Department of Bioengineering, University of Utah, 72 S Central Campus Drive, Salt Lake City, UT 84112, USA.
Phys Med Biol. 2012 Jul 21;57(14):4527-44. doi: 10.1088/0031-9155/57/14/4527. Epub 2012 Jun 22.
Accurate determination of the specific absorption rates (SARs) present during high intensity focused ultrasound (HIFU) experiments and treatments provides a solid physical basis for scientific comparison of results among HIFU studies and is necessary to validate and improve SAR predictive software, which will improve patient treatment planning, control and evaluation. This study develops and tests an analytical solution that significantly improves the accuracy of SAR values obtained from HIFU temperature data. SAR estimates are obtained by fitting the analytical temperature solution for a one-dimensional radial Gaussian heating pattern to the temperature versus time data following a step in applied power and evaluating the initial slope of the analytical solution. The analytical method is evaluated in multiple parametric simulations for which it consistently (except at high perfusions) yields maximum errors of less than 10% at the center of the focal zone compared with errors up to 90% and 55% for the commonly used linear method and an exponential method, respectively. For high perfusion, an extension of the analytical method estimates SAR with less than 10% error. The analytical method is validated experimentally by showing that the temperature elevations predicted using the analytical method's SAR values determined for the entire 3D focal region agree well with the experimental temperature elevations in a HIFU-heated tissue-mimicking phantom.
准确确定高强度聚焦超声 (HIFU) 实验和治疗过程中的比吸收率 (SAR)，为 HIFU 研究结果的科学比较提供了坚实的物理基础，并且对于验证和改进 SAR 预测软件也是必要的，这将改善患者的治疗计划、控制和评估。本研究开发并测试了一种分析解决方案，可显著提高从 HIFU 温度数据中获得的 SAR 值的准确性。通过将一维径向高斯加热模式的分析温度解拟合到施加功率后的温度与时间数据，并评估分析解的初始斜率，可获得 SAR 估计值。该分析方法在多个参数模拟中进行了评估，与常用的线性方法和指数方法相比，除了在高灌注情况下外，在焦域中心的最大误差始终小于 10%，而线性方法和指数方法的最大误差分别高达 90%和 55%。对于高灌注情况，分析方法的扩展可将 SAR 的估计误差控制在 10%以内。该分析方法通过实验进行了验证，结果表明，使用针对整个 3D 焦域的 SAR 值通过分析方法预测的温度升高与 HIFU 加热的组织模拟体中的实验温度升高非常吻合。
