Department of Electrical and Computer Engineering, Kansas State University, Manhattan, Kansas, USA.
Med Phys. 2024 Nov;51(11):8442-8453. doi: 10.1002/mp.17404. Epub 2024 Sep 17.
Thermochromic gel phantoms provide a controlled medium for visual assessment of thermal ablation device performance. However, there are limited studies reporting on the comparative assessment of ablation profiles assessed in thermochromic gel phantoms against those in ex vivo tissue. The objective of this study was to compare microwave ablation zones in a thermochromic tissue-mimicking gel phantom and ex vivo bovine liver and to report on measurements of the temperature-dependent dielectric and thermal properties of the phantom.
Thermochromic polyacrylamide phantoms were fabricated following a previously reported protocol. Phantom samples were heated to temperatures in the range of 20°C-90°C in a temperature-controlled water bath, and colorimetric analysis of images of the phantom taken after heating was used to develop a calibration between color changes and the temperature to which the phantom was heated. Using a custom, 2.45 GHz water-cooled microwave ablation antenna, ablations were performed in fresh ex vivo liver and phantoms using 65 W applied for 5 min or 10 min (n = 3 samples in each medium for each power/time combination). Broadband (500 MHz-6 GHz) temperature-dependent dielectric and thermal properties of the phantom were measured over the temperature range of 22°C-100°C.
Colorimetric analysis showed that the sharp change in gel phantom color commences at a temperature of 57°C. Short and long axes of the ablation zone in the phantom (as assessed by the 57°C isotherm) for 65 W, 5 min ablations were aligned with the extents of the ablation zone observed in ex vivo bovine liver. However, for the 65 W, 10 min setting, ablations in the phantom were on average 23.7% smaller in the short axis and 7.4 % smaller in the long axis than those observed in ex vivo liver. Measurements of the temperature-dependent relative permittivity, thermal conductivity, and volumetric heat capacity of the phantom largely followed similar trends to published values for ex vivo liver tissue.
Thermochromic tissue-mimicking phantoms provides a controlled, and reproducible medium for comparative assessment of microwave ablation devices and energy delivery settings. However, ablation zone size and shapes in the thermochromic phantom do not accurately represent ablation sizes and shapes observed in ex vivo liver tissue for high energy delivery treatments (65 W, 10 min). One cause for this limitation is the difference in temperature-dependent thermal and dielectric properties of the thermochromic phantom compared to ex vivo bovine liver tissue, as reported in the present study.
温变凝胶体模为评估热消融设备性能提供了一种可控的介质。然而，目前仅有有限的研究报告了温变凝胶体模与离体组织中评估的消融曲线的对比评估。本研究的目的是比较温变凝胶体模与离体牛肝组织中微波消融区域，并报告体模的温度相关介电和热性能的测量结果。
根据先前报道的方案制备温变聚丙烯酰胺体模。将体模样品在控温水浴中加热至 20°C-90°C 的温度范围内，对加热后体模图像进行比色分析，以建立颜色变化与体模加热温度之间的校准关系。使用定制的 2.45GHz 水冷微波消融天线，在新鲜离体肝组织和体模中进行消融，分别施加 65W 功率 5 分钟或 10 分钟（每种功率/时间组合的每种介质各有 3 个样本）。在 22°C-100°C 的温度范围内，测量体模的宽带（500MHz-6GHz）温度相关介电和热性能。
比色分析表明，凝胶体模颜色的急剧变化始于 57°C 的温度。对于 65W、5 分钟消融的体模（通过 57°C 等温线评估），消融区域的短轴和长轴与离体牛肝中观察到的消融区域的范围一致。然而，对于 65W、10 分钟设置，体模中的消融在短轴上平均缩小了 23.7%，在长轴上缩小了 7.4%，而离体肝组织中观察到的消融则更小。体模的温度相关相对介电常数、热导率和体积热容的测量结果与已发表的离体肝组织值基本一致。
温变组织模拟体模为比较评估微波消融设备和能量输送设置提供了一种可控且可重复的介质。然而，对于高能量输送治疗（65W、10 分钟），温变体模中的消融区域大小和形状并不能准确代表离体肝组织中观察到的消融区域大小和形状。造成这种限制的一个原因是，如本研究所述，温变体模与离体牛肝组织的温度相关介电和热性能存在差异。
