磁共振拉莫尔频率下生物组织介电参数温度特性

Temperature- dependent dielectric properties of biological tissues at Larmor frequencies in magnetic resonance imaging

磁共振成像(MRI)在生物医学上的应用越来越广泛,其中在肿瘤热消融过程中进行图像引导和温度监控是很有前景的应用之一。肿瘤组织接受热消融时,会在体内形成一定的温度梯度分布,由于组织介电特性是温度的函数,热消融引起的温度梯度会改变人体组织的介电特性分布,进而改变磁共振(MR)射频电磁场在组织内的分布,这种射频电磁场分布的改变将直接影响MRI质量和温度监测结果。同时组织的介电特性又是频率的函数,因此研究组织介电特性在MR不同拉莫频率下随温度的变化规律,对MRI引导的热消融治疗研究等具有重要价值。然而,组织在MR拉莫频率下的温度特性的相关研究未见文献报道。本文采用开端同轴传输线测量方法,研究了猪肝脏和膀胱组织介电特性在42.58MHz(1 T)、64 MHz(1.5 T)、128 MHz(3 T)、170 MHz(4 T)、298 MHz(7 T)、400 MHz(9 T)、468 MHz(11 T)等不同拉莫频率下随温度的变化规律,为相关研究提供基础数据支撑,部分填补了组织在MR拉莫频率下的温度特性研究空白。

In recent years, the application of magnetic resonance imaging （MRI） in biomedical field is more and more extensive. Among them, the MRI-guided and thermometry-monitoring of tumor thermal ablation is promising. When the tumors are treated by high energy in thermal ablation, the temperature gradient will be formed inside the human body. Because the dielectric properties are temperature-dependent, the formed temperature gradient will change the dielectric properties distribution of human tissues, resulting in the alteration of the MR electromagnetic field inside the human body, which will directly influence the quality of MRI and thermometry-monitoring. Meanwhile, the dielectric properties are frequency- dependent, so the research on the dielectric properties varying with temperature at different Larmor frequencies is meaningful for the further study of MRI-guided thermal ablation of tumors. However, the research on the temperature-dependent dielectric properties of tissues at various Larmor frequencies has not been reported. In this paper, open-ended coaxial transmission line method was used to measure the temperature-dependent dielectric properties of porcine liver and bladder at 42.58 MHz （1 T）, 64 MHz （1.5 T）, 128 MHz （3 T）, 170 MHz （4 T）, 298 MHz （7 T）, 400 MHz （9 T）, and 468 MHz （11 T）. The obtained data could be used in further research.