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首页> 外文期刊>IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control >Modeling and Measurement of the Nonlinear Force on Nanoparticles in Magnetomotive Techniques
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Modeling and Measurement of the Nonlinear Force on Nanoparticles in Magnetomotive Techniques

机译：磁力传递技术中纳米粒子非线性力的建模与测量

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Magnetomotive (MM) ultrasound (US) imaging is the identification of tissue in which magnetic nanoparticle tracers are present by detecting a magnetically induced motion. Although the nanoparticles have a magnetization that depends nonlinearly on the external magnetic field, this has often been neglected, and the presence of resulting higher harmonics in the detected motion has not been reported yet. Here, the magnetization of nanoparticles in gelatin was modeled according to the Langevin theory of superparamagnetism. This nonlinear relationship has a fundamental effect on the resulting force and motion. However, the magnetic field must contain regions with a strong magnetic gradient and a low absolute magnetic field to allow the significant generation of higher harmonics in the force. To validate the model, an MM setup that has a constant magnetic gradient on one axis superimposed by a homogeneous time-varying magnetic field was used. After the magnetic characterization of the nanoparticles and calculations of the expected displacement in the setup, experiments were conducted. A laser Doppler vibrometer was used to quantify the small displacements at higher harmonics. The experimental results followed theoretical predictions. Deviations between model and experiment were attributed to a simplified mechanical modeling and temperature rise during measurements. It is concluded that in MM techniques, the nonlinear magnetization of nanoparticles must generally be considered to reconstruct quantitative parameters, to achieve optimum matching of fields and particles, or to exploit nanoparticle magnetization for tissue characterization. In addition, with the presented experimental setup, the magnetization properties of nanoparticles can be determined by MM techniques alone.
机译：磁场（MM）超声（US）成像是通过检测磁感应运动来存在磁性纳米粒子示踪剂的组织的识别。尽管纳米粒子具有在外部磁场上非线性地取决于非线性的磁化，但是通常忽略了这一点，并且尚未报告在检测到的运动中产生更高的谐波的存在。这里，根据SuperParamnetism的Langevin理论，对明胶中的纳米颗粒的磁化。这种非线性关系对所产生的力和运动具有基本影响。然而，磁场必须包含具有强磁梯度和低绝对磁场的区域，以允许在力中实现显着的更高谐波。为了验证模型，使用在一个轴上叠加在一个轴上的磁性梯度的MM设置，由均匀的时变磁场叠加。在纳米颗粒的磁性表征和设置中的预期位移的计算之后，进行实验。激光多普勒振动计用于量化更高谐波的小位移。实验结果遵循理论预测。模型和实验之间的偏差归因于测量期间简化的机械建模和温度升高。结论是，在MM技术中，纳米颗粒的非线性磁化通常必须考虑重建定量参数，以实现场和颗粒的最佳匹配，或利用纳米颗粒磁化进行组织表征。另外，通过呈现的实验装置，纳米颗粒的磁化性能可以单独通过MM技术确定。

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