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Gupta D, Choi D, Lu N, Allen SP, Hall TL, Noll DC, Xu Z. Magnetic Resonance Thermometry Targeting for Magnetic Resonance-Guided Histotripsy Treatments. ULTRASOUND IN MEDICINE & BIOLOGY 2023; 49:1102-1107. [PMID: 36801181 PMCID: PMC10938365 DOI: 10.1016/j.ultrasmedbio.2022.12.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 12/08/2022] [Accepted: 12/16/2022] [Indexed: 05/11/2023]
Abstract
OBJECTIVE The potential of transcranial magnetic resonance (MR)-guided histotripsy for brain applications has been described in prior in vivo studies in the swine brain through an excised human skull. The safety and accuracy of transcranial MR-guided histotripsy (tcMRgHt) rely on pre-treatment targeting guidance. In the work described here, we investigated the feasibility and accuracy of using ultrasound-induced low-temperature heating and MR thermometry for histotripsy pre-treatment targeting in ex vivo bovine brain. METHODS A 15-element, 750-kHz MRI-compatible ultrasound transducer with modified drivers that can deliver both low-temperature heating and histotripsy acoustic pulses was used to treat seven bovine brain samples. The samples were first heated to an approximately 1.6°C temperature increase at the focus, and MR thermometry was used to localize the target. Once the targeting was confirmed, a histotripsy lesion was generated at the focus and visualized on post-histotripsy MR images. DISCUSSION The accuracy of MR thermometry targeting was evaluated with the mean/standard deviation of the difference between the locus of peak heating identified by MR thermometry and the center of mass of the post-treatment histotripsy lesion, which was 0.59/0.31 mm and 1.31/0.93 mm in the transverse and longitudinal directions, respectively. CONCLUSION This study determined that MR thermometry could provide reliable pre-treatment targeting for transcranial MR-guided histotripsy treatment.
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Affiliation(s)
- Dinank Gupta
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
| | - Dave Choi
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
| | - Ning Lu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
| | - Steven P Allen
- Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT, USA
| | - Timothy L Hall
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
| | - Douglas C Noll
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
| | - Zhen Xu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
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Luo H, Sigona MK, Manuel TJ, Phipps MA, Chen LM, Caskey CF, Grissom WA. Reduced-field of view three-dimensional MR acoustic radiation force imaging with a low-rank reconstruction for targeting transcranial focused ultrasound. Magn Reson Med 2022; 88:2419-2431. [PMID: 35916311 PMCID: PMC9529839 DOI: 10.1002/mrm.29403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 06/14/2022] [Accepted: 07/12/2022] [Indexed: 11/11/2022]
Abstract
PURPOSE To rapidly image and localize the focus in MR-guided focused ultrasound (FUS) while maintaining a low ultrasound duty cycle to minimize tissue effects. METHODS MR-acoustic radiation force imaging (ARFI) is key to targeting FUS procedures such as neuromodulation, and works by encoding ultrasound-induced displacements into the phase of MR images. However, it can require long scan times to cover a volume of tissue, especially when minimizing the FUS dose during targeting is paramount. To simultaneously minimize scan time and the FUS duty cycle, a 2-min three-dimensional (3D) reduced-FOV spin echo ARFI scan with two-dimensional undersampling was implemented at 3T with a FUS duty cycle of 0.85%. The 3D k-space sampling scheme incorporated uniform undersampling in one phase-encoded axis and partial Fourier (PF) sampling in the other. The scan interleaved FUS-on and FUS-off data collection to improve displacement map quality via a joint low-rank image reconstruction. Experiments in agarose and graphite phantoms and living macaque brains for neuromodulation and blood-brain barrier opening studied the effects of the sampling and reconstruction strategy on the acquisition, and evaluated its repeatability and accuracy. RESULTS In the phantom, the distances between displacement centroids of 10 prospective reconstructions and a fully sampled reference were below 1 mm. In in vivo brain, the distances between centroids ranged from 1.3 to 2.1 mm. Results in phantom and in vivo brain both showed that the proposed method can recover the FUS focus compared to slower fully sampled scans. CONCLUSION The proposed 3D MR-ARFI reduced-FOV method enables rapid imaging of the FUS focus while maintaining a low FUS duty cycle.
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Affiliation(s)
- Huiwen Luo
- Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA
| | - Michelle K Sigona
- Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA
| | - Thomas J Manuel
- Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA
| | - Marshal A Phipps
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA
- Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Li M Chen
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA
- Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Charles F Caskey
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA
- Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - William A Grissom
- Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA
- Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
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Considerations for ultrasound exposure during transcranial MR acoustic radiation force imaging. Sci Rep 2019; 9:16235. [PMID: 31700021 PMCID: PMC6838326 DOI: 10.1038/s41598-019-52443-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 10/15/2019] [Indexed: 12/15/2022] Open
Abstract
The aim of this study was to improve the sensitivity of magnetic resonance-acoustic radiation force imaging (MR-ARFI) to minimize pressures required to localize focused ultrasound (FUS) beams, and to establish safe FUS localization parameters for ongoing ultrasound neuromodulation experiments in living non-human primates. We developed an optical tracking method to ensure that the MR-ARFI motion-encoding gradients (MEGs) were aligned with a single-element FUS transducer and that the imaged slice was prescribed at the optically tracked location of the acoustic focus. This method was validated in phantoms, which showed that MR-ARFI-derived displacement sensitivity is maximized when the MR-ARFI MEGs were maximally aligned with the FUS propagation direction. The method was then applied in vivo to acquire displacement images in two healthy macaque monkeys (M fascicularis) which showed the FUS beam within the brain. Temperature images were acquired using MR thermometry to provide an estimate of in vivo brain temperature changes during MR-ARFI, and pressure and thermal simulations of the acoustic pulses were performed using the k-Wave package which showed no significant heating at the focus of the FUS beam. The methods presented here will benefit the multitude of transcranial FUS applications as well as future human applications.
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Odéen H, de Bever J, Hofstetter LW, Parker DL. Multiple-point magnetic resonance acoustic radiation force imaging. Magn Reson Med 2018; 81:1104-1117. [PMID: 30257059 PMCID: PMC6642829 DOI: 10.1002/mrm.27477] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 07/09/2018] [Accepted: 07/11/2018] [Indexed: 12/13/2022]
Abstract
PURPOSE To implement and evaluate an efficient multiple-point MR acoustic radiation force imaging pulse sequence that can volumetrically measure tissue displacement and evaluate tissue stiffness using focused ultrasound (FUS) radiation force. METHODS Bipolar motion-encoding gradients were added to a gradient-recalled echo segmented EPI pulse sequence with both 2D and 3D acquisition modes. Multiple FUS-ON images (FUS power > 0 W) were interleaved with a single FUS-OFF image (FUS power = 0 W) on the TR level, enabling simultaneous measurements of volumetric tissue displacement (by complex subtraction of the FUS-OFF image from the FUS-ON images) and proton resonance frequency shift MR thermometry (from the OFF image). Efficiency improvements included partial Fourier acquisition, parallel imaging, and encoding up to 4 different displacement positions into a single image. Experiments were performed in homogenous and dual-stiffness phantoms, and in ex vivo porcine brain. RESULTS In phantoms, 16-point multiple-point magnetic resonance acoustic radiation force imaging maps could be acquired in 5 s to 10 s for a 2D slice, and 60 s for a 3D volume, using parallel imaging and encoding 2 displacement positions/image. In ex vivo porcine brain, 16-point multiple-point magnetic resonance acoustic radiation force imaging maps could be acquired in 20 s for a 3D volume, using partial Fourier and parallel imaging and encoding 4 displacement positions/image. In 1 experiment it was observed that tissue displacement in ex vivo brain decreased by approximately 22% following FUS ablation. CONCLUSION With the described efficiency improvements it is possible to acquire volumetric multiple-point magnetic resonance acoustic radiation force imaging maps, with simultaneous proton resonance frequency shift MR thermometry maps, in clinically acceptable times.
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Affiliation(s)
- Henrik Odéen
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah
| | - Joshua de Bever
- Department of Radiology, Stanford University, Palo Alto, California
| | - Lorne W Hofstetter
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah
| | - Dennis L Parker
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah
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Vappou J, Bour P, Marquet F, Ozenne V, Quesson B. MR-ARFI-based method for the quantitative measurement of tissue elasticity: application for monitoring HIFU therapy. ACTA ACUST UNITED AC 2018; 63:095018. [DOI: 10.1088/1361-6560/aabd0d] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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de Bever JT, Odéen H, Hofstetter LW, Parker DL. Simultaneous MR thermometry and acoustic radiation force imaging using interleaved acquisition. Magn Reson Med 2017; 79:1515-1524. [PMID: 28795419 DOI: 10.1002/mrm.26827] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Revised: 05/15/2017] [Accepted: 06/15/2017] [Indexed: 12/25/2022]
Abstract
PURPOSE A novel and practical method for simultaneously performing MR acoustic radiation force imaging (ARFI) and proton resonance frequency (PRF)-shift thermometry has been developed and tested. This could be an important tool for evaluating the success of MR-guided focused ultrasound procedures for which MR-thermometry measures temperature and thermal dose and MR-ARFI detects changes in tissue mechanical properties. METHODS MR imaging was performed using a gradient recalled echo segmented echo-planar imaging pulse sequence with bipolar motion encoding gradients (MEG). Images with ultrasound pulses (ON) and without ultrasound pulses (OFF) during the MEG were interleaved at the repetition time (TR) level. ARFI displacements were calculated by complex subtraction of ON-OFF images, and PRF temperature maps were calculated by baseline subtraction. Evaluations in tissue-mimicking phantoms and ex vivo porcine brain tissue were performed. Constrained reconstruction improved the temporal resolution of dynamic measurements. RESULTS Simultaneous maps of displacement and temperature were acquired in 2D and 3D while keeping tissue heating < 1°C. Accuracy of the temperature maps was comparable to the standard PRF sequence. Using constrained reconstruction and subsampled k-space (R = 4.33), 3D simultaneous temperature and displacement maps can be acquired every 4.7 s. CONCLUSION This new sequence acquires simultaneous temperature and displacement maps with minimal tissue heating, and can be applied dynamically for monitoring tissue mechanical properties during ablation procedures. Magn Reson Med 79:1515-1524, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Joshua T de Bever
- School of Computing, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA.,Department of Radiology, Stanford University, Stanford, California, USA
| | - Henrik Odéen
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Lorne W Hofstetter
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Dennis L Parker
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
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Zheng Y, Marx M, Miller GW, Butts Pauly K. High sensitivity MR acoustic radiation force imaging using transition band balanced steady-state free precession. Magn Reson Med 2017. [PMID: 28631853 DOI: 10.1002/mrm.26793] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
PURPOSE MR acoustic radiation force imaging (MR-ARFI) provides a method to visualize the focal spot of a focused ultrasound (FUS) beam without introducing a significant temperature rise. With conventional spoiled MR-ARFI pulse sequences, the ARFI phase always equals the motion-encoded phase. In this work, MR-ARFI using transition band balanced steady-state free precession (bSSFP) is presented, which improves the sensitivity of MR-ARFI with high acquisition speed. THEORY AND METHODS Motion-encoding gradients (MEG) are inserted into bSSFP sequences for MR-ARFI. By applying an ultrasound pulse during the MEG, motion-encoded phase is generated, which leads to an amplified change in the image phase when operating in the bSSFP transition band. MR-ARFI was performed on a homemade gel phantom using both the proposed technique and a spoiled gradient echo ARFI sequence with identical MEG and FUS, and ARFI images were compared. RESULTS The bSSFP-ARFI sequence generated an ARFI image phase that is more than 5 times larger than the motion-encoded phase in a few seconds with 2DFT readout. By keeping FUS pulses as short as 1.45 ms, temperature rise was insignificant during the measurement. CONCLUSION bSSFP-ARFI has enhanced sensitivity compared with conventional MR-ARFI pulse sequences and could provide an efficient way to visualize the focal spot. Magn Reson Med 79:1532-1537, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Yuan Zheng
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Michael Marx
- Department of Radiology, Stanford University, Stanford, California, USA
| | - G Wilson Miller
- Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, Virginia, USA
| | - Kim Butts Pauly
- Department of Radiology, Stanford University, Stanford, California, USA
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Kuroda K. MR techniques for guiding high-intensity focused ultrasound (HIFU) treatments. J Magn Reson Imaging 2017; 47:316-331. [PMID: 28580706 DOI: 10.1002/jmri.25770] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 05/02/2017] [Indexed: 12/17/2022] Open
Abstract
To make full use of the ability of magnetic resonance (MR) to guide high-intensity focused ultrasound (HIFU) treatment, effort has been made to improve techniques for thermometry, motion tracking, and sound beam visualization. For monitoring rapid temperature elevation with proton resonance frequency (PRF) shift, data acquisition and processing can be accelerated with parallel imaging and/or sparse sampling in conjunction with appropriate signal processing methods. Thermometry should be robust against tissue motion, motion-induced magnetic field variation, and susceptibility change. Thus, multibaseline, referenceless, or hybrid techniques have become important. In cases with adipose or bony tissues, for which PRF shift cannot be used, thermometry with relaxation times or signal intensity may be utilized. Motion tracking is crucial not only for thermometry but also for targeting the focus of an ultrasound in moving organs such as the liver, kidney, or heart. Various techniques for motion tracking, such as those based on an anatomical image atlas with optical-flow displacement detection, a navigator echo to seize the diaphragm position, and/or rapid imaging to track vessel positions, have been proposed. Techniques for avoiding the ribcage and near-field heating have also been examined. MR acoustic radiation force imaging (MR-ARFI) is an alternative to thermometry that can identify the location and shape of the focal spot and sound beam path. This technique could be useful for treating heterogeneous tissue regions or performing transcranial therapy. All of these developments, which will be discussed further in this review, expand the applicability of HIFU treatments to a variety of clinical targets while maintaining safety and precision. LEVEL OF EVIDENCE 2 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2018;47:316-331.
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Affiliation(s)
- Kagayaki Kuroda
- Department of Human and Information Science, School of Information Science and Technology, Tokai University, Hiratsuka, Kanagawa, Japan.,Center for Frontier Medical Engineering, Chiba University, Inage, Chiba, Japan
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Odéen H, Almquist S, de Bever J, Christensen DA, Parker DL. MR thermometry for focused ultrasound monitoring utilizing model predictive filtering and ultrasound beam modeling. J Ther Ultrasound 2016; 4:23. [PMID: 27688881 PMCID: PMC5032243 DOI: 10.1186/s40349-016-0067-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 09/02/2016] [Indexed: 12/28/2022] Open
Abstract
Background A major challenge in using magnetic resonance temperature imaging (MRTI) to monitor focused ultrasound (FUS) applications is achieving high spatio-temporal resolution over a large field of view (FOV). This is important to accurately monitor all ultrasound (US) power depositions. Magnetic resonance (MR) subsampling in conjunction with thermal model-based reconstruction of the MRTI utilizing Pennes bioheat transfer equation (PBTE) is one promising approach. The thermal properties used in the thermal model are often estimated from a pre-treatment, low-power sonication. Methods In this proof-of-concept study we investigate the use of US simulations computed using the hybrid angular spectrum (HAS) method to estimate the US power deposition density Q, thereby avoiding the pre-treatment sonication and any potential tissue damage. MRTI reconstructions are performed using a thermal model-based reconstruction method called model predictive filtering (MPF). Experiments are performed in a homogeneous gelatin phantom and in a gelatin phantom with embedded plastic skull. MPF reconstructions are compared to separate sonications imaged with fully sampled data over a smaller FOV. Temperature root-mean-square errors (RMSE) and focal spot positions and shapes are evaluated. Results HAS simulations accurately predict the location of the focal spot (to within 1 mm) in both phantoms. Accurate temperature maps (RMSE below 1 °C), where the location of the focal spot agrees well with fully sampled “truth” (to within 1 mm), are also achieved in both phantoms. Conclusions HAS simulations can be used to accurately predict the focal spot location in homogeneous media and when focusing through an aberrating plastic skull. The HAS simulated power deposition (Q) patterns can be used in the MPF thermal model-based reconstruction to obtain accurate temperature maps with high spatio-temporal resolution over large FOVs.
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Affiliation(s)
- Henrik Odéen
- Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA
| | - Scott Almquist
- School of Computing, University of Utah, Salt Lake City, UT USA
| | - Joshua de Bever
- Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA
| | - Douglas A Christensen
- Department of Bioengineering, University of Utah, Salt Lake City, UT USA ; Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT USA
| | - Dennis L Parker
- Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, UT USA
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Shi YC, Parker DL, Dillon CR. Sensitivity of tissue properties derived from MRgFUS temperature data to input errors and data inclusion criteria: ex vivo study in porcine muscle. Phys Med Biol 2016; 61:N373-85. [PMID: 27385508 DOI: 10.1088/0031-9155/61/15/n373] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
This study evaluates the sensitivity of two magnetic resonance-guided focused ultrasound (MRgFUS) thermal property estimation methods to errors in required inputs and different data inclusion criteria. Using ex vivo pork muscle MRgFUS data, sensitivities to required inputs are determined by introducing errors to ultrasound beam locations (r error = -2 to 2 mm) and time vectors (t error = -2.2 to 2.2 s). In addition, the sensitivity to user-defined data inclusion criteria is evaluated by choosing different spatial (r fit = 1-10 mm) and temporal (t fit = 8.8-61.6 s) regions for fitting. Beam location errors resulted in up to 50% change in property estimates with local minima occurring at r error = 0 and estimate errors less than 10% when r error < 0.5 mm. Errors in the time vector led to property estimate errors up to 40% and without local minimum, indicating the need to trigger ultrasound sonications with the MR image acquisition. Regarding the selection of data inclusion criteria, property estimates reached stable values (less than 5% change) when r fit > 2.5 × FWHM, and were most accurate with the least variability for longer t fit. Guidelines provided by this study highlight the importance of identifying required inputs and choosing appropriate data inclusion criteria for robust and accurate thermal property estimation. Applying these guidelines will prevent the introduction of biases and avoidable errors when utilizing these property estimation techniques for MRgFUS thermal modeling applications.
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Affiliation(s)
- Y C Shi
- Department of Engineering Physics, Tsinghua University, HaiDian District, Beijing 100084, People's Republic of China
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Svedin BT, Beck MJ, Hadley JR, Merrill R, de Bever JT, Bolster BD, Payne A, Parker DL. Focal point determination in magnetic resonance-guided focused ultrasound using tracking coils. Magn Reson Med 2016; 77:2424-2430. [PMID: 27418429 DOI: 10.1002/mrm.26294] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 05/07/2016] [Accepted: 05/11/2016] [Indexed: 11/08/2022]
Abstract
PURPOSE To develop a method for rapid prediction of the geometric focus location in MR coordinates of a focused ultrasound (US) transducer with arbitrary position and orientation without sonicating. METHODS Three small tracker coil circuits were designed, constructed, attached to the transducer housing of a breast-specific MR-guided focused US (MRgFUS) system with 5 degrees of freedom, and connected to receiver channel inputs of an MRI scanner. A one-dimensional sequence applied in three orthogonal directions determined the position of each tracker, which was then corrected for gradient nonlinearity. In a calibration step, low-level heating located the US focus in one transducer position orientation where the tracker positions were also known. Subsequent US focus locations were determined from the isometric transformation of the trackers. The accuracy of this method was verified by comparing the tracking coil predictions to thermal center of mass calculated using MR thermometry data acquired at 16 different transducer positions for MRgFUS sonications in a homogeneous gelatin phantom. RESULTS The tracker coil predicted focus was an average distance of 2.1 ± 1.1 mm from the thermal center of mass. The one-dimensional locator sequence and prediction calculations took less than 1 s to perform. CONCLUSION This technique accurately predicts the geometric focus for a transducer with arbitrary position and orientation without sonicating. Magn Reson Med 77:2424-2430, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Bryant T Svedin
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Michael J Beck
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - J Rock Hadley
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Robb Merrill
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Joshua T de Bever
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Bradley D Bolster
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Allison Payne
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | - Dennis L Parker
- Radiology Department, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
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