1
|
M'Rad Y, Charbonnier C, de Oliveira ME, Guillemin PC, Crowe LA, Kössler T, Poletti PA, Boudabbous S, Ricoeur A, Salomir R, Lorton O. Computer-Aided Intra-Operatory Positioning of an MRgHIFU Applicator Dedicated to Abdominal Thermal Therapy Using Particle Swarm Optimization. IEEE OPEN JOURNAL OF ENGINEERING IN MEDICINE AND BIOLOGY 2024; 5:524-533. [PMID: 39050977 PMCID: PMC11268946 DOI: 10.1109/ojemb.2024.3410118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 04/30/2024] [Accepted: 05/29/2024] [Indexed: 07/27/2024] Open
Abstract
PURPOSE Transducer positioning for liver ablation by magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) is challenging due to the presence of air-filled organs or bones on the beam path. This paper presents a software tool developed to optimize the positioning of a HIFU transducer dedicated to abdominal thermal therapy, to maximize the treatment's efficiency while minimizing the near-field risk. METHODS A software tool was developed to determine the theoretical optimal position (TOP) of the transducer based on the minimization of a cost function using the particle swarm optimization (PSO). After an initialization phase and a manual segmentation of the abdomen of 5 pigs, the program randomly generates particles with 2 degrees of freedom and iteratively minimizes the cost function of the particles considering 3 parameters weighted according to their criticality. New particles are generated around the best position obtained at the previous step and the process is repeated until the optimal position of the transducer is reached. MR imaging data from in vivo HIFU ablation in pig livers was used for ground truth comparison between the TOP and the experimental position (EP). RESULTS As compared to the manual EP, the rotation difference with the TOP was on average -3.1 ± 7.1° and the distance difference was on average -7.1 ± 5.4 mm. The computational time to suggest the TOP was 20s. The software tool is modulable and demonstrated consistency and robustness when repeating the calculation and changing the initial position of the transducer.
Collapse
Affiliation(s)
- Yacine M'Rad
- University of Geneva, Faculty of MedicineImage Guided Interventions Laboratory (GR-949)CH-1211GenevaSwitzerland
| | | | | | - Pauline Coralie Guillemin
- University of Geneva, Faculty of MedicineImage Guided Interventions Laboratory (GR-949)CH-1211GenevaSwitzerland
| | | | - Thibaud Kössler
- University Hopsitals of GenevaOncology Department1205GenevaSwitzerland
| | | | - Sana Boudabbous
- University of Geneva, Faculty of MedicineImage Guided Interventions Laboratory (GR-949)CH-1211GenevaSwitzerland
- University Hospitals of GenevaRadiology Department1205GenevaSwitzerland
| | - Alexis Ricoeur
- University of Geneva, Faculty of MedicineImage Guided Interventions Laboratory (GR-949)CH-1211GenevaSwitzerland
- University Hospitals of GenevaRadiology Department1205GenevaSwitzerland
| | - Rares Salomir
- University of Geneva, Faculty of MedicineImage Guided Interventions Laboratory (GR-949)CH-1211GenevaSwitzerland
- University Hospitals of GenevaRadiology Department1205GenevaSwitzerland
| | - Orane Lorton
- University of Geneva, Faculty of MedicineImage Guided Interventions Laboratory (GR-949)CH-1211GenevaSwitzerland
- University Hospitals of GenevaRadiology Department1205GenevaSwitzerland
| |
Collapse
|
2
|
Holman R, Gui L, Lorton O, Guillemin P, Desgranges S, Contino-Pépin C, Salomir R. PFOB sonosensitive microdroplets: determining their interaction radii with focused ultrasound using MR thermometry and a Gaussian convolution kernel computation. Int J Hyperthermia 2022; 39:108-119. [PMID: 35000497 DOI: 10.1080/02656736.2021.2021304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
Abstract
Purpose: Micron-sized perfluorocarbon droplet adjuvants to focused ultrasound therapies allow lower applied power, circumvent unwanted prefocal heating, and enhance thermal dose in highly perfused tissues. The heat enhancement has been shown to saturate at increasing concentrations. Experiments were performed to empirically model the saturating heating effects during focused ultrasound.Materials and methods: The measurements were made at varying concentrations using magnetic resonance thermometry and focused ultrasound by circulating droplets of mean diameter 1.9 to 2.3 µm through a perfused phantom. A simulation was performed to estimate the interaction radius size, empirically.Results: The interaction radius, representing the radius of a sphere encompassing 90% of the probability for the transformation of acoustic energy into heat deposition around a single droplet, was determined experimentally from ultrasonic absorption coefficient measurements The simulations suggest the interaction radius was approximately 12.5-fold larger than the geometrical radius of droplets, corresponding to an interaction volume on the order of 2000 larger than the geometrical volume.Conclusions: The results provide information regarding the dose-response relationship from the droplets, a measure with 15% precision of their interaction radii with focused ultrasound, and subsequent insights into the underlying physical heating mechanism.
Collapse
Affiliation(s)
- Ryan Holman
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Laura Gui
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Orane Lorton
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Pauline Guillemin
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | | | | | - Rares Salomir
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland.,Radiology Division, University Hospitals of Geneva, Geneva, Switzerland
| |
Collapse
|
3
|
Development of a Simple In Vitro Artery Model and an Evaluation of the Impact of Pulsed Flow on High-Intensity Focused Ultrasound Ablation. Ing Rech Biomed 2021. [DOI: 10.1016/j.irbm.2020.11.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
|
4
|
Guillemin PC, Gui L, Lorton O, Zilli T, Crowe LA, Desgranges S, Montet X, Terraz S, Miralbell R, Salomir R, Boudabbous S. Mild hyperthermia by MR-guided focused ultrasound in an ex vivo model of osteolytic bone tumour: optimization of the spatio-temporal control of the delivered temperature. J Transl Med 2019; 17:350. [PMID: 31651311 PMCID: PMC6814062 DOI: 10.1186/s12967-019-2094-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Accepted: 10/11/2019] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Magnetic resonance guided focused ultrasound was suggested for the induction of deep localized hyperthermia adjuvant to radiation- or chemotherapy. In this study we are aiming to validate an experimental model for the induction of uniform temperature elevation in osteolytic bone tumours, using the natural acoustic window provided by the cortical breakthrough. MATERIALS AND METHODS Experiments were conducted on ex vivo lamb shank by mimicking osteolytic bone tumours. The cortical breakthrough was exploited to induce hyperthermia inside the medullar cavity by delivering acoustic energy from a phased array HIFU transducer. MR thermometry data was acquired intra-operatory using the proton resonance frequency shift (PRFS) method. Active temperature control was achieved via a closed-loop predictive controller set at 6 °C above the baseline. Several beam geometries with respect to the cortical breakthrough were investigated. Numerical simulations were used to further explain the observed phenomena. Thermal safety of bone heating was assessed by cross-correlating MR thermometry data with the measurements from a fluoroptic temperature sensor inserted in the cortical bone. RESULTS Numerical simulations and MR thermometry confirmed the feasibility of spatio-temporal uniform hyperthermia (± 0.5 °C) inside the medullar cavity using a fixed focal point sonication. This result was obtained by the combination of several factors: an optimal positioning of the focal spot in the plane of the cortical breakthrough, the direct absorption of the HIFU beam at the focal spot, the "acoustic oven effect" yielded by the beam interaction with the bone, and a predictive temperature controller. The fluoroptical sensor data revealed no heating risks for the bone and adjacent tissues and were in good agreement with the PRFS thermometry from measurable voxels adjacent to the periosteum. CONCLUSION To our knowledge, this is the first study demonstrating the feasibility of MR-guided focused ultrasound hyperthermia inside the medullar cavity of bones affected by osteolytic tumours. Our results are considered a promising step for combining adjuvant mild hyperthermia to external beam radiation therapy for sustained pain relief in patients with symptomatic bone metastases.
Collapse
Affiliation(s)
- Pauline C Guillemin
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland.
| | - Laura Gui
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Orane Lorton
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Thomas Zilli
- Radiation Oncology Division, University Hospitals of Geneva, Geneva, Switzerland
| | - Lindsey A Crowe
- Radiology Division, University Hospitals of Geneva, Geneva, Switzerland
| | - Stéphane Desgranges
- Equipe Chimie Bioorganique et Systèmes Amphiphiles, Institut des Biomolécules Max Mousseron, UMR 5247, Avignon Université, 84911, Avignon, France
| | - Xavier Montet
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
- Radiology Division, University Hospitals of Geneva, Geneva, Switzerland
| | - Sylvain Terraz
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
- Radiology Division, University Hospitals of Geneva, Geneva, Switzerland
| | - Raymond Miralbell
- Radiation Oncology Division, University Hospitals of Geneva, Geneva, Switzerland
| | - Rares Salomir
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
- Radiology Division, University Hospitals of Geneva, Geneva, Switzerland
| | - Sana Boudabbous
- Image Guided Interventions Laboratory (GR-949), Faculty of Medicine, University of Geneva, Geneva, Switzerland
- Radiology Division, University Hospitals of Geneva, Geneva, Switzerland
| |
Collapse
|
5
|
Papadopoulos N, Menikou G, Yiannakou M, Yiallouras C, Ioannides K, Damianou C. Evaluation of a small flat rectangular therapeutic ultrasonic transducer intended for intravascular use. ULTRASONICS 2017; 74:196-203. [PMID: 27835808 DOI: 10.1016/j.ultras.2016.10.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 09/26/2016] [Accepted: 10/28/2016] [Indexed: 06/06/2023]
Abstract
BACKGROUND The aim of the proposed study was to evaluate the performance of a flat rectangular (2×10mm2) transducer operating at 4MHz. The intended application of this transducer is intravascular treatment of thrombosis and atherosclerosis. METHODS The transducer's thermal capabilities were tested in two different gel phantoms. MR thermometry was used to demonstrate the thermal capabilities of this type of transducer. RESULTS Temperature measurements demonstrated that this simple and small transducer adequately produced high temperatures, which can be utilized for therapeutic purposes. These high temperatures were confirmed using thermocouple and MR measurements. Pulsed ultrasound in combination with thrombolytic drugs and microbubbles was utilized to eliminate porcine thrombi. CONCLUSIONS The proposed transducer has the potentials to treat atherosclerotic lesions using the thermal properties of ultrasound, since high temperatures can be achieved in less than 5s. The results revealed that the destruction of thrombi using pulsed ultrasound requires long exposure time and high microbubble dosage.
Collapse
Affiliation(s)
- N Papadopoulos
- Department of Bioengineering, City University, London, UK
| | - G Menikou
- Department of Bioengineering, City University, London, UK
| | - M Yiannakou
- Electrical Engineering Department, Cyprus University of Technology, Cyprus
| | - C Yiallouras
- Electrical Engineering Department, Cyprus University of Technology, Cyprus; R&D, MEDSONIC LTD, Limassol, Cyprus
| | - K Ioannides
- Radiology, Ygia Polyclinic, Limassol, Cyprus
| | - C Damianou
- Electrical Engineering Department, Cyprus University of Technology, Cyprus.
| |
Collapse
|
6
|
Goharrizi AY, N'Djin WA, Kwong R, Chopra R. Development of a new control strategy for 3D MRI-controlled interstitial ultrasound cancer therapy. Med Phys 2013; 40:033301. [DOI: 10.1118/1.4793261] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
7
|
N'djin WA, Burtnyk M, Kobelevskiy I, Hadjis S, Bronskill M, Chopra R. Coagulation of human prostate volumes with MRI-controlled transurethral ultrasound therapy: results in gel phantoms. Med Phys 2012; 39:4524-36. [PMID: 22830784 DOI: 10.1118/1.4730288] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
PURPOSE The feasibility and safety of magnetic resonance imaging (MRI)-controlled transurethral ultrasound therapy were demonstrated recently in a preliminary human study in which a small subvolume of prostate tissue was treated prior to radical prostatectomy. Translation of this technology to full clinical use, however, requires the capability to generate thermal coagulation in a volume up to that of the prostate gland itself. The aim of this study was to investigate the parameters required to treat a full 3D human prostate accurately with a multi-element transurethral applicator and multiplanar MR temperature control. METHODS The approach was a combination of simulations (to select appropriate parameters) followed by experimental confirmation in tissue-mimicking phantoms. A ten-channel, MRI-compatible transurethral ultrasound therapy system was evaluated using six human prostate models (average volume: 36 cm(3)) obtained from the preliminary human feasibility study. Real-time multiplanar MR thermometry at 3 T was used to control the spatial heating pattern in up to nine planes simultaneously. Treatment strategies incorporated both single (4.6 or 8.1 MHz) and dual (4.6 and 14.4 MHz) frequencies, as well as maximum acoustic surface powers of 10 or 20 W cm(-2). RESULTS Treatments at 4.6 MHz were capable of coagulating a volume equivalent to 97% of the prostate. Increasing power from 10 to 20 W cm(-2) reduced treatment times by approximately 50% with full treatments taking 26 ± 3 min at a coagulation rate of 1.8 ± 0.4 cm(3) min(-1). A dual-frequency 4.6∕14.4 MHz treatment strategy was shown to be the most effective configuration for achieving full human prostate treatment while maintaining good treatment accuracy for small treatment radii. The dual-frequency approach reduced overtreatment close to the prostate base and apex, confirming the simulations. CONCLUSIONS This study reinforces the capability of MRI-controlled transurethral ultrasound therapy to treat full prostate volumes in a short treatment time with good spatial targeting accuracy and provides key parameters necessary for the next clinical trial.
Collapse
|
8
|
N'djin WA, Burtnyk M, Bronskill M, Chopra R. Investigation of power and frequency for 3D conformal MRI-controlled transurethral ultrasound therapy with a dual frequency multi-element transducer. Int J Hyperthermia 2012; 28:87-104. [PMID: 22235788 DOI: 10.3109/02656736.2011.622343] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Transurethral ultrasound therapy uses real-time magnetic resonance (MR) temperature feedback to enable the 3D control of thermal therapy accurately in a region within the prostate. Previous canine studies showed the feasibility of this method in vivo. The aim of this study was to reduce the procedure time, while maintaining targeting accuracy, by investigating new combinations of treatment parameters. Simulations and validation experiments in gel phantoms were used, with a collection of nine 3D realistic target prostate boundaries obtained from previous preclinical studies, where multi-slice MR images were acquired with the transurethral device in place. Acoustic power and rotation rate were varied based on temperature feedback at the prostate boundary. Maximum acoustic power and rotation rate were optimised interdependently, as a function of prostate radius and transducer operating frequency. The concept of dual frequency transducers was studied, using the fundamental frequency or the third harmonic component depending on the prostate radius. Numerical modelling enabled assessment of the effects of several acoustic parameters on treatment outcomes. The range of treatable prostate radii extended with increasing power, and tended to narrow with decreasing frequency. Reducing the frequency from 8 MHz to 4 MHz or increasing the surface acoustic power from 10 to 20 W/cm(2) led to treatment times shorter by up to 50% under appropriate conditions. A dual frequency configuration of 4/12 MHz with 20 W/cm(2) ultrasound intensity exposure can treat entire prostates up to 40 cm(3) in volume within 30 min. The interdependence between power and frequency may, however, require integrating multi-parametric functions in the controller for future optimisations.
Collapse
Affiliation(s)
- William Apoutou N'djin
- Imaging Research, Sunnybrook Health Sciences Centre, and Department of Medical Biophysics, University of Toronto, Ontario, Canada.
| | | | | | | |
Collapse
|
9
|
Vincenot J, Melodelima D, Chavrier F, Vignot A, Chapelon JY. Augmentation du volume traité par ultrasons focalisés de haute intensité pour le traitement des métastases hépatiques. Ing Rech Biomed 2011. [DOI: 10.1016/j.irbm.2011.08.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
|
10
|
N'Djin WA, Melodelima D, Parmentier H, Rivoire M, Chapelon JY. In vivopreclinical evaluation of the accuracy of toroidal-shaped HIFU treatments using a tumor-mimic model. Phys Med Biol 2010; 55:2137-54. [DOI: 10.1088/0031-9155/55/8/002] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
11
|
Melodelima D, N'Djin WA, Favre-Cabrera J, Parmentier H, Rivoire M, Chapelon JY. Thermal ablation produced using a surgical toroidal high-intensity focused ultrasound device is independent from hepatic inflow occlusion. Phys Med Biol 2009; 54:6353-68. [DOI: 10.1088/0031-9155/54/20/021] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
|
12
|
Lafon C, Melodelima D, Salomir R, Chapelon JY. Interstitial devices for minimally invasive thermal ablation by high-intensity ultrasound. Int J Hyperthermia 2007; 23:153-63. [PMID: 17578339 DOI: 10.1080/02656730601173029] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Interstitial ultrasound applicators have been proposed for treating deep-seated tumours that cannot be reached with extra-corporeal high-intensity focused ultrasound. In addition, interstitial ultrasound offers several advantages compared with conventional ablation technology (radiofrequency, microwaves, cryotherapy) in terms of penetration, speed of coagulation, ability to direct and control the thermal lesion and compatibility with image monitoring. The ultrasound source is brought as close as possible to the target in order to minimize the effects of attenuation and phase aberration along the ultrasound pathway. The present paper is a review of the interstitial applicators that were described during the last decade in the literature. It is presented in three sections. The technical aspects common to all applicators are first described. For example, most-described applicators are sideview applicators whose active element is water-cooled and operates at rather high frequency (above 3 MHz) in order to promote heating. Then the different potential techniques for monitoring treatment administered by the interstitial route are presented and illustrated through a review of image-guided interstitial thermal ablation. Three major techniques of imaging are used for guiding interstitial treatment: MRI, ultrasound and fluoroscopy. The third section goes in to further detail on diverse described medical applications.
Collapse
Affiliation(s)
- C Lafon
- Inserm, U556, Lyon, F-69003 France.
| | | | | | | |
Collapse
|
13
|
Melodelima D, Salomir R, Chapelon JY, Theillère Y, Moonen C, Cathignol D. Intraluminal high intensity ultrasound treatment in the esophagus under fast MR temperature mapping: in vivo studies. Magn Reson Med 2006; 54:975-82. [PMID: 16155893 DOI: 10.1002/mrm.20638] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
New curative and palliative treatments are needed to respond to the poor prognosis of esophageal cancer. The purpose of this study was to determine whether magnetic resonance imaging (MRI) and MR thermometry can be used to monitor the thermal ablation induced by an intraluminal high-intensity ultrasound applicator positioned in the esophagus. Experiments were performed in vivo in 2 pig esophagi (25 thermal lesions per pig). Respiratory gated or cardiac gated MR thermometry was performed with segmented echo-planar imaging gradient echo sequences. All MR acquisitions were performed without susceptibility artifacts or radiofrequency interference with the ultrasound device. The experimental procedure proposed for accurate measurement of temperature in the esophagus was found to achieve an SD of +/- 1.5 degrees C for respiratory gating and +/- 3.1 degrees C for cardiac gating. Gd-enhanced T(1)-weighted images were used to depict coagulation necrosis. Autopsy was performed immediately after the treatment. Ultrasound effects were inspected visually, and the dimensions of the lesions in the liver neighboring the esophagus were compared with those determined on the MRI images. The visually assessed thermal lesions showed good correlation with the MRI data (10% mean volume difference). The feasibility of esophageal thermal ablation using intraluminal high-intensity ultrasound and of on-line MR temperature monitoring was demonstrated.
Collapse
|
14
|
Ross AB, Diederich CJ, Nau WH, Rieke V, Butts RK, Sommer G, Gill H, Bouley DM. Curvilinear transurethral ultrasound applicator for selective prostate thermal therapy. Med Phys 2005; 32:1555-65. [PMID: 16013714 DOI: 10.1118/1.1924314] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Thermal therapy offers a minimally invasive option for treating benign prostatic hyperplasia (BPH) and localized prostate cancer. In this study we investigated a transurethral ultrasound applicator design utilizing curvilinear, or slightly focused, transducers to heat prostatic tissue rapidly and controllably. The applicator was constructed with two independently powered transducer segments operating at 6.5 MHz and measuring 3.5 mm x 10 mm with a 15 mm radius of curvature across the short axis. The curvilinear applicator was characterized by acoustic efficiency measurements, acoustic beam plots, biothermal simulations of human prostate, ex vivo heating trials in bovine liver, and in vivo heating trials in canine prostate (n=3). Each transducer segment was found to emit a narrow acoustic beam (max width <3 mm), which extended the length of the transducer, with deeper penetration than previously developed planar or sectored tubular transurethral ultrasound applicators. Acoustic and biothermal simulations of human prostate demonstrated three treatment schemes for the curvilinear applicator: single shot (10 W, 60 s) schemes to generate narrow ablation zones (13 x 4 mm, 52 degrees C at the lesion boundary), incremental rotation (10 W, 10 degrees/45 s) to generate larger sector-shaped ablation zones (16 mm x 180 degrees sector), and rotation with variable sonication times (10 W, 10 degrees/15-90 s) to conform the ablation zone to a predefined boundary (9-17 mm x 180 degrees sector, 13 min total treatment time). During in vivo canine prostate experiments, guided by MR temperature imaging, single shot sonications (6 W/transducer, 2-3 min) with the curvilinear applicator ablated 20 degree sections of tissue to the prostate boundary (9-15 mm). Multiple adjacent sonications ("sweeping") ablated large sections of the prostate (180 degrees) by using the MR temperature imaging to adjust the power (4-6.4 W/transducer) and sonication time (30-180 s) at each 10 degrees rotation such that the periphery of the prostate reached 52 degrees C before the next rotation. The conclusion of this study was that the curvilinear applicator produces a narrow and penetrating ultrasound beam that, when combined with image guidance, can provide a precise technique for ablating target regions with a contoured outer boundary, such as the prostate capsule, by rotating in small steps while dynamically adjusting the net applied electrical power and sonication time at each position.
Collapse
Affiliation(s)
- Anthony B Ross
- Thermal Therapy Research Group, UCSF Radiation Oncology, UCSF Mt. Zion Cancer Center, 1600 Divisidero St., Box 1708, San Fransisco, California 94115-1708, USA
| | | | | | | | | | | | | | | |
Collapse
|