时变磁场激励的磁纳米温度测量方法研究

发布时间：2019-05-19 08:27

【摘要】：温度是肿瘤诊断与热疗治疗的关键参数,也是现代生物热物理与信息学科研究的前沿交叉领域的重要指标。针对在生物体内复杂的生化环境,基于磁纳米粒子温度敏感性的磁纳米温度测量方法被认为是一种有效的非侵入式的测温手段。本文针对肿瘤热疗提出的高精度与快速响应的温度测量系统需求,优化升级现有低频磁场激励下的磁纳米温度测量方法,研究了磁纳米粒子在中高频时变激励磁场下的动态特性(磁弛豫现象)并在此基础上提出了中高频时变磁场激励磁纳米温度测量方法。全文的具体内容如下：首先,为提高温度测量精度,在现有低频时变磁场激励下磁纳米温度测量方法基础上,本文分析了模型中的参数对温度测量精度的影响,研究设计了磁纳米粒子的粒径的大小及离散激励磁场的优化方法。实验结果发现,激励磁场大小相同的前提下,温度测量精度随着超顺磁性磁纳米粒子的粒径的增大而提高。此外,本文对激励磁场的离散分布进行优化,优化结果表明该方法可使温度测量精度提高30%。优化方法可用于细胞内等特殊环境下的温度测量。其次,为提高温度测量速度,本文研究了磁纳米粒子在中高频时变磁场激励下的动态特性(磁弛豫现象)。通过研究布洛赫弛豫方程,分析了磁纳米粒子在时变磁场激励下的磁化响应随时间的变化关系。实验结果分析发现在中高频磁场激励下,超顺磁性的磁纳米粒子表现出的磁滞现象导致了现有低频磁场激励下的温度测量技术不再适用于中高频时变磁场激励的情形。基于此,有必要研究在中高频磁场激励下的磁纳米温度测量方法。为了研究在中高频激励磁场下的磁纳米温度测量方法,本文利用布洛赫弛豫方程将描述磁纳米粒子的宏观磁化响应的交流磁化率与动态特性参数(有效弛豫时间)相结合。鉴于有效弛豫时间表现出的温度敏感性,利用有效弛豫时间作为中间过渡的变量,将交流磁化率与温度信息相结合从而建立了有效的温度测量模型。根据温度测量模型,搭建了相应的温度测量装置。通过该温度测量装置,验证了该磁纳米温度测量模型的可行性。实验结果表明,该温度测量最大测量误差为0.3 K,温度误差标准差达到0.1 K。最后,本文讨论了粒径分布与直流场等参数对温度测量的影响。考虑到基于磁纳米粒子的浓度及温度成像需要使用高梯度直流激励磁场这一因素,本文分析了在高幅度激励磁场下磁化响应强度的变化对温度测量的影响。该研究为进一步优化温度测量模型、温度测量的精度及速度提供了理论依据。
[Abstract]:Temperature is the key parameter of tumor diagnosis and hypertherapy, and it is also an important index in the frontier cross field of modern biothermic physics and information research. For the complex biochemical environment in organisms, the magnetic nano-temperature measurement method based on the temperature sensitivity of magnetic nanoparticles is considered to be an effective non-invasive temperature measurement method. In order to meet the requirements of high precision and fast response temperature measurement system proposed by tumor hypertherapy, the existing magnetic nanometer temperature measurement methods excited by low frequency magnetic field are optimized and upgraded in this paper. The dynamic characteristics (magnetic relaxation phenomenon) of magnetic nanoparticles excited by time-varying magnetic field at medium and high frequency are studied, and a method for measuring the temperature of magnetic nanoparticles excited by time-varying magnetic field at medium and high frequency is proposed. The main contents of this paper are as follows: firstly, in order to improve the accuracy of temperature measurement, based on the existing magnetic nanotemperature measurement methods excited by low frequency time-varying magnetic field, the influence of the parameters in the model on the accuracy of temperature measurement is analyzed in this paper. The particle size of magnetic nanoparticles and the optimization method of discrete excitation magnetic field are studied and designed. The experimental results show that the temperature measurement accuracy increases with the increase of the particle size of superparamagnetic magnetic nanoparticles on the premise that the excitation magnetic field is the same. In addition, the discrete distribution of excitation magnetic field is optimized in this paper, and the optimization results show that the accuracy of temperature measurement can be improved by 30%. The optimization method can be used to measure the temperature in special environment such as cell. Secondly, in order to improve the temperature measurement speed, the dynamic characteristics (magnetic relaxation phenomenon) of magnetic nanoparticles excited by medium and high frequency time-varying magnetic field are studied in this paper. By studying the Bloch relaxation equation, the relationship between the magnetization response of magnetic nanoparticles excited by time-varying magnetic field and time is analyzed. The experimental results show that the lag phenomenon of superparamagnetic magnetic nanoparticles excited by medium and high frequency magnetic field leads to the fact that the existing temperature measurement technology under low frequency magnetic field excitation is no longer suitable for the case of medium and high frequency time-varying magnetic field excitation. Based on this, it is necessary to study the magnetic nano-temperature measurement method excited by medium and high frequency magnetic field. In order to study the measurement method of magnetic nano-temperature under medium and high frequency excitation magnetic field, the AC magnetic susceptibility describing the macroscopic magnetization response of magnetic nanoparticles is combined with the dynamic characteristic parameters (effective relaxation time) by using the Bloch relaxation equation. In view of the temperature sensitivity of the effective relaxation time, an effective temperature measurement model is established by combining the AC magnetic susceptibility with the temperature information by using the effective relaxation time as the variable of the intermediate transition. According to the temperature measurement model, the corresponding temperature measuring device is built. The feasibility of the magnetic nano-temperature measurement model is verified by the temperature measuring device. The experimental results show that the maximum measurement error of the temperature measurement is 0.3 K, and the standard deviation of the temperature error is 0.1 K. Finally, the effects of particle size distribution and DC field on temperature measurement are discussed. Considering that high gradient DC excitation magnetic field is needed for magnetic nanoparticles concentration and temperature imaging, the influence of magnetization response intensity on temperature measurement under high amplitude excitation magnetic field is analyzed in this paper. This study provides a theoretical basis for further optimizing the temperature measurement model and the accuracy and speed of temperature measurement.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：R730.5;TB383.1

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