Study Of Magnetic Nanothemometer Excited By Time-varying Magnetic Field

Temperature is a key parameter for tumor diagnosis and therapy, which is one of the frontiers in the research of modern biological thermal physics and information science. Aiming at the complex biochemical environment in vivo, magnetic nanothermometer based on the temperature sensitivity of magnetic nanoparticles has been considered to be a non-invasive effective means of temperature probing. For requirements of high accuracy and fast response in the temperature probing system applicated to tumor therapy, this thesis puts forward the optimization method of existing temperature probing using magnetic nanoparticles excited by time-varying low frequency applied field; and studies the dynamic properties of magnetic nanoparticles under middle and high frequency applied field. And this thesis proposes a magnetic nanothermometer under middle and high frequency applied field based on the dynamic properties of magnetic nanoparticles. The main content is as follows.Firstly, in order to improve accuracy, this thesis firstly analysis the influence of model parameters on temperature probing based on the current magnetic nanothermometry under time-varying low frequency applied field, which studies the optimization method of size of magnetic nanoparticle and discrete applied field. Simulation and experimental results prove that at the same applied field, the accuracy of temperature probing is improved as the size of superparamagnetic nanoparticles increasing. Furthermore, the discrete applied field is optimized in this thesis. The results show that the accuracy can be improved by 30%. The proposed optimization methods can be utilized to probe temperature in some special environments such as in the cell.Secondly, in the premise of improving response speed, this thesis studies the dynamic properties of magnetic nanoparticles (relaxation behavior). The time-varying magnetization of magnetic fluid is obtained by studying the Bloch relaxation equation. The study shows the hysteresis phenomenon appears in superparamagnetic nanoparticles under time-varying magnetic field, which indicates that the existing temperature probing technology under low frequency applied field is no longer suitable for the situation of middle and high frequency applied field. As a result, it is necessary to explore a new temperature probing method for middle and high frequency applied field.In order to study temperature probing method under middle and high frequency applied field, the Bloch relaxation equation is employed to combine the ac susceptibility and effective relaxation time. In view of the temperature sensitivity of the effective relaxation time, the effective relaxation time is used as the variable of the intermediate transition to establish an effective temperature probing model between ac susceptibility and temperature. The temperature measurement system is built according to the above temperature probing method. The feasibility of the proposed method is verified under this system. And the experimental results shows that the maximum temperature error is 0.3 K with a standard deviation of 0.1 K.Finally, the influence of particle size distribution and applied field on temperature probing are discussed in this thesis. Taking into account the high gradient applied field employed in the magnetic nanopartile imaging, the change of the magnetization under large applied field which influences on temperature probing is analyzed. The study provides a theoretical basis for further optimization of the temperature probing method to improve the accuracy and response speed of temperature probing.