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Dual-slot antennas for microwave tissue heating: Parametric design analysis and experimental validation

机译：用于微波组织加热的双缝天线：参数设计分析和实验验证

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>Purpose: 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.>Methods: 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.>Results: 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.>Conclusions: 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.
机译：>目的：设计并验证高效的双缝同轴微波消融天线，该天线可产生近似球形的加热模式，以匹配大多数腹部和肺部肿瘤靶标的形状。>方法：本研究利用双缝天线的几何形状。使用有限元电磁模拟分析了使用从1到10 mm分开1-20 mm的近端和远端缝隙宽度的天线几何排列。从该系列中，使用两项S型目标函数选择了最佳的天线几何形状，以最小化天线反射系数并最大化发热量的直径与长度纵横比。还通过数值模型评估了对组织特性和插入深度变化的敏感性。然后，由半刚性同轴电缆制造出参数分析的最佳双槽几何形状。在离体牛肝中记录了在不同插入深度的天线反射系数，并将其与数值结果进行了比较。然后在模拟和离体肝脏中通过施加50 W 2-10分钟来创建消融区。然后将加热前后的平均区域直径，长度，纵横比和反射系数与使用ANOVA进行事后t检验的常规单极天线进行比较。统计学意义为P <0.05。>结果：天线性能对双缝几何高度敏感。性能最佳的设计采用近端槽缝宽度为1 mm，远端槽缝宽度为4 mm±1 mm和间距为8 mm±1 mm。这些设计的特征在于主动的阻塞机制，该机制将热量集中到天线的远端。在最佳设计中观察到双频谐振，在2.45和1.25 GHz处的最小反射系数为-20.9 dB。总工作带宽大于1 GHz，但仅在2.45 GHz附近获得了所需的加热模式。结果，天线性能对于插入深度的变化和周围组织介质的相对介电常数的变化具有鲁棒性。在模拟和离体肝脏中，双缝天线产生的消融直径均大于同轴单极子（35 mm±2 mm与31 mm±2 mm； P <0.05），而长度也较短（49 mm±2） 10分钟后，相对于60毫米±6毫米； P 0.001）。在2和5分钟后也获得了类似的结果。>结论：双缝天线可以产生更多的球形消融区，同时保持低反射系数。在不增加天线直径的情况下获得了这些好处。似乎有必要对临床微波消融进行进一步评估。

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