión Integrada de las zonas Costeras, Universitat Politècnica de València, Carretera Nazaret-Oliva S/N, 46730 Valencia, Spain.
| | - Sergio Jiménez-Gambín
- Instituto de Instrumentación para Imagen Molecular, Centro Mixto CSIC-Universitat Politècnica de València, Camino de Vera S/N, 46022 València, Spain.
| | - Noé Jiménez
- Instituto de Instrumentación para Imagen Molecular, Centro Mixto CSIC-Universitat Politècnica de València, Camino de Vera S/N, 46022 València, Spain.
| | - Francisco Camarena
- Instituto de Instrumentación para Imagen Molecular, Centro Mixto CSIC-Universitat Politècnica de València, Camino de Vera S/N, 46022 València, Spain.
| | - Juan Vicente Sánchez-Pérez
- Centro de Tecnologías Físicas, Universitat Politècnica de València, Camino de Vera S/N, 46020 Valencia, Spain.
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10
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Maimbourg G, Houdouin A, Deffieux T, Tanter M, Aubry JF. Steering Capabilities of an Acoustic Lens for Transcranial Therapy: Numerical and Experimental Studies. IEEE Trans Biomed Eng 2019; 67:27-37. [PMID: 30932823 DOI: 10.1109/tbme.2019.2907556] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
For successful brain therapy, transcranial focused ultrasound must compensate for the time shifts induced locally by the skull. The patient-specific phase profile is currently generated by multi-element arrays which, over time, have tended toward increasing element count. We recently introduced a new approach, consisting of a single-element transducer coupled to an acoustic lens of controlled thickness. By adjusting the local thickness of the lens, we were able to induce phase differences which compensated those induced by the skull. Nevertheless, such an approach suffers from an apparent limitation: the lens is a priori designed for one specific target. In this paper, we demonstrate the possibility of taking advantage of the isoplanatic angle of the aberrating skull in order to steer the focus by mechanically moving the transducer/acoustic lens pair around its initial focusing position. This study, conducted on three human skull samples, demonstrates that tilting of the transducer with the lens restores a single -3 dB focal volume at 914 kHz for a steering up to ±11 mm in the transverse direction, and ±10 mm in the longitudinal direction, around the initial focal region.
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11
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Ferri M, Bravo JM, Redondo J, Sánchez-Pérez JV. Enhanced Numerical Method for the Design of 3-D-Printed Holographic Acoustic Lenses for Aberration Correction of Single-Element Transcranial Focused Ultrasound. ULTRASOUND IN MEDICINE & BIOLOGY 2019; 45:867-884. [PMID: 30600128 DOI: 10.1016/j.ultrasmedbio.2018.10.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 10/19/2018] [Accepted: 10/19/2018] [Indexed: 06/09/2023]
Abstract
The correction of transcranial focused ultrasound aberrations is a relevant issue for enhancing various non-invasive medical treatments. The emission through multi-element phased arrays has been the most widely accepted method to improve focusing in recent years; however, the number and size of transducers represent a bottleneck that limits the focusing accuracy of the technique. To overcome this limitation, a new disruptive technology, based on 3-D-printed acoustic lenses, has recently been proposed. As the submillimeter precision of the latest generation of 3-D printers has been proven to overcome the spatial limitations of phased arrays, a new challenge is to improve the accuracy of the numerical simulations required to design this type of ultrasound lens. In the study described here, we evaluated two improvements in the numerical model applied in previous works for the design of 3-D-printed lenses: (i) allowing the propagation of shear waves in the skull by means of its simulation as an isotropic solid and (ii) introduction of absorption into the set of equations that describes the dynamics of the wave in both fluid and solid media. The results obtained in the numerical simulations are evidence that the inclusion of both s-waves and absorption significantly improves focusing.
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Affiliation(s)
- Marcelino Ferri
- Centro de Tecnologías Físicas, Universidad Politécnica de Valencia, Valencia, Spain.
| | - José M Bravo
- Centro de Tecnologías Físicas, Universidad Politécnica de Valencia, Valencia, Spain
| | - Javier Redondo
- Instituto para la Gestión Integrada de las zonas Costeras, Universidad Politécnica de Valencia, Valencia, Spain
| | - Juan V Sánchez-Pérez
- Centro de Tecnologías Físicas, Universidad Politécnica de Valencia, Valencia, Spain
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12
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Hughes A, Huang Y, Schwartz ML, Hynynen K. The reduction in treatment efficiency at high acoustic powers during MR-guided transcranial focused ultrasound thalamotomy for Essential Tremor. Med Phys 2018; 45:2925-2936. [PMID: 29758099 DOI: 10.1002/mp.12975] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Revised: 05/07/2018] [Accepted: 05/07/2018] [Indexed: 12/19/2022] Open
Abstract
PURPOSE To analyze clinical data indicating a reduction in the induced energy-temperature efficiency relationship during transcranial focused ultrasound (FUS) Essential Tremor (ET) thalamotomy treatments at higher acoustic powers, establish its relationship with the spatial distribution of the focal temperature elevation, and explore its cause. METHODS A retrospective observational study of patients (n = 19) treated between July 2015 and August 2016 for (ET) by FUS thalamotomy was performed. These data were analyzed to compare the relationships between the applied power, the applied energy, the resultant peak temperature achieved in the brain, and the dispersion of the focal volume. Full ethics approval was received and all patients provided signed informed consent forms before the initiation of the study. Computer simulations, animal experiments, and clinical system tests were performed to determine the effects of skull heating, changes in brain properties and transducer acoustic output, respectively. All animal procedures were approved by the Animal Care and Use Committee and conformed to the guidelines set out by the Canadian Council on Animal Care. MATLAB was used to perform statistical analysis. RESULTS The reduction in the energy efficiency relationship during treatment correlates with the increase in size of the focal volume at higher sonication powers. A linear relationship exists showing that a decrease in treatment efficiency correlates positively with an increase in the focal size over the course of treatment (P < 0.01), supporting the hypothesis of transient skull and tissue heating causing acoustic aberrations leading to a decrease in efficiency. Changes in thermal conductivity, perfusion, absorption rates in the brain, as well as ultrasound transducer acoustic output levels were found to have minimal effects on the observed reduction in efficiency. CONCLUSIONS The reduction in energy-temperature efficiency during high-power FUS treatments correlated with observed increases in the size of the focal volume and is likely caused by transient changes in the tissue and skull during heating.
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Affiliation(s)
- Alec Hughes
- Department of Medical Biophysics, University of Toronto, 101 College St, Room 15-701, Toronto, Canada.,Physical Sciences Platform, Sunnybrook Research Institute, Room C713, 2075 Bayview Ave, Toronto, Canada
| | - Yuexi Huang
- Physical Sciences Platform, Sunnybrook Research Institute, Room C713, 2075 Bayview Ave, Toronto, Canada
| | - Michael L Schwartz
- Division of Neurosurgery, Department of Surgery, Sunnybrook Health Sciences Centre, Toronto, Canada
| | - Kullervo Hynynen
- Department of Medical Biophysics, University of Toronto, 101 College St, Room 15-701, Toronto, Canada.,Physical Sciences Platform, Sunnybrook Research Institute, Room C713, 2075 Bayview Ave, Toronto, Canada
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Chaplin V, Phipps MA, Caskey CF. A random phased-array for MR-guided transcranial ultrasound neuromodulation in non-human primates. Phys Med Biol 2018; 63:105016. [PMID: 29667598 PMCID: PMC6941739 DOI: 10.1088/1361-6560/aabeff] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Transcranial focused ultrasound (FUS) is a non-invasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in non-human primates at 650 kHz. The array is randomized with 128 elements 6.6 mm in diameter, radius of curvature 7.2 cm, opening diameter 10.3 cm (focal ratio 0.7), and 46% coverage. Simulations were used to optimize transducer geometry with respect to focus size, grating lobes, and directivity. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. A novel combination of optical tracking and acoustic mapping enabled measurement of the 3D pressure distribution in the cortical region of an ex vivo skull to within ~3.5 mm of the surface, and allowed accurate modelling of the experiment via non-homogeneous 3D acoustic simulations. The data demonstrates acoustic focusing beyond the skull bone, with the focus slightly broadened and shifted proximal to the skull. The fabricated design is capable of targeting regions within the S1 sensorimotor cortex of macaques.
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Affiliation(s)
- Vandiver Chaplin
- Vanderbilt University Institute of Imaging Science, 1161 21st Avenue South, Nashville, TN 37232
| | - Marshal A. Phipps
- Vanderbilt University Institute of Imaging Science, 1161 21st Avenue South, Nashville, TN 37232
| | - Charles F. Caskey
- Vanderbilt University Institute of Imaging Science, 1161 21st Avenue South, Nashville, TN 37232
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, 1161 21st Avenue South, Nashville, TN 37232
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Hughes A, Hynynen K. Design of patient-specific focused ultrasound arrays for non-invasive brain therapy with increased trans-skull transmission and steering range. Phys Med Biol 2017; 62:L9-L19. [PMID: 28665289 DOI: 10.1088/1361-6560/aa7cd5] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The use of a phased array of ultrasound transducer elements to sonicate through the skull has opened the way for new treatments and the delivery of therapeutics beyond the blood-brain barrier. The limited steering range of current clinical devices, particularly at higher frequencies, limits the regions of the brain that are considered treatable by ultrasound. A new array design is introduced that allows for high levels of beam steering and increased transmission throughout the brain. These improvements are achieved using concave transducers normal to the outer-skull surface in a patient-specific configuration to target within the skull, so that the far-field of each beam is within the brain. It is shown that by using pulsed ultrasound waves timed to arrive in-phase at the desired target, sufficient levels of acoustic energy are delivered for blood-brain barrier opening throughout the brain.
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Affiliation(s)
- Alec Hughes
- Sunnybrook Research Institute, Physical Sciences Platform, Toronto, M4N 3M5, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Canada
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