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Hyvärinen M, Huang Y, David E, Hynynen K. Comparison of computer simulations and clinical treatment results of magnetic resonance guided focused ultrasound surgery (MRgFUS) of uterine fibroids. Med Phys 2021; 49:2101-2119. [PMID: 34601729 PMCID: PMC9314069 DOI: 10.1002/mp.15263] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 08/31/2021] [Accepted: 08/31/2021] [Indexed: 11/15/2022] Open
Abstract
Purpose Magnetic resonance‐guided focused ultrasound surgery (MRgFUS) can be used to noninvasively treat symptomatic uterine fibroids by heating with focused ultrasound sonications while monitoring the temperature with magnetic resonance (MR) thermometry. While prior studies have compared focused ultrasound simulations to clinical results, studies involving uterine fibroids remain scarce. In our study, we perform such a comparison to assess the suitability of simulations for treatment planning. Methods Sonications (N = 67) were simulated retrospectively using acoustic and thermal models based on the Rayleigh integral and Pennes bioheat equation followed by MR‐thermometry simulation in seven patients who underwent MRgFUS treatment for uterine fibroids. The spatial accuracy of simulated focus location was assessed by evaluating displacements of the centers of mass of the thermal dose distributions between simulated and treatment MR thermometry slices. Temperature–time curves and sizes of 240 equivalent minutes at 43°C (240EM43) volumes between treatment and simulation were compared. Results The simulated focus location showed errors of 2.7 ± 4.1, −0.7 ± 2.0, and 1.3 ± 1.2 mm (mean ± SD) in the anterior–posterior, foot–head, and right–left directions for a fibroid absorption coefficient of 4.9 Np m–1 MHz–1 and perfusion parameter of 1.89 kg m–3 s–1. Linear regression of 240EM43 volumes of 67 sonications of patient treatments and simulations utilizing these parameters yielded a slope of 1.04 and a correlation coefficient of 0.54. The temperature rise ratio of simulation to treatment near the end of sonication was 0.47 ± 0.22, 1.28 ± 0.60, and 1.49 ± 0.71 for 66 sonications simulated utilizing fibroid absorption coefficient of 1.2, 4.9, and 8.6 Np m–1 MHz–1, respectively, and the aforementioned perfusion value. The impact of perfusion on peak temperature rise is minimal between 1.89 and 10 kg m–3 s–1, but became more substantial when utilizing a value of 100 kg m–3 s–1. Conclusions The results of this study suggest that perfusion, while in some cases having a substantial impact on thermal dose volumes, has less impact than ultrasound absorption for predicting peak temperature elevation at least when using perfusion parameter values up to 10 kg m–3 s–1 for this particular array geometry, frequencies, and tissue target which is good for clinicians to be aware of. The results suggest that simulations show promise in treatment planning, particularly in terms of spatial accuracy. However, in order to use simulations to predict temperature rise due to a sonication, knowledge of the patient‐specific tissue parameters, in particular the absorption coefficient is important. Currently, spatially varying patient‐specific tissue parameter values are not available during treatment, so simulations can only be used for planning purposes to estimate sonication performance on average.
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Affiliation(s)
- Mikko Hyvärinen
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, M5G 1L7, Canada
| | - Yuexi Huang
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada
| | - Elizabeth David
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada
| | - Kullervo Hynynen
- Sunnybrook Research Institute, Toronto, Ontario, M4N 3M5, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario, M5G 1L7, Canada
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Development of temperature controller-integrated portable HIFU driver for thermal coagulation. Biomed Eng Online 2019; 18:77. [PMID: 31242902 PMCID: PMC6595699 DOI: 10.1186/s12938-019-0697-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Accepted: 06/21/2019] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND Temperature monitoring during high-intensity focused ultrasound (HIFU) therapy on tissue is essential to regulate the degree of thermal coagulation and to achieve the desired treatment outcomes eventually. The aim of the current study was to design and investigate the feasibility of a proportional-integral-derivative (PID) temperature controller-integrated portable HIFU driver for thermal coagulation. METHODS A portable HIFU driver was designed and operated at a maximum output voltage of 50 V with pulse-width modulation signals at 2 MHz. The temperature of ex vivo bovine liver tissue was monitored using a K-type thermocouple during the 2-MHz HIFU exposure. RESULTS The tissue temperature was maintained at 60 °C using a PID controller-integrated HIFU driver that modulated the output voltage during the 300-s HIFU exposure. The ex vivo testing demonstrated that the tissue temperature at the focal point approached the chosen temperature, i.e., 60 °C, within 70 s. The temperature was maintained with a deviation of less than 4 °C until the HIFU driver voltage was turned off at 300 s. CONCLUSIONS The designed PID controller-integrated HIFU driver can be used as a small portable tool to regulate the tissue temperature in real time and achieve thermal coagulation via HIFU sonication.
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Dillon C, Rezvani M, McLean H, Adelman M, Dassel M, Jarboe E, Janát-Amsbury M, Payne A. A tissue preparation to characterize uterine fibroid tissue properties for thermal therapies. Med Phys 2019; 46:3344-3355. [PMID: 31152601 DOI: 10.1002/mp.13639] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 05/22/2019] [Accepted: 05/22/2019] [Indexed: 11/08/2022] Open
Abstract
PURPOSE Treating uterine fibroids with less invasive therapies such as magnetic resonance-guided focused ultrasound (MRgFUS) is an attractive alternative to surgery. Treatment planning can improve MRgFUS procedures and reduce treatment times, but the tissue properties that currently inform treatment planning tools are not adequate. This study aims to develop an ex vivo uterine fibroid model that can emulate the in vivo environment allowing for characterization of the uterus and fibroid MR, acoustic, and thermal tissue properties while maintaining viability for the necessary postsurgical histopathological assessments. METHODS Women undergoing a hysterectomy due to fibroid-related symptoms were invited to undergo a preoperative pelvic MRI and to permit postoperative testing of their uterine specimen. Patients that declined or could not be scheduled for a pre-operative MRI were still able to allow post-operative testing of their excised tissue. Following surgical removal of the uterus, nonmorcellated tissues were reperfused with a Krebs-Henseleit buffer solution. An MR-compatible perfusion system was designed to maintain tissue viability inside the MR suite during scanning. MR imaging protocols utilized preoperatively were repeated on whole sample, reperfused ex vivo uterus specimens. Thermal properties including thermal diffusivity and thermal conductivity of the uterus and fibroids were determined using an invasive needle sensor device in 50% of the specimens. Acoustic property measurements (density, speed of sound and attenuation) were obtained for approximately 20% of the tissue samples using both through-transmission and radiation force balance techniques. Differences between fibroid and uterus and in vivo and ex vivo measurements were evaluated with a two-tailed Student t test. RESULTS Fourteen patients participated in the study and measurements were obtained from 22 unique fibroids. Of the 16 fibroids available for preoperative MRI testing, 69% demonstrated classic hypo-intensity relative to the myometrium, with the remainder presenting with iso- (25%) or hyper-intensity (6%). While thermal diffusivity was not significantly different between fibroid and myometrium tissues (0.217 ± 0.047 and 0.204 ± 0.039 mm2 /s, respectively), the acoustic attenuation in fibroid tissue was significantly higher than myometrium (0.092 ± 0.021 and 0.052 ± 0.023 Np/cm/MHz, respectively). When comparing in vivo with ex vivo MRI T1 and T2 measurements in fibroids and myometrium tissue, the only difference was found in the fibroid T2 property (P < 0.05). Finally, the developed perfusion protocol successfully maintained tissue viability in ex vivo tissues as evaluated through histological analysis. CONCLUSIONS This study developed an MR-compatible extracorporeal perfusion technique that effectively maintains tissue viability, allowing for the direct measurement of patient-specific MR, thermal, and acoustic property values for both fibroid and myometrium tissues. These measured tissue property values will enable further development and validation of treatment planning models that can be utilized during MRgFUS uterine fibroid treatments.
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Affiliation(s)
- Christopher Dillon
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
| | - Maryam Rezvani
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
| | - Hailey McLean
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
| | - Marisa Adelman
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA
| | - Mark Dassel
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA
| | - Elke Jarboe
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA.,Department of Pathology, University of Utah, Salt Lake City, UT, 84112, USA
| | - Margit Janát-Amsbury
- Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, UT, 84132, USA
| | - Allison Payne
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84132, USA
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Huang H, Ran J, Xiao Z, Ou L, Li X, Xu J, Wang Q, Wang Z, Li F. Reasons for different therapeutic effects of high-intensity focused ultrasound ablation on excised uterine fibroids with different signal intensities on T2-weighted MRI: a study of histopathological characteristics. Int J Hyperthermia 2019; 36:477-484. [PMID: 30915864 DOI: 10.1080/02656736.2019.1592242] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
OBJECTIVE The objective of this study was to explore the correlations between the therapeutic effect of high intensity focused ultrasound (HIFU) and histopathological characteristics of excised uterine fibroids with different signal intensities as visualized on T2-weighted magnetic resonance imaging (MRI). METHODS We collected 47 specimens of uterine fibroids after surgical resection and classified them into four groups according to preoperative T2-weighted MRI hypo-intense, isointense, heterogeneous intense and homogeneous hyper-intense. Then, specimens in each group were irradiated by HIFU with the same parameters and the necrotic tissue volume was calculated. The smooth muscle cell (SMC) count and collagen fiber content were quantitatively measured and compared between different groups. We analyzed the correlation between the necrotic tissue volume and SMC count and the collagen fiber content. RESULTS Necrotic tissue volume gradually decreased from the hypo-intense group to the homogeneous hyper-intense group (p = .008). The SMC count from the hypo-intense group to the homogeneous hyper-intense group was 215.6 ± 59.3, 237.0(89.5), 232.3 ± 72.5 and 330.5 ± 30.9, respectively; collagen fiber content was 0.65 ± 0.07, 0.64 ± 0.10, 0.53 ± 0.11 and 0.41 ± 0.06, respectively. Comparison among the four groups showed that SMC count progressively increased (p = .001) but collagen fiber content progressively decreased (p = .000) from the hypo-intense group to the homogeneous hyper-intense group. Correlation analysis showed that necrotic tissue volume was negatively correlated with SMC count (R = -0.488, p=.013) but positively correlated with collagen fiber content (R = 0.534, p = .005). CONCLUSIONS Differences in histopathological characteristics may be one of the reasons for different therapeutic effects of HIFU ablation on uterine fibroids with different signal intensities on T2-weighted MRI.
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Affiliation(s)
- Haoran Huang
- a State Key Laboratory of Ultrasound Engineering in Medicine Co-founded by Chongqing and the Ministry of Science and Technology, Chongqing Key Laboratory of Biomedical Engineering, College of Biomedical Engineering , Chongqing Medical University , Chongqing , PR China
| | - Jianbo Ran
- a State Key Laboratory of Ultrasound Engineering in Medicine Co-founded by Chongqing and the Ministry of Science and Technology, Chongqing Key Laboratory of Biomedical Engineering, College of Biomedical Engineering , Chongqing Medical University , Chongqing , PR China
| | - Zhibo Xiao
- b Department of Radiology , The First Affiliated Hospital of Chongqing Medical University , Chongqing , PR China
| | - Liping Ou
- c The Key Laboratory of Diagnostics Medicine Designated by the Ministry of Education , Chongqing Medical University , Chongqing , PR China
| | - Xing Li
- a State Key Laboratory of Ultrasound Engineering in Medicine Co-founded by Chongqing and the Ministry of Science and Technology, Chongqing Key Laboratory of Biomedical Engineering, College of Biomedical Engineering , Chongqing Medical University , Chongqing , PR China
| | - Jie Xu
- d National Engineering Research Center of Ultrasound Medicine , Chongqing , PR China
| | - Qi Wang
- d National Engineering Research Center of Ultrasound Medicine , Chongqing , PR China
| | - Zhibiao Wang
- a State Key Laboratory of Ultrasound Engineering in Medicine Co-founded by Chongqing and the Ministry of Science and Technology, Chongqing Key Laboratory of Biomedical Engineering, College of Biomedical Engineering , Chongqing Medical University , Chongqing , PR China
| | - Faqi Li
- a State Key Laboratory of Ultrasound Engineering in Medicine Co-founded by Chongqing and the Ministry of Science and Technology, Chongqing Key Laboratory of Biomedical Engineering, College of Biomedical Engineering , Chongqing Medical University , Chongqing , PR China
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Bing C, Cheng B, Staruch RM, Nofiele J, Staruch MW, Szczepanski D, Farrow-Gillespie A, Yang A, Laetsch TW, Chopra R. Breath-hold MR-HIFU hyperthermia: phantom and in vivo feasibility. Int J Hyperthermia 2019; 36:1084-1097. [PMID: 31707872 PMCID: PMC6873809 DOI: 10.1080/02656736.2019.1679893] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Revised: 09/04/2019] [Accepted: 10/06/2019] [Indexed: 01/01/2023] Open
Abstract
Background: The use of magnetic resonance imaging-guided high-intensity focused ultrasound (MR-HIFU) to deliver mild hyperthermia requires stable temperature mapping for long durations. This study evaluates the effects of respiratory motion on MR thermometry precision in pediatric subjects and determines the in vivo feasibility of circumventing breathing-related motion artifacts by delivering MR thermometry-controlled HIFU mild hyperthermia during repeated forced breath holds.Materials and methods: Clinical and preclinical studies were conducted. Clinical studies were conducted without breath-holds. In phantoms, breathing motion was simulated by moving an aluminum block towards the phantom along a sinusoidal trajectory using an MR-compatible motion platform. In vivo experiments were performed in ventilated pigs. MR thermometry accuracy and stability were evaluated.Results: Clinical data confirmed acceptable MR thermometry accuracy (0.12-0.44 °C) in extremity tumors, but not in the tumors in the chest/spine and pelvis. In phantom studies, MR thermometry accuracy and stability improved to 0.37 ± 0.08 and 0.55 ± 0.18 °C during simulated breath-holds. In vivo MR thermometry accuracy and stability in porcine back muscle improved to 0.64 ± 0.22 and 0.71 ± 0.25 °C during breath-holds. MR-HIFU hyperthermia delivered during intermittent forced breath holds over 10 min duration heated an 18-mm diameter target region above 41 °C for 10.0 ± 1.0 min, without significant overheating. For a 10-min mild hyperthermia treatment, an optimal treatment effect (TIR > 9 min) could be achieved when combining 36-60 s periods of forced apnea with 60-155.5 s free-breathing.Conclusion: MR-HIFU delivery during forced breath holds enables stable control of mild hyperthermia in targets adjacent to moving anatomical structures.
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Affiliation(s)
- Chenchen Bing
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Bingbing Cheng
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Robert M. Staruch
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX
- Clinical Sites Research Program, Philips Research North America, Cambridge, MA
| | - Joris Nofiele
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX
| | | | - Debra Szczepanski
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX
| | - Alan Farrow-Gillespie
- Department of Anesthesiology and Pain Management, University of Texas Southwestern Medical Center, Dallas, TX
| | - Adeline Yang
- Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX
| | - Theodore W. Laetsch
- Department of Pediatrics and Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX
- Pauline Allen Gill Center for Cancer and Blood Disorders, Children’s Health, Dallas, TX
| | - Rajiv Chopra
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX
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Freeman NJ, Odéen H, Parker DL. 3D-specific absorption rate estimation from high-intensity focused ultrasound sonications using the Green's function heat kernel. Med Phys 2018; 45:3109-3119. [PMID: 29772066 DOI: 10.1002/mp.12978] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Revised: 03/12/2018] [Accepted: 04/19/2018] [Indexed: 11/12/2022] Open
Abstract
PURPOSE To evaluate a numerical inverse Green's function method for deriving specific absorption rates (SARs) from high-intensity focused ultrasound (HIFU) sonications using tissue parameters (thermal conductivity, specific heat capacity, and mass density) and three-dimensional (3D) magnetic resonance imaging (MRI) temperature measurements. METHODS SAR estimates were evaluated using simulations and MR temperature measurements from HIFU sonications. For simulations, a "true" SAR was calculated using the hybrid angular spectrum method for ultrasound simulations. This "true" SAR was plugged into a Pennes bioheat transfer equation (PBTE) solver to provide simulated temperature maps, which were then used to calculate the SAR estimate using the presented method. Zero mean Gaussian noise, corresponding to temperature precisions between 0.1 and 2.0°C, was added to the temperature maps to simulate a variety of in vivo situations. Experimental MR temperature maps from HIFU sonications in a gelatin phantom monitored with a 3D segmented echo planar imaging MRI pulse sequence were also used. To determine the accuracy of the simulated and phantom data, we reconstructed temperature maps by plugging in the estimated SAR to the PBTE solver. In both simulations and phantom experiments, the presented method was compared to two previously published methods of determining SAR, a linear and an analytical method. The presented numerical method utilized the full 3D data simultaneously, while the two previously published methods work on a slice-by-slice basis. RESULTS In the absence of noise, SAR distribution estimates obtained from the simulated heating profiles match closely (within 10%) to the initial true SAR distribution. The resulting temperature distributions also match closely to the corresponding initial temperature distributions (<0.2°C RMSE). In the presence of temperature measurement noise, the SAR distributions have noise amplified by the inverse convolution process, while the resulting temperature distributions still match closely to the initial "true" temperature distributions. In general, temperature RMSE was observed to be approximately 20-30% higher than the level of the added noise. By contrast, the previously published linear method is less sensitive to noise, but significantly underpredicts the SAR. The analytic method is also less sensitive to noise and matches SAR in the central plane, but greatly underpredicts in the longitudinal direction. Similar observations are made from the phantom studies. The described numerical inverse Green's function method is very fast - at least two orders of magnitude faster than the compared methods. CONCLUSION The presented numerical inverse Green's function method is computationally fast and generates temperature maps with high accuracy. This is true despite generally overestimating the true SAR and amplifying the input noise.
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Affiliation(s)
- Nicholas J Freeman
- Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84108, USA
| | - Henrik Odéen
- Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84108, USA
| | - Dennis L Parker
- Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, 84108, USA
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Dillon CR, Rieke V, Ghanouni P, Payne A. Thermal diffusivity and perfusion constants from in vivo MR-guided focussed ultrasound treatments: a feasibility study. Int J Hyperthermia 2017; 34:352-362. [DOI: 10.1080/02656736.2017.1340677] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Affiliation(s)
- Christopher R. Dillon
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA
| | - Viola Rieke
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA
| | - Pejman Ghanouni
- Department of Radiology, Stanford University, Stanford, CA, USA
| | - Allison Payne
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, UT, USA
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Screening Magnetic Resonance Imaging-Based Prediction Model for Assessing Immediate Therapeutic Response to Magnetic Resonance Imaging-Guided High-Intensity Focused Ultrasound Ablation of Uterine Fibroids. Invest Radiol 2016; 51:15-24. [PMID: 26309184 DOI: 10.1097/rli.0000000000000199] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES The aim of this study was to fit and validate screening magnetic resonance imaging (MRI)-based prediction models for assessing immediate therapeutic responses of uterine fibroids to MRI-guided high-intensity focused ultrasound (MR-HIFU) ablation. MATERIALS AND METHODS Informed consent from all subjects was obtained for our institutional review board-approved study. A total of 240 symptomatic uterine fibroids (mean diameter, 6.9 cm) in 152 women (mean age, 43.3 years) treated with MR-HIFU ablation were retrospectively analyzed (160 fibroids for training, 80 fibroids for validation). Screening MRI parameters (subcutaneous fat thickness [mm], x1; relative peak enhancement [%] in semiquantitative perfusion MRI, x2; T2 signal intensity ratio of fibroid to skeletal muscle, x3) were used to fit prediction models with regard to ablation efficiency (nonperfused volume/treatment cell volume, y1) and ablation quality (grade 1-5, poor to excellent, y2), respectively, using the generalized estimating equation method. Cutoff values for achievement of treatment intent (efficiency >1.0; quality grade 4/5) were determined based on receiver operating characteristic curve analysis. Prediction performances were validated by calculating positive and negative predictive values. RESULTS Generalized estimating equation analyses yielded models of y1 = 2.2637 - 0.0415x1 - 0.0011x2 - 0.0772x3 and y2 = 6.8148 - 0.1070x1 - 0.0050x2 - 0.2163x3. Cutoff values were 1.312 for ablation efficiency (area under the curve, 0.7236; sensitivity, 0.6882; specificity, 0.6866) and 4.019 for ablation quality (0.8794; 0.7156; 0.9020). Positive and negative predictive values were 0.917 and 0.500 for ablation efficiency and 0.978 and 0.600 for ablation quality, respectively. CONCLUSIONS Screening MRI-based prediction models for assessing immediate therapeutic responses of uterine fibroids to MR-HIFU ablation were fitted and validated, which may reduce the risk of unsuccessful treatment.
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Liu J, Foiret J, Stephens DN, Le Baron O, Ferrara KW. Development of a spherically focused phased array transducer for ultrasonic image-guided hyperthermia. Phys Med Biol 2016; 61:5275-96. [PMID: 27353347 DOI: 10.1088/0031-9155/61/14/5275] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A 1.5 MHz prolate spheroidal therapeutic array with 128 circular elements was designed to accommodate standard imaging arrays for ultrasonic image-guided hyperthermia. The implementation of this dual-array system integrates real-time therapeutic and imaging functions with a single ultrasound system (Vantage 256, Verasonics). To facilitate applications involving small animal imaging and therapy the array was designed to have a beam depth of field smaller than 3.5 mm and to electronically steer over distances greater than 1 cm in both the axial and lateral directions. In order to achieve the required f number of 0.69, 1-3 piezocomposite modules were mated within the transducer housing. The performance of the prototype array was experimentally evaluated with excellent agreement with numerical simulation. A focal volume (2.70 mm (axial) × 0.65 mm (transverse) × 0.35 mm (transverse)) defined by the -6 dB focal intensity was obtained to address the dimensions needed for small animal therapy. An electronic beam steering range defined by the -3 dB focal peak intensity (17 mm (axial) × 14 mm (transverse) × 12 mm (transverse)) and -8 dB lateral grating lobes (24 mm (axial) × 18 mm (transverse) × 16 mm (transverse)) was achieved. The combined testing of imaging and therapeutic functions confirmed well-controlled local heating generation and imaging in a tissue mimicking phantom. This dual-array implementation offers a practical means to achieve hyperthermia and ablation in small animal models and can be incorporated within protocols for ultrasound-mediated drug delivery.
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Affiliation(s)
- Jingfei Liu
- Department of Biomedical Engineering, University of California, Davis, CA 95616-8686, USA
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Dillon CR, Borasi G, Payne A. Analytical estimation of ultrasound properties, thermal diffusivity, and perfusion using magnetic resonance-guided focused ultrasound temperature data. Phys Med Biol 2016; 61:923-36. [PMID: 26741344 DOI: 10.1088/0031-9155/61/2/923] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
For thermal modeling to play a significant role in treatment planning, monitoring, and control of magnetic resonance-guided focused ultrasound (MRgFUS) thermal therapies, accurate knowledge of ultrasound and thermal properties is essential. This study develops a new analytical solution for the temperature change observed in MRgFUS which can be used with experimental MR temperature data to provide estimates of the ultrasound initial heating rate, Gaussian beam variance, tissue thermal diffusivity, and Pennes perfusion parameter. Simulations demonstrate that this technique provides accurate and robust property estimates that are independent of the beam size, thermal diffusivity, and perfusion levels in the presence of realistic MR noise. The technique is also demonstrated in vivo using MRgFUS heating data in rabbit back muscle. Errors in property estimates are kept less than 5% by applying a third order Taylor series approximation of the perfusion term and ensuring the ratio of the fitting time (the duration of experimental data utilized for optimization) to the perfusion time constant remains less than one.
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Affiliation(s)
- C R Dillon
- Department of Radiology, University of Utah, 729 Arapeen Dr, Salt Lake City, UT 84108, USA
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