Research On Magnetic Nanoparticles Thermometry And Nuclear Magnetic Resonance Thermometry Enhanced By Magnetic Nanoparticles

Temperature can reflect the metabolism and health status of organism,so the accurate measurement of temperature in vivo has been the direction of many researchers.Magnetic temperature measurement/imaging has gradually become one of the most promising medical imaging methods due to the resistance and opacity of organisms,as well as the consideration of safety and comfort.Therefore,this paper mainliy studies the two types of magnetics-based thermometry,including magnetization-based magnetic nanoparticle(MNP)thermometry and nuclear magnetic resonance(NMR)thermometry.Based on the modulation law of the temperature sensitivity of MNP magnetization to the external excitation magnetic field,the temperature measurement performance of the direct current(DC)temperature measurement model of MNPs is optimized,and the feasibility of realizing high-sensitivity NMR temperature measurement and temperature imaging by using iron oxide MNPs as the temperature sensor is emphatically explored.The main content is as follows.Firstly,the magnetic-temperature parameters such as particle size distribution and magnetization characteristics of MNPs are characterized.Then,in order to optimize the temperature performance of magnetization-based MNP thermometry,the temperature sensitivity of MNP magnetization is established and simulated to investigate its dependence on the particle size and the magnetic field.On this basis,the application conditions of temperature measurement of MNPs are pointed out,that is,small-sized MNPs are suitable for temperature measurement under high magnetic field,while large-sized MNPs are more suitable for temperature measurement under low magnetic field.Simulation results show that the optimal magnetic field that maximizes the temperature sensitivity of MNP magnetization decreases with the particle size.Therefore,small-sized MNPs are more suitable for thermometry under high magnetic field,while large-sized MNPs are more suitable for thermometry under low magnetic field.Then,based on the conclusion above,the temperature sensitivity of MNP magnetization is regulated by superimposing DC bias magnetic field in triangular wave excitation magnetic field,so as to improve the temperature measurement performance of magnetization-based MNP thermometry based on the DC temperature measurement model.Simulation results show that this method can significantly improve the temperature performance of small-size MNPs,and optimize the standard deviation of temperature measurement error to about 0.15 K,which provides a new application idea for the temperature measurement of small-size MNPs.Further,because of the enhancement effect of MNPs on the relaxation mechanism of NMR,this paper subsequently proposes to combine the temperature-sensitive MNPs with the MR thermometry,and by introducing the temperature sensitivity of MNP magnetization into the relaxation enhancement model,a thermometry model based on the transverse relaxation rate(R₂)of NMR under the enhancement of MNPs is established.By analyzing the regulation of the particle size,saturation magnetization and excitation magnetic field on the temperature sensitivity of R₂ relaxation rate,it was found that high-accuracy temperature measurement and temperature imaging can be realized using this model only by finding the parameters suitable for the MNPs and the MR system and making the temperature sensitivity of the MNPs tend to be optimal.Finally,according to the measured temperature sensitivity of MNPs and its dependence on the magnetic field,the temperature sensitivity experiment of R₂ relaxation rate is carried out with the suitable MNPs and NMR.By analyzing the temperature characteristics of R₂ relaxation rate enhanced by MNPs,the best overall temperature measurement accuracy of 0.05? is obtained.In addition,through the T₂-weighted temperature imaging experiment,the feasibility of this method for temperature imaging is verified.