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Radiofrequency heating studies on anesthetized swine using fractionated dipole antennas at 10.5 T.

ABSTRACT: PURPOSE:To validate electromagnetic and thermal simulations with in vivo temperature measurements, and to demonstrate a framework that can be used to predict temperature increase caused by radiofrequency (RF) excitation with dipole transmitter arrays. METHODS:Dipole arrays were used to deliver RF energy in the back/neck region of the swine using different RF excitation patterns (n = 2-4 per swine) for heating. The temperature in anesthetized swine (n = 3) was measured using fluoroscopic probes (n = 12) and compared against thermal modeling from animal-specific electromagnetic simulations. RESULTS:Simulated temperature curves were in agreement with the measured data. The root mean square error between simulated and measured temperature rise at all locations (at the end of each RF excitation) is calculated as 0.37°C. The mean experimental temperature rise at the maximum temperature rise locations (averaged over all experiments) is calculated as 2.89°C. The root mean square error between simulated and measured temperature at the maximum temperature rise location is calculated as 0.57°C. (Error values are averaged over all experiments.) CONCLUSIONS: Electromagnetic and thermal simulations were validated with experiments. Thermal effects of RF excitation at 10.5 Tesla with dipoles were investigated. Magn Reson Med 79:479-488, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Eryaman Y

PROVIDER: S-EPMC5623597 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Radiofrequency heating studies on anesthetized swine using fractionated dipole antennas at 10.5 T.

Eryaman Yiğitcan Y Lagore Russell L RL Ertürk M Arcan MA Utecht Lynn L Zhang Patrick P Torrado-Carvajal Angel A Türk Esra Abaci EA DelaBarre Lance L Metzger Gregory J GJ Adriany Gregor G Uğurbil Kâmil K Vaughan J Thomas JT

Magnetic resonance in medicine 20170331 1

<h4>Purpose</h4>To validate electromagnetic and thermal simulations with in vivo temperature measurements, and to demonstrate a framework that can be used to predict temperature increase caused by radiofrequency (RF) excitation with dipole transmitter arrays.<h4>Methods</h4>Dipole arrays were used to deliver RF energy in the back/neck region of the swine using different RF excitation patterns (n = 2-4 per swine) for heating. The temperature in anesthetized swine (n = 3) was measured using fluoro ...[more]

PMID: 28370375

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Project description:Design and validate an efficient dual-slot coaxial microwave ablation antenna that produces an approximately spherical heating pattern to match the shape of most abdominal and pulmonary tumor targets.A dual-slot antenna geometry was utilized for this study. Permutations of the antenna geometry using proximal and distal slot widths from 1 to 10 mm separated by 1-20 mm were analyzed using finite-element electromagnetic simulations. From this series, the most optimal antenna geometry was selected using a two-term sigmoidal objective function to minimize antenna reflection coefficient and maximize the diameter-to-length aspect ratio of heat generation. Sensitivities to variations in tissue properties and insertion depth were also evaluated in numerical models. The most optimal dual-slot geometry of the parametric analysis was then fabricated from semirigid coaxial cable. Antenna reflection coefficients at various insertion depths were recorded in ex vivo bovine livers and compared to numerical results. Ablation zones were then created by applying 50 W for 2-10 min in simulations and ex vivo livers. Mean zone diameter, length, aspect ratio, and reflection coefficients before and after heating were then compared to a conventional monopole antenna using ANOVA with post-hoc t-tests. Statistical significance was indicated for P <0.05.Antenna performance was highly sensitive to dual-slot geometry. The best-performing designs utilized a proximal slot width of 1 mm, distal slot width of 4 mm +/- 1 mm and separation of 8 mm +/- 1 mm. These designs were characterized by an active choking mechanism that focused heating to the distal tip of the antenna. A dual-band resonance was observed in the most optimal design, with a minimum reflection coefficient of -20.9 dB at 2.45 and 1.25 GHz. Total operating bandwidth was greater than 1 GHz, but the desired heating pattern was achieved only near 2.45 GHz. As a result, antenna performance was robust to changes in insertion depth and variations in relative permittivity of the surrounding tissue medium. In both simulations and ex vivo liver, the dual-slot antenna created ablations greater in diameter than a coaxial monopole (35 mm +/- 2 mm versus 31 mm +/- 2 mm; P<0.05), while also shorter in length (49 mm +/- 2 mm versus 60 mm +/- 6 mm; P < 0.001) after 10 min. Similar results were obtained after 2 and 5 min as well.Dual-slot antennas can produce more spherical ablation zones while retaining low reflection coefficients. These benefits are obtained without adding to the antenna diameter. Further evaluation for clinical microwave ablation appears warranted.

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Radiofrequency heating studies on anesthetized swine using fractionated dipole antennas at 10.5 T.

Publications

Radiofrequency heating studies on anesthetized swine using fractionated dipole antennas at 10.5 T.

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