Medical magnetic nanoparticles are nano-medical materials with superparamagnetism, which can be collected in the tumor tissue through blood circulation, and magnetic particle imaging technology can be used to visualize the concentration of magnetic nanoparticles in the living body to achieve the purpose of tumor imaging. Based on the nonlinear magnetization characteristics of magnetic particles and the frequency characteristics of their magnetization, a differential detection method for the third harmonic of magnetic particle detection signals is proposed. It was modeled and analyzed, to study the nonlinear magnetization response characteristics of magnetic particles under alternating field, and the spectral characteristics of magnetic particle signals. At the same time, the relationship between each harmonic and the amount of medical magnetic nanoparticle samples was studied. On this basis, a signal detection experimental system was built to analyze the spectral characteristics and power spectral density of the detected signal, and to study the relationship between the signal and the excitation frequency. The signal detection experiment was carried out by the above method. The experimental results showed that under the alternating excitation field, the medical magnetic nanoparticles would generate a spike signal higher than the background sensing signal, and the magnetic particle signal existed in the odd harmonics of the detected signal spectrum. And the spectral energy was concentrated at the third harmonic, that is, the third harmonic magnetic particle signal detection that meets the medical detection requirement could be realized. In addition, the relationship between each harmonic and the particle sample volume had a positive growth relationship, and the detected medical magnetic nanoparticle sample volume could be determined according to the relationship. At the same time, the selection of the excitation frequency was limited by the sensitivity of the system, and the detection peak of the third harmonic of the detection signal was reached at the excitation frequency of 1 kHz. It provides theoretical and technical support for the detection of medical magnetic nanoparticle imaging signals in magnetic particle imaging research.
医用磁性纳米粒子是一种具有超顺磁性的纳米医学材料，可以通过血液循环聚集于肿瘤组织内部，并利用磁性粒子成像技术令生物体内的磁性粒子浓度可视化，达到肿瘤成像的目的。基于磁性粒子的非线性磁化特性及磁化频率特性，本文提出了磁性粒子信号三次谐波的差分检测方法。通过建模仿真分析，研究交变场下磁性粒子的非线性磁化响应特性以及磁性粒子信号的频谱特性，同时针对各次谐波与医用磁性纳米粒子样品量之间的关系进行研究。在此基础上，搭建信号检测实验系统，分析检测信号的频谱特性及功率谱密度，研究信号与激励频率之间的关系。通过以上方法进行信号检测实验，结果表明：在交变激励场下，医用磁性纳米粒子会产生高于背景场感应信号的尖峰信号，且磁性粒子信号存在于检测信号频谱的奇次项谐波中，频谱能量集中在三次谐波处，可以实现满足医用检测需求的三次谐波磁性粒子信号检测。各次谐波幅值与粒子样品量呈正比关系，可根据其关系确定检测得到的医用磁性纳米粒子样品量。同时，激励频率的选择受到系统灵敏度的限制，在 1 kHz 的激励频率下达到检测信号三次谐波的检测峰值。本文提出的磁性粒子信号三次谐波的差分检测方法为磁性粒子成像研究中的医用磁性纳米粒子成像信号检测提供了理论及技术支持。.
Keywords: magnetization characteristics; medical magnetic nanoparticles; signal detection; third harmonic.